AirSport Avionics has closed out its line of Portable Altitude Alerters. We have appreciated serving all of our customers over the past 20+ years. We will continue to honor the full 26 month warranty on all previous purchases and will provide upgrades and repair capabilities after that for as long as parts are available. There are currently 2 Airsport Altitude Alerters being offered on eBay. To view aircraft systems engineering them, click on the items below.
AirSport Avionics is the only manufacturer of Altitude Alerters/Transponder Monitors that receive everything your transponder and encoder are reporting to ATC, both Mode A (squawk code) and Mode C (altitude). Our Altitude Alerters are completely portable and they do not require permanent installation into your aircraft. Our instruments are compatible with your existing headset and they have a variety of features that are beneficial to the safety of all General Aviation Pilots. To learn more about our Altitude Alerters/Transponder Monitors, click on the links below.
Which Model do I need? That depends on how high you fly. The AirSport IFR is the most popular model, it offers the features most pilots need. If you fly above 18,000 ft (or if you fly in parts of the world that use Millibars) then you need the AirSport PRO. The PRO and the IFR are supplied with all accessories, in a protective carrying case.
Are AirSport Alerters different than the competition?Our competitors make fine equipment, and strictly as alerters they are all good investments. But they are wired to the altitude encoder. What if something happens to your altitude data after it leaves the encoder? Other alerters don’t monitor health or status of the transponder. Only AirSport Altitude Alerters monitor actual transponder data, both Mode A (squawk code) and Mode C (altitude). We see the same data being sent to ATC. Your transponder signal is what the controller sees, you should know what your equipment is actually reporting.
Where do I put it? Most pilots place their Alerter on the glareshield. Depending on the aircraft, you may prefer to locate it under the instrument panel or elsewhere. Since it’s portable, pilots find a variety of locations. It comes with Velcro strong enough to hold during turbulence. Some AirSport Alerters have been permanently installed and FAA approved via 337s. (For installation notes, Click Here) This equipment is really intended to be portable, and is legal per FAR 92.21(b)&(c).
How long does the Battery last before recharging? The general answer is about 8 hours, enough for an average day’s flying. If backlighting is not used, much more time is available before recharging is needed. It can be recharged overnight with the 110 volt charger supplied. Or, if you operate your Alerter from aircraft power, then there is no time limit, and the battery is recharged automatically.
Does it work with 28 volt systems? Yes. Either 14 or 28, just plug it in.
What about pressurized aircraft? It doesn’t matter. Your alerter is a receiver, not an air pressure instrument. It receives the transponder signal and displays the same altitude that ATC is seeing.
Does it really work without connection to the plane? Yes. These Altitude Alerters will even work in an airliner. (You should have a window seat, and it’s up to you to smuggle it aboard!) It needs no connection to aircraft systems because it picks up the transponder signal and decodes all the data. To hear the pilot altitude reminder, you should connect the unit to your headset or intercom with the supplied cable. AirSport Altitude Alerters are compatible with all audio panels, regular and stereo intercoms, and all types of regular and noise-cancelling headsets.
Do I have to enter my squawk code? No. Your squawk code is being received from your transponder, and is displayed to let you know your transponder is operating correctly.
What about barometric pressure? Each time you reset pressure on your altimeter, you should reset your alerter. Your encoder puts out pressure altitude. (Pressure altitude is what you would read if your altimeter were set to 29.92″). On the ground, ATC equipment automatically adds barometric correction before the controller sees your altitude. AirSport Alerters do the same, so everyone is working with the same numbers.
Does it work at Flight Levels? Flight Levels are handled by the AirSport PRO, but not by the IFR models. On the PRO, any assigned altitude can be chosen up to 17,900 ft, plus FL180 to FL555. The PRO changes to standard pressure automatically when entering Flight Levels, and a tone reminds you to change your altimeter. Prior to descent, you can set the new barometric pressure, and the PRO will switch back to altitudes at the legally correct point in accordance with FAR 91.81, and will again remind you to put the new setting in your altimeter.
How does it know which transponder is mine? It’s a matter of signal strength, yours is the strongest! If your transponder is not on, it may receive another transponder within about a half mile. Otherwise, it will receive only yours.
Is it easy to use? Yes. The outer knob selects functions, they are shown in the function window. The inner knob adjusts a value. For instance, in the Set Target function, the small knob sets your assigned altitude. Plus, every unit contains a demonstration mode which allows you to learn before you take it flying. You can practice setting cruise altitudes, become familiar with the many tones, and so on. The User’s Manual is written from a pilot’s perspective, we’re proud of the many compliments it has received.
In cruise, how much altitude tolerance do I have? It’s your choice, you can select a band with a total thickness of 100 ft or more. ATC violation can occur if you deviate 300 ft from your assigned altitude, so it’s a good idea to set the tolerance less than that. You will receive audible and visual warning if you fly outside of your selected tolerance. The tones indicate how far you are off, and which way you need to go to return to assigned altitude.
How big is it? Two inches high, 5-1/4 inches wide, and 5-1/4 inches deep. It weighs 28 ounces. The battery and antenna are inside.
How long has it been on the market? The first AirSport PRO’s were delivered to customers in April 1991. The IFR model was introduced in 1993. They have been protecting pilots worldwide since.
What about reliability? AirSport Alerters have demonstrated excellent reliability. All components are high quality, and we take pride in our workmanship. Unlike many units on the market, our equipment is 100% designed and built in the USA. The design team members are all pilots, so we understand why reliability is important. And we back it up with a 26 month warranty on parts and labor.
As always, we appreciate any additional questions or comments you may have.
Author Peter Lert said this about the Airsport PRO in February 1994 AIR PROGRESS: “Overall, I’m extremely impressed with both the quality and the overall cleverness of this product…I’ve been using it instead of the factory-installed altitude alerters in the Part 135 charter turboprops I fly…I have no hesitation whatsoever in recommending this fine product to any pilot who flies a significant amount of IFR — or even VFR in or near Class B or C airspace…The first time an Airsport saves you from getting caught for an inadvertent altitude violation, its price will more than make up for the cost of an aviation attorney to defend you or mitigate the punishment.”
Seth Golbey, Editor of AOPA PILOT, wrote in the November 1991 issue: “We may be dealing with a gentler, kinder FAA, but when it comes to altitude busts and transponder accuracy, pilots can’t be too careful….AOPA PILOT editors have made a number of long cross-country flights with the Airsport Pro and found it to work exactly as advertised. If you don’t already have an altitude alerter, consider this unit. If you want to continuously monitor the health of your transponder, it’s your only choice. It’s the sort of equipment that you come to miss when you don’t have it.”
“I flew the PRO on a recent trip, and it did everything as advertised. Unlike other altitude alerters, the PRO is completely self-contained and portable. No installation, no FAA paperwork, no panel space needed.” Keith Connes, PLANE & PILOT January 1992.
“The Airsport PRO is well-made, well thought-out, logical, and it works as advertised.” Andrew B. Douglas, THE AVIATION CONSUMER, September 1991.
The September 1992 issue of AVIONICS REVIEW contained a comparison of three altitude alerters: Icarus AltAlert II, Morrow Alti-Trak, and Airsport PRO. “Operationally, the Airsport PRO is the easiest of the three to use…..The Airsport PRO is the only one that has a demonstration mode…..The Airsport PRO is a handy gadget for keeping you straight with the Feds, because it sees what they do.”
Oakland Center: “Grumman One Six Lima Charlie, you’ve just busted your assigned altitude!”
One Six Lima Charlie: “(GULP!)”
Actually, I presume that the controller’s phraseology under these circumstances would be a little more formal, but equally forbidding. Fortunately, I’ve never been on the receiving end of this type of stern message, but the very possibility of an inadvertent deviation from an assigned altitude is something I think about on every IFR flight, and I imagine most other instrument pilots share this concern.
Bust your assigned altitude while under IFR, or even while negotiating through a TCA, and you’re almost sure to have an unpleasant interlude with FAA. An even greater punishment could be inflicted by metal-to-metal contact resulting from your intrusion into another plane’s airspace. This, of course, could happen if you dope off while flying VFR as well.
Enter the AirSport Pro, a device that warns you if you stray from your desired altitude, and also does a number of other things. Unlike other altitude alerters, the Pro is completely self-contained and portable. No installation, no FAA paperwork, no panel space needed. It comes in the form of a compact box that measures 2x5x5-inches. Power is supplied by a rechargeable lead-acid battery.
So how does it work? The Pro is a receiver with a computer, and what it receives is the Mode A output of your transponder and the Mode C output of your encoder. The set’s display is a 32-character LCD (liquid crystal display). The controls consist of two concentric knobs plus switches for display backlighting and an alert horn. A headphone jack is on the back of the unit.
The display is divided into six sections, referred to as “windows” by the manufacturer: Altitude, Squawk, Baro, Target, Delta and Function.
The Altitude window shows the aircraft’s altitude as reported by the onboard encoder, in 100-foot increments. Thus, there can be an error or lag of up to 50 feet or so before the displayed altitude changes from, say, 2900 to 3000 feet. What you’re seeing in that window is what your local controller is seeing on his or her radar screen, so the Pro lets you know whether your encoder is operating properly.
Likewise, the Squawk window displays the Mode A squawk that your transponder is putting out. The User’s Manual suggests that if there is a difference between the code you’ve dialed into the transponder and the code it is transmitting, it might be due to dirty switch contacts, a slipped knob or other problem in the transponder.
Bear in mind that your transponder does not transmit when it is not being interrogated, so in areas of poor or nonexistent radar coverage, you will get a NO XPONDER message, meaning no Mode A and no Mode C transmissions are being made. Under these conditions, it is possible that your Mode C will be interrogated by a TCAS-equipped airliner or corporate plane, in which case the Squawk window will show a series of dashes (Mode A, no; Mode C, yes). This will tell you that there’s some heavy iron in the vicinity.
The Baro window shows the barometric setting you have entered. Since your encoder is permanently set at 29.92 Hg, it is necessary to update the display by entering a current barometric setting, as you do with your altimeter.
The Target window shows the altitude you have selected for alerting purposes. There is a cruise altitude setting and a descent altitude setting, the latter used during an approach.
The Delta window displays the difference, in hundreds of feet, between your present altitude and your target altitude. There is also a “fly up” or “fly down” arrow (two arrows when the difference is 1000 feet or more).
The Function window shows which function has been selected for entry or display. An Info function can be selected that will enhance the information in the Delta window with such annunciations as Climb, Level and Descend.
An Approach mode can be selected and a Descent Altitude entered into the computer. When you are in this mode and reach an altitude that is 500 feet above the Descent Altitude, the word Gear will appear in the Function window and an aural alert will sound. (Even if you have a fixed gear plane, this might be a good reminder to perform certain checklist functions.) The next annunciation will be Descent Altitude, when you have arrived there, accompanied by a tone. When you descend below your Descent Altitude, that’s what you’ll see: Warning-Below DA. And you’ll hear another warning sound.
The Sounds Of Warning
When it comes to aural warnings, the Pro is a veritable orchestra. When you are 900 feet above or below your target altitude, a single tone will sound. Once you reach your cruising altitude, if you deviate, a number of ascending or descending notes will be heard, depending on whether you’ve wandered above or below the target altitude. For example, if you’ve deviated three hundred feet on the high side, you’ll hear three descending tones.
You can program a variety of altitude buffers, within which no alert will sound.
In the Approach mode, the Gear alert is a chirping sound, meant to suggest the sound of tires kissing asphalt. There are yet other sounds when you reach and go below Descent Altitude, the latter being particularly urgent.
This means that you don’t have to be watching the Pro’s display to interpret its altitude-related messages. (But it helps to have a degree from the Juilliard School of Music.) You will get this panoply of sounds through your headset or aircraft speaker, if the unit is so connected. A less musical alternative is the Pro’s built-in horn, which sounds only one note for any given type of alert.
The Pro will also calculate your rate of climb by measuring the time it takes to make a 100-foot altitude change.
I flew the Pro on a recent trip, and it did everything as advertised. Its main market would appear to be instrument pilots who don’t fly with a 2- or 3-axis autopilot and want all the help they can get to avoid an unplanned altitude excursion. However, as I indicated earlier, the Pro certainly can be a safety aid for the VFR pilot as well. The pilot who rents wings, or flies more than one aircraft, can easily take the Pro from plane to plane.
The AirSport Pro lists for $899. Included are a carrying case, 110V AC charger, 12-24V DC cigarette lighter power cord, headset patch cord, and Velcro for mounting the unit.
Two lower-priced versions of AirSport’s self-contained altitude alert system are now available for pilots who don’t need all the options available on the PRO model. Both the AirSport IFR and AirSport VFR work the same way by receiving your transponder signals and displaying the code and altitude you’re squawking so that you can see the same altitude the controller is seeing on his ground equipment. Since the alerters do not require any installation, they can work in any airplane.
In all three versions, the 5¼-by-5¼-by-2-inch box features a 32-character lighted display that provides six windows of information: altitude, squawk, baro, target, delta x 100, and function. Two concentric knobs on the right side of the box control up to 16 functions. Once the box senses.your transponder signal, it displays the code the transponder is squawking and, with the barometric setting entered, the altitude it is reporting. As you change the barometric setting with updates from controllers, the box continues to display the altitude the controllers are seeing on their scopes. The “target” window lets the pilot set the altitude to which he has been cleared or that he wants to maintain. As the altitude the encoder is transmitting comes within 900 feet of the target altitude, there is an audible tone and the “delta x 100” display changes from double arrows in the direction required to reach the target altitude to a single arrow and a digit representing hundreds of feet to go to reach the target altitude. When the target and actual altitude agree there is another tone. The “function” window displays the current mode in use. If turned to “information,” the window will display “climb,” “descend” or “level,” depending on what is required to maintain the target altitude.
An “approach” function warns the pilot to check gear at 500 feet before the preset descent altitude is reached. Once level at the descent altitude, any farther descent causes an insistent warning tone. When the AirSport is connected to the pilot’s headset with the interface cable, the warning tones are descriptive of the required action. A climb command is an ascending tone. If the pilot needs to descend to reach the target altitude, the warning is a descending tone. For each 100 feet above or below the target altitude a tone sounds. For example, if the airplane has climbed 300 feet above the target altitude there will be three descending tones repeated at 10-second intervals until the plane descends. Two other handy features are a density altitude mode that computes the actual density altitude and a Fahrenheit-to-Centigrade conversion that simultaneously shows both temperatures in two windows as you turn the knob to change the setting.
During some 30 hours of flying with the IFR model, I often noticed that the difference between the altitude indicated by my altimeter and that being transmitted by my transponder varied by as much as 200 feet-meaning my 300-foot ATC-dictated margin for error was really 100 feet, which explains why I’m occasionally being reminded by controllers of the correct altimeter setting, a subtle way they have of warning pilots to check their altitude.
Although the unit comes with heavy-duty Velcro to affix it to the top of the panel (or other cockpit location), I was most comfortable wedging it between the pilots’ seats rather than obscuring my outside view.
The AirSport models will run for about nine hours on the internal rechargeable battery or they can be connected to onboard power through a cigarette lighter adapter. On one long day, flying from Panama City, Florida, to Denver, Colorado, the battery ran down and I couldn’t get the system to work through the lighter adapter because the fuse in the adapter had blown. I was surprised at how much I missed the alerter’s insistent, but strangely reassuring, tones.
Occasionally the almost-constant tones as I bumped along at the edge of the tolerance range became annoying, but a toggle switch on the left side allows the warning horn to be switched off. You can also reset the tolerance to make the unit more or less sensitive to altitude excursions. A second three-position switch turns the system on and off and activates the internal light.
