The cause was traced to the cargo door latching system , which had failed to close and latch the door completely without any indication to the crew that it was not safely closed . A separate locking system was supposed to ensure this could not happen , but proved to be inadequate . McDonnell Douglas instituted a number of minor changes to the system in an attempt to avoid a repeat . These were unsuccessful , however ; on March 3 , 1974 , the rear cargo door of Turkish Airlines Flight 981 blew open for the same reason , causing the aircraft to go out of control and crash in a forest near Paris , France . This crash killed all 346 people on board , making it the deadliest in aviation history until the 1977 Tenerife airport disaster and the deadliest single-aircraft crash until the 1985 crash of Japan Airlines Flight 123
Tenerife airport disaster
Tenerife airport disaster
American Airlines Flight 96