Air Crash Investigation - Mayday

BOAC Flight 781 ,South African Airways Flight 201, Aloha Airlines Flight 243, British Airways Flight 5390, United Airlines Flight 811, Helios Airways Flight 522. This special looks at accidents and incidents where pressurization failure or explosive decompression played a part. Episodes re-visited: Hanging by a Thread, Blow Out, Unlocking Disaster, Ghost Plane.