TWA Flight 800 was a Boeing 707 that crashed during take off on runway 25 at Leonardo da Vinci-Fiumicino Airport, Rome at 13:05 GMT on a flight to Athens International Airport, Greece on 23 November 1964. As the Boeing 707 was at 80 knots, the instruments for No. 4 engine indicated zero thrust and the thrust reverser deployment light for No. 2 engine illuminated. The crew aborted the takeoff at a speed below V1 at 800-900m down the runway. The aircraft did not slow down as quickly as the crew expected and veered to the right, whereupon No. 4 engine struck a pavement roller. The aircraft caught fire and traveled another 260m before coming to rest. The accident killed 50 passengers and crew on board, with 23 passengers and crew surviving.
The cause of the accident was an inoperative No. 2 engine reverse thrust system, even though indications in the cockpit were that the reverser had deployed. This was caused by the disconnection of a duct with resulting lack of pressure in the pneumatic clamshell door actuating mechanism. This malfunction allowed the development of considerable forward thrust by No. 2 engine even though the thrust levers for all four engines were in the "reverse" position.