One thing I particularly like about the AirSport is its ability to verify the performance of my transponder. It’s hard to know how often a problem on the ground is mistakenly blamed on airborne equipment and results in a needless visit to the shop. When a controller complains, “I’m not getting your Mode C,” it’s satisfying to be able to respond, “I have transponder-monitoring equipment on board and I’m squawking the assigned code.”
The IFR model, priced at $699, displays altitudes to 99,900 feet, has the approach function with gear warning, includes a rate-of-climb calculation, and displays the ratio of Mode A to C replies in the area. The IFR model also comes with the cigarette lighter cord adapter and a carrying case. The top-of-the-line PRO model ($899) can display altitudes as high as FL 999 (the target altitude can be set as high as FL 555), automatically switches between altitudes and flight levels, has the capability of setting the barometric pressure in either inches or millibars, and features a “sponder-scope” that can be used by technicians to analyze the transponder signals.
For additional information, contact AirSport Avionics, at 866/ 215-2295.
One of the nice things about moving up into heavier aircraft is that you get better equipment to help you do your job. While airline pilots might not agree – after all, they have their jobs to worry about! – the old saw about “the bigger they are, the easier they are to fly” holds true to some extent. Not only do you generally have more performance; you also get more sophisticated (and more reliable!) avionics, a better autopilot, and sometimes even people to help you…an old TWA instructor once told me that the first “memory item” on any mechanical malfunction checklist was “waken Flight Engineer…”
Not all the improved equipment has to be the latest, fanciest GPS or integrated nav system, either – some of the most useful gadgets are ones that address relatively simple tasks. When I first moved up into turbine equipment – in my case, an elderly Learjet – I was immediately impressed by a device called an altitude alerter. Not only was it extremely useful – in fact, given the old “straight pipe” Lear’s available rates of climb and descent, almost indispensable! – it was also just about the only gadget my crusty old captain would let a neophyte copilot fiddle with.
All joking aside, an altitude alerter is, indeed, an exceedingly handy device – so much so that FAA requires it in all airliners, and some of the high-end avionics manufacturers (notably Bendix/King) make it available as an option to their lightplane autopilots. In its most basic form, it’s a panel-mounted window into which the pilot sets a desired altitude. It’ll then provide a warning sound (a beep or, in bigger airplanes, an elevator-like chime) when you get within 1000 feet of the desired altitude on a climb or descent, and again when you reach the set value. Once you’ve levelled off, it’ll monitor your altitude, sounding off with the same beep or chime whenever you deviate from it by some preset value (normally 300 feet). Since its set altitude is also visible from the panel, it’s a handy reminder. Watch any turbine pilot at work, and you’ll see him or her automatically dial in a new altitude as soon as it’s received from ATC.
Until the almost universal acceptance of encoding altimeters or blind encoders, only the largest aircraft had altitude alerters, since only they had the expensive “air data computer” systems to run them. Once Mode C transponders came online, however, altitude alerting became considerably more affordable; the lightplane systems mentioned above are wired to the encoding altimeter, rather than being plumbed to the static system.
Even so, they still aren’t cheap, and they have to be installed and signed off by a certificated avionics shop. Or do they? Well, there’s one system that doesn’t: The Sallisaw, Oklahoma, firm of AirSport has a line of three altitude alerter Systems – and since they’re self-contained and portable, they don’t require any installation or aircraft documentation change. Moreover, since designer and builder Darryl Phillips didn’t have to jump tlrrough all of the FAA certification hoops, he was able to incorporate a number of advanced “just plain clever” features that even a major avionics manufacturer probably couldn’t afford to certificate, while still keeping the price to a very affordable range from $699 to $899.
All three units – the basic AirSport, the AirSport IFR and the AirSport Pro – appear physically identical: a neat black plastic case about four inches wide, five inches deep, and a bit over an inch high. Controls and the two-line backlit LCD display are on the one-inch side, so the whole thing fits very nicely on top of your instrument panel or glareshield. All also have audio outputs; they can be interconnected with your headphones or audio panel via supplied patch cords. All three are also powered either by a cigarette lighter plug or an onboard rechargeable battery. This means that no matter how you choose to use them, there’s no permanent connection with aircaft systems; hence, the AirSports aren’t considered “installed equipment,” so no paperwork is required.
How does a system work with no physical connection to either the static system or the encoding altimeter? Very simply: the “guts” of all AirSport systems incorporate a receiver tuned to the 1090 mHz frequency on which your transponder transmits, as well as a microprocessor to decode your aircraft’s transponder code and Mode C altitude squawk. What this means, of course, is that an AirSport will only work in an airplane that has a transponder and encoding altimeter. Moreover, it’ll only work if your transponder is actively being interrogated by a ground radar – in other words, if its little “reply” light is blinking.
I initially thought this might be a hindrance at our remote southwestern Colorado location, since based on the frequent “radar contact lost” or “radar service unavailable” calls I get from Center when flying VFR at low level, I assumed that radar coverage was very limited. (Of course, around here “low level” means 10,000 ft. MSL!) I was pleasantly surprised, however, to find out that this isn’t the case: even if radar coverage may not be good enough for Center to see me, there seems to be plenty of transmitted energy around to trigger the transponder (and thus provide a signal for the AirSport). On a recent flight to Denver at 13,500 ft. MSL – which means we were generally 500 to 1000 feet below the highest peaks – there was only one period, of less than 5 minutes, when we saw the AirSport’s “NO XPONDER” message.
Given a signal to work with, in its most basic mode the AirSport works the same as any “heavy iron” altitude alerter: after you’ve dialed in the altimeter setting, just as you would for an altimeter, and the desired “target altitude,” which is displayed in clear dot-matrix numerals, it’ll beep once as you get within 1000 feet of the target, beep once again when you reach it, and then beep again anytime you deviate by more than the tolerance value you’ve chosen (anything you want from 100 to 900 feet, rather than the 300 feet to which you’re limited with other alerter systems). The actual “beep” comes – again, we’re talking the most basic mode here – from a buzzer on the back of the unit that’s loud enough to be heard in any cockpit environment.
That’s only the most basic mode, however. Even here, the two-line LCD display shows more than just the altitude number of a standard encoder; it also shows the code your transponder is sending, both target and actual altitudes, and the difference or ‘delta” between them, as well as an up or down arrow to show which way that delta should apply.
Things get even more interesting when you connect the AirSport to your audio system or headset using the supplied adapter cords. Now you still get the beep at the same altitudes as before – but, in addition, once you’ve levelled off, any deviation causes a little trill – either upward if you’re too low, indicating you should climb, or downward if you’re too high. The number of trills indicates how many hundreds of feet you’re off, so you can get a good deal of information without even having to look at the display. In its “INFO” mode, the display will also read “CLIMB,” “DESCEND,” or “LEVEL” as appropriate. Further functions let you enter an altitude – either from the panel or automatically via your encoder – dial in the temperature, and get density altitude.
That’s the basic AirSport. The IFR model adds an extremely useful approach monitor mode: dial in the DH or MDA of your approach, and as you start the descent the AirSport will advise you when you’re 1000 and 500 feet above the descent altitude (at the 500-foot point, it’ll show a “GEAR” reminder and simulate the sound of wheels touching down). At the final altitude, it produces a distinctive sound – and an even more distinctive one anytime you go below the minimum altitude. Another IFR function will monitor and display your rate of climb, either quasi-instantaneously or cumulatively.
The “Pro” model incorporates all these functions and even more: it’s the only one that can handle altitudes above 18,000 feet (at which point the display changes to flight levels and the altimeter setting changes automatically to 29.92 in. Hg.). It can also be changed from inches to millibars for altimeter settings by switching a single jumper inside the case. A special “Sponder-Scope” mode changes it into a miniature transponder and encoding altimeter test set – ideal for technicians as well as for those interested in what’s really going on behind the scenes. In this mode, in addition to displaying your transponder code and reported altitude, it becomes a mini-oscilloscope and lets you see the actual digital pulses for troubleshooting.
Opening the case reveals, in addition to a very clean and well-laid out circuit board, excellent quality control and attention to detail. In contrast to most avionics manufacturers who keep the workings of their equipment a deep, dark secret from all but franchised repair stations, Darryl Phillips encloses a complete schematic for each system right inside the case, where any competent maintenance technician will find it in the unlikely event that it should fail.
Phillips’ attention to detail is also evident in the way the AirSports are packaged and shipped. Each includes a foam-lined hard plastic case which accommodates the unit itself, the plug-in charger for its onboard battery, the audio interconnect cable, a cigarette lighter power cord, and a concise but very clear instruction manual. There’s even a sheet of paper showing you how to put the unit into its case to avoid scratching the display!
Overall, I’m extremely impressed with both the quality and the overall cleverness of this product. In fact, I’ve been using it instead of the factory-installed altitude alerters in the Part 135 charter turboprops I fly so that I can afford to write for Air Progress. I have no hesitation whatsoever in recommending this fine product to any pilot who flies a significant amount of IFR or even VFR in or near Class B or C Airspace. According to Phillips, approach controllers’ radars are less than foolproof, and a controller who claims your altitude squawk isn’t showing up, and advises you to stay out of the Class B or C airspace, may change his mind after you tell him “my monitor system shows normal replies on code 1234, with mode C showing 2500 feet” or whatever. It can go further, too: the first time an AirSport saves you from getting caught for an inadvertent altitude violation, its price will more than make up for the cost of an aviation attorney to defend you or mitigate the punishment.
Did you know that when Air Traffic Control says “radar contact” it usually isn’t?
Did you know that most of the replies from your Mode C transponder are Mode A?
Did you know that as many as 90% of transponder replies are discarded by ATC computers and never appear on any scope?
Did you know that there are thousands of places where a controller can see the transponder on an IFR aircraft but cannot see a fully-functioning transponder on a conflicting VFR aircraft, and there is nothing you or the controller can do about it? Worse yet, did you know that FAA has these places all mapped out, but does not provide the data to pilots or controllers?
Did you know that some altitude encoders take as much as 15 minutes to start working?
Did you know that when you install an altitude encoder with 10 foot increments, the controller only sees your altitude in 100 foot steps anyway?
Did you know that Mode A, Mode C, Mode S, and TCAS signals interfere with each other because they are on the same frequency at the same time?
Did you know that traffic spacing is often determined by the need to keep transponder signals from interfering? If the Lincoln Labs plan to use the transponder frequency for weather and traffic pictures is approved, our airspace capacity will be drastically reduced!
Did you know that the “reply” light blinks from interrogations, not replies?
Did you know that the official FAA Sun’n Fun arrival NOTAM specifies that we must turn off our transponders when approaching Lakeland? Isn’t the purpose of the transponder to help protect against collisions? And aren’t collisions more likely when there are lots of planes? Don’t you think it’s time to ask the officials why we should turn off our transponders when we need them the most?
Did you know that your transponder is rarely at fault when the controller says it has a problem? The fault is almost always overload of the antiquated, obsolete FAA equipment.
Did you know that the common ATC phrase “recycle your transponder” has no meaning?
Did you know that, inside your transponder, it knows when it is exchanging data with a nearby TCAS-equipped airliner or other heavy aircraft? If your transponder’s only purpose is safety, and it is sitting there on your panel, and it knows you have traffic, shouldn’t your transponder warn you about the traffic?
Did you know that the Airsport Transponder Monitor/Altitude Alerteris a great help in dealing with these problems? This column only scratched the surface, there are many aspects of the pilot-controller relationship that depend on the transponder signal.
Do you have AT-Crabs?–Part 1 of 7
“Radar Contact”. What does it mean when the controller utters those words? Well, like most government gobbledegook, it usually does NOT mean radar contact.
Suppose you key your mike and ask “Is anybody out there?” And somebody answers “Yes, I am ten miles west.” That is “RAdio Detection And Ranging all right, but it certainly is not radar. Bouncing a signal off the aircraft skin and picking up the echo is what radar is all about. Controllers call skin reflection “primary radar”. And they don’t use it much, because it shows too many cars and trucks.
The box we call a transponder is called a beacon by the feds. Air Traffic Control Radar Beacon Service, or ATCRBS. Pronounced AT-crabs. As the primary radar dish spins around, it carries another antenna for ATCRBS. Hundreds of ATCRBS interrogations are sent out each second on 1030 mhz. (The radar is on a much higher frequency.) In the plane, the transponder listens constantly on 1030. Each time it hears an interrogation, it issues a reply on 1090 mhz. If everything works right, that reply results in a blip on the controller’s screen. Since it’s a “radar” screen, the controller thinks he has radar contact! But it’s really just one box asking if anybody is out there, and another box answering back. ATCRBS, not radar.
Incidentally, it’s the 1090 mhz transponder reply that is picked up by the antenna inside the Airsport Altitude Alerter. It receives and decodes all the signals sent down to ATC.
Long ago there was just one type of interrogation. Mode A. Pilots call it squawk code. When the transponder receives a Mode A request, it sends out a string of pulses that carry the four digit code. Mode A interrogations are still the most common. And regardless of the code set by the pilot, the frequency is always 1090 mhz.
The second type of ATCRBS request is Mode C. When this interrogation is received, the transponder sends out a string of pulses that look very much like Mode A pulses. Indeed, it’s often impossible to look at a reply and know if the information is Mode A or C. But the Mode C data isn’t squawk, it’s altitude. This data is supplied to the transponder by the altitude encoder. Mode C replies are on 1090 mhz too.
When ATCRBS sends out a Mode A interrogation, it assumes the reply is Mode A and interprets the reply as squawk code. If Mode C, the pulses are decoded as altitude.
Usually an aircraft is receiving interrogations from many radar sites. Civil ATC, military interrogators, Customs and DEA and more. Transponders don’t know which way the request came from and they don’t care. Transponders reply to everything, in all directions. With many interrogators and many aircraft, this single frequency can get very busy.
Is Mode S a Good Idea?–Part 2 of 7
In Part 1 we discussed the basics of ATCRBS. Mode A is squawk code, and Mode C is altitude. Interrogations from ATC are on 1030 mhz, and transponders always reply on 1090 mhz.
On the same frequency we also find Mode S. “S” stands for select, meaning ATC can selectively interrogate any transponder it desires. That’s a great idea, it was revolutionary when first proposed in the 1960s. Mode S was refined in the 1970s, the scheme was signed off in 1983, and more than a decade has passed since then. How’s it coming?
All commercial carriers of 30 seats or more have Mode S installed, as do some smaller ones and a few general aviation aircraft. FAA is struggling to get it’s first ground stations on line, without much success. So there aren’t many ATC Mode S interrogations yet.
Mode S replies are different than A/C, but they are on the same frequency, 1090 mhz. The average ATCRBS reply contains around 3 or 4 microseconds of energy, Mode S contains either 30 or 58 uS! That means that each Mode S signal contains 10 to 20 times as much energy.
Since there aren’t any “S” interrogations yet, why does it matter how long the reply is? If it weren’t for TCAS, it wouldn’t matter at all. But the airliners continually use this collision-avoidance equipment to interrogate other planes. The feds can’t see Mode S, but other planes can. And do.
Suppose there are ten airliners within radio range of each other. Each sends out interrogations, and for each interrogation the other nine reply. Ten requests, 90 replies. Why is each plane sending a separate message to every other plane? Since the data (his altitude and ID) are the same for each recipient, why can’t he just send it once? Those are good questions to ask the feds.
Ten planes are easy. But suppose there are a hundred. That is 9900 replies. Big long troublesome interference-producing replies. Repeated many times per second.
