On June 12, 1972, American Airlines Flight 96 lost its aft cargo door above Windsor, Ontario. Before takeoff, the door appeared secure, but the internal locking mechanism was not fully engaged. When the aircraft reached approximately in altitude, the door blew out, and the resulting explosive decompression collapsed the cabin floor. Many control cables to the empennage were cut, leaving the pilots with very limited control of the aircraft. Despite this, the crew performed a safe emergency landing. U.S. National Transportation Safety Board (NTSB) investigators found the cargo door design to be dangerously flawed, as the door could be closed without the locking mechanism fully engaged, and this condition was not apparent from visual inspection of the door nor from the cargo-door indicator in the cockpit. The NTSB recommended modifications to make it readily apparent to baggage handlers when the door was not secured, and also recommended adding vents to the cabin floor, so that the pressure difference between the cabin and cargo bay during decompression could quickly equalize without causing further damage. Although many carriers voluntarily modified the cargo doors, no airworthiness directive was issued, due to a gentlemen's agreement between the head of the FAA, John H. Shaffer, and the head of McDonnell Douglas's aircraft division, Jackson McGowen. McDonnell Douglas made some modifications to the cargo door, but the basic design remained unchanged, and problems persisted.