Under Pressure.

On March 3, 1974, Turkish Airlines Flight 981 took off from Orly International Airport in Paris on its way to London’s Heathrow Airport with 346 people on board. After taking off under good flight conditions, the DC-10 jet was cleared to ascend. At 11,000 feet, the rear cargo door opened and detached from the aircraft. The pressure difference between the passenger and cargo areas caused the cabin floor to buckle, trapping the pitch controls in the nose-down position. A minute later the plane crashed in a forest near the town of Senlis, France. There were no survivors.?

Aircraft passenger doors ordinarily open inward to allow pressurization to hold them in place, but cargo doors almost universally open outward for ease of loading. The DC-10’s cargo door was designed with an electric motor that would first close the door and then drive latches to an over-center position. Ground crews would then move a manual lever that locked the over-center latches. In flight, pressurization forces the latches further closed.?

A few years earlier, a problem in the design had been noted when ground crews forced the locking lever shut, breaking the mechanism and defeating the door-sensing system. Modifications were recommended, including reinforcement of the mechanism and installation of inspection windows so latch positions could be verified prior to flight.?

The Turkish Airlines jet had only the inspection window installed and not the locking mechanism reinforced. Normally both a ground engineer and flight engineer checked the cargo doors, but on the day of the crash there was no ground engineer and the plane’s flight engineer did not check the door.?

Soon after the crash, the Federal Aviation Administration changed aircraft certification rules. Required venting now enables all wide-body aircraft to withstand a pressure differential between the cabin and cargo hold.