On 3 March 1974, Turkish Airlines flight 981 crashed in the Ermenonville forest north of Paris shortly after leaving Orly for London. All 346 people aboard died. At the time it was the deadliest accident in aviation history, and what makes it hard to read about is that it had already happened once, in a survivable form, and the warning was not acted on with force.
The design problem
The DC-10's rear cargo door opened outwards rather than inwards. An inward-opening plug door is held shut by cabin pressure; an outward-opening door must be held by its latches against the full pressure load. The DC-10's latching mechanism could, if the door was forced closed when not properly latched, give the external appearance of being secure while the latches were not fully engaged.
Under pressurisation, such a door bursts open. The resulting explosive decompression collapses the cabin floor above the hold, because the floor is not designed to take a large pressure differential across it. Control cables to the tail run under that floor.
The warning: American Airlines 96
In June 1972, an American Airlines DC-10 over Windsor, Ontario, lost its rear cargo door in exactly this way. The floor partially collapsed, damaging control cables. The crew, with limited control, managed to land at Detroit. Nobody died.
The NTSB recommended that the FAA mandate design changes. What followed instead was a "gentleman's agreement" between the FAA and McDonnell Douglas to fix the problem through service bulletins rather than a binding airworthiness directive. Service bulletins are advisory; airworthiness directives are compulsory.
The aircraft that crashed near Paris had reportedly received some of the modifications, but the door could still be improperly closed. A ground handler at Orly, working in a language he did not read on a placard, closed it in a way that left the latches incomplete.
What happened over Ermenonville
Twelve minutes after takeoff, passing about 11,000 feet, the door failed. Six passengers and part of the cabin floor were ejected. The floor collapse severed the control lines to the tail. The crew had no elevator control and no ability to arrest the descent. The aircraft struck the forest at high speed.
What changed
The response, when it finally came, was thorough. The cargo door latching mechanism was redesigned across the DC-10 fleet under a mandatory directive. More importantly, the certification requirement changed: transport aircraft must now be able to survive a sudden decompression of any single compartment without losing control. In practice this means floor vents that equalise pressure fast enough to prevent floor collapse, and control system routing that does not concentrate everything in one vulnerable path.
The regulatory lesson was equally durable. The Windsor incident is now the standard example of why a known design defect must be addressed by binding directive rather than voluntary agreement. It is cited whenever a regulator considers letting a manufacturer handle a safety issue on its own terms.