Korean Air Flight 801

Investigation and probable cause

The U.S. National Transportation Safety Board (NTSB) investigated the accident, as it occurred in U.S. territory.

A special weather observation made at 01:32, 10 minutes before the impact, reported:

Wind 090° at 6 knots; visibility—7 miles; present weather—shower vicinity; sky condition—scattered 1,600 feet, broken 2,500 feet, overcast 5,000 feet [above ground level]; temperature—27 °C; dew point—25 °C; altimeter setting 29.85 inches Hg; remarks—showers vicinity northwest-northeast.

Another special weather observation made at 01:47, five minutes after the impact, reported:

Wind variable at 4 knots; visibility—5 miles; present weather—light rain shower; sky condition—few 1,500 feet, scattered 2,500 feet, overcast 4,000 feet; temperature—26 °C; dew point—24 °C; altimeter 29.85 inches Hg.

The crew had been using an outdated aeronautical chart that was missing a 724 ft obstruction symbol depicted at the NIMITZ VOR, and that map stated the minimum safe altitude while crossing the NIMITZ VOR for a landing aircraft was 1300 ft as opposed to the updated altitude of 1440 ft. Flight 801 crashed near the NIMITZ VOR, which is situated on Bijia Peak at an altitude of 680 ft at 1:42 am, when it descended below the minimum safe altitude of 1440 ft during its landing approach. The report also identified that the captain may have mistakenly believed that the airplane was closer to the airport than it was, and confusion may have existed about the location of the distance measuring equipment (DME) in relation to the airport, with the crew anticipating the VOR/DME to be located at the airport. The DME was sited at the NIMITZ VOR some 3.3 nmi from the airport and such a configuration had not been part of Korean Air's simulator training, the crew's training for such non-precision approaches having been carried out in scenarios where the DME was located at the airport. Nevertheless, the correct DME distances were shown on the approach chart.

The NTSB was critical of the flight crew's monitoring of the approach, and even more critical of why the first officer and flight engineer did not challenge the captain for his errors. Even before the accident, Korean Air's crew resource management program was already attempting to promote a free atmosphere between the flight crew, requiring the first officer and flight engineer to challenge the captain if they felt concerned. The flight crew only began to challenge the captain six seconds before impact, though, when the first officer urged the captain to make a missed approach. According to the cockpit voice recorder, the flight crew suggested to the captain that he had made a mistake, but did not explicitly warn him. The flight crew had the opportunity to be more aggressive in its challenge and the first officer even had the opportunity to take over control of the aircraft and execute a missed approach himself, which would have prevented the accident, but he did not do this. Despite examining Korean Air's safety culture and previous incidents, the NTSB was unable to determine the exact reasons why the flight crew failed to challenge the captain, but at the same time noted that "problems associated with subordinate officers challenging a captain are well known".

Air traffic control (ATC) also played a role in the accident. The center/approach controller, 39-year-old Kurt James Mayo, did not adhere to standard ATC procedures and failed to monitor the aircraft during its descent. Specifically, he did not monitor the flight after the crew switched to the tower frequency as required, did not give a position advisory to the flight crew when clearing them for the approach (which would have advised them to cross-check their position on the radar with that of other flight instruments), and did not monitor the flight on the terminal radar display, which showed the terrain in the area because radar service had been terminated at the time. The NTSB said that had Mayo followed the procedures, the accident could have been prevented or at least reduced in severity. The tower controller, Marty Irvin Theobald (also 39), was also criticized for not alerting the crew, as Mayo had been unaware of the aircraft's low altitude, and did not provide an alert to him.

The NTSB also criticized the emergency responders for their delayed rescue operation, citing that most of the factors that delayed the response were preventable. These factors included ATC's initial unawareness of the accident, a brake failure on a fire truck, and a delayed notification of the fire department. The NTSB also concluded that at least one person who survived the initial crash could have recovered had the response not been delayed.

The NTSB presented its findings on March 24, 25, and 26, 1998, at the Hawaii Convention Center in Honolulu.

The section of the report entitled "Probable Cause" concluded:

The National Transportation Safety Board determines that the probable cause of this accident was the captain's failure to adequately brief and execute the non-precision approach and the first officer's and flight engineer's failure to effectively monitor and cross-check the captain's execution of the approach. Contributing to these failures were the captain's fatigue and Korean Air's inadequate flight crew training.

Contributing to the accident was the Federal Aviation Administration's intentional inhibition of the minimum safe altitude warning system at Guam and the agency's failure to adequately manage the system.The investigation report stated that a contributing factor was that the ATC Minimum Safe Altitude Warning (MSAW) system at Antonio B. Won Pat International Airport had been deliberately modified to limit spurious alarms and could not detect an approaching aircraft that was below minimum safe altitude. The probable cause of the accident was the captain's poor execution of the non-precision approach, the captain's fatigue, poor communication between the flight crew, and Korean Air's lack of flight crew training.