by
Darryl Phillips
See and be seen. In automotive terms, keep your windshield clean (see) and turn your lights on at night (be seen). In aviation, see and be seen has been the rule since the second airplane came along and it has served us well. But with faster speeds and instrument flying something else was needed. Air Traffic Control evolved, with radio position reports, then radar, then transponders.
What if automobiles had evolved that way? Can you imagine the spacing needed between vehicles if controllers were giving the orders? There would be miles and miles of nothing but miles and miles, exactly what we see aloft today.
Think of what life would be like if cars were controlled by ATC. Rather than trying to visualize a whole city, consider your local shopping mall parking lot. How many controllers would it take, how long would you wait for clearance before backing out of a parking space? Could you get from where you are to where you need to go? How many frequency changes between here and the other side? Could your mother drive in such an environment? How many cars per hour could the system handle? Could the mall survive so few customers? Are you beginning to see why aviation is doing so poorly?
We can each drive one car, or fly one plane. This isn't a political argument about giving up control to Big Brother, it's a simple statement of physical reality. Nobody can drive as well as the person behind the wheel, and that is equally true on the road or in the sky. See and be seen is proven and efficient. It works. What aviation needs is a way to extend the concept beyond the human limitations of vision and of reaction time. We need a way to know if traffic is out there, whether they are a threat, and what to do about it. The same things the human eyes and brain do automatically.
Mode T is such a system. One of the best things about Mode T is that it wasn't dreamed up by the feds. It came from people who own and operate airplanes, people who foot the bills, who benefit the most when the system works and pay the highest price when it doesn't. People who fly.
Since taillights are simpler machines than eyeballs, let's tackle the "be seen" part of Mode T first. Simply put, we need a way to tell others where we are. Using GPS technology, that part is easy and inexpensive. Latitude, longitude, and altitude are available from little receiver modules currently available for a couple hundred bucks, with $29 prices expected soon. These modules lack any readout, but remember the data isn't for the pilot, it's for the other guy in the same way that taillights are for the other guy to see. Mode T transmits this three-dimensional data, together with aircraft ID, in quick little bursts several times each second.
And who receives this Mode T data? Anyone and everyone who has an interest in what traffic is out there. FAA can receive the data and present it on "radar" scopes for the controllers. It's much more accurate than current or future transponder technology. It's cheaper too, since the feds no longer have to operate or maintain all those antiquated rotating antennae. Mode T gives the controller virtually instantaneous data, rather than waiting 5 or 10 seconds for the dish to sweep around. Plus, it gives them total access to traffic all the way to the ground or hidden behind the mountain, something Mode S will never do. And it eliminates a number of other vexing problems.
Others can watch traffic too. Wouldn't it be interesting to watch the area traffic on your computer or TV screen? Easy and inexpensive with Mode T.
The biggest benefit comes when the other planes pick up the data. Here we come to the "see" part of Mode T. Traffic can be displayed on a screen alone, or combined with a moving map, color radar, or whatever. That's a major leap forward. Now the pilot can know who may be climbing toward his path, and who may be overtaking from behind. By timing successive positions of target aircraft, the receiver can compute speed, direction of flight, rate of climb and of turn, and evaluate possible conflicting paths.
Once we have Mode T in place, we can begin to evolve more complex rules of the road. Some of these automated rules have been developed for TCAS, but it can't begin to offer the precision nor handle a large volume of aircraft. TCAS is bulky, heavy, and costs more than your airplane. TCAS was designed by the government.
In contrast, Mode T is tiny, elegant, cost effective, and was not designed by the government. With Mode T, traffic spacings can be reduced. We may never approach the bumper to bumper spacings of rush hour on the freeway, but if we just cut spacing in half, vertically and horizontally, we can accommodate 8 times as many planes in the same airspace. Which means ATC can allow you to fly direct rather than around. And around.
Next, consider that other aircraft aren't the only impediments to flight. Tiny Mode T units can be placed on broadcast towers or mountain tops. They need no GPS, they know where they are. And if you fly nearby you'll know it too. They do the same thing in fog that the warning beacon does in fair weather, at a miniscule cost.
It's only a small step from putting a Mode T unit on a tall tower, to placing one at the end of runways. Now we have a DGPS approach to each end of each runway. The equipment in your aircraft receives it, compares it's 3D position with yours, and displays the difference. Perhaps presented to the pilot on a conventional ILS head, or perhaps on a modern EFIS display. This data will be more accurate than the present ILS, will offer all the advantages of MLS, and will cost each airport about as much as the paint on the runway!
We have a window of opportunity opening at this very moment. Coming together simultaneously are all the factors necessary to permit Mode T to happen. First, the technology is here, GPS is a reality today. Second, the need is now. TCAS is encroaching on ATCRBS, and this hurts ATC's ability to see traffic. Mode S will make things worse, indeed is making it worse already. Something must fill the need. Third, and most fortunately, the money is missing. While high cost programs flourish in fat times, low cost programs succeed in tough times. Mode T is exactly the right technology for today. The next Congress has more new faces than most of us have ever seen, and they arrive with a strong message. If they follow through on what the voters are saying, they'll be axing things like the outdated and useless MLS program, and a whole lot more. It's even possible that the runaway costs of Mode S may force a halt to that expensive program.
Mode S was a good idea when it was proposed. It was state of the art, and would serve ATC needs for the foreseeable future. But programs, particularly well-funded government programs, expand to fill the time available and the foreseeable future has come and gone. Technology is advancing at blinding speed, and any program must be finished quickly if it's to compete at all. Mode S is 20 years behind right now, and will be 30 years old by the time it's all in place. It makes little sense to spend money on that.
Is Mode T any better? Yes, for a couple of reasons. First because it's an aircraft oriented system, not ground based. If two planes collide it's equally tragic whether they are in a radar environment or not. Mode T works on either side of the mountain, and it works in the pattern at outlying fields that are below radar coverage. The other benefits of providing precision approaches or better data to ATC are nice, too. Second, Mode T is better because it is a small cost-effective idea that will move from concept to reality in a short period of time. No technological idea is any good if it has a 20 year gestation period. Finally, perhaps most important, Mode T will be affordable, whether you fly a C-150 or a Starship.
Don't think of all this in terms of VFR or IFR. Those terms are too restrictive. In the final analysis, Air Traffic Control exists only to keep planes from bumping into each other. Mode T promises to change the way we do aviation.