Computer Glitch Cited in Jet Crash

AGANA, Guam — A ground radar system that should have warned air traffic controllers that Korean Air Flight 801 was dangerously below the normal airport approach path failed to work properly because of a programming glitch, federal officials said Sunday.

This glitch, which could be affecting other Minimum Safe Altitude Warning Systems at airports throughout the world, was not discovered until after the jumbo jet slammed into a hill during a predawn rainstorm while preparing to land at the airport here, killing 225 of the 254 people on board.

George Black, the National Transportation Safety Board member heading up the investigation of Wednesday’s crash, stressed that while a radar system failure probably was not the cause of the tragedy, “it could have made a difference.”

Despite the failure of the altitude-warning system, and despite the fact that one of the multiple ground-based navigation systems was not operational, the pilot apparently still had plenty of functioning navigational aids to have made a safe landing, officials said.

The altitude-warning system “is a safety redundancy that does not relieve the pilot of responsibility,” Black said.

The official cause of the crash will not be determined for months, but NTSB sources have indicated that there is a strong likelihood that pilot error will be considered a major factor.

Black said that in the course of the crash investigation, members of an air traffic control team headed by NTSB investigator Richard Wentworth checked Sunday to determine at what point the altitude-warning system had issued its warnings. To their surprise, they found that it had failed completely.

Further checks showed that the culprit was software installed by the Federal Aviation Administration recently to replace earlier programming that had triggered spurious warnings.

Thus far, the only known system failure has been at the airport here, but the FAA is concerned that the systems at scores of other airports where programming was replaced could be affected, Black said.

Wentworth said that when working properly, the computer-driven altitude-warning system alerts controllers with an aural alarm if a plane appears to be on a path that would bring it dangerously close to the terrain surrounding an airport.

At the same moment, a warning is printed on a controller’s screen and the data box beside the plane’s image on the screen begins to flash.

The controller would immediately warn the pilot by radio. Because the system is supposed to provide its warning 15 seconds before the danger is imminent, the pilot, in most cases, should be able to pull up in time.

The crash claimed another victim late Sunday. Grace Chung, an 11-year-old from Georgia, died at Brooke Army Medical Center in San Antonio, Texas, the Associated Press reported.