Boeing 747 Explosive Decompression Accidents, AI 182, PA 103, UAL 811, TWA 800

From NTSB AAR 92/02 for UAL 811: "The National Transportation Safety Board determines that the probable cause of this accident was the sudden opening of the forward lower lobe cargo door in flight and the subsequent explosive decompression. The door opening was attributed to a faulty switch or wiring in the door control system which permitted electrical actuation of the door latches toward the unlatched position after initial door closure and before takeoff. Contributing to the cause of the accident was a deficiency in the design of the cargo door locking mechanisms, which made them susceptible to deformation, allowing the door to become unlatched after being properly latched and locked."

Article in Flying magazine July 1992.

J. Mac McClellan Editor

'Door bomb?

John Barry Smith, of Carmel Valley, California, wrote with a provocative comment on the Pan Am 103 crash. Smith points out the similarities between the damage caused by the cargo door failure of United Flight 811 over the Pacific and that of Pan Am's 103 over Scotland. Both airplanes involved were Boeing 747s and both suffered massive structural damage to the lower forward fuselage. The United flight made it safely to Hawaii while Pan Am's 747 came down in pieces.

The cargo door from the United airplane was retrieved from very deep water, and examination of the door forced the NTSB to change its probable-cause finding for the accident. The Board had originally concluded that improper latching of the door before takeoff caused the

failure; but the minimal damage found on the door now indicates that an electrical malfunction probably caused electrically operated latches to open in flight. Smith points out how the cargo door opening at 23,000 feet on the United flight ripped a large hole in the fuselage and sent baggage and other debris into the number-three engine. He notes that the Pan Am flight was at a higher altitude when it suffered massive structural failure and that baggage and debris were also found in the number-three engine. He believes the greater differential cabin pressure of the higher altitude could have been enough to cause loss of the airplane if the cargo door opened on the Pan Am flight.

It's an interesting theory. British and U.S. investigators are working
with microscopic evidence of a bomb when in fact damage caused by thefailure of the cargo door on the United flight proves door failure could have caused the Pan Am crash. Actual bomb evidence is small and we're told finding it was one of the most astute investigative feats ever. Investigators also tell us that the bomb evidence is incontrovertible.
Could they be wrong? The NTSB was wrong about the United cargo door failure until the actual door was recovered from the ocean floor. The bomb on board the Pan Am flight may have been the cargo door latches, not plastic explosive hidden in a portable radio. Politics drives the investigation to search for terrorists but aviation safety demands a totally open mind and the suspicion that the airplane could have failed without outside interference. Smith has no evidence that a cargo door failed on Pan Am 103-but he gives us something to think about.'

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The linchpin clue match for UAL Flight 811 to the other three is the extremely rare sudden loud sound on the cockpit voice recorder of all four aircraft implying that one unifying initiating event caused the accidents. The below chart 12 is from the TWA 800 Public Docket created by NTSB and shows the acoustic analysis of the sudden loud sound on the CVR of TWA Flight 800, Pan Am Flight 103, and Air India Flight 182. The sound is not a bomb sound because of absent necessary frequencies and the rise time is too slow for a bomb explosion but the spectrum is consistent with a sudden explosive decompression which would occur with an inadvertent opening of the forward cargo door while the aircraft is in flight and fuselage pressurized.