Incident Overview
United Airlines Flight 97, a transpacific flight en route to Tokyo Narita Airport, experienced a fuel system issue approximately four hours after departure while cruising at FL360. The flight, scheduled for 11 hours, had its fuel system configured for all engines to feed from tanks 2 and 3.
Fuel System Problem
During the flight, the crew received indications of uneven fuel flow from main tanks 2 and 3. It was later determined that the number 2 crossfeed valve had failed in the closed position. However, when the flight engineer moved the valve selector to the closed position, the intransit light illuminated, which the flight engineer interpreted as normal operation. Consequently, the fuel system problem was misdiagnosed as faulty fuel gauge indications.
Engine Flameout and Emergency Descent
Fuel monitoring showed insufficient fuel flow from tank 2 when crossfeeding was attempted. As a result, engines 1, 3, and 4 flamed out after fuel was depleted from all tanks except tank 2. The crew initiated an emergency descent to Tokyo Narita Airport.
Landing and Aftermath
Upon landing, the crew reported using flaps-20, but the digital flight data recorder (DFDR) indicated that flaps-1 was actually used. Three tires blew during the landing. All three flight crew members had qualified in the Boeing 747 within the 13 months prior to the incident.