1975 Tan Son Nhut Lockheed C-5 crash

Investigation

Given the explosive manner in which the rear doors failed, sabotage was initially suspected.

Many of the components were looted from the crash site, thereby complicating the investigation; the U.S. Air Force paid a bounty for parts from the wreckage to recover them from the local populace. The United States Navy rescue salvage USS Deliver (ARS-23), fleet tug USS Abnaki (ATF-96) amphibious cargo ship USS Durham (LKA-114), frigate USS Reasoner (FF-1063), and command ship USS Blue Ridge (LCC-19) were assigned to search for the flight data recorder in the South China Sea. The rear hatch and flight recorder were found by the USS Abnaki and USS Deliver and helicopters also discovered wreckage from the doors in the South China Sea as well as the body of a crew member aboard the C-5.

When the rear doors were eventually recovered from the sea, investigators determined that some of the locks had not engaged properly. Maintenance records showed that some locks from other C-5s had been cannibalized for spares and improperly refitted, which then degraded their performance significantly. Accounts also indicated the initial maintenance inspection noticed that five of the seven locks were not operating and failed while the aircraft was performing the flight. With external organizational pressure to get the flight airborne, a second off-shift maintenance team was called in. They missed the locks during their inspection, and the unairworthy aircraft was cleared for flight. Furthermore, the flight crew confirmed that they had encountered difficulty closing the doors before take-off, having to open and close the doors multiple times to make them lock. As the air pressure differential increased with altitude, the few locks that were working correctly were unable to bear the load, and the door failed in flight, leading to the subsequent explosive decompression, flight control problems and ultimately, the crash.