Collision-Avoidance Gear--Preparing for a Takeoff

It was back in 1956 that a United Air Lines DC-7 and a Trans World Airlines Super Constellation slammed together over the Grand Canyon, killing all 128 aboard the two airliners and setting off a search for equipment to prevent midair collisions.

Thirty years later, on Sept. 19 of this year--spurred in part by the recent collision of an Aeromexico jetliner and a light plane over Cerritos that claimed 82 lives--Federal Aviation Administration chief Donald D. Engen announced that his agency finally intends to order the nation’s airlines to install collision-avoidance equipment.

The airlines, which carried about 345 million passengers last year, say they had expected Engen’s announcement and had been planning to outfit their approximately 3,000 planes with the gear--despite a total cost that could exceed $300 million.

But that still leaves three questions hanging uneasily over the aviation community:

--Why has it taken so long?

--When will the devices actually be in place?

--Will they work?

Some critics say that bureaucratic foot-dragging by the FAA and indifference by the aviation industry delayed the implementation of a traffic alert and collision-avoidance system (TCAS) that could already have saved hundreds of lives.

“The inaction of the FAA on this issue is nothing short of disgraceful,” said Rep. Robert Dornan (R-Garden Grove).

“Nothing happened because the FAA didn’t push it and because folks in the aviation industry didn’t want to deal with the cost of it,” said Rep. Dan Glickman (D-Kan.).

Others say reluctance of the White House and Congress to free up money for research from the $8-billion aviation trust fund and other government sources held up the search for acceptable collision-avoidance equipment.

“The money should be going to aviation safety . . . but it’s generally agreed that it’s being used to offset other spending in the unified budget,” said Tom Tripp, an official with the airlines industry’s Air Transport Assn.

FAA engineers who worked on the collision-avoidance project said it took a long time “because it involved every damned problem you can think of--both technical and operational . . . and not every path we took was the right one.”

Engen, whose planned mandate for collision-avoidance equipment heralds abandonment of a much-criticized voluntary approach that the FAA has taken since 1981, refused to single out politicians, the aviation community, manufacturers or his own agency for criticism.

“There is enough blame to go around for everybody,” he said.

‘By the End of the Decade’

The FAA is predicting that TCAS II, the generation of collision-avoidance systems that the agency plans to mandate, will be appearing in regular commercial service “by the end of the decade . . . optimistically, within two years, pessimistically within five.”

Others in government and the aviation industry refuse to predict a start-up date. They note that further testing, certification and commercial manufacture--each with its own uncertainties--must still take place before the airlines can actually purchase and install the systems--estimated to cost between $75,000 and $100,000 apiece.

And there are those, noting unresolved technical problems, who say that no matter when it comes, TCAS II will not do the job properly. In fact, they say the equipment’s shortcomings could actually cause a midair collision, the disaster pilots have dreaded since the first time two planes ended up in the air near each other more than 70 years ago.

Pilots still rely primarily on the so-called “see-and-avoid” technique to prevent collisions. Using this technique, they continuously search the skies around their planes, scanning back and forth in a series of short, regularly spaced eye movements, looking for other aircraft.

Since World War II and the invention of radar, pilots have relied secondarily on air traffic controllers, who use ground-based radar to monitor the planes overhead, radioing advisories designed, as the FAA puts it, “to maintain adequate separation of aircraft.”

Now, the agency is preparing to offer TCAS II, a system that would use on-board radar, computers and other equipment that can figure out where the other planes are and tell its pilots how to get out of the way if a collision is imminent.

TCAS II uses the on-board radar to broadcast repeated signals, or “interrogations.” These signals radiate out from the “host” aircraft, much like the ripples emanating from a stone dropped into a still pond.

When TCAS II’s interrogations hit an “intruder” plane in the area, a transmitter aboard that intruder responds with radio signals indicating the intruder’s altitude, rate of ascent or descent, heading and speed. The host aircraft receives these responses, and a computer aboard the host compares the projected course of the intruder with that of the host to determine if there is a potential for a collision.

Amber Caution Light

Forty seconds before such a collision might occur, TCAS II alerts the host plane pilot with an amber caution light, a three-second honk from a horn and a computer-generated voice advising, “Traffic.” At the same time, the host aircraft’s weather radar screen lights up with a graphic display showing the intruder’s position and bearing relative to the host, marked in amber.

