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Airliners and muggers

By Lawrence Henry
web posted October 8, 2001

I've just finished reading Tom Clancy and Gen. Chuck Horner's non-fiction book, Every Man a Tiger, about Gen. Horner's role in the Gulf War. Our various expert commentators on airline security ought to give it a careful read, too. Airplanes, airports, and air traffic control are widely misunderstood.

Air traffic controlFirst, there's radar. Most people assume that radar emanates from control towers and reads impulses from every airplane within a certain radius. That's true only to a very minor extent; that's "active" radar. But in fact, most civilian air traffic is controlled by passive radar, which responds to signals from transponders carried by commercial airliners. Within the comparitively small reach area of active, airport-based ground radar (about 30 miles), small private planes (which generally do not carry transponders) have to be "passed" from one terminal control area (TCA) to another across the country. How? The pilots notify the towers and identify themselves. ("Hello, SMO control, this is Cessna three-five-niner, on heading…")

Those two deadly flights from Boston could meander all over the air map without alerting anybody to much of anything until it was far too late. Private planes would have escaped notice until well inside the Kennedy or LaGuardia TCA.

In combat zones, of course, radar is active throughout. Could we employ active radar in civilian commercial aviation? Yes, but it would require something like the military's E-3 AWACS aircraft. These are modified commercial airliners that fly aloft and direct air traffic, via radar, from altitude. Why? Because of the curvature of the earth, ground-based radar can't see very far. Only flying radar platforms can provide real-time, thorough coverage of the distances covered by airliners.

A more reasonable and - in the long run - cheaper solution, based on the same concept, would be a satellite-based air traffic control system. Such a system is apparently being Beta-tested in Alaska right now. The FAA's releases on this system, called Capstone, emphasize that it is based on Global Positioning Satellite (GPS) technology, does not involve radar "inquiries," but is organized around on signals generated from transponder-equipped airplanes.

The Capstone system is a kind of mini-test of a proposed national satellite-based ATC system called National Airspace System Architecture 4.0. The Capstone and NAS systems provide fantastic, almost television-like airspace visuals for pilots and ground controllers alike.

Could a hijacker turn off a Capstone-style transponder and effectively "get lost"? I don't know.

There's more.

When the military sets up air traffic control over an area like that covered by the Gulf War - and one of the illuminating maps in Every Man a Tiger shows how big that area was; as big as the whole eastern United States - they also institute a procedure called "Identification Friend of Foe" (IFF). The IFF procedure creates, and constantly alters, a secure method of radio signaling ("squawking") to identify aircraft as belonging to enemy or friendly forces.

Failure to set up and maintain a proper IFF system can cause accidental shoot-downs, like the one that just occurred over the Black Sea, when a Ukrainian missile knocked down a Russian airliner.

Should the United States develop and implement an airplane- or satellite-based air traffic control system for domestic airports? The NAS system, to judge from the FAA's own press releases, appears to be in the works already. The NAS architecture may be thorough, but essentially no more secure than the present system. An AWACs-style control would be fearsomely expensive. If the U.S. airline industry ends up crippled through extensive costs - high prices driving away passengers and cargoes - it's just as bad in an economic sense as being crippled through knock-downs.

But the commentators who say that terrorists have already struck airliners, so we don't have to worry about that now, are wrong, too. Terrorists are like muggers. They stake out vulnerable territories, then bump off vulnerable targets.

If airplanes continue to be the functional equivalent of little old ladies with welfare checks, they're going to continue to get mugged.

Lawrence Henry is a regular contributor to Enter Stage Right.

Buy Tom Clancy's Every Man a Tiger at Amazon.com in hardcover for only $19.56 (30% off) or in paperback for only $13.56 (20% off)

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