Originally Posted by EastMids
PS: With the exception of the FedEx incident when an off-duty staff member axed the crew, its hard for me to recall at present a documented incident where a jump-seater caused a significant accident. Except, that is, for the Aeroflot A310 when the driver let his kid sit in the front seat. Maybe therefore, the rules are actually there to protect the crew from themselves!
Worst of all was the Pacific Southwest BAe 146 incident in 1987 in which an employee shot both pilots, causing the loss of the aircraft and all on board.