Plus, TCAS interrogates our transponders too! The requests are only for altitude, TCAS never asks for squawk code. So in addition to all the Mode S clamor on the frequency, there is also a tremendous amount of Mode C. These extra Mode C replies are how the Airsport Altitude Alerters can spot TCAS traffic. And of course there are still all the replies to ATC.
Like ripples in a pond, transponder signals radiate in all directions. Mode A/C replies are 3.3 NM long, when the last of the databurst leaves the plane the leading edge has rippled 3.3 miles in all directions. Mode S replies are as much as 20 miles long! Take an old sectional and draw a circle with a radius of 3.3 NM. Now draw another circle with 20 mile radius. That gives you a picture of the difference between ATCRBS and Mode S, and illustrates why we’re seeing so much interference to our transponders.
Disaster on 1090 Mhz–Part 3 of 7
“Turn your transponder OFF as you approach Lake Parker”. That is in the official FAA Sun’n Fun arrival NOTAM. Too much traffic, all those airplanes will overload the radar, so turn it off.
Is that a joke? Isn’t the whole purpose of Air Traffic Control to keep airplanes from running into each other? And doesn’t the chance of collision increase when there are lots of airplanes?
Why do we have transponders anyway? They don’t do anything to help the pilot, just take up valuable space on the panel, add weight and battery drain, increase antenna drag. It ain’t for us, fellow pilots, the transponder is to help ATC do their job. And their job is to keep us from bumping. So why do they tell us to turn it off when it is needed the most?
Because they can’t handle very many replies, that’s why. The system overloads and goes haywire. Not at Lakeland, but at Orlando and Tampa where the airliners go. And ATC can’t have that!
The problem isn’t limited to Sun’n Fun and Oshkosh. Mark Twombly wrote in January AOPA PILOT about flow control through Jacksonville Center that kept aircraft separated 20 miles in trail because of frequency congestion. And this was because of some football game! What ATC didn’t tell him was that it’s not communications overload, it is overload of the 1090 mhz transponder frequency. Friends, if the capacity and safety of our airspace is upset by a ballgame, we’re in deep —-, er, trouble.
General Accounting Office has documented instances of Tracons shutting down for as much as 15 minutes in rush hour traffic. FAA calls it computer capacity, and they’re right as far as it goes. But the basic problem is that they cannot deal with all the TCAS and Mode S signals that have been piled on top of our transponder signals.
The most common symptom of overload is when ATC cannot see a particular plane. Maybe your plane. Sometimes they lose you altogether. Other times they get squawk, but no altitude. Or the reverse. And sometimes they get both, but altitude is inaccurate. This can lead to altitude violations, but usually ATC and the pilot work it out verbally. The problem comes when a VFR flight is well above the terminal area (or perhaps a military restricted area) and not talking to them, and ATC mistakenly decodes his altitude as within the regulated airspace. The unfortunate pilot did everything right, his equipment was performing properly, but he may get violated anyway.
Sometimes ATC can lose your transponder when they’re not overloaded at all. It’s called AGC, transponders are designed to reply to the closer interrogators and ignore the weaker ones. If you have several nearby TCAS planes constantly interrogating your transponder, it will sometimes refuse to cooperate with the much weaker ATC interrogation. Everything is working as designed, it just wasn’t designed by people who fly.
What? ATC says your Transponder is bad?–Part 4 of 7
OK, the transponder frequency is overloaded. We covered that in the past 3 columns. Now we get to the good stuff. What you can do when the controller says your transponder is faulty.
If ATC says they’re not getting good transponder data, turn your DME off. The books don’t tell you this, but DME and transponder operate on nearby frequencies and they cannot stand each other. So there is a “suppression” wire between them, if DME is busy the transponder has to wait, and vice versa. If you don’t need DME, shut it down. (By the same token, if you’re having trouble getting a DME fix, you might try putting the transponder on standby. Not legal, but it works sometimes.)
The next trick is to ask ATC to go to their backup equipment. Honestly, I don’t know if they do it, or if they just pretend. But sometimes it succeeds. Partly it works because the controller now knows you’re serious. And partly it works because anything that uses up time gives your signal a better chance of succeeding against the overload. So it’s worth a try.
Another ploy is to request a different squawk. Maybe another bit pattern will get through, but it’s probably just the extra controller time.
He will often ask you to recycle your transponder. Nobody knows what that means, just do it! Personally, I do nothing and it works. Whatever you do, don’t turn the transponder all the way off. In most units there is a warm-up timer that begins at turn-on, operation can’t begin until it times out, and you don’t want that.
Most transponders have a “reply” light. If it’s blinking you assume there are good replies. Not necessarily true. The light may say “reply”, but in most units it is activated by an interrogation, not a reply. There could be an internal fault that prevents a reply, but the light will blink anyway. The answer here is a Transponder Monitor.
When ATC reports transponder difficulties, many pilots respond that they have an onboard Transponder Monitor, and it shows that the transponder is operating normally and is squawking the proper code and reporting such and such altitude. Under FAR 91.215(d), the controller can permit the flight to continue even though he isn’t receiving the transponder signal.
Other tricks. Contact another facility. Talk to Center, for instance, even if you are VFR. Verify that your transponder looks OK to them. Then negotiate a handoff to the controller that wasn’t getting your signal. Let Center argue with him on the landline!
Or wait until the last minute before calling approach. Signal strength is twice as strong at the Mode C veil as it was just 12 miles further out. Just don’t penetrate without permission.
Or call from above. If you absolutely positively must get into the terminal area, fly over it and call from there. Again, signal strength is a weapon.
Encoders and Altitude–Part 5 of 7
So far, this series has concentrated on the relationship between the transponder and Air Traffic Control, particularly the overload on the transponder frequency caused by Mode S and TCAS. But what about Mode C? What is it, how does it work?
A few years ago, most of us appended an encoder to our transponder, so it’s easy to think that the altitude data is somehow appended to the transponder reply. But it doesn’t work that way. When ATC wants squawk, they issue a Mode A interrogation, and the transponder sends out squawk code only. When they want altitude, they issue a Mode C request, and the data sent by the transponder contains altitude information only. Interrogations are repeated hundreds of times each second, typically A,A,C,A,A,C and so on.
Mode C data begins as static pressure. Airspeed, VSI, altimeter, and the encoder are all connected to the static system. Imagine an altimeter with no face or hands, just wires coming out. That is the encoder. Most modern encoders use an electronic pressure sensor, but some still use the same mechanical mechanism found in an altimeter.
We frequently reset the barometric pressure on the altimeter, but never reset the encoder. Why? All encoders are permanently set for standard pressure, 29.92″. This is equally true of encoding altimeters, resetting baro only changes the display, it doesn’t affect the electrical data. If this weren’t so, ATC would need to know whether you are using an encoding altimeter or a blind encoder.
Imagine a huge cake, and a tiny insect burrowing through. The layers are vanilla, chocolate, strawberry, lemon, and so on. At each altitude request, the insect shouts “strawberry”. There is no such thing as strawberry and a half. It’s either strawberry, or it’s chocolate, or whatever. The Mode C system works the same way, with layers approximately 100 ft thick. A Mode C interrogation will result in a report of, say, 5000 ft regardless of where you are in that layer.
Another analogy. A calendar shows what day it is. And we know each day is 24 hours. Does that mean ±12 hours? Well, at exactly noon it does, but a calendar cannot tell when it’s noon. 24 hours isn’t the same as ±12 hours, and likewise 100 ft. is not the same as ±50 ft. Forget plus and minus, it’s either strawberry or it ain’t.
If everything were perfect, and pressure was exactly 29.92″, then the encoder would switch at the 50 ft points. As you climb through 1000 ft, for instance, it would read 1000 until you reach 1050, at which time it would change to chocolate!
But the world isn’t perfect. One slice may be 120 ft thick, the next 90, and so on. Every encoder is different. And usually barometric pressure is not 29.92. At 29.97, for example, the report changes from strawberry to lemon at the exact altitude rather than 50 ft higher. As the plane flies along, the Mode C data is jumping up and down a hundred feet and that’s what the controller sees.
What is your transponder telling ATC ?–Part 6 of 7
In Part 5 we discussed Altitude Encoders, and the hundred foot increments. The altitude layers are like a huge cake. Vanilla, strawberry, chocolate layers. When an encoder reports altitude, it doesn’t know where it is within the layer, it’s strawberry until it changes to chocolate.
Consider this scenario: A pilot owns a beautiful aircraft and bases it at an outlying field near a major city. He strives to keep his airplane in perfect shape, he certainly wants everything to be legal. On a beautiful morning he goes out to the field, along with his instructor and mechanic and all the FAA inspectors and legal brass he can find. He asks them to find something illegal about the plane, or about the flight he is preparing to make. They swarm all over the plane and it’s paperwork. And they check his papers too. After consultation, they all agree that both the pilot and the aircraft are legal and ready for the flight.
The pilot gets in, starts up, taxis out and takes off. He makes no mistakes at all. And when he lifts off the runway, he is instantly illegal!
How could this be? It is simple: He is flying within the Mode C veil, and his encoder isn’t warmed up yet!
Warmed up? Most encoders have a pressure sensor housed in a tiny “oven”, and until it reaches operating temperature the encoder output is inhibited. Which is good, if the data weren’t turned off it would be erroneous, and that’s both illegal and unsafe. (AR-500 owners, beware!) The pilot should be provided with an indication that the encoder is alive, but the manufacturer chose not to give him that information.
Some encoders take as long as 15 minutes to reach operating temperature. Most take 5 to 7 minutes. And the mechanical encoders and encoding altimeters have no warm-up time at all.
A Transponder Monitor is the best way for the pilot to see when his encoder comes alive.
What about accuracy? We must get correlation checks every 24 months, but what does that mean? Many shops only check 4 or 5 specific altitudes, they cannot take the time to check every 100 foot increment. It’s usually not necessary. But some encoders can check good at certain spots, yet be off in between. Plus, the correlation check is done at just one temperature. What happpens when the weather gets hot or cold? And the correlation test is done on the ground with the engine off. Vibration prone intermittent connections between encoder and transponder often aren’t found. A Transponder Monitor is the answer here, too. The pilot can see exactly what his equipment is reporting to ATC all the time.
A few encoders have ten foot increments. In the plane they do. But the Mode C world is made of 100 ft layers, and there is no place in the bit codes for anything finer. So, no matter what encoder you have, your transponder only broadcasts altitude data in hundred foot slices.
In the final installment, we’ll wrap up by discussing reasons the pilot needs to see everything his equipment is telling ATC, and leave you with a puzzler.
Flying in Two Worlds–Part 7 of 7
The theme of this series of articles has been the transponder. As pilots, we give more attention to fancy GPSs and moving maps and such. The transponder is a rather ho-hum piece of equipment. Yet it is the link between the aviation community and the feds. What they see about us is what the transponder tells them. When it tells the truth we benefit. When it doesn’t tell the truth we risk violations or worse.
And when the link overloads and the truth gets lost, or the link breaks down due to obsolete equipment and idiotic rules, aviation suffers needlessly.
We fly in two worlds at the same time. In the real world are the majestic towering CUs, fantastic sunsets never seen by surface-dwellers, and a thousand other experiences that mere mortals never enjoy. The real world contains embedded thunderstorms and uncharted towers and magneto failure, too. And we fly in the regulatory world, full of restrictions and FARs and thou-shalt-nots of every description. We must successfully navigate through both of these worlds simultaneously.
The transponder is sort of a bridge between the two worlds. That’s why it’s important to know what your transponder is reporting.
Here at Airsport, we know our Altitude Alerter / Transponder Monitors don’t have the sex appeal of color moving maps, but they serve an important need. We’re very proud of them. Our PRO model has been proven on the market for more than 3 years, they are flying on every continent. During that time we’ve listened to our customers and added many features, including baro pressure in millibars for Europe, and the ability to see the actual transponder pulses for avionics shops and the technically inclined. Two other models have been added, offering the features most pilots need at money-saving prices.
Call or write and we’ll be pleased to provide information on the full range of AirSport’s Altitude Alerter models.
I promised to finish the series with a puzzler. How about this one:
Imagine two identical aircraft. Not just similar, but aircraft absolutely identical in every respect. All instruments are calibrated precisely alike. No differences whatever. These planes are flown by pilots that are exact duplicates as well. They do everything precisely the same, in accord with common operating practice.
On the flight in question, we find these two planes flying along at the same speed, wingtip to wingtip. Same altitude, same heading, same temperature, same everything. And there has been no equipment failure, no damage, no ice, no problems. Got the picture?
But when we look inside, we find that the altimeter in one aircraft is reading hundreds of feet lower than the altimeter in the other plane. Yet when they land, both altimeters agree perfectly. How can this be?
Drop me a card or letter if you figure it out! Or contact me and I’ll let you in on the answer. Fly safely!
Imagine a powered aircraft that is as silent as a sailplane with smooth torque that produces no airframe vibration and is compatable with a silent propeller.
Imagine quietly cruising above the weather in a single engine plane at 30,000 or 40,000 or 50,000 feet with a powerplant that increases power with altitude.
Imagine burning a fuel that is less flammable and safer in the event of an accident.
These five stories are set slightly in the future, but only slightly. Perhaps five years from now. The technology described is an accurate portrayal of ATC systems of today, or in the case of ADS-B, an accurate portrayal of systems that are test flying today. The individuals and situations are fictional of course.
A lone mideast terrorist comes to the United States and purchases (or rents or steals) a light aircraft such as a Cessna 172 or Beech Bonanza or Piper Arrow. While selecting his plane, he is looking for just one item: ADS-B collision avoidance equipment. He knows that ADS-B, installed on all airliners and some business and pleasure aircraft, automatically reports the precise position of the aircraft and also the identity of the aircraft, twice per second.
He has no particular target, his only desire is to cause as much fear and destruction and death to The Great Satan as possible. Having waited for a day of poor visibility, he completes his prayers. Then he flies at low altitude and slow speed above the busy highway toward a major airport. He knows that Air Traffic Control radar will not see him because he has disabled his transponder output, thereby assuring that there will be no secondary returns nor any ADS-B transmissions. His aircraft is smaller than the tractor-trailers on the highway below, and the ATC primary radar has been programmed to eliminate highway clutter from the display. He will not be seen.
The terrorist also knows that the interval when a large aircraft is most vulnerable is on final approach. It is moving slowly at low altitude, flaps and slats and gear are extended and engines spooled down, this is the point in the flight when the plane is least maneuverable. Using the ADS-B readout to spot his target, he flies up the glideslope and directly toward the doomed airliner.
Until the last moment he cannot see the oncoming plane but he knows it is there. The display on his ADS-B is showing its altitude and position with an accuracy of a few meters. The airline crew, monitoring their instruments and complying with pre-landing checklists, never sees him at all. At the last instant he shouts “Allah Akbar” as he flies thru the windshield of the larger aircraft, taking hundreds of people to their death.
I’ll call him Joe. He is not mentally disturbed, at least not any more disturbed than the average guy in this hurried-up society. His intelligence is above par, it’s just that he doesn’t have any ethical constraints. Joe might have become a successful bank robber or con artist. But Joe is a loner and has long understood that the cops can’t infiltrate a group of one. Plus, he’d rather have 100% of the take than to split it with guys who might get drunk and tell the whole story to some hooker. Joe is sharp on computers and enjoys playing with model airplanes, and would rather be tinkering with technology than shooting pool at the neighborhood bar.
In the vernacular, Joe is a geek.
One day Joe reads an article about ADS-B. It tells how the planes are precisely reporting their 3D position, in the clear on 1090 MHz, twice per second. And here’s the best part: the identification of the specific aircraft is included along with the position. Suddenly he envisions the whole plan. Extortion! A million dollar bank robbery would be impossible for one man, but a million dollars is pocket change to the airlines. He flips a coin and decides that UAL is his target.