Twenty-five seconds before a potential collision, TCAS II flashes a red warning light and gives a two-second blast from a siren that is followed by a sharp verbal command to “climb,” “descend” or “limit vertical rate” of ascent or descent. At the same time, the symbol on the screen marking the intruder’s position changes from amber to red.

TCAS II is the latest generation of collision-avoidance equipment to emerge in an evolutionary process dating to the disastrous Grand Canyon collision in 1956.

During the 15 years that followed that collision, the FAA, the avionics industry and the airlines pursued--with varying degrees of intensity--the search for a workable airborne collision-avoidance system to supplement the FAA’s ground-based air traffic control network. Several theoretically workable concepts emerged.

In 1971, two House subcommittees heard testimony that collision-avoidance systems should be made mandatory. The FAA responded that the commercial equipment being developed was not ready yet.

The proposal for a mandate was shelved, but the FAA agreed to continue testing three of the airborne collision-avoidance system concepts under development--Minneapolis-Honeywell’s avionic observation of intruder danger system (AVOIDS), McDonnell-Douglas’ eliminate range zero system (EROS) and the Radio Corp. of America’s separation and control of aircraft using nonsynchronous techniques (SECANT).

On Dec. 16, 1975, at a closed-door meeting of the FAA’s executive committee, David Israel, one of the chief researchers on the testing project, told James E. Dow, deputy FAA administrator, that “none of the systems worked as they were delivered by the manufacturer.” But Israel added that after additional refinements had rendered it effective, the AVOIDS equipment was the “clear choice for implementation” among the three. He concluded that an “early decision” by the FAA to proceed with AVOIDS could result in “a high level of effectiveness by 1983-84.”

Different Priority Urged

However, Israel recommended instead that priority be given to alternative airborne equipment known generically as beacon-compatible collision-avoidance system (BCAS), the precursor of what later became TCAS.

The FAA said that BCAS performed as well as the Honeywell equipment, if not better, and had several distinct advantages.

FAA engineers say BCAS permitted an aircraft to detect and avoid any other plane equipped with a transmitting device called a Mode C transponder. Since all commercial and military planes and any general aviation planes operating near the nation’s nine largest airports or at an altitude above 12,500 feet are required to carry such transponders, a BCAS-equipped aircraft would be protected against a majority of the more than 200,000 planes operating over U.S. skies.

In contrast, the FAA said, aircraft with the Honeywell equipment would be protected only against other planes carrying matching equipment. The FAA estimated that 190,000 aircraft would have to be equipped with the Honeywell systems at an estimated total cost of of $600 million. The FAA says it would cost half that to make BCAS, and now TCAS II, work.

In addition, the FAA said BCAS equipment uses radar frequencies compatible with the air traffic control radar in use throughout the nation, while ACAS equipment did not.

Using these and other arguments, the FAA decided to dump ACAS and concentrate instead on development of the BCAS equipment, to the considerable consternation of one of its own top officials, a man named James C. Pope.

Pope, then 52, charged in a letter to one of his supervisors that the agency had resorted to “subterfuge, delay tactics and technological hocus-pocus,” sacrificing a preferable ACAS concept because BCAS--and later, TCAS--fit more neatly into the FAA bureaucracy’s long-range research-and-development plans.

Pope said that when he continued to object, “they decided to get rid of me,” first shunting him off to Seattle and “a job where there was nothing to do,” and eventually firing him. Pope fought back, and his dismissal was later changed to a disability retirement.

Continuing his battle, Pope testified before a House aviation subcommittee and eventually won an investigation of the matter by the Department of Transportation. At the conclusion of the probe last January, Transportation Secretary Elizabeth Dole noted in her summary that “we did not find any instance of perjury, misfeasance or mismanagement as alleged by . . . Pope.”

Stuck With Its Decision

The FAA stuck with its decision to pursue the development of the evolving BCAS equipment. Additional refinements led BCAS, in 1981, to evolve into TCAS--TCAS I for light aircraft, somewhere down the line, if anyone wants it; TCAS II for the airline industry, as soon as possible; and TCAS III, a more sophisticated version of TCAS II that Anthony Broderick, an associate administrator of the FAA, describes as “optional extra equipment.”

