by
Darryl Phillips
At long last, the feds have caught on to the idea that we pilots have a better idea where our airplanes are than FAA does. That is, GPS position is more accurate than their ancient radar. They've finally come to realize that if we were to automatically broadcast our three dimensional position, they could pick up that data easier than the cumbersome equipment they use now.
Wow, that's a daring leap for an agency that has great difficulty in simply maintaining the status quo.
So much for the good news. It goes downhill rapidly from there. For starters, FAA believes that all this new data should be broadcast on the single most overloaded frequency we have. The frequency is already occupied by Mode A, Mode C, Mode S, TCAS, and whatever games the military is playing at that spot on the dial. The frequency is 1090 MHz.
Ed Bayliss of Lincoln Labs recently authored a paper sponsored by FAA. "Demonstration of GPS Automatic Dependent Surveillance of Aircraft Using Spontaneous Mode S Broadcast Messages." In fedspeak it goes on page after page, describing how the system will work. Much is too technical to get into here, if you'd like to see the full text let me know.
On the other hand, some parts of it can only be understood by us simple folk. Take Mr. Bayliss' claim that the new system will add an insignificant load on the frequency. "Use of Mode S for GPS-Squitter adds only 0.03 percent per transponder to the current 1090 MHz channel occupancy." Those are his words. But his numbers are startlingly different.
He makes the assumption that a Mode S transponder currently puts out a signal 2192 microseconds each second. He then states that the GPS stuff will add another 264, for a total of 2456 microseconds. Does that sound like 0.03 percent to you? I've figured it on paper, and on three different calculators, and it comes up a smidge over 12 percent every time. He is off by a factor of more than 400!
Doesn't matter whether we're talking dollars or donuts or microseconds, 2192 to 2456 is an increase of 12 percent. The channel is overloaded now. What will another 12 percent do to us?
Why does the FAA pay for hogwash like this? If they are so dense that they believe it, we're in serious trouble. Or, if they know they're being lied to and choose to accept it, we're in serious trouble. Either way you slice it, the result is the same. Aviation is in serious trouble.
But that is just the math. Whether Mr. Bayliss' numbers are right or wrong isn't really the point. Let's strip away the fedspeak and talk about what they are planning for our airplanes.
To start with, every plane will have to install a Mode S transponder. And another GPS, not the one you already have on your panel. It must be a GPS that never gets turned off, so the transponder will always have position information. Plus, you'll have to install a WADGPS receiver and antenna to pick up the correction signal. (It is needed to compensate for the GPS error intentionally added by the US military.) And of course you'll need an altitude encoder. These things cost money, our money. Not something for Mr. Bayliss to worry about.
The encoder requirement is interesting. In the data budget there are 11 bits for altitude, exactly what we have in Mode C. One hundred foot increments. Although a number of planes already have 10 foot resolution in their encoders and technology exists to do even better, this system the FAA is dreaming up doesn't improve on what we now have in Mode C, which in turn goes back to what would fit in the World War II IFF pulses. They totally disregard the advances we've made in electronics in the last half of the 20th century. Sad.
Besides altitude, the datastream will contain longitude and latitude. Twice each second this information will be automatically broadcast, with so much power that the feds can pick it up at a range of 250 miles or more.
It will contain something else, too. Identification. One of the reasons general aviation has long fought Mode S is the matter of ID. Every broadcast contains a 24 bit address that is essentially the serial number of the transponder. As we move toward a world where every service will be billed to the recipient, continually broadcasting your identification has obvious implications.
Now Mr. Bayliss and his non-flying friends at Lincoln Labs have added another datafield, which contains the ICAO aircraft ID. Never before has the FAA talked about actually requiring us to put our N number in the datastream. But under the guise of making the system more accurate, N number has been added. Are we going to stand still for this? Does AOPA or EAA have a position at all? Where are our associations when these things are happening?
It's not a question of what we have to hide. The fact that I don't want to be tracked every inch of the trip does not imply that I'm doing something illegal. Unfortunately, part of society has come to believe that if you have nothing to hide, you shouldn't mind being searched by the cops. Or tracked by the feds. Some people believe that only criminals need the fifth amendment or other constitutional protections. Personally, I make a clear distinction between having something to hide, and having something to protect.
When we go to bed at night, we draw the curtains. Not because we have something to hide. We have something very important to protect.
And that is the essence of the ID question. It is a matter of what we have to protect. Freedom of movement, guaranteed by the Constitution, means the freedom to not be watched by government agents everywhere we go.
In most of the world today, aviation has less freedom than we enjoy in the USA. Much less. Instead of giving up freedom in this country and becoming more like the others, why don't we advance the cause of individual choice all over the world? The equipment we design is likely to become the world standard, and if we do it right we can strike a blow for individuality everywhere. Let's think how we can make aviation MORE attractive, not less so.
"Flying just isn't fun anymore" is increasingly heard in this country, but in much of the world it hasn't been fun for a long long time. We need to do everything possible to bring back the freedom and utility and pure fun that aviation once enjoyed, and spread it over the earth.
Every year the number of pilots shrinks. We're growing older and our ranks are not being replenished. The younger generation can ski or scuba or even skydive without big brother watching every move, ready to pounce if they zig when some regulation says zag. As we mull over the technical details, let's keep the big picture in mind. Do we design for control, or for freedom?
Next month, part two. This Lincoln Labs system makes no sense for collision avoidance. Stay tuned.