The question is, should he ask for the money first and only destroy an airliner if his demands are refused? Or should he begin by dropping one flight unannounced? The former requires credibility, he will have to reveal how he is going to carry out the threat if his demands are not met. This means he will have to disclose some of his ideas and perhaps provide a photograph of his weapon. Worse yet, it requires more than one exchange of information with the airline. After the first letter, the FBI and everyone else will be scurrying to find him. Best to keep the exchanges to a minimum.
The latter choice, destroying one plane first to demonstrate his capability, seems more foolproof. He can do that before anyone knows what is going on. Then, if the airline balks on payment, he can threaten to publicize the reason the plane went down and drive their customers away overnight. United might fear the publicity as much as they would fear another crash.
Joe goes to work. He builds a model plane, a large one. He has already attended model meets where 1/4 scale planes were flown, he knows that some models weigh nearly as much as a real airplane. Joe’s plane will only have one flight, it need not be pretty nor fast nor powerful, its sole purpose is to precisely meet an airliner on final approach while carrying a gallon of gasoline to explode inside the airliner cockpit when the planes collide head on.
He doesn’t have access to ADS-B equipment, but that doesn’t matter. It’s a simple task to put a $100 GPS receiver from WalMart in the model plane, coupled to a readily available wireless LAN card. With a similar card in his laptop, he can monitor precisely where his aircraft is. Joe doesn’t have a lot of test equipment either, and it might be time consuming to build a 1090 MHz ADS-B receiver from scratch. Instead, he simply takes the receiver from a DBS satellite system he purchased at the discount store for $199 cash. That receiver, half the size of a deck of cards, tunes from 950 to 1450 MHz which is precisely what he requires. All Joe needs to do is write a little software, and voila, he can monitor the exact position and identification of every airliner within 20 or 30 miles.
At this point, Joe has been able to do the entire job single-handedly with information and materials that are readily available and 100% legal. While finishing construction of the plane, he spends a few days listening to the tower and watching the ADS-B data on his computer. Soon he has a good list of United Airlines ADS-B ID tags. He is ready to go, and no other person on earth has any idea what is about to happen.
Thomas Whitten, Ph.D., is a brilliant scientist. He served honorably in the Army during VietNam, finished his education soon after, and has been working for a major pharmaceutical firm ever since. His career reached its peak when he developed the latest miracle drug which will ease suffering and save untold lives worldwide.
“I was a loyal employee” Tom said. “Many of my colleagues jumped from one firm to another, always at an increase in pay. I didn’t. I stayed here year after year, decade fading into decade, because I truly believed in what I was doing. For the past 17 years I have been working on a single project, trying to unravel the relationship between DNA and this particular disease. It was rewarding when we made progress, it was discouraging when we didn’t, and altogether too much time was wasted cajoling management to fund our work. Several times the project was almost canceled, and each time I managed to convince the executives that we should continue.
“And look at the company now. We were the stars of the latest mega-merger, the largest ever in the pharmaceutical arena. Our stockholders made billions, literally billions, because of my work. The CEO himself received a $14 Million bonus, other top management guys received millions more.
“And me? What do they give me? A nice little write-up in the company newsletter, that’s what I got. I’m making $94k a year, and when I retire next year I’ll drop to 60% of that. Don’t those bastards understand who produced the drug that created all the wealth? Yes, I think they understand. I think they just don’t give a damn.”
That was all Dr. Whitten said aloud. But the longer he thought, the angrier he got.
It ate and ate at him, eventually reaching the point where he couldn’t take it any longer. He briefly contemplated rigging a virus release in the laboratory but that didn’t make sense. His fellow workers weren’t the problem and he wouldn’t do anything to harm them. Management was the problem and they didn’t work in the laboratory, they divided their time between the head office in New York and company facilities scattered across the globe. They spent their time flitting from place to place on one of the company jets rather than working………..wait a minute – that’s it. The company aircraft! Planes carry top executives. And planes crash.
He established several guidelines. First, his plan must not put him in physical danger. Second, to the greatest extent possible it must not put innocent parties in danger. Third, it must be repeatable because it may take several crashes to achieve the objective. That ruled out trying to plant a bomb on a company aircraft. He might get by with it once – or he might get caught or be blown up in the attempt – and in any event he couldn’t manage it repeatedly. Bombs were out, he had to find another way.
If there was one thing Tom Whitten knew how to do, it was research. He had no aviation knowledge beyond a lot of coach class business trips and a handful of trips in company jets, plus the little he remembered from his military days. He had no specific knowledge of how to cause a plane to crash but he had faith it could be done.
So he went to work. He combed aviation journals at the university. He combed the internet. He kept meticulous notes. Under an assumed name he called various aircraft and avionics manufacturers and interviewed engineers about system specifics. He talked with FAA maintenance personnel too. All the information was there, in the open. It wasn’t classified, it wasn’t trade secret, it wasn’t even company confidential. He asked how a plane was navigated, how it interfaced with Air Traffic Control. He learned what the crew did and what systems they depended on for guidance. He learned what portion of the flight was most hazardous and vulnerable. He studied the localizer and glide slope and marker beacons and DME and GPS and all the rest. He bought a Radio Shack airband radio and became familiar with communications jargon. Eventually Tom found the RTCA documents that contain the standards each navigation system must meet. Every tiny detail was openly available.
And he learned about ADS-B. When Dr. Whitten located RTCA DO-242 he knew he had found the mother lode. This was the key to the whole plan. He wanted to destroy specific aircraft while causing no harm to others. ADS-B reports the precise location of the aircraft, in 3D coordinates, and simultaneously reports the identity of the aircraft. That was exactly what his plan had been missing, the means to target a specific plane, and ADS-B provided it.
Outsiders imagine that lab researchers spend their days stirring test tubes and peering into microscopes. Once upon a time that was an accurate picture, but electronics is the dominant force today. Tom was skilled in designing instrumentation to solve fresh problems. Now he turned this talent to his new field of interest.
In ADS-B, every plane has a unique 24 bit identifier which remains with the aircraft. In fact, there is an algorithm to convert tail number to ADS-B identification number. It was a simple matter, with binoculars, to get the “N” number of the company jets when they came to town. Dr. Whitten then hand-processed the algorithm and learned the 24 bit ID code of each plane. Now he could receive the 1090 MHz frequency and know which plane was which.
His plan was simple. On an instrument landing the plane is following electronic signals. The localizer gives left/right guidance, the glide slope provides up/down information. The former is on VHF, the latter UHF, with the frequencies openly available on aircraft approach charts and other documents. The signals are not encrypted, they aren’t even digital. The ILS signal, like most of aviation technology, was established near the end of World War II and long before the invention of the transistor or integrated circuit. Some systems (such as the ancient amplitude modulation used for voice communications) date back far earlier. Aviation is unlike other fields of endeavor because the people who develop the technology are not the people who use the technology. And a third group who are neither skilled in the technology – nor skilled in the use thereof – are the ones who make the decisions. Through the years a lot of wacky decisions have been made. In the case of ILS, the radio carrier is amplitude modulated by two tones, 90 and 150 Hz, which are equal amplitude if the plane is centered on the beam. If a particular aircraft receives a false signal it will follow a false path.
Traditionally the marker beacons, all on 75 MHz, give the pilot an indication when he is nearing the airport but do not allow any sort of readout to the touchdown point, so Tom could ignore them. Often the pilot monitors his Distance Measuring Equipment, DME, to determine his distance to touchdown. Tom reasoned that it would be easiest to simply jam the DME frequency for the critical few seconds. Likewise with GPS, once he had identified his particular aircraft he would jam the very weak Global Positioning Satellite signals on 1575 MHz.
None of this was particularly difficult for an experienced researcher such as Dr. Whitten. Indeed, a kid with an interest in ham radio could do as much. But Tom had access to decades of obsolete instrumentation from which he could scrounge the necessary bits and pieces. The ultimate irony, he could use company material to accomplish the objective.
It was easy to phase lock the ILS spoofing transmitters to the real ILS signal, from a van parked a mile or so from the airport and under the final approach. He used directional antennas that beamed his signals upwards to the particular flight while anyone else on the approach would receive the proper ILS signal. Phase locking his signals to the actual ILS would assure that there would be no flag or indication when the target aircraft transitioned from the correct signal to the spoof. Sure, it took some effort, but the specifications were all available so it was far easier than other projects he had accomplished.
The weather was miserable the night of the first crash. Most flights were landing successfully, but missed approaches weren’t uncommon. Some planes were experiencing airframe ice, winds were gusty and unpredictable, the rain was heavy at times, and ATC had traffic backed up halfway to Cleveland. The company Gulfstream IV was making what appeared to be a normal approach when it began to drift to the right. It descended prematurely about a half mile from the end of the runway, struck an embankment at the outer perimeter road, bounced over two maintenance buildings and a communications shack, hit the ground with its left wing, cartwheeled, and burned. All aboard were killed.
The NTSB accident investigation concentrated on the navigational aids, aircraft systems, ATC actions, and crewmember performance. The ILS checked out perfectly and no other plane had experienced any ILS problems. The aircraft systems checked out OK, at least the parts that could be reconstructed. ATC had made no blunder and there was nothing on the communications or radar recordings to indicate a problem. Predictably, the crash was blamed on pilot error.
But Thomas Whitten, Ph.D., wasn’t finished. Several months later, at a different airport, the same pharmaceutical company mysteriously lost another flight.
Scenario Four….Data Mining
One hot new field in the information age is data mining, extracting and refining nuggets of valuable information from the immense field of electronic data that exists all around us. Some data mining is legal, some is illegal, but most is too new and expanding too fast for any legal or ethical framework to develop. The old fashioned concepts of privacy and ownership are being questioned in ways that were unimaginable 20 years ago.
Meet DataMiners, LLC. For a small fee, DataMiners makes it easy for a company to track its fleet of aircraft. Or the fleet of the competitor. For an additional fee, DataMiners will reduce and analyze the information. For instance, the news that the competitor’s bizjet traveled to a specific plant is not particularly useful. But when travel patterns are analyzed and combined with data from other sources, a message emerges that the competitor is having quality problems, or vendor problems, or management problems. Or perhaps the competitor is secretly developing a new product or negotiating a merger. Information like this is quite valuable in the marketplace.
Wouldn’t a stock trader have liked to know that the Chrysler and Daimler Benz aircraft were visiting the same destination – on the same days – in the months leading up to their merger? Our securities laws protect the market from insider information, but DataMiners LLC is an outsider and whatever they discover is available to the highest bidder.
Whether it’s a mid sized company or a multinational corporation, conducting business in privacy (and thus traveling anonymously) is essential to survival and maintaining the competitive advantage. In an ADS-B world, the company aircraft will be a liability rather than an asset.
The National Business Aircraft Assn, NBAA, has already learned this lesson and has done a complete turnaround from their earlier support of Aircraft Situational Display (ASD). ASD is somewhat similar to ADS-B, it also reports which aircraft is where. But ASD is limited to aircraft operating under Instrument Flight Rules, the data is compiled by the FAA, sensitive data such as military flights is deleted, the position of the aircraft is not sufficiently precise for tactical purposes, and the data is slightly delayed before release by the FAA. (For more on this from NBAA’s perspective, seehttp://www.nbaa.org/digest/1998/11/opsnotes2.htm and http://www.nbaa.org/pr/1998/98-18.htm .
Unlike Aircraft Situational Display, ADS-B comes directly from the aircraft and is freely available to anyone with a 1090 MHz receiver without passing through any agency for filtering or control. ADS-B and efficient use of the corporate fleet are incompatible. If we are promoting aviation for business purposes, we must oppose ADS-B.
Scenario Five….User Fees for General Aviation
Harvey Patton started his company for the best of reasons. His city was about to close the airport and turn the land into an industrial park. The various factions had fought over this issue for years and Harvey realized that if the airport users were seen to be paying their own way, and perhaps paying a bit extra, then the city could be convinced to keep the airport open.
In that light, local airport user fees didn’t look so bad. If the fees were structured according to the weight of each aircraft, the bulk of the expense would be borne by the companies that could afford it while the pleasure pilots would only pay a token sum. It sure beat losing the airfield.
So Harvey went to the city with this proposal: He would supply and maintain the equipment at no cost to the city, all the city had to supply was a place to house a PC and antenna. The equipment would receive and log the ADS-B signals and routinely modem the data to Harvey’s business where billing and collecting would be done. The city would receive 85% of the monthly billings without lifting a finger to do any work. All aircraft activity would be monitored 24 hours a day, 7 days a week whether the tower or FBO were on duty or not.
The city accepted, and the idea worked. Every month the city received a substantial check which went into the airport fund and provided a surplus. Everyone was happy. Well, the users weren’t totally happy but they realized it was better than closing the airport altogether. And many users, the smaller aircraft, were escaping user fees by not installing ADS-B. True, not having the collision avoidance equipment meant a higher risk, but many pilots were more concerned with high costs than improved margins of safety.
Harvey realized that we are losing an airport a day in the United States and some of those are important GA facilities similar to his airport. He went to those cities and sold the same deal, it was easy to do the automatic billing and collections from his location. He was getting 15% of the take from a number of fields and the revenue began to roll in. Next step was to approach the Westchesters and Addisons all over the country with the same arrangement, every airport needs additional funding and this deal was too good for them to resist. Business increased by leaps and bounds (or takeoffs and landings) and Patton Aviation Revenue was a resounding success.
Within a few years Patton equipment was working all over the country. It was installed, it was functioning, it was a proven source of aviation funding. Of course the users were unhappy, particularly at the fields where the fees were set to limit traffic or limit noise or for some other artificial reason. But the corporate users, those who were required to use ADS-B, had no alternative but to pay.
Then the new Congress instituted federal user fees for General Aviation. This hadn’t happened previously because there was no billing and collecting infrastructure, but Harvey Patton had changed all that. Or more accurately, ADS-B had changed all that.
The feds contracted with Patton Aviation Revenue in the same way they contract with Jeppesen or Flight Safety or others who provide a service. Patton did the billing and kept a percentage of the take. Suddenly every takeoff, every flight mile, every landing was computer monitored. VFR or IFR, the airspace bill arrived at the end of the month.
The users screamed, they cursed Harvey Patton, but it was no use. If they were going to fly with ADS-B they were going to be billed. Yet the pilots with foresight, those who had never installed ADS-B, weren’t paying a cent. Until a court action was filed, that is.
The US Federal Court for the Ninth District ruled that all airspace users must be treated equally. The court left it up to the FAA to determine what “equally” consisted of but the edict was firm, equality in user fees had to be maintained.
What happened then? There are many possible endings to this story. Maybe each non-ADS-B aircraft received an “average” bill every month whether they flew or not. Or maybe every plane was forced to install ADS-B and the resulting frequency overload created the same situation we’ve had at Oshkosh for many years: “turn your transponder to standby when 30 miles out”. Then the planes, with their ADS-B turned off, were prohibited from flying in controlled airspace. Or maybe the aircraft owners simply gave up and sold the birds for whatever they could get and pleasure flying died, taking FBOs and manufacturers with it.
Today it is not possible to saddle General Aviation with user fees for one simple reason – there is no infrastructure to collect those fees. The test that aviators must apply to ADS-B (or any similar technology) is simple: Are there any words that Congress could say that will hurt us? If the answer to that question is yes, then pilots and aircraft owners must reject the technology.
Proponents of ADS-B tell us that there will be an “anonymous” mode that the pilot can select. But that will be true only as long as the rules permit it. Once upon a time we could turn off the transponder if we wanted to, but as the years passed that choice was eliminated. The same will inevitably be true of an anonymous setting, it can only be used until it is prohibited. First prohibited at flight levels and at major hubs, then prohibited in IFR, then prohibited, period.
