Radar Information

Each aircraft had radar information at door rupture/opening. Cargo door coming off DC-10 was seen on radar. Cargo door on B747 was tracked to surface of ocean, UAL 811. Pan Am 103, and TWA 800 both had radar anomalies just before destruction, AI 182 was too far away for primary radar returns to show any anomaly.

United Airlines Flight 811:

"Navy radar near Honolulu tracked debris that fell from the airplane when the cargo door was lost. Refinement of the radar data led to a probable 'splashdown' point in the ocean." Radar tape unavailable but would show primary return of door after it departed aircraft.
NTSB/AAR 92/02 Page 26

Air India Flight 182:

"The Shannon Air Traffic Control Centre was in contact with VT-EFO and recorded radio communications with the aircraft. At the time of the accident. 5.4 seconds of noise was recorded, and the transponder signal seen on the radar scope was lost from the aircraft. This signal which displays aircraft altitude showed no deviation before disappearing from the radar scope."
Canadian Aviation Safety Board Air India 23 June 1985, page 20

Pan Am Flight 103:

"There was a single primary return received by both Great Dun Fell and Claxby radars approximately 16 seconds before SSR returns were lost." This image matches the radar plot of TWA 800 showing cargo door as primary return.
UK AAIB Report 2/90 Page C-11
"The last secondary return from the aircraft was recorded at 19:02:46:9 hrs, identifying N739PA at flight Level 310, and at the next radar return there is no SSR data, only 4 primary returns."
UK AAIB Report 2/90 Page 34

Trans World Airlines Flight 800:

"But law enforcement and aviation officials were particularly perplexed by an unidentified ''blip,'' signaling the presence of some object, that appeared on air traffic control radar near the plane just before the crash, a senior law enforcement source said. Authorities were repeatedly replaying recordings of the radar transmission ''but we are stymied,'' the source said."
News Reports from Associated Press, Reuters, major newspapers, press releases from NTSB, FBI

Radar tapes show mystery blips near TWA 800. The image matches the Pan Am 103 radar plot of radar anomaly just before destruction.

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 rupture/opening of the forward cargo door inflight. Updated 16 Mar 97 27 Mar 97 2 Nov 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