LAST WEEK`S tragic mid-air collision between a small plane and an Aeromexico jetliner in California bears a strong parallel to the person who dies of a disease shortly before a cure is found.
If the two craft had been converging on, say, Aug. 31, 1990, instead of Aug. 31, 1986, it is possible that they would not have crashed.
That`s because a new airborne-warning system being evaluated by the Federal Aviation Administration probably will be installed on planes operated by major airlines by the decade`s end.
The system, the Traffic Alert and Collision Avoidance System, or TCAS
(pronounced TEE cass), permits big planes to sense the approach of other aircraft so that pilots can take evasive action.
Though critics charge that the FAA has moved far too slowly in developing it, TCAS in the next few years is expected to join such innovations now in the works as a ground-based windshear detection system and a new generation of sophisticated radar equipment. All hold the promise of increasing the margin of air safety.
Last Sunday`s crash over Cerritos, Calif., which claimed the lives of 67 people aboard the two planes and a still undetermined number on the ground, was a relatively rare occurrence.
Out of hundreds of thousands of flights in the United States annually, there are an average of only 27 such accidents a year, almost all of them involving small private planes smashing into one another, according to the FAA.
Before last week, the last mid-air accident involving a major carrier was in 1978 over San Diego when a small plane collided with a Pacific Southwest Airlines Boeing 727, killing 137 people.
Nevertheless, the skies have become increasingly crowded as more and more airlines operate a mounting number of flights. With an accompanying growth in the number of reported near-collisions, ”it doesn`t take a lot of common sense to look at that trend and predict an accident like the one we just had,” said John O`Brien, director of engineering and air safety for the Air Line Pilots Association.
A recent survey by the pilots group found that the danger is the No. 1 concern of people who fly for a living.
”Far and away, the most critical item as far as our 39,000 members are concerned is the risk of mid-air collision,” O`Brien said.
So important is the issue to the union that it has negotiated clauses in contracts with some airlines requiring installation as soon as a proven collision avoidance system becomes available.
In an ironic twist, the Aeromexico plane plunged to the ground not far from the home of a man who has been intimately involved in development of TCAS.
Jack Graham, a senior staff engineer at Douglas Aircraft Co.`s Long Beach, Calif., offices, heads a special committee of the Radio Technical Commission for Aeronautics, an advisory agency to the government that has helped draft specifications for the system.
TCAS is ”a combination of a radar and a sophisticated computer,”
Graham said. ”It `interrogates` . . . other aircraft–maybe 30 aircraft within 5 miles–measures direction and distance of each and receives their reported altitudes.”
TCAS` main piece of hardware is a box about 7 inches high, 7 inches wide and 15 inches deep.
The system gives the pilot about a 45-second advance warning of a potential collision. If conditions for a crash exist 20 seconds later, it tells the pilot whether to take evasive action up or down. A cockpit-mounted instrument and a mechanical voice warning sound the alarm.
A computer simulation of the 1979 San Diego collision has shown that TCAS would have prevented the accident, Graham said.
Development of TCAS began in 1981, though research on collision avoidance systems had been conducted for years before then. Tests indicate that TCAS`
reliability and evaluation phase is ready to begin.
A Piedmont Airlines Boeing 727 has been outfitted with a prototype TCAS unit that is to go into operation this month, and planes in the fleets of three other carriers are to get similar installations in the coming months.
”The bottom line of TCAS is that it must be totally and completely reliable,” said Dick Stafford, an FAA spokesman in Washington. ”Otherwise, pilots are not going to pay any attention to it, and we don`t put black boxes in airplanes until we know pilots will pay attention to them. If it works 90 percent of the time, that`s no good.”
If the evaluation proves positive, officials say it is possible that airlines will be able to have TCAS units installed on their fleets by 1990.
Critical to the effectiveness of the collision avoidance system is the presence on smaller planes of a piece of equipment called a transponder, a small electronic device that enhances a craft`s radar image. And for maximum effectiveness, the transponders must have an extra-cost feature that broadcasts altitude.
A small plane without a transponder, or one whose transponder is turned off or malfuctioning, renders TCAS totally ineffective.
Joe Fee, airborne collision avoidance system program manager for the FAA, said that 90 percent of the small planes that fly in the same areas as big planes nationally already have transponders, 60 percent of them outfitted with the altitude feature.
Federal officials have raised the possibility of requiring transponders on small aircraft. But any regulation mandating installation is likely to meet opposition from private pilots who traditionally fight anything that smacks of encroaching regulation.
”We have a philosophy that equipment required should be based on the type of airspace to be entered,” said Edmund Pinto, senior vice president of the Aircraft Owners and Pilots Association. Present rules requiring altitude- encoding transponders only on those small aircraft that enter busy areas near major airports have worked well, he asserted.
In the eight years between the San Diego and Cerritos collisions, there have been 1 billion flights of all kinds, he said.
The cost of a transponder for a small plane runs roughly from $700 to $2,000. Expense of the TCAS system will be much greater. The price has been estimated at as much as $100,000 a copy, though it could come down with mass production and competition among manufacturers.
O`Brien, of the pilots association, said that a ground proximity warning device originally estimated to cost between $25,000 and $30,000, ultimately was priced at $10,000 after the FAA mandated its installation in 1975.
Even if TCAS were to bear a $100,000 pricetag, the biggest airlines are not expected to quibble about price. They have pushed for development of the system and are believed to consider it cheap insurance for their multimillion- dollar flying machines and the precious cargo they carry.