But the Air Line Pilots Assn. says Broderick’s priorities are out of line; that TCAS II is dangerous and should be abandoned; that “TCAS III isn’t optional; it’s absolutely essential.”

John E. O’Brien, a former Pan American Airways captain serving as director of the pilot association’s engineering and air safety division, said TCAS II’s simple “climb,” “descend” and “limit vertical rate” commands do not give a pilot sufficient options for evasion in this era of congested skies and high-speed, high-altitude aircraft. He said the FAA should leapfrog over TCAS II to TCAS III, which has the increasingly sophisticated telemetry and programming that enable it to tell a pilot to “turn right” or “turn left,” as well as climb or dive.

O’Brien said TCAS II could be especially dangerous when airplanes are “stacked,” one above another, in a vertical series of holding patterns to await clearance to land at a busy airport. O’Brien said a sudden climb or dive by one plane in the stack could set off a dangerous and unplanned “domino effect” on aircraft in the patterns above or below.

He said TCAS II assumes a capability to climb or dive at a rate of 1,500 feet per minute, but at the top of commercial airliners’ “performance envelope”--about 35,000 feet for a Boeing 727, for example--fully laden jetliners can climb at only about 500 feet per minute.

While landing, he noted, an aircraft’s ability to dive in an evasive maneuver would be limited by its proximity to the ground. He also noted that altimeters are permitted discrepancies of plus or minus 300 feet, pointing out that two jetliners with the maximum allowable error could be in serious danger if limited to vertical maneuvers.

And he said that TCAS II still has a lot of of flaws--flaws that currently prohibit the system’s use in bad weather and in heavily congested airport approach corridors like the one where the Cerritos collision occurred; flaws that have led the system to command “fake-out” maneuvers that could actually direct two aircraft into one another.

Broderick said the problems with TCAS II are being corrected, that “none of them will be barriers to the implementation of TCAS II.”

But he said that to eliminate such problems takes time, much as it has since the outset of the development of collision-avoidance systems.

Eliminating Interference

Two of the toughest problems solved along the way were “fruit” and “garble”--interference caused when several planes in congested airspace simultaneously were sending out and receiving signals. These problems were eventually resolved with sophisticated “whisper/shout” radar and advanced computer “logic” that enhance the systems’ ability to ignore planes that are not a direct threat.

The FAA says other difficulties are being dealt with during the continuing research with TCAS II prototypes.

One prototype has been installed in a Boeing 727 flight simulator at NASA’s Ames research facility in Palo Alto, where engineers and psychologists are studying how well pilots react to the new equipment.

Another prototype was placed in a Piedmont Airlines jetliner during regular service in 1981. The equipment was monitored by FAA personnel in the back of the plane, but the data, alarms, verbal commands and radar displays were screened from the flight crew in the cockpit. As a result of these continuing tests and further research by FAA engineers in New Jersey, standards for TCAS II were adopted in 1983.

A third prototype has been installed in another Piedmont Airlines jetliner. Piedmont pilots who are acclimating themselves to the equipment on a flight simulator will use this version of TCAS II in the cockpit on regularly scheduled flights, including transcontinental trips from the East Coast to Los Angeles. The flights are expected to start by Christmas.

Yet to begin is the FAA’s limited installation program, under which 14 commercial prototypes of TCAS will be manufactured, seven by Sperry/Dalmo Victor and seven by Allied Bendix. The commercial prototypes will be placed in Piedmont, United Airlines and Republic Airlines planes for use on regular commercial flights. These flights are scheduled to start in about nine months.

Broderick said the tests will take up to two years, with certification and commercial production--which requires planning, financing and the development of manufacturing systems--perhaps six to 30 months after that, assuming no unforeseen complications.

$100,000 Per Plane

While TCAS II is expected to cost up to $100,000 per plane, that is a relatively modest sum compared to the price of airliners. A Boeing 747, for example, has a base price of about $125 million.

Tripp, of the Air Transport Assn., said the airline industry does not consider FAA Administrator Engen’s proposed mandate an unfair imposition “because we had been planning to install (TCAS II) anyway.”

Because financing for government research and development is limited, Broderick said, TCAS II is receiving the FAA’s primary attention right now, with TCAS III relegated to the back burner.

