Subject: Software error may have contributed to Guam crash

National Transportation Safety Board investigators say that a software error may have been a contributing factor in the crash of the Korean Air 747, Flight 801, in Guam. The bug didn't cause the crash; however, if it were not for the bug, the crash might have been averted.

The airport at Guam has a system known as Radar Minimum Safe Altitude Warning. It notifies controllers if a plane is too low; they in turn can notify the pilot. It normally covers a circular area with a 63-mile radius. Because of the bug, it was only covering a one-mile wide strip around the circumference of the circular area.

An NTSB member said "This is not a cause -- it might have possibly been a prevention".

And why was the code changed? Because the old version gave too many false alarms. [Source: An AP wire story]

225 of the 254 people on board were killed. The bug in the upgraded software apparently existed in airports throughout the world, and was not detected until analysis after the crash. Seeking to discover the exact point in time at which the altitude-warning system had failed, investigators discovered that the system had not issued any expected warnings and had failed completely. PGN.

Last updated 97/08/18