Proponents of ADS-B also tell us that we can be tracked today. That is somewhat true, but recent experience in the well publicized JFK Jr. accident is instructive. His plane went down around 9 PM Friday and the search and rescue efforts began at 6 AM Saturday. Those efforts continued, under intense press scrutiny, through all of Saturday, all of Sunday, and all of Monday. Around midday Tuesday the FAA finally decoded enoughof their radar tapes to determine the location where the plane went into the water. After the spot was pointed out, the remains of the aircraft were promptly found.
It took FAA more than 72 hours to find one aircraft, an aircraft that the President of the United States and the world press corps were actively interested in finding. Given the number of flights daily, it is clear that the FAA does not begin to have the resources to track and bill every flight.
Tracking every IFR flight would be somewhat easier, but many of those will switch to VFR if there is a substantial money saving. And if it comes to that, safety will suffer. Isn’t safety what ADS-B was for in the first place? Don’t you detect something wrong here?
This is Who I Am – This is Where I Am
Automatic Dependent Surveillance – Broadcast, ADS-B, links an unambiguous “This is Who I Am” with a very precise “This is Where I Am”. Never before in aviation have we put those two pieces of information together and broadcast them in the open for anyone to receive and use as they see fit. We should not do so now.
Decades of ATC experience have proven that identification of traffic is not something the pilot needs. He or she needs to know where the traffic is, which way it is moving, perhaps its size or its speed, but never its identification number. ADS-B flies in the face of this experience.
ADS-B has not been widely deployed yet. There is still time to stop it. Most airlines have not invested any money in it yet, nor have the government entities nor the general aviation community. I suggest that it is not in the best interest of aviation to deploy ADS-B in its present form. Like AAS, MLS, and other recent systems, its gestation has exceeded its usefulness. ADS-B made a great deal of sense when it was first proposed. But data processing capability is not the same today as it was twenty years ago. We live in a different technological world now, just as we live in a different political environment.
The ADS-B community will laugh off my scenarios. They will explain that identification is necessary in order for aircraft to autonomously interchange information and automatically negotiate evasive techniques. That was true 20 years ago, it is not true today because of the great strides made in computer and DSP technologies. “Not Invented Here” is alive and well in the ADS-B community, these people have devoted major parts of their careers to ADS-B and its understandable that they are unwilling to see their system rejected. Nevertheless, aviation deserves a collision avoidance and traffic management tool that achieves the positive objectives without the serious negatives I have described.
Would Anyone Use a Transponder Reply to Destroy an Aircraft?
In a word, yes. Litton Guidance & Control Systems makes such equipment and offers it openly on the internet. Read the Litton AN/PPX-3B overview, FAQ, and specifications.A similar Litton product is their TPI-10, here are links to the overview, FAQ, and specifications.
If Litton (and their competitors around the world) can do that with a common transponder, think what they can accomplish when ADS-B reports the aircraft’s exact identification (not just a squawk code) and simultaneously reports a very precise 3D position!
The potential ADS-B threat is immense.
Why Am I Writing This?
My purpose in writing these scenarios is to illustrate the problems that I perceive. I am not delivering a threat, rather I am delivering the message that ADS-B is a threat. ADS-B is a terrorist’s dream and security’s worst nightmare. I have previously talked with various people within the FAA, with no success. It seems to be a matter of compartmentalization or jurisdiction. I have talked with those charged with “aviation security”, they see their job as one of gates and fences and bomb-sniffing machines. They are not concerned with anything that happens after the wheels leave the runway. I have talked with ATC and ADS-B systems people, they have no interest beyond air traffic control and airspace utilization. I have spoken personally with FAA Administrators Hinson and Garvey. In essence, the ADS-B security problem falls in an FAA department that hasn’t been created yet. In addition, there is a great deal of buck-passing between FAA and ICAO and RTCA and the EU and other participants. No one wants to reject “progress”, and ADS-B inches closer to reality.
Am I Shouting Fire in a Crowded Theatre?
Is my message “shouting fire in a crowded theatre”? No, it is not. I am shouting the grave potential of fire in a theatre that has not yet been built. There is no danger to the public, nor to the republic, from my message. The danger is within ADS-B itself, and my sole intent is to educate the aviation community as to that danger in time to stop the construction of this dangerous system.
My background in this topic comes from a decade of designing, producing and marketing general aviation equipment that receives the 1090 MHz frequency, and as a pilot and aircraft owner with more than 30 years experience. I have learned how easy it is to receive the data, and how much diverse data is available on that frequency. I understand that any data can be used for good or it can be used for evil. And I believe that the systems of tomorrow must be designed with both in mind.
Do we need ADS-B?
Something like ADS-B is necessary as we move into the future. As aviation matures, there are compelling reasons why we must move beyond a manually operated Air Traffic Control. Traffic density is already straining the limits of what a human-centered control system can accomplish. For the forseeable future there will be a human involved when needed, but the routine separation chores can be handled more easily and more efficiently by technology.
So yes, we need an ADS-B sort of system, but without all the negative attributes of ADS-B. Identification is not needed, every databurst will contain a unique identifier within the lat/lon/alt. If two aircraft have the exact same position, they have collided already. Conversely, if they have not collided, by definition they have different positions and thus different and unique identifiers. There is no need for any further ID to permit automated data exchanges between various aircraft.
As we move from an old fashioned manual method of sequencing aircraft toward an automated system we must plan for a larger number of aircraft. ADS-B as presently envioned does not have the capacity for tomorrow, in fact it does not have the capacity for maximum situations today such as the EAA Oshkosh event in Wisconsin every August or the Sun’n Fun event held at Lakeland Florida in April of each year. System capacity is an important matter that has been neglected by the proponents of ADS-B.
One way to maximized capacity is to limit the quantity of information to only that which is needed. This is a further argument against ID, decades of air traffic control experience have shown that the pilot does not need the registration number of his traffic. Maximizing capacity also argues against the concept of reporting at regular time intervals such as once per second or twice per second. The fact is, aircraft do not collide because of time, they collide because of distance (or rather the lack thereof!). It makes sense for an aircraft that is moving at 600 knots to report every second, but makes no sense whatever for an 85 knot aircraft to report that it has managed to travel a few yards since it’s last report one second earlier.
A far better idea is for aircraft to report based on distance travelled, such as every 1000 ft. That would provide for six reports per nautical mile while reducing the spectrum usage by a great factor. That same factor would allow for many more aircraft.
Besides providing for traffic densities beyond those we experience today, such a system must be robust, it must provide the maximum in operating efficiencies and airspace utilization, it must work equally well at any location whether in radar view or not, it must be able to fail gently and with a maximum of safety margin, it must be sufficiently affordable for all airspace users, and it must do all of these things in a manner that does not aid terrorism nor espionage nor infringe civil liberties.
There are proposed systems that provide the benefits of ADS-B without the deficiencies and dangers. The flying community must speak out on this matter, only then will our concerns be heard and acted upon. My goal in authoring this paper has been to aid pilots, aircraft owners, system developers, and the general public in understanding the situation from a viewpoint different from the FAA.
Do you disagree? Or agree? Will you participate in a dialog?
Most messages I have received in response to this article have said, essentially, that I don’t need to worry because there are people taking care of my concerns. I don’t buy that argument because the RTCA document defining ADS-B contains all the problems and none of the solutions. On the other hand, there have been a few messages that are both reasonable and articulate, and I’d like to share them with you(click here). If you would like to contribute to the dialog, please email me and I’ll post your message.
Who is doing this to aviation?
Here is the list of participants in RTCA Special Committee #186, the people who created ADS-B. If it is a success, here are the people you can thank. On the other hand, if ADS-B provides the structure for terrorist activities, for corporate espionage, and for General Aviation user fees, here are the people you can thank.
I have listed employees of the US government agencies in red, FAA contractors in pink, and general aviation representatives in blue. FAA frequently makes the point that RTCA is an “industry” group which “advises” the agency. As you can see for yourself, there are 271 members of SC-186. Of that 271, 58 (21%) are US government employees, mainly FAA employees. Another 35 (13%) are employees of think tanks operating on FAA money and under the direct FAA control. Beyond that are the many government hardware contractors such as Lockheed, Hughes, Honeywell, and Litton; the foreign aviation regulatory agencies; the airlines and their suppliers; plus a myriad of manufacturers, satellite communications companies, and others who want a piece of the ADS-B pie.
Balanced against all of the above are six (2%) members supporting General Aviation. Only six. Just think, 90% of the United States aircraft registry only gets 2% of the representation!
Everything connects to everything. In this case, we are talking about the AirSport Altitude Alerter, aircraft transponder and altitude encoder; plus the Air Traffic Control ground equipment and TCAS gear now used in airliners. In order to understand how the AirSport Alerters work, we need to discuss a little about the system overall.
First there was radar. It bounces a radio signal off the aircraft, and measures how long it takes to make the trip. This works, not only on planes, but on trucks and weather and so on. To keep extraneous echoes off the controller’s scope, the FAA developed ATCRBS, or Air Traffic Control Radar Beacon System. The “beacon” is what we call a transponder. It isn’t radar at all, but it comes up on the same scope and the controller calls it radar. ATCRBS sends out an “interrogation” and the transponder in the aircraft replies. It is this reply that is used by the AirSport Altitude Alerter.
There are two types of interrogations and two replies. If the interrogation is Mode A, the reply is a coded pulse stream consisting of the four digit Squawk code. Mode A means squawk. But if the interrogation is Mode C, the transponder replies with coded pulses containing the altitude.
Mode C interrogations also come from TCAS. This collision avoidance equipment installed in airliners asks other aircraft for their altitude. It is possible to be out of range of ground based radar, but still be responding to an airliner with TCAS.
All transponders use the same data encoding scheme and transmit on the same frequency of 1090 MHz. This commonality is what allows you to use the AirSport in any aircraft. The receiver in the AirSport Alerter is tuned to 1090 MHz and it picks up the data.
There is no difference between Mode A and Mode C data. They are identical. The ground equipment asks for a squawk and they interpret the reply pulses as a squawk. Or, they request altitude and decode the reply as altitude. It’s easy for them, since they know what they requested.
Inside the Airsport Alerter, it is a more difficult task. Sorting Mode A from Mode C is an important part of the microcomputer’s job. There are 4096 squawk codes, and 1280 of them also decode as altitudes. This gives a range, in 100 ft steps, from -1200 to 126,700 ft.
The Airsport Alerter produces audible warnings via the headset and/or aircraft audio system. It also provides a direct, audible warning from the internal horn located on the back panel. The headset tones use a variety of distinctive sounds, and are adjustable in volume. The HORN switch on the front panel turns all the sounds off and enables the pilot to quickly silence the Airsport unit when needed.
At 900 ft. prior to reaching the selected target, a single tone sounds. When the target is reached, a single tone is again heard. After reaching target altitude, any deviation outside the tolerance zone produces warnings. The tolerance zone is user selectable. If the aircraft climbs above or below the tolerance zone, a musical trill is heard for each one hundred feet of deviation from target. These fly up and fly down tones are repeated every ten seconds until the altitude is within tolerance.
Inside the PRO is the 1090 MHZ receiver, a microcomputer, and the circuitry required to display the data, make the warning tones, and so on. The antenna is contained within the case.
The Airsport Altitude Alerters are very easy to use and will work in any aircraft, with any headset, in nearly any location. There are a variety of other features that you will use every time you fly, such as setting a Descent Altitude and calculating your Rate of Climb.
Click on the link below to return you to the AirSport Avionics home page and learn more about these unique products!
Tightrope artists amaze me, especially the ones that pull stunts like walking between skyscrapers, or across Niagra Falls. Creeping along that narrow wire, with nothing but a long pole to help maintain balance. As long as the same weight is kept on each side, stability is maintained. You just never see a walker standing upright on the wire with the pole extended all to one side. It doesn’t work. Balance is the key.
Aircraft are a lot like tightrope walkers. Balance. The lift on each side must be balanced exactly. A plane may have a critical engine, but it doesn’t have a critical wing, both wings are equally important. Asymmetric lift causes the craft to roll; uncorrected, it develops into an ever-tightening maneuver and disaster.
I’ve been thinking about this matter of balance, about how it applies not only to the physical machine, but to aviation itself. Since the 1950s, General Aviation has been in exactly that sort of maneuver, a tightening spiral toward extinction. Aircraft production figures declining steadily, rules and restrictions ever tightening, costs exploding. It is tempting to blame the FAA, it is easy to blame liability and the lawyers, it is convenient to blame the stodgy manufacturers or this group or that group, but the fact is that none of those are going to save us. We are flying this plane, and nobody on the ground is going to do anything to correct our problems or straighten our path. It is up to us who love to fly. We must get our act together, determine our priorities, and get this bird to straighten up and fly right.
During the same years that General Aviation has been declining, other similar interests have grown by leaps and bounds. We all exist in the same economy, all compete for the available dollars. Why didn’t aviation keep it’s market share? What are we doing wrong? There are many answers, but part of it relates to the people we attract and, more importantly, to those we turn away. Example: You can read boating magazines without encountering pictures and stories of attack submarines or amphibious assault vehicles. You can subscribe to car magazines, and find no reference to army tanks or military vehicles. Yet it’s hard to find airplane magazines that don’t feature military aviation, past or present. I’m not singling out the magazine publishers, it’s true throughout aviation. We turn a big segment of the population off.
We pilots tend toward politics that might be termed right wing. That’s why we have the close tie between military aviation and general aviation, a tie that isn’t found in boats or cars or motorcycles. We tend to earn a higher income, and more of us are ex-military than the non-pilot population. So it’s natural that we tend toward right wing politics. Unfortunately, a plane with only a right wing won’t fly. Tightrope walkers understand this.
This explains the name of the series, The Other Wing. I hope in future months to offer ideas on how we can regain our equilibrium and fly out of this death spiral. Not by cutting off our good wing, but by building an equally good left wing, by adopting and adapting the best from both sides, combining strengths and canceling weaknesses.
The Other Wing involves a lot more than that. It is a different viewpoint of general aviation. We are a tiny minority in a society ruled by majority, and we need to find alternative methods to protect our interests. We must learn how to compromise with society while ensuring our survival. We need to learn techniques that have been, frankly, developed by the left wing and often despised by the right wing. Many pilots have been “Law and Order” advocates for so long, it’s difficult to switch when they become the target of law and order. This is why we are so ineffective, why we seem in a constant state of shock as wave after wave of new government restrictions sweep over us. We are being treated as minorities are always treated, but haven’t yet faced the fact that we must fight back with minority techniques. The Other Wing is an attempt to explore effective ways to preserve our freedom to fly.
Some of the mounting restrictions are visible, such as the security fences that keep us from our planes, unfair customs practices not applied to boats or cars, unwieldy requirements on aircraft sales, the coming photo ID pilot licenses that must be renewed in person, and the constant reductions in available airspace. Others are costly, such as requirements for new avionics or unnecessary ADs. But some are more deeply hidden, for instance the reduced traffic flow caused by saturation of the 1090 MHZ transponder frequency. This is only a small sampling of the problems with which we must deal.
In future columns, we’ll be discussing various aspects of how we got into this spiral, and what we can do to fly out of it. Don’t expect simple answers, it isn’t a simple problem. And don’t expect to agree with me. That’s why I say “we” will be discussing, it must come in large part from you, all of you. I have some strong opinions on these subjects, but strong isn’t the same as popular. Or conventional. Or correct. I hope you have strong opinions also. We will be discussing some technical subjects, particularly the black boxes that form our relationship with Air Traffic Control.