Also on a back burner is TCAS I, the relatively unsophisticated, general aviation version of the TCAS family that is being designed to provide intruder proximity warnings, but it offers no radar displays or recommendations on evasive maneuvers.

A preliminary draft of the federal standards for TCAS I has been completed, but enthusiasm for the system is lukewarm, at best. Cost estimates for TCAS I run between $4,000 and $15,000 per plane, as much as some owners paid for their aircraft.

“We don’t perceive that the problem of midair collisions is big enough for large numbers of general aviation pilots to equip their planes,” said John Sheehand, a senior vice president of the Airline Owners and Pilots Assn. “There’s no demand for TCAS I.”

AN AIR-COLLISION SYSTEMS GLOSSARYSome of the terms of air-collision systems:

ACAS: Airborne collision-avoidance system, the first generation of on-board electronic equipment designed to prevent planes from crashing into one another.

AVOIDS: Avionic observation of intruder danger system, one of the first examples of ACAS equipment.

BCAS: Beacon-compatible collision-avoidance system, the second generation of collision-avoidance equipment. This system uses existing ground control radar frequencies.

TCAS I: Traffic alert and collision-avoidance system, No. 1, equipment from the current generation of collision-avoidance systems, designed specifically for light planes.

TCAS II: Traffic alert and collision-avoidance system, No. 2, equipment from the current generation of collision-avoidance systems, designed for commercial airliners.

TCAS III: Traffic alert and collision-avoidance system, No. 3, enhanced versions of TCAS II equipment that, proably sometime in the 1990s, will become the next generation of collision-avoidance equipment.

Host: A plane equipped with one of the more sophisticated collision-avoidance systems.

Interrogation: A radar signal transmitted by a host plane.

Intruder: An aircraft that may post a potential threat of collision with a host plane.

Mode C Transponder: A radio transmitter aboard an intruder that responds to an interrogation from a host plane with a signal indicating the bearing and altitude of the intruder plane carring the transponder.

HOW AN AIR COLLISION AVOIDANCE SYSTEM WORKS

For years, pilots have relied on their eyes and on warnings from ground-based air traffic controllers to avoid colliding with other aircraft. Now, after more than 30 years of discussion, research and development, the FAA is preparing to mandate on-board, electronic devices--Traffic Alert and Collision Avoidance Systems (TCAS II.) As planned, radar, receiver, computer and other equipment included in TCAS II would be installed within the next few years in the 3,000 airliners in service over the United States. Full operation of the system is dependent on transmitters called “Mode C transponders” currently installed in most planes in U.S. skies.

Finding the Intruder

1. TCAS II radar broadcasts “interrogation” signals from the “host” plane in all directions.

2. When radar hits an “intruder” plane, the intruder’s Mode C transponder returns radio signals indicating its altitude, rate of ascent or descent, heading and velocity.

3. TCAS II analyzes these responses, comparing the projected course of the intruder to that of the host to determine potential for collision.

In the Cockpit

40 seconds before possible collision, TCAS II alerts the pilot with an amber caution light, a three-second horn blast and a computer-generated voice advising, “Traffic.” The aircraft’s weather radar screen lights up with a graphic display showing the intruder’s range, bearing, altitude and whether it is climbing or descending.

25 seconds before possible collision, TCAS II flashes a red warning light and gives a two-second blast from a siren followed by a sharp verbal command to “climb,” “descend” or “limit vertical rate” of ascent or descent. The symbol on the screen marking the intruder’s position changes from amber to red.

Radar signals from TCAS II bounce back from an intruder without a functioning Mode C transponder, showing bearing and range, but not altitude. The screen displays such an intruder’s range and bearing, but with question marks in the spaces reserved for altitude and whether it is climbing or descending. TCAS II offers no audible warnings for such intruders.

On The Screen

A. Amber caution: Intruder at 10 o’clock, 1,000 feet above host, ascending.

B. Amber caution: Intruder at 1 o’clock, same altitude as host, level.

C. Red warning: Intruder at 2 o’clock, 500 feet below host, climbing.

D. Blue chevron: Host aircraft.

E. Asterisks: Twelve positions on the bearing clock face, corresponding to numbers on the face of a clock.