False Alarms Buffet Pilots, Air Controllers

The news was startling: A jetliner headed for Burbank Airport carrying 61 people aborted a landing to avert an imminent midair collision.

A sophisticated cockpit device sounded the warning, directing the pilot of Southwest Airlines Flight 1451 to pull sharply up and out of the approach pattern on Jan. 9. Radar controllers at Burbank, jolted by the jetliner’s sudden deviation, scrambled to guide the plane and two other aircraft out of potentially conflicting paths.

The warning proved to be a false alarm.

Federal and commercial officials called it a “nuisance alarm,” one of thousands of false alerts that have plagued the airline industry since Congress mandated nine years ago that computerized radar warning devices be installed in the cockpits of all aircraft used by scheduled passenger airlines. The midair collision over Cerritos in 1986 that killed 82 people was among the factors prompting Congress to act.

Despite improvements, pilots today do not respond to 26% of the average 383 alarms daily nationwide, according to the Federal Aviation Administration. Pilots estimate the percentage of noncompliance is even higher. That’s because up to 40% of the warnings still may be unnecessary. Pilots who heed the warnings by suddenly veering off course often trigger instant heartburn for air traffic controllers.

“We got a lot of complaints, quite frankly,” said Lawrence J. Knivert, an FAA official monitoring the warning system.

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Still, the FAA credits the devices for a steady reduction in potential midair collisions during the last five years while the volume of air traffic has soared.

This summer, another improvement to the device--a Traffic Alert and Collision Avoidance System, known as TCAS II, version 7.0--will allow planes to fly closer together without sounding a warning. Pilots say this will allow the radar bubble around the aircraft to be reduced, significantly trimming the number of nuisance alarms and, it is hoped, giving greater credibility to the warning system.

The issue is particularly critical in the FAA’s Western Pacific region, which includes California, because near-misses here during the last five years account for 29% of the total reported in all nine regions across the United States and its territories. The figure is more than double the number of near-misses in the second-riskiest region: the southern states surrounding Atlanta.

The high number of potential collisions in the Western Pacific, and particularly Southern California, “is a direct reflection of the [high volume of] air traffic out there,” said spokesman Paul Takemoto at the FAA’s Washington, D.C., headquarters.

The new software uses a technical filter that reduces the distance between potentially conflicting aircraft that will sound an alarm, said David Lubkowski, who developed the software for Mitre Corp. in Virginia. The new system is expected to reduce all warnings by 25% to 40%, he said.

The change is expected to make the alarm more believable. “When this TCAS barks, a committed intruder is headed into your space,” said Terry Hanson, a San Fernando Valley resident and veteran airline pilot who is active in the national Air Line Pilots Assn. “I’m telling my pilots, ‘Follow the [alarm].’ ”

The development was approved in December by a technical advisory committee composed of aviation industry and government representatives. The FAA is now debating whether to mandate installation of the new version in airliners operating in the U.S.

The warning system is not required on cargo planes, an exemption that many passenger airline pilots consider dangerous. The system also provides no protection against many small, private aircraft that do not have a transponder--a device that identifies and shows the altitude of an aircraft on radar screens.

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However, the warning system is popular with pilots, despite its shortcomings. “I don’t know a pilot today who would fly without it,” said Bob Flocke, spokesman for the 49,000-member Air Line Pilots Assn. He said the system can be crucial to safety in the event of radar or communication problems at ground control centers.

The devices are now on the more than 5,000 planes flown by passenger carriers in the U.S. Another 5,000 or so private aircraft also are now equipped with the system, according to the FAA.

The FAA’s Knivert blames much of the initial problem with the warning system on inadequate pilot training and pilot misunderstanding.

However, flaws in the system also are significant, pilots and government officials agree. The system can trigger nuisance alarms for traffic on a parallel course as far as three to four miles apart, generally considered a safe distance. The system also, at times, sends a “ghost image” of itself, showing a false picture of an imminent collision on a display screen.

“I’ve seen it five or six times when flying. There’s nobody in sight, then you suddenly get a pop-up, a target right in front of you, coming right at you,” said Bill Banks, a pilot and aviation safety inspector at the Van Nuys FAA Flight Standards District. “You get all the whoop-whoops and whirs going off in the cockpit. A recording says ‘climb, climb, climb’ or ‘dive, dive, dive.’ It gets your attention pretty quick.”

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FAA officials said the system also is designed to guide airplanes around other traffic. The newest version measures all air traffic in an area to avoid a domino effect of a series of airplanes changing course because of warnings.

The TCAS II display screen shows the approximate distance of other aircraft and an arrow indicating whether it is climbing, descending or traveling level. The image appears in white to indicate an aircraft in the approximate area, in yellow as a traffic warning or red for an imminent collision, which triggers alarms and a prerecorded order for action.

In the January incident, it was the red warning with alarms that sent the startled crew into a steep, white-knuckled ascent 1,000 feet above their assigned altitude.

“It really scared the crew,” Banks said. “Climbing 1,000 feet is pretty excessive.”

That prompted controllers to order pilots of two other aircraft to change altitude, although investigators said there never was any danger of a collision. FAA investigators never determined the cause of the false alarm.

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Airliner Alarms

The number of near-midair collisions has dropped as reliability of warning system improves.

Critical Midair*

1992: 46

1997: 26

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Potential Midair**

1992: 195

1997: 93

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Total Alarms

1992: 280,000

1997: 140,000

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Percentage of Nuisance Alarms

1992: up to 80%

1997: up to 40%

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Percentage of Alarms Ignored

1992: 50%

1997: 25%

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* Critical: a situation in which collision avoidance was due to chance rather than an act on the part of the pilot. Less than 100 feet of aircraft separation would be considered critical.

** Potential: an incident that would probably have resulted in a collision if no action had been taken by either pilot. Closest proximity of less than 500 feet would usually be required.

Source: The Federal Aviation Administration, Mitre Corp.