Pan Am Flight 845

Pan Am Flight 845 was a scheduled international passenger flight between Los Angeles and Tokyo, with an intermediate stop at San Francisco. The flight was operated by a Boeing 747 registered N747PA and named Clipper America.

On July 30, 1971, at 15:29 PDT, while it was taking off from San Francisco International Airport bound for Tokyo, the aircraft struck approach lighting system structures located past the end of the runway; this initial mishap seriously injured two passengers and caused significant physical damage to both the runway structures and the aircraft.

The crew continued the takeoff, flew out over the ocean, circled while dumping fuel, and returned to SFO. After coming to a stop, the crew ordered an emergency evacuation, during which 27 passengers were injured exiting the aircraft, eight of whom suffered serious back injuries.

The accident was investigated by the National Transportation Safety Board (NTSB), which determined the probable cause was the pilot's use of incorrect takeoff reference speeds. The NTSB also found various procedural failures in the dissemination and retrieval of flight safety information, which had contributed to the accident.

Accident history

Flight 845's crew had planned and calculated its takeoff for runway 28L but discovered only after pushback that this runway had been closed hours earlier for maintenance, and that the first 1000 ft of runway 01R, the preferential runway at that time, had also been closed. After consulting with Pan Am flight dispatchers and the control tower, the crew decided to take off from runway 01R, shorter than 28L, with less favorable wind conditions.

Runway 01R was about 8500 ft long from its displaced threshold (from which point the takeoff was to start) to the end, which was the available takeoff length for Flight 845. Because of various misunderstandings, the flight crew was erroneously informed that the available takeoff length from the displaced threshold was 9500 ft, or 1000 ft longer than actually existed. Despite the shorter length, it was later determined that the aircraft could have taken off safely if the proper procedures had been followed.

As the crew prepared for takeoff on the shorter runway, it selected 20 degrees of flaps, instead of the originally planned 10 degree setting, but did not recalculate the takeoff reference speeds (V1, Vr and V2), which had been calculated for the lesser flap setting and were thus too high for their actual takeoff configuration.

Consequently, the critical speeds were achieved late and the aircraft's takeoff roll was abnormally prolonged. In fact, the first officer called Vr at 160 kn, instead of the planned 164 kn, because the end of the runway was "coming up at a very rapid speed".