If you love aviation, and have hopes that your grandchildren will have the same freedoms you’ve enjoyed, you have a stake in this ongoing discussion. Write letters to the editor, offer another viewpoint, fresh ideas, criticism, anything. Most importantly, get involved. You must fly the plane, don’t ever let it fly you. Don’t just sit there. Do it.
What is a Stirling Engine?
The Stirling is an external combustion engine, and in that respect is similar to a steam engine. Fuel is not critical, it can run on anything that produces heat. It was invented in 1816 by Dr. Robert Stirling, a Scottish minister, and for many years competed with the steam engine.
How does it work?
When a confined body of gas (air, helium, whatever) is heated, it’s pressure rises. This increased pressure can push on a piston and do work. The body of gas is then cooled, pressure drops, and the piston can return. The same cycle repeats over and over, using the same body of gas. That is all there is to it. No ignition, no carburetion, no valve train, no explosions. Many people have a hard time understanding the Stirling because it is so much simpler than conventional internal combustion engines.
Why would the Stirling make a good aircraft powerplant?
First, the Stirling is silent. Aviation needs quiet airplanes. Smooth torque and lack of vibration are good reasons too. General aviation is the last major user of leaded fuel, and we need to find an engine that doesn’t cause this pollution. For safety reasons, we also need a fuel that is less explosive. Stirlings will burn turbine fuel, home heating oil, or whatever.
The Stirling is a very fuel efficient cycle. In fact, it comes closest to the Carnot theoretical limit of efficiency, and is better than the diesel or otto or turbine engines. The Stirling has cool exhaust!
Altitude performance is a strong reason to develop the Stirling. Imagine what would happen if we had powerplants that didn’t lose power at altitude. If a Bonanza, for example, could hold constant power, it would cruise twice as fast at 40,000 ft as it can at sea level. This is due to reduced airframe drag in thinner air. Since the Stirling operates on the ratio of outside ambient temperature to burner temperature, as OAT drops the power actually increases. So the plane can fly more than twice as fast. We can expect to develop general aviation aircraft that easily fly nonstop coast to coast when we have the Stirling powerplant. Plus, flying above the weather rather than through it has safety advantages, too.
Those are just a few reasons why we need this new powerplant. Most of us are flying with the same basic engine the Wright brothers used in 1903! Isn’t it time we moved on?
What is being done to develop the Stirling for aviation use?
While millions are being spent on museums and monuments to the past, very little effort is being directed to the future. Aviation seems to be waiting for 1940 to come back. Well, that is not going to happen. Time marches on. One small example: we still use the same magneto ignition used by farm tractors half a century ago. Tractors improved, automobiles improved, but aircraft powerplants haven’t. Aviation has the choice of moving forward, or being left behind.
Probably the most common question asked about Stirlings is “If they’re so good, why don’t we have them already?” There are many answers.
First, a lot of ideas don’t take off immediately. It took centuries for most folks to accept that the world was round.
Second, there are Stirlings that touch our daily lives. The Stirling is bidirectional, that is, if temperature difference is applied, rotation is produced. But if rotation is applied, temperature difference is produced. So the Stirling makes a refrigerator. If you go to your local welding supply company and purchase liquefied gas (such as liquefied oxygen or liquefied nitrogen), it was made in a Stirling machine. When you watch the satellite weather pictures, they are courtesy of a tiny Stirling cryocooler, used in the satellite to cool the image sensor to near absolute zero. So the answer is that we do have them already.
The third answer is found in the history of the technology. Steam and Stirling grew up together early in the industrial revolution. Indeed, Rev. Stirling developed the machine in response to the human suffering of steam boiler explosions. But cast iron was the material of the day, and cast Stirlings didn’t fare as well as steam engines. Plus, workers were cheap and liability was nil. The fuel efficiency of the Stirling didn’t matter when coal was a few cents per ton. So steam won out. If Bessemer had come along sooner with his steel, we might have enjoyed the Stirling age rather than the age of steam.
Once a technology is established and has a constituency, it’s difficult to displace. We see that today in the effort to interest the aviation community in a new powerplant. Spark plugs are available, piston rings are available, exhaust valves are available, crankshaft grinding equipment is available, there are experts in every tiny engine component. Mass production makes most of the parts reasonable in price, and the technology is well understood.
Most of the Stirling R&D of the past 25 years has been directed toward the automotive field. This is the ultimate example of established technology versus the newcomer. There is an advantage in Stirlings, but not enough advantage to outweigh the present investment in doing engines the way they’re done. (And Stirlings don’t make very good car engines, anyway.)
But aviation is different. We make very few engines, they are hand assembled, and prices are outrageous. Plus, present engines don’t do what we need. As we climb, they put out less and less. Although the plane wants to fly faster due to decreased drag, the engine is losing power faster than the airframe is losing drag. So we reach a ceiling. We’ve always been limited by a powerplant ceiling so we accept it. Likewise, airplanes make a lot of noise because they’ve always made a lot of noise. But it doesn’t need to be that way.
Why don’t we have them already? Perhaps we’ve lost the sense of adventure. Perhaps we believe everything has been invented. Or perhaps in a few years we will have Stirling powered aircraft. Then the question will no longer exist.
For the latest in Stirling engine development news, see Quiet Revolution Motor Company, LLC.
In the year 1816 a Scottish minister, Robert Stirling, invented an engine. It runs without noise or vibration and burns any fuel from 100 LL to kerosene to whale blubber. It competed with steam engines of that time, and was even sold by Sears Roebuck to pump household water in the 1920s. Stirling engines are used today in much of the “undeveloped” world, yet most Americans have scarcely heard of it.
This is a fictional account of what it might be like to fly a Stirling-powered aircraft. It hasn’t happened yet, but work is progressing. Read on, and share the dream….
It was early, he wasn’t supposed to be here for another hour, but I wanted to be sure to witness the arrival. I’d heard a little about the Stirling powerplant, mostly how they were used a century ago in mines and so on, how they weighed 800 pounds and only put out a few horses. So of course I was curious to see the Stirling principle applied in a modern design, all the more so since it was powering an old Cessna 150.
Turned out he was early too. In fact I just barely got to witness the landing at all. He taxied in, and it was obvious the aircraft itself had seen better days. He explained that he had purchased it from an EAAer who wanted the Continental O-200 for his homebuilt. Good deal for both parties.
I was anxious to get a better look at the Stirling, but he began with a familiarization walk-around of the plane. It was mostly plain-vanilla C-150, no major surprises. The prop was stock, as was the cowl, though the cooling-air intakes had been closed over. Sort of strange, seeing these intakes missing. He explained that the engine was liquid cooled, and we examined the ducted radiator on the belly between and behind the main gear. He mentioned that it was somewhat larger that would be necessary with an internal combustion engine, only later did I learn why.
We checked fuel quantity and climbed aboard. I thought we’d missed checking the oil, but he said no, the oil is like the lubricant in a refrigerator. It is sealed inside a pressurized system and if the pressure is there, the oil is too!
Controls and instruments didn’t look much different. There was the familiar look of the throttle, although it was labeled “Bypass” and had a vernier knob. The mixture control had been replaced with another vernier, labeled “Temperature”. There was the normal looking EGT, but it was marked “Heater Temp”, and another similar gage read “Cooler Temp”. The other unusual gage was marked “Engine Pressure”, and it’s 300 PSI reading let us know we still had our lubricant. The familiar oil pressure and oil temp gages were missing altogether.
Oh, yes, there was a horn button!
Starting the Stirling engine is a bit different from anything I had experienced before. He explained each step, indicating that he expected soon to have the whole process automatic, just turn the key. But for now it is a manual operation. The first step is to turn on the electric combustion air blower, then the electric fuel pump and ignition spark. Once the fire is started the spark isn’t needed anymore. We watch heater temp and after a few seconds it passes 1000 degrees F. He eases the Bypass control forward.
It was then that I realized the prop had begun to spin. Somehow it didn’t seem so much like an aircraft prop as a lightweight toy windmill that had caught a breeze. It was just sitting out there spinning, without any engine noise, without any starter grind, without much of anything. It just began to turn.
Checking the gages, he shut down the electric blower and pump, with the comment that they weren’t needed while the mechanicals were being driven by the engine. Temperature was still climbing, and he kept the engine at about 400 RPM by occasionally retracting the Bypass control a little more.
It wasn’t silent, but it sure was close.
Checking for other aircraft, we taxied out. He left the temperature control set to produce about 1400 degrees, and controlled engine power with the Bypass.
With no mags or carb heat to check, run up consisted mostly of just running it up and looking at temperatures, and the checklist was more concerned with the usual takeoff items. We set the temperature to maximum, 1700 degrees, and noted the engine pressure, now up a little from the cold reading. He was particularly interested in the Cooler temp reading, which has a bigger effect on engine output than does the heater. Scanning for traffic, he taxied into position, pushed the Bypass full forward, and released the brakes.
I don’t know exactly what I had expected, but somehow had thought there would be a trumpet fanfare or breathtaking acceleration or something equally dramatic. But what we had was a rather normal Cessna 150 takeoff. Except for the noise, it was different. The sound of wheels and tires, perhaps a brake dragging a little. The creak and groan of an old airframe that had seen too many students. Definitely noise from the prop. And the sound of air flowing over, under, and around all the non-aerodynamic parts of the plane.
But I didn’t hear much from the engine. And perhaps more surprisingly, I didn’t FEEL much from the engine. The power impulses were missing. We have come to accept two of them each time the prop goes around on a four cylinder engine, but they were gone. He explained that the engine mount had no rubber isolators, everything just bolts together.
We climbed out at the same rate I’d have expected with the O-200, and leveled out at 2500 AGL. During the takeoff and climb, both the Temp and Bypass controls had been full forward. Setting cruise power was just a matter of pulling back the temperature to select the desired RPM. Since it took a few seconds for the temp to stabilize, the response was somewhat slower than we’ve come to expect from a throttle, but quicker than the present practice of setting cruise RPM and then carefully leaning the mixture.
I remembered being surprised at the noise level the first time I’d taken a ride in a sailplane. Quieter than a powered craft to be sure, but not silent. This was the same feeling. But the lack of engine vibration was wonderful. And we were able to converse easily without an intercom.
He pointed out that we were consuming about 0.44 pounds of fuel per horsepower per hour. Engineers call this SFC, and it compares with something like 0.59 for the O-200. Better than that, though, is the fact that we were burning turbine fuel. He said it really didn’t matter, he would have burned heating oil if it had been available, but most anything including diesel fuel would be fine.
There are several reasons for the superior fuel economy. First, the Stirling is a much more efficient powerplant. An internal combustion engine takes in new air and fuel for each stroke, saving nothing from the previous one. But the Stirling re-uses the same heat energy on successive strokes, the fuel is only needed to make up the losses. The second reason is that the fuel is always burned full lean, at the best air/fuel ratio, while normal aircraft engines actually use gasoline as a coolant. Expensive coolant. The Stirling also uses the exhaust from the burner to preheat the incoming combustion air. Since the Stirling exhaust is cool, it is obvious that less energy is being thrown away.
We flew it around for awhile, as he demonstrated the operation of the engine controls. There are basically four ways to control Stirling power output, he said. These are to change the temperature, or the pressure, or the phase angle, or to waste power with a bypass valve. Each has it’s good and bad points.
Temperature control is very fuel efficient, and simple to accomplish by just turning the burner up or down. The problem is that it is slow.
Pressure control can also be fuel efficient, and response time is quite rapid. This is the method used in road vehicles NASA and General Motors and Ford have developed. The problem here is complexity, as the several hundred PSI must be introduced into and removed from the engine quickly in accord with throttle position. This takes sophisticated compressors, reservoirs, servo loops, and so on. Too costly and trouble prone.
Phase angle control can be rapid, and fairly simple mechanically, but not very fuel efficient.
Wasting power sounds like the worst possible choice, and for cars and trucks it is, but it turns out to be OK for aircraft.
Here’s why. The “mission profile” only requires that a small part of the flight needs rapid power control. During taxi, takeoff, and landing the pilot needs to be ready to instantly add power. Most of the trip, however, is made at a steady climb or cruise power setting, and it is during this time that fuel efficiency is of paramount importance.
So, the aircraft Stirling powerplant uses temperature control to set the power. Takeoff and landing is made at maximum temperature. When landing, the unneeded power is wasted with the bypass. During this time operation is fuel inefficient, but it gives the pilot the ability to apply power instantly if needed, and doesn’t last long anyway.
Then he demonstrated how it worked. We entered the pattern, no other traffic, and turning base to final he pulled the Bypass all the way back. I saw that the temperature remained at maximum, but no power was being produced. He initiated a go-around just before we touched, and by advancing the Bypass control, full power was instantly available. The next time around we made a normal landing, and taxied in at modest temperature, controlling power again with the Bypass. Shutdown consisted of turning off the fuel.
Since the Stirling is so well insulated, there isn’t much to see under the cowl. It looks perhaps a little more like a small turbine from the outside because it has a cylindrical shape, but the similarity ends there. The combustion air intake is at the bottom, the coolant hoses exit the engine toward the belly-mounted radiator, and the alternator and vacuum pump are clearly visible. Other than that, not much familiar can be seen.
He explained about the oversized radiator. An internal combustion engine takes in fuel, makes heat, and divides it roughly into thirds. One third becomes shaft horsepower, another third exits as heat in the exhaust stream, and the final third is disposed of by the cooling system. This is equally true in air-cooled and water-cooled engines. The Stirling, on the other hand, puts over 40% into shaft horsepower, very little out the exhaust, and half into the cooling, thus the bigger radiator requirement.
Furthermore, since the Stirling works on the ratio of hot and cold temperatures, it needs a somewhat bigger radiator to keep the coolant as near ambient as can be. No thermostat is ever used. On cold days the engine has greater output, and at high altitudes where the temperature gets very cold this engine puts out even more for the same fuel burned.
Since a given aircraft naturally wants to go faster at altitude where the air is thinner and drag is less, and since the Stirling puts out more at the high altitudes, the possibility for major improvement in light aircraft speed is evident.
He made a quick walk around, climbed aboard, started the Stirling, and as he taxied silently out, gave me a couple of toots of the horn!
I was impressed. We had consumed less fuel than in internal combustion engine would have needed, and it was safer, less explosive fuel. As 100LL production declines the price is bound to rise and availability will become a problem. We need an engine that can burn jet fuel. Plus the benefits of less operator fatigue due to lower noise and vibration levels, and less airframe fatigue too.
But perhaps a bigger benefit from the Stirling is less tangible. It involves the public image of general aviation. We make a lot of noise, and do it over people’s homes. People equate noise with danger. This may be a false impression, but it is a fact that most non-fliers connect a sailplane or balloon with peace and tranquility, and connect poorly-muffled screaming engines with danger. The motorcycle manufacturers learned this lesson, and now it is acceptable to park you Yamaha next to your Oldsmobile, without being considered a member of Hell’s Angels.
Quieting the motorcycle didn’t make it safer, but it certainly changed the public perception. Perception drives legislation, and aviation cannot survive much more of that.
It’s not the 1920s anymore, friends. Barnstorming is gone, Waldo Pepper has been replaced by EPA and Friends of the Owl. And those people have some valid points. We cannot keep making noise and be accepted in modern society. Do we want to give up noise, or just give up?
Once each year, major federal agencies solicit proposals from small businesses on a wide variety of topics. In the 1994 cycle, NASA listed 108 topics. While I’m not a great believer in socialized research and development, I found one topic that was too good to pass up:
“General Aviation Propulsion Systems… Proposals are invited for innovative concepts or integration of technologies in aircraft propulsion that are appropriate for use in general aviation aircraft. Objectives are to improve performance, safety and reliability, simplify operation, reduce maintenance and costs, and improve environmental compatibility (e.g. reduce community noise from aircraft operations). Areas of interest include the following:
- Simplified (single lever) power and/or airspeed controller systems.
