Approaching Won Pat International Airport at night, Korean Air Lines Flight 801 impacted Nimitz Hill at 658ft, nearly 800ft below the minimum altitude at that point on the approach.

While initially the accident seemed to have little to do with automated systems, it turned out that the Minimum Safe Altitude Warning (MSAW) System used by the Agana tower controllers and installed at nearby Andersen Air Force Base, some 10 nautical miles beyond the departure end of the runway, had unbeknowst to controllers, not been operational due to software errors in a new software installation. It was due to a bug introduced into the MSAW system by a software upgrade developed by the FAA Technical Center in New Jersey intended to reduce the number of false-positive alarms the system was generating, in response to complaints by the Cerap operators. During subsequent testing at 191 MSAW installations in the U.S., three occurrences of software errors were found and corrected. Investigators said that the lack of MSAW advisories did not cause the crash, but could have helped prevent it.

Furthermore, when the descent profile and CVR transcript became available, questions were raised about the crew’s “resource management” that are also pertinent to dealing with more recent automation and procedures. (#1)

A landing-guidance system known as the glide slope, which guides planes to the runway, had not been in service at the airport for a month said sources at the FAA. According to a notice the agency sent pilots, the system was to be down for maintenance until mid September. When glide-slope guidance is not available, pilots can use other methods, including an electronic device that gives them their distance from the airport. Knowing that distance, they follow a stair-step pattern to the runway. (#2)

There were 254 passengers and crew aboard the aircraft; 228 lost their lives.