Abrupt Power Cut

Each aircraft had an abrupt power cut less than a second after the loud sound on the cockpit voice recorder. The nose has come off after it was crumpled into the cargo door hole by the 300 knot CAS wind force.

United Airlines Flight 811:

"However, the decompression event caused a data loss of approximately 2 1/2 seconds. When the data resumed being recorded, all values appeared valid with the exception of the pitch and roll parameters. Lateral acceleration showed a sharp increase immediately following the decompression. Vertical acceleration showed a sharp, rapid change just after the decompression and a slight increase as the airplane began its descent."
NTSB AAR 92/02. page 25

Air India Flight 182:

"From the CVR and DFDR, AI 182 was proceeding normally en route from Montreal to London at an altitude of 31,000 feet and an indicated airspeed of 296 knots when the cockpit area microphone detected a sudden loud sound. The sound continued for about 0.6 seconds, and then almost immediately, the line from the cockpit area microphone to the cockpit voice recorder at the rear of the pressure cabin was most probably broken. This was followed by a loss of electrical power to the recorder."
Canadian Aviation Safety Board Air India 23 June 1985, page 21
"When synchronized with other recordings it was determined, within the accuracy that the procedure permitted, that the DFDR stopped recording simultaneously with the CVR." "Irregular signals were observed over the last 0.27 inches of the DFDR tape. Laboratory tests indicated that the irregular signals most likely occurred as a result of the recorder being subjected to sharp angular accelerations about the lateral axis of the recorder, causing rapid changes in tape speed over the record head."
Canadian Aviation Safety Board Air India 23 June 1985, page 22

Pan Am Flight 103:

"The analysis of the recording from the DFDR fitted to N739PA, which is detailed in Appendix C, showed that the recorded data simply stopped. Following careful examination and correlation of the various sources of recorded information, it was concluded that this occurred because the electrical power supply to the recorder had been interrupted at 19:02:50 +- second."
UK AAIB Report 2/90 Page 37

"The analysis of the cockpit voice recording, which is detailed in Appendix C, concluded that there were valid signals available to the DVR when it stopped at 19:02.50 +- second because the power supply to the recorder was interrupted. It is not clear if the sound at the end of the recording is the result of the explosion or is from the break-up of the aircraft structure."
UK AAIB Report 2/90 Page 38

Trans World Airlines Flight 800:

"The wire that carried electrical power from the cockpit to the tape recorder mounted in the rear of TWA Flight 800 ran down the right side of he airplane. The wire that carried power to the flight data recorder ran down the left side. Yet the two were severed within an instant, without any warning."
News Reports from Associated Press, Reuters, major newspapers, press releases from NTSB, FBI

Comment: The distinct crash similarities of aircraft type, radar returns, wreckage plot, sudden short loud sound, abrupt power cut, fodded engines, inflight damage, missing bodies, torn off noses, and start place of damage qualify three aircraft into one class from which the deduction may be made that one unifying cause had the same effects. Another accident with the same similarities except for a torn off nose and less wreckage may also be included in that class. The unifying cause for all four accidents is the inadvertent opening of the forward cargo door inflight. 27 Mar 97

Boeing 747 nose picts right side cargo door
811 picture
AD Airworthiness Directive 79-17-02
Airworthiness Directive Amendment to 89-05-54 amending 88-12-04
Airworthiness Directive 88-12-04 Boeing 747
More pictures of UAL 811 cargo door hole
Cargo door accidents