- Automated engine performance monitoring systems.
- Innovative, alternative fuel engine concepts (e.g. rotary and diesel concepts).
- Improved propeller performance with reduced propeller noise.
- Reduced interior and exterior engine noise.
- Reduced cooling drag.
- Reduced vibrations.
- Simplified inspection and maintenance.
Anticipated performance and/or cost benefits of introducing or integrating proposed innovative propulsion technologies into general aviation aircraft shall be quantitatively defined in the proposal using appropriate theoretical or experimental data. Proposals must be hardware-oriented for near-term problem solutions and applications; proposals for analyses or system studies are not acceptable.”
Readers who have followed my love of the Stirling engine will understand why I jumped at the opportunity to make a proposal. Reduced interior and exterior noise YEAH! Reduced vibrations SURE THING! Improved propeller performance ABSOLUTELY! Alternative fuel THEY’RE TALKING ABOUT MY ENGINE! They may not know it, but they’ve just described the Stirling aircraft powerplant.
Here’s a sampling from the proposal that AirSport submitted to NASA:
How the Stirling will Benefit the Aircraft.
Fuel efficiency is a prime element in the design of any aircraft. Every pound of fuel is a lost pound of payload. For a given payload, every extra pound of fuel spirals into extra airframe weight, thus drag, thus increased engine power, which in turn requires even more fuel. This spiral runs both ways, however. A design that requires less fuel needs less of everything else, and thus even less fuel.
A key feature of the Stirling is the regenerator, which stores and re-uses heat energy. The Stirling cycle comes the closest to the Carnot limit of efficiency. Contemporary Otto cycle powerplants, on the other hand, actually use fuel as expendable coolant during takeoff and climb, whenever power is set above 75%. This is exceedingly poor use of a depleting natural resource, and results in a high level of unburned hydrocarbon emissions, as well as being a waste of payload and an increase in operating cost.
Vibration is another area where the Stirling excels. Shaft torque on a 4 cylinder spark ignition engine varies from a negative 100% to a positive 350% of mean torque twice each revolution, while a Stirling with the same number of cylinders may vary only 5%! Besides the obvious increase in comfort to the occupants, the aircraft itself also benefits. With less vibration, airframe fatigue is greatly reduced and the weight of engine mount and vibration isolators can be largely eliminated. An even greater factor is the advantage of smooth, non-reversing torque to the propeller. At present, variable pitch propeller designs are hampered by the extreme torque pulses. As long as the prop is also the flywheel it must be heavy and robust. When the propeller can be treated as an aerodynamic surface first, rather than a flywheel first, designers can concentrate on silence and efficiency.
Powerplant reliability stands to materially improve with the Stirling. The most trouble-prone part of the piston engine is the ignition system. Magneto failures are common, as are problems with spark plugs and ignition harnesses. In the Stirling, no ignition is needed once the fire is started. The second most common failure is in the valve train. Stirlings have no valves. Other failure mechanisms are eliminated, too. While the increase in reliability will not be achieved overnight, the possibilities are tremendous.
Altitude performance is an immense potential of the Stirling aircraft powerplant. The piston engines of today are rated for continuous operation at 75% of maximum power. As the aircraft climbs and air density lessens, it is necessary to open the throttle further to maintain 75%. Full throttle 75% power is reached in non-supercharged designs at about 8000 ft. MSL. Above that altitude, today’s engine cannot achieve 75% power. The airframe is experiencing less drag due to thinner air and wants to go faster, but the engine won’t allow it. As the climb continues, airspeed decreases and finally the air is so thin that the volumetric engine cannot develop power to climb any higher. Service ceiling is often between 12 and 15 thousand feet.
Supercharging, usually turbocharging, permits higher altitudes to be reached, but at some point the same limit applies. And turbocharging is a costly and high maintenance game. Even with boost an aircraft cannot fly above all the weather. And the majority of planes, those not supercharged, can only fly through the weather, not over it.
On the other hand, Stirling engines are sealed systems with no reference to ambient air density, so they are not directly affected by altitude as Otto engines are. Since the Stirling operates on the difference between combustion and ambient temperatures, it actually benefits at altitude. As the outside temperature declines, engine power increases. This compounds the natural ability of the aircraft to fly faster as air density decreases. If a plane could hold constant power, it would fly twice as fast at 40,000 ft. as it did at sea level due to drag reduction alone! And the Stirling will substantially increase power at high altitudes, allowing even faster speed. This will lead the way to reasonable coast-to-coast nonstop operation of single and light twin engine aircraft.
This is NOT to suggest that a Cessna 172 or a Bonanza should be flown at forty thousand feet. And that is the point. Totally new aircraft designs will be needed to realize the altitude and speed potential of the Stirling powerplant. These new designs will shape the renaissance of general aviation. As always, every advance in aircraft design is preceded by an advance in powerplant design.
Stirling Benefits to the Passengers and Crew
Safety in the event of mishap or accident is a prime concern in aircraft design. The present requirement for large quantities of high octane gasoline is detrimental to safety. Of necessity, aircraft are lightweight structures and cannot provide a level of physical protection between fuel and occupants equal to the protection found in road vehicles. Plus, a single engine plane often carries 70 or more gallons of fuel. Compared to the automobile, this represents several times the fuel quantity at a higher speed in a lighter structure. It is inevitable that fuel containment will sometimes be breached in accidents. Simple incidents such as botched landings or forced off-airport landings occur where the occupants are not injured. The extremely volatile gasoline sometimes ignites and kills people who would otherwise have walked away. For safety alone, we need a less hazardous and explosive fuel.
The Stirling can burn anything. Turbine fuel is the obvious choice since it’s widely available at airports. This may not be the ideal fuel from a safety standpoint, but it’s a big improvement over high octane gasoline. Long-term availability of aviation gasoline is in question. This is a specialty product with a tiny market, faced with legislated deadlines to eliminate lead content. Fuel suppliers have expressed concerns as to their capability or willingness to continue to supply avgas to the general aviation market.
Many aircraft accidents are weather related. As outlined above, the Stirling will allow the plane to cruise above the weather rather than through it. The safety implications are tremendous, as are the improvements in utilization of the aircraft investment. Planes will always have to climb and descend through the weather, but the ability to cruise in clear air and avoid enroute weather is a powerful inducement to develop this powerplant. In addition, when the pilot has a wider choice of operating altitudes, he can better optimize his use of winds. That is, he can climb into high altitude winds if they are blowing his way, but he can also cruise below them if they aren’t. Turbine operators usually don’t have this luxury, operating efficiency often dictates that they climb regardless of the wind penalty.
Another safety consideration is noise. The exposure to high levels of noise and vibration hour after hour is fatiguing to the pilot. Headsets are typically worn and this helps. But we don’t need intercoms in our cars, why should we need them in our planes? Many pilots suffer from permanent hearing loss, which has public health ramifications. The Stirling will go a long way toward reducing noise fatigue, a benefit to both pleasure and safety.
Still another benefit of the Stirling involves ease of operation. No carburetor heat is needed. No concerns for shock cooling exist. No mixture control, no worries of overboost, the list goes on and on. Each of these gives the pilot less to worry about, more time to fly the plane.
Benefits of the Stirling Aircraft Powerplant to Society
Airplanes make a lot of noise, and they do it over people’s homes. Society objects to this intrusion, and rightly so. This incompatibility between aviation and the rest of society has led to the closing of many airports, the land has been given to other uses and will never be recovered. To keep peace with our non-flying neighbors, it is incumbent on us in aviation to quiet our machines. Plus, there is a perceived link between noise and danger. This is the source of much of the societal bias against general aviation, resulting in more and more regulation. If personal flying is to survive in this regulatory society, we must fly safely, AND WE MUST SOUND LIKE WE’RE FLYING SAFELY. We need the silent Stirling powerplant, if for this reason alone.
In addition to engine noise, it is recognized that much sound originates from the propeller. As noted above, propeller design is linked closely to the characteristics of the internal combustion piston engine. The Stirling tends to produce peak power at somewhat slower RPMs, this will lead to lower propeller tip velocity, further from the noise-producing transonic region. Once the engine is a silent producer of smooth torque, we can go to work on the propeller.
Exhaust emissions are another environmental plus for the Stirling. Present aviation gasoline is termed 100LL, the “LL” standing for Low Lead. But low is only relative to the formerly higher lead content. Unlike auto fuel, aviation gasoline still contains lead. For environmental reasons we need to get the lead out! Much research in MTBE and other octane boosting compounds has been accomplished, but major compatibility problems remain. In California, EPA has proposed regulations beginning in the year 2001 that will severely restrict aviation because of exhaust emissions. Aviation needs to begin work on a new powerplant now, not waste time on more bandaids for the same cycle flown by the Wright brothers in 1903.
Besides concerns for lead and other pollutants, gross fuel efficiency of the Stirling cycle has positive benefits to society and the environment as well. Whatever we burn, we need to burn less of it. The Stirling offers the greatest fuel efficiency of all the thermal engine cycles.
That’s only a small part of the proposal. It went on to describe an engine suitable to power an ultralight. We didn’t want to bite off too much, especially since there was a $70,000 contract limit, so an ultralight seemed like a good compromise between a model engine and a larger aircraft powerplant. With the right pilot and airframe, we figured a 15 horse engine would be adequate to demonstrate the concept. Personally, I wanted to include actually flying the ultralight in the contract, but wiser heads convinced me not to propose too much. Credibility and all that. It was agreed around here that we could sneak to the airport and fly the engine, contract or not!
After agonizing over every word, every table, every illustration, every cost analysis, the proposal was mailed. All eight required copies! Then the waiting began. First the short wait for the certified mail receipt, then the wait for confirmation that the proposal had met NASA’s criteria and would be considered. Then months of excruciating waiting. NASA’s acceptance date got pushed back (twice), and in October we went to the AOPA Palm Springs convention not knowing our fate. It was a long trip.
Finally the announcement came. We didn’t get the contract. NASA made a total of 412 awards, including three in this classification. One was titled “Quasi-constant speed fixed-pitch composite propellers”. The second was for “Regenerated engines for general aviation propulsion”. And the last was “Single lever power control for general aviation and unmanned aircraft”.
I’m still trying to figure out who would operate the single lever in an unmanned aircraft.
It’s almost 1996, in just four short years the new century will begin. What will personal aviation look like in the coming century?
There are two ways to think about the future, pragmatic or hopeful. Reality, versus the world of possibility. The latter is more fun, but let’s get the pragmatic view out of the way first and then turn to the wonderful changes in store for aviation.
The reality is that most of the pilots who will be flying in the year 2000 are flying already. The airplanes of 2000 are the airplanes we see on the ramp today, plus a few thousand more just like them. By 2000 we will have lost some aircraft to accident, export, and old age, so we’ll have about as many in the fleet as we have today. We can realistically expect the next four years in aviation to be similar to the last four.
The regulations will increase in number and complexity during the next four years, and the penalties will grow more harsh, just as they have in the last four. The number of pilots who quit flying because it just isn’t fun anymore will exceed the number of students who complete their training, and the pilot population will decline a little more. The past is prologue.
More FSDOs will move from airports to offices inaccessable to airplanes. Private airfields will continue to be purchased, sued, or zoned out of existence. Public airports will add more security restrictions, more landing fees, and continue to make life more difficult for the private pilot, just as they have in the preceeding quadrennial.
During the past four years we’ve seen more aerostats, more tall towers, more restricted airspace. We have witnessed an increase in airspace jurisdiction by the National Park Service and the Wildlife Service. Probably this trend will continue. More military bases will close, and sell the land and buildings (or give them away), but the military airspace over them will still be military. Empty airspace where we are not allowed to fly.
If the last four years are any indication, AOPA will continue to be overloaded with struggles to save local airports, their resources will be strained in fights against unreasonable noise restrictions, they will be so busy putting out fires that they will have no time to plan for the long term. And if we can judge from the past, EAA will be busy too. Oshkosh was once the annual pilgrimage of pilots working to expand the scope of aviation technology. Today it is a huge state fair with jet truck races and vendors selling cheap gold jewelry and miracle car wax. By the year 2000, will it include carnival rides and a circus? Maybe a water park? Will the fake (but already very loud) bombing demonstrations be replaced by the real thing? Whatever sells the most tickets.
At the beginning of the next century, aviation will be just as it is now. Only moreso.
That’s the pragmatic view as general aviation prepares to enter the new century. Ninety-six years ago when we began the present century, man had not yet experienced the joy of powered flight. From 1903 when the Wright boys first coaxed a motor-driven machine into the air, until 1927 when Lindy flew the Atlantic alone, only 24 years passed. In that timespan we learned airfoils, propulsion, navigation, night flight, instruments, and aviation weather. We advanced from fabric biplanes to metal monoplanes, and developed a coast to coast airmail network. Twenty-four years.
How much has aviation advanced in the last 24 years? Not much. The most recent major achievement was when man set foot on the moon, and that was more than 26 years ago. General aviation hasn’t changed engines, most of us are still flying the same spark ignition four strokes that powered the Wright Flyer and the Spirit of St. Louis. Our propellers haven’t changed much, our fuel efficiency hasn’t changed much, our noise hasn’t changed much. Aviation is overdue for some major improvements in the way we fly.
There are two ideas that hold great promise. One is FreeFlight, the other is the Stirling engine.
FreeFlight has been described as “IFR utility with VFR flexibility while putting the information and decision making in the cockpit.” Or it might be VFR utility (you can go more places) with IFR flexibility (in any weather). Either way you slice it, FreeFlight will greatly increase our freedom to fly. Improvement in GA utility will increase the number of hours flown, the number of new students, the demand for more aircraft, the need for more airport services, it will be the force to rebuild general aviation.
On CompuServe AVSIG I’ve been following an ongoing discussion about FreeFlight. Although FAA has announced that they support the concept, the air traffic controllers aren’t about to sign on. It amazes me to see so many controllers use the word “control” in the same sentence with the word “free”. The controllers will have to learn that free and control are opposites. To the extent that anything is controlled, it is not free. And vice versa.
Why do we want to fly free? One reason is LEAST WIND MILES. Christopher Columbus understood that a straight line is not the shortest path, if “shortest” is measured in time rather than distance. Seagoing voyagers have known this for untold centuries. Crossing the ocean in a sailing vessel, the miles traveled cost nothing, the cost is in the days of rations consumed. If you can get there quicker it therefore costs less, and the length of the trip (in miles) doesn’t enter into it.
The airplane is a time machine. It gets us to the destination sooner. Aircraft owners pay dearly for this speed, a 15 or 20 knot difference can sometimes double the cost of the plane, and virtually double the fuel expense too. Any idea that can reduce the trip time without increasing the dollar cost has immense value. FreeFlight is that idea.
One version of least wind miles is PRESSURE PATTERN NAVIGATION. This was used in WWII to ferry planes across the ocean. Some of those aircraft simply didn’t have enough range to reach Europe flying a straight line (great circle) route. They would have gone down in the drink hundreds of miles short of the coast. But by routing the planes in a curve, taking advantage of tailwinds, it was routine to make the trip with fuel to spare.
The idea is to deviate around a high or a low to gain the tailwind advantage. In the northern hemisphere, fly to the left around a high, to the right around a low. Airline dispatchers use the same idea, the Atlantic and Pacific routes change every day, sometimes every few hours, in accordance with the winds.
