Sunday's collision of an Aeromexico airliner and a small plane has spotlighted longstanding attempts to develop in-flight electronic technology that would help warn pilots of the approach of other aircraft they might not see from their cockpits. The systems, which work independently of ground-based systems, warn pilots both audibly and visibly of collision danger and recommend escape maneuvers.
The number of reported near-collisions in the United States was 777 in 1985, up 188 over the previous year. The rise is partly attributed to improved FAA procedures for collecting such reports.
The accident has brought renewed charges that technological, bureaucratic, and funding hurdles have slowed testing and adoption of collision-avoidance devices.
James Pope, a former Federal Aviation Administration ombudsman, and Patricia Goldman, vice-chairwoman of the National Transportation Safety Board, have long accused the FAA of dragging its feet on technology which they say could have been in use for at least 10 years.
A system developed by Honeywell Corporation and known as ``ACAS'' (Airborne Collision Avoidance System) was given a favorable rating by the FAA after extensive tests from 1972 to 1976.
But according to FAA spokesman John Leyden, such systems were prohibitively expensive ($50,000 to $100,000) for general aviators. Since they would be useless unless every aircraft carried one, Mr. Leyden says, the FAA decided to look for alternatives.
Another system, known as TCAS (Traffic Alert and Collision Avoidance System) and manufactured by Allied Bendix and Dalmo Victor, was developed as early as 1974. It was tested on Piedmont Airlines planes in 1981. TCAS was certified for use in the air, and prototypes were to be tested in commerical flights on Boeing 727 aircraft owned by Piedmont Airlines last June.
Contacted after the Los Angeles collision, a company spokesman said the testing was to begin ``certainly sometime this month'' but gave no reason for the delay.
The TCAS series of devices bases its warning on signals already emitted by a piece of standard airplane equipment known as a ``transponder,'' says Mr. Leyden. Transponders emit identifying signals that appear as blips on radar screens watched by airport traffic controllers.
Transponders have different capabilities, and different TCAS series models have different capabilities. And therein lies another controversy.
John Mazor, spokesman for the Air Line Pilots Association, has said airlines would rather use the current ``TCAS-2'' which audibly and visually warns pilots when a threatening aircraft is 40 seconds away. If the approach is within 25 seconds, a siren sounds and a voice warns to climb or descend.
But pilots want a more sophisticated model that gives not only vertical escape routes, but horizontal ones as well. They say the current model being tested is too limited and too dangerous under crowded conditions. The Air Transport Association, which represents most major airlines, says the airlines want a system that can accommodate more-sophisticated versions as they are devised.
All models, from the ACAS to the TCAS-1, TCAS-2, and TCAS-3, are subject to the possibility of computer error, according to Leyden, with devices giving false alarms in highly congested areas.
``It is a very complex problem of computer logic, especially when the air gets crowded,'' says Leyden. ``And that's exactly when they are needed most.'' The devices work well in controlled lab experiments or in out-of-the way airports, Leyden notes, adding, ``People don't understand how complex the problem is. We've been working on it for 20 years, and there is still no satisfactory system out there that works.''
While Piedmont Airlines gears up to test its TCAS-2 models this month, asking pilots and ground crews for feedback via questionnaires, the FAA is testing the TCAS3 -- with horizontal escape routes -- in Atlantic City and Los Angeles. The most advanced models, based on this test, will be delivered for more testing by next February.
If they prove effective, the $75,000-to-$100,000 devices could become common features in commercial airline cockpits by the end of the decade, says Joe Fee, manager of the TCAS project at the FAA.
An FAA official said the agency's budget for testing and running of collision-avoidance systems was $10 million for the current fiscal year and will go down to $7.3 million in fiscal 1987. The amount budgeted up to now, he said, has been $60 million to $70 million.