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Radar Faulted in Plane Crashes

Associated Press

Last Updated: Oct. 18, 1999 at 3:45:05 p.m.

WASHINGTON - A radar system that is supposed to warn low-flying planes of nearby obstacles was plagued with problems and fixed nationwide only after a 1997 fatal airplane crash in Guam, according to a published report.

In some cases, programming errors caused the Minimum Safe-Altitude Warning system not to operate over wide areas, including near busy airports such as those in Chicago and Dallas-Ft. Worth. In other cases, false alarms were so numerous that air traffic controllers put cardboard over warning speakers to silence the noise.

The Federal Aviation Administration was warned about the trouble after a business jet crashed outside Washington in 1994, but it did not take decisive action to resolve it until after a Korean Air jumbo jet slammed into a hill on approach to Guam in August 1997, killing 228, said USA Today, which reported about the problems on Monday.

The National Transportation Safety Board, which will hold a final hearing about the Korean Air crash on Nov. 2, is expected to recommend that the FAA acknowledge that system problems contributed to the accident.

Investigators have found plenty of blame for the crew: It appears they did not follow charts outlining a step-down approach procedure to the airport. Tapes also show there was cockpit confusion about whether another landing system using radio waves to outline the proper approach path was operational. It was not - as some crew members acknowledged on the tape.

The FAA said in response to the story that it would have had difficulty correcting the problems until it got new computer database-management tools in 1997. The agency has since standardized the operation of the system, inspects it monthly and checks each airport site with test aircraft every 18 months.

However, the agency also said the system is ``a tool'' and pilots have the ultimate responsibility for maintaining the proper altitude.

``In 20/20 hindsight, we wish we could have done a better job prior to the (Guam) accident, but now the system is being managed in a uniform way rather than as a number of individual entities,'' said FAA spokesman Les Dorr.

The first Minimum Safe-Altitude Warning systems were installed in 1977 in an effort to curb ground collisions, a vexing problem known within the industry as ``controlled flight into terrain.''

The systems divide the area around an airport into a grid and are programmed with the highest point in each square. When radar detects a plane descending within 500 feet of one of those points, an alarm sounds in the air traffic center and radar screens flash with a sign saying ``LA'' or ``LOW ALT.'' The controller is then supposed to warn the pilot by radio.

The systems are now installed in 193 air traffic control facilities and monitor airspace around almost every airport with commercial traffic.

NTSB investigators blamed the 1994 crash outside Washington on the flight crew, but they also found that an incorrect compass heading was entered into the altitude-warning system, preventing an alarm.

The safety board warned the FAA about the problem, and the agency replied that it had checked the remaining systems. Three more fatal crashes followed. Each was blamed on the pilots, and in each case the system produced alerts that were either not seen or heard by controllers.

After the Guam crash, though, the FAA assembled a team of top computer experts to reanalyze the system. The team soon found that repairs were needed at nearly half of the 130 smaller airports that had the system.

In some cases, incorrect obstacle heights were entered into the database. In the case of the Chicago and Texas airports, errors led computers to calculate planes were hundreds of feet higher that they actually were, effectively blocking alarms in wide areas.

In the case of Guam, a programmer disabled the system for all but a 1-mile band encircling the airport some 55 miles out at sea.

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-- Homer Beanfang (Bats@inbellfry.com), October 18, 1999

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...related article...

Tuesday October 12, 8:33 pm Eastern Time

Midair near-miss tied to computer glitch

SEATTLE, Oct 12 (Reuters) - Two Boeing Co. (NYSE:BA - news) 747s nearly collided last June over China after a computer system designed to prevent crashes erroneously steered one plane directly into the path of the other, industry sources confirmed on Tuesday.

The incident, reported in Tuesday's Wall Street Journal, involved a British Airways Plc (quote from Yahoo! UK & Ireland: BAY.L) passenger jet and a Korean Air Lines Co. freighter whose on-board systems miscalculated its own altitude.

Thinking the BA plane was just below it, the KAL jet's Traffic Alert and Collision Avoidance System (TCAS) warned its pilots to climb to avoid a crash, though the BA plane was in fact just above it, according to initial tests by AlliedSignal Inc. (NYSE:ALD - news).

AlliedSignal, one of a handful of TCAS makers, also owns the manufacturer of the air data computer on the KAL plane, Bendix, which it bought in 1984.

``Our preliminary test results indicate a component of the air data computer on the KAL jet could have failed and caused this problem by providing incorrect altitude data to the TCAS,'' said AlliedSignal spokesman Ron Crotty.

The problem was compounded by the failure of another component that normally shuts down the TCAS when its two altitude readings differ significantly, as they did in this case, Crotty said.

Both events are extremely rare, he added.

``It's very, very unlikely for these two things to happen at the same time,'' he said.

The original analog model air data computer was replaced with a more reliable digital version in 1979, Crotty said.

Within two weeks AlliedSignal will issue an industry advisory known as a service bulletin instructing airline operators how to check for and correct any problems, Crotty said.

A Boeing spokeswoman said the aerospace giant did not install the air data computers on its planes, though it has issued its own service bulletin to airlines.

It is not known how many Boeing or Airbus Industrie planes currently use the Bendix air data computer.

A Federal Aviation Administration spokesman said the agency is studying the situation closely but has not yet drawn any conclusions.

Britain's Civil Aviation Authority, its FAA counterpart, has issued an airworthiness directive describing the problem, industry sources said.

-- Homer Beanfang (Bats@inbellfry.com), October 18, 1999.

Kosky & Garvey, up in a plane, Rollover hits, never see them again ...

-- Ashton & Leska in Cascadia (allaha@earthlink.net), October 18, 1999.