Pan Am Flight 125

Pan Am Flight 125 was a scheduled flight from London Heathrow Airport to New York's John F. Kennedy International Airport. It suffered a cargo door failure that pointed to a fundamental design flaw in the early model Boeing 747's, a failure mode that was repeated with fatal consequences on United Airlines Flight 811.

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On 10 March, 1987, a Pan American World Airways Boeing 747-121 (registration number airreg|N|740PA|disaster) named "Clipper Ocean Pearl" with 245 passengers and crew [ [http://www.asias.faa.gov/pls/portal/STAGE.AIDS_BRIEF_REPORT_PUB?EV_ID=19870310025169C&NARR_VAR= Aviation Safety Information Analysis and Sharing (ASIAS) Brief Report #19870310025169C] , Federal Aviation Administration, Office of Aviation Safety.] experienced an incident involving the forward cargo door. According to Pan Am and Boeing officials who investigated this incident, the flight crew experienced pressurization problems as the aircraft was climbing through about 20,000 feet. The crew began a descent and the pressurization problem ceased at about 15,000 feet. The crew began to climb again, but around 20,000 feet, the cabin pressure altitude began to rise rapidly again. The flight returned to London. [http://amelia.db.erau.edu/reports/ntsb/aar/AAR92-02.pdf Aircraft Accident Report NTSB/AAR-92/02 (United Airlines Flight 811)] (PDF), National Transportation Safety Board, p. 57, adopted 18 March, 1992.]

Cause

When the aircraft was examined on the ground, the forward cargo door was found open about 1.5 inches along the bottom with the latch cams unlatched and the master latch lock handle closed. The cockpit cargo door warning light was off.

According to the people who examined the aircraft, the cargo door had been closed manually and the manual master latch lock handle was stowed, in turn closing the pressure relief doors and extinguishing the cockpit cargo door warning light. Subsequent investigation on N740PA revealed that the latch lock sectors had been damaged and would not restrain the latch cams from being driven open electrically or manually. It was concluded by Boeing and Pan Am that the ground service person who closed the cargo door apparently had back-driven (opened) the latches manually after the door had been closed and locked. The damage to the sectors, and the absence of other mechanical or electrical failures supported this conclusion.

Further testing of the door components from N740PA and attempts to recreate the events that led to the door opening in flight revealed that the lock sectors, even in their damaged condition, prevented the master latch lock handle from being stowed, until the latch cams had been rotated to within 20 turns (using the manual half-inch socket drive) of being fully closed. A full cycle, from closed to open, is about 95 turns with the manual drive system.

Related incident

A similar incident occurred 24 February, 1989, with far worse consequences. United Airlines Flight 811 experienced the loss of its cargo door after climbing out of Honolulu, Hawaii. The cargo door in this incident was lost in-flight, which caused a portion of the aircraft and 9 passengers to separate from the aircraft after explosive decompression.

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