That’s a step in the right direction. Unfortunately, oceanic controllers often can’t approve the desired route. There are only about 800 transatlantic flights per day during the busiest season (and sometimes only 300 per day) spread all over the Atlantic ocean. But the huge blocks of protected airspace assigned to each flight prevent reasonable use of pressure pattern navigation.
Meanwhile, the newest GPS units still only take us along a straight line. (The correct term is great circle, if we literally travelled a straight line between LAX and JFK we would be tunneling deep under Kansas! A great circle is a straight line as drawn on a globe.)
Suppose a Cherokee, a Bonanza, and a P-210 fly from Dallas to Oshkosh. What path should they take? If left up to ATC, they will all three fly the same zig-zag course. If they are able to fly GPS direct, they will all take the same straight path. Each pilot will make some determination as to optimum altitude, depending on wind forecasts. If they’re VFR they can choose 3500, 5500, 7500, etc. If IFR, they’re at the mercy of the system.
It’s not practical, perhaps not humanly possible, to figure every combination of wind and altitude and fuel flow and TAS and rate of climb and descent to arrive at the quickest trip. And that’s before even considering deviation around high or low pressure areas. How much to deviate? And where? The calculations would take the pilot longer than it would take to just get in the plane and fly the trip straight. Furthermore, the FAA-supplied wind data is old and not very reliable so the answer wouldn’t be dependable anyway.
But that is about to change. Pilots shouldn’t make repetitive calculations, computers should. The GPS is a computer, the Loran is a computer, modern autopilots are computers, there is no shortage of computers in the cockpit. What they need is the right software, and the right data input.
Software is easy, we have plenty of experience with pressure pattern navigation. And with NEXRAD, the atmospheric data is available. At least it’s available on the ground, and soon with datalink it will be available in the air. If FAA drags it’s feet and won’t uplink it to us, some entrepreneur will work out a way to do it. The volume of data coming out of NEXRAD is beyond anything a human can use, it’s custom made for computer analysis.
So, what path should our three aircraft take? Each will take a different path. They will be three dimensional twisting, curving paths. Neither course nor altitude will be constant, they will be slowly changing all the time.
The fundamental idea is to take up a HEADING and hold it throughout the flight. Allowances need to be made for changing magnetic variation and other factors, but when you depart the point of origin there is one heading that, if held, will bring you to the destination. If there were no wind, then obviously the heading and the course would be the same. But the wind is always there, constantly varying in direction and velocity. Flying GPS or Loran direct, a plane will trace the shortest path over the earth, but it will fly through more miles of air than necessary. Least wind miles will trace a curve, perhaps an S curve, between origin and destination as plotted on a map, but if plotted in the airmass it will be a straight line. In a car the shortest path is a straight line on the ground, regardless of the vagaries of the wind. But in an airplane it’s shorter to trace a straight line through the air, regardless of the drift over the ground!
Overall, the plane will fly where the winds are a maximum aid, or at least a minimum hindrance, in accord with the flight characteristics of the individual aircraft and the loading on this particular trip. And with datalink, the GPS will be recalculating the path as the flight progresses and new wind data is available. Any desired fuel stops can be planned in advance. On the return trip, a very different route will be taken.
In a slower aircraft the least wind miles path will be more curved, in a faster plane it will be less so. But fast aircraft typically have more altitude capability, so there is more freedom to maximize speed in the vertical dimension.
Obviously this degree of FreeFlight isn’t totally compatible with today’s ATC, or with the FARs. But it is more compatible with safety than the way we do aviation today. Most pilots have learned to not cross directly over a VOR because of the focusing effect VORs have on airplanes. There is less chance of a midair if you miss the VOR by a mile or so. Likewise, if all VFR traffic is religiously adhereing to the legally correct altitudes there is a much higher chance of collision than if they are spread out at random altitudes. The Victor airways decrease safety too, anything that puts more planes in the same place increases the chance of collision. The FARs make sense until you enter the real world. FreeFlight will put all the planes at random headings and random altitudes, which is the least likely chance of collision. Of course we will have electronic means to see our traffic in FreeFlight, we just won’t have as much traffic to see.
There is another safety benefit to FreeFlight. If the trip is quicker and the aircraft is aloft a shorter time, there is less exposure. Less chance of mechanical trouble, less chance of a weather problem, less chance for anything to go wrong. On many trips, saving an hour means saving a fuel stop, which means saving the extra hour that a stop typically takes, which means getting home before dark, which means more safety.
FAA and ATC claim to be working for safety, but in fact many components of the system actually reduce the margin of safety in our flying environment. FreeFlight contains many improvements.
Notice that FreeFlight will work with the planes in the fleet today, the same planes that will be in the fleet in the year 2000. It will take a new black box, but we can pitch several of the old ones. And it will save enough time and fuel to more than offset the cost of the box.
Least wind miles is only one small part of FreeFlight, there are more advantages than I can cover here. The airlines want FreeFlight, general aviation wants FreeFlight, the budget people at FAA want FreeFlight. The controllers don’t. It will be interesting to see who wins.
The second major improvement coming to general aviation is the Stirling engine. If you’re a regular reader of THE OTHER WING you’re aware of the advantages of this powerplant.
In the history of manned flight, we have had four sources of power. The first was burning straw under a paper bag. This is the way man first rose above the surface of the earth. Today, balloons are fueled by propane rather than straw, but the idea is the same.
The second engine was the four stroke spark ignition powerplant. It allowed man, for the first time, to fly forward thru the airmass under power. Orville and Wilbur used it, Piper and Beech and Mooney use it today, and when Cessna gets their new plant going in Independence they’ll be using it again too. Piston engines advanced rapidly at first, but little has changed in the last 50 years.
Third, we have the turbine. It allows us to fly higher and faster. It also developed rapidly during the first 15 or 20 years, and much slower since.
The fourth powerplant is the rocket engine. With it, man was able to leave his home planet. But rockets are not the answer for the flying most of us do.
In each case, when we developed a new powerplant we were able to expand aviation and accomplish things that were simply impossible before. Sadly, in the four steps aviation has seen, most of us are stuck at step two. The Stirling engine can be step five.
A Stirling engine is silent, a major plus in the relationship between aviation and society. It has smooth torque without vibration, allowing it to drive a quiet, more efficient propeller. The Stirling cycle is the most fuel efficient engine possible, which means we can fly further and at a lower cost. It burns kerosene or other less explosive fuel, which is a big safety factor in an accident.
And the Stirling is the only powerplant applicable to general aviation that puts out more power as the plane climbs. Think of it! No ceiling limitations due to the engine. If a plane can hold constant power, it will fly twice as fast at 40,000 ft. as it does at sea level. The Stirling will actually put out more power at high altitude, so the plane will go even faster. Of course we won’t want to take a Baron or Archer to that altitude, we will need a whole new design. With Stirling power there will finally be a reason to advance beyond the airframes of the last 40 years. A renaissance in aviation.
Imagine smooth quiet flight above the weather nonstop coast to coast in a single engine personal aircraft. Imagine flying where you want, when you want, with datalink feeding the onboard computer to get you there in minimum time. Imagine being able to see all your traffic and obstructions regardless of weather.
It’s all possible, we have the technology today. All we need is the will. The vision. The year 2000 represents more than a new century, it is the beginning of a new millenium. Four years, and counting.
When President Eisenhower first proposed the interstate highway system, the grass medians were envisioned as landing strips. Isn’t that a great idea? The same money was being expended for land acquisition and improvement whether the center strip was used for aviation or not. In those days most light aircraft didn’t have any nav equipment at all, or perhaps just a low-freq receiver to pick up the A-N beacons. Navigation and weather were the nemesis of General Aviation. Ike reasoned that highways went where most people wanted to go. When the pilot was following the road he wouldn’t get lost, and if weather became a factor he could set down anywhere.
Detroit understood the idea very well. Their lobbying quashed the concept of dual use, and a window of opportunity was closed forever. It’s unthinkable today to mix Citations and semi-trucks. But our world needn’t have evolved as it did, there were alternate possibilities.
There exists a timespan when a thing is possible. A window of opportunity. Prior to that time, the thing wasn’t do-able, perhaps because a key part hadn’t been built yet. And if the window is missed the idea once again becomes impossible to achieve.
Perhaps the earliest missed window in aviation is the way the brothers rigged the rudders. In all machinedom, steering with the feet is done by pressing on the pedal opposite to the turn. Whether you consider a little cart like we kids used to nail together, or a sled, or steering a bicycle by putting your feet on the handlebars, or any other example, they all turn left by pressing with the right foot. And it’s not just machines, the physics applies to people as well. We turn left by relaxing the left foot and pressing harder with the right. It’s true in humans and in all the creatures. Instinct is strong, we naturally push the “outside” foot.
I guess rigging the rudder cables was one of the final tasks in building the Flyer and it was simpler to run them straight than to cross them over. Whatever the reason, a window of opportunity closed that day and we’re stuck forever with pedals that are contrary to nature and to other machines.
One of my joys is taking kids on their first airplane ride. Frequently the 8 to 14 age set. I explain it all in detail, and let them taxi out. While they usually fly great, taxiing is miserable. They often make some comment about how hard it is to steer with feet. They are too overloaded by the unfamiliar surroundings to realize the obvious, the pedals are backwards. Fortunately, humans are adaptable creatures and we learn to fly just fine. But occasionally things get hairy and millisecond response is needed. Deep in the brain, training is pulling one way and instinct the other. Sometimes instinct wins. It’s called pilot error, but it’s really the result of a window of opportunity missed long ago.
We can’t do much about windows that are closed. One thing we can do is learn from them. Try to spot opportunities that are still open today, maybe dive through that window before it slams shut, or at least try to prop the window open for awhile.
What windows are open now? We covered one last month called Mode T. It does everything right that Mode S does wrong. Mode T saves the FAA bundles, it provides coverage all the way to the ground, and it lets aircraft see each other. Before GPS became a reality Mode T wasn’t feasible. Now it is.
Another open window involves powerplants for light aircraft. We’ve been reasonably content with the piston engine since the beginning of aviation. Of course the turbine is enviable, but when you examine the engineering realities the turbine is about as useful as a rocket engine on most aircraft. Yet the day of avgas availability is coming to an end. What will replace our present powerplant? We need an engine that runs on kerosene, since that’s what will be available at the airport. At the same time, we need an engine that is silent so the community won’t want to close the airport. When gas was cheap and airports were miles from town, the window wasn’t yet open. But it’s open now, the time to develop a better engine is here. The technology exists, no new inventions are required, all we need is the will to proceed. At some point, if we continue to fight the future rather than cooperate with it, that window of opportunity will also close.
A bright new window has opened with the election of a fresh administration. Individual freedom is what aviation is all about, and now we’ve chosen a government that understands that idea. We can expect a judiciary more receptive to aviators’ rights. Whether it’s the poor treatment we get from Customs, illegal actions by the DEA, or unconstitutional moves by the FAA, we’ve been unable to get relief in court. A fresh and welcome breeze is coming through this open window, ushering in a period when aviators can share in rights and freedoms guaranteed by the Constitution to us all. Including people who fly little airplanes!
Remember when anyone riding a motorcycle was assumed to be a member of Hell’s Angels? When motorcycles were loud and dangerous?
A couple of decades ago the motorcycle manufacturers realized they had a problem. If the bikes were noisy, they were dangerous. And by extension, the riders were dangerous too. The answer: good mufflers. Of course that didn’t make motorcycles safer, they are just as hard to see as ever. And I doubt the morals of the riders were raised or lowered by running the engine exhaust thru a silencer. But society THOUGHT they were safer because they were quieter, and today it’s perfectly acceptable to park your Yamaha in the drive next to your Oldsmobile.
There is a lesson here, if we can but learn it. Airplanes are noisy, so they are dangerous. Society knows this. Facts don’t matter much. Airplanes should be tightly regulated. Pilots shouldn’t be eligible for life insurance. Airports should be closed as public nuisances. And so on.
What should we, the flying community, do about this? Well, before we come to that question, lets look at what we ARE doing about it. We have airshows, where the general public (society) has it’s only opportunity to get close to little airplanes. At these airshows, we fly the noisiest planes we can find. We perform the most dangerous looking maneuvers we can. Nevermind that the FAA has approved each performer and set strict guidelines on what and where and when and how. Society hears none of this, they only hear the roar of the engines and the announcer that impresses them with the daring-do of the men in their flying machines.
And what do they see? Airplanes that almost collide with each other, airplanes that fly upside down, airplanes with people riding on the wing or hanging from ropes. Mostly, they see airplanes trailing lots of smoke. Obviously dangerous.
Would the Medical Association hold public exhibitions of doctors throwing scalpels? Would the Bar Association show lawyers flipping coins to see who goes to prison? Maybe it happens that way, maybe not, but they have enough understanding of Public Relations to never put it on exhibition.
A 727 captain for a major carrier told me some years ago, with a knowing grin, that his aircraft would loop and roll very nicely. I never got a ride, but I believe he knew from experience. His skill in this regard is a benefit, I’d rather my family was riding with him than with a pilot who would be terrified if the airliner went over on it’s back. But knowing how to do it is one thing, showing off to the public is another. You wouldn’t expect the airline to feature barrel rolls in it’s TV spots.
Aerobatic flying isn’t the problem. Aerobatic competition is a wonderful sport, and has produced both highly skilled pilots and advances in our understanding of aerodynamics. Besides, aerobatics is fun, and that’s reason enough. Out of sight of the general public, we should have all the fun the pocketbook (and the stomach) allows!
In public, however, it certainly makes sense to put our best foot forward. And the noisiest planes, trailing smoke and almost colliding in front of the crowd, isn’t our best foot. Can we blame the news media when they report, as they almost always do, that the plane exploded in midair? Even when it’s a Bonanza skillfully put down on a golf course, where all occupants walk away unscratched, the news people know how it looked because they saw something similar at the air show. Our PR stinks, and in part it’s the aroma of corvus oil.
We are trying to have it all, and in the process we are losing it all. Almost every pilot flying today has been flying long enough to remember when restrictions were less severe. Restrictions on the aircraft, the airspace, and the pilot. We must face the fact that a tiny minority cannot exist in a society ruled by majority unless we manage to adapt, to fight where we can, and yield where we must. If we continue as we have for the last 40 years, griping about the FAA and doing little else, we most assuredly don’t have another 40.
So, let us begin a dialog to determine what is most important to us in the flying community. If we can categorize what is worth fighting for, what is desirable but not absolutely essential, and what we can do without, then we can begin to establish priorities. We, the pilots and lovers of flying, must do this. If we leave it to society, we’ll find ourselves continuing to lose this war of attrition.
Which brings us back to the subject of noise. Not just airshows, but everyday flying. If we make a list of the things we love about aviation, where does noise fall in the list? Essential? Desirable? Willing to give up? I’m not just willing to give it up, I yearn for the day when it’s gone. It makes no more sense to wear a headset in a plane than it does in a car. Why is an intercom needed in a Beech, not in a Buick? To me, the best airshow act is when Bob Hoover shuts down both engines on the Aero Commander and continues to loop, roll, land, and taxi back to his parking spot silently. I’ll bet I’ve seen that act 30 times thru the years, and each time I thought “someday we’re all going to have planes that sound like that”.
Later in this series, I’ll go into specifics on how we can move toward silent powerplants. There is an engine that burns most any fuel, is more fuel efficient than anything we’re flying today, actually gains power at higher altitudes, and is quiet and vibration free. It would permit aviation and society to co-exist rather than clash.
Now it’s your turn. Make a list of what is worth fighting for in aviation. What do we need, what do we merely want, what can we do without. Send me a copy. We’ll have a tabulation of your views. Fly this plane, don’t let it fly you.