WATCH YOUR ALTITUDE!
AirSport's Altitude Alerter systems not
only do everything
the heavy-iron systems can (plus a whole lot more)
-
they could save you from an expensive FAA violation
By Peter Lert
Reprinted from Air Progress, February
1994
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.