The Tenerife airport disaster happened on March 27, 1977, when two Boeing 747s collided on the ground of Los Rodeos Airport (now Tenerife North Airport). This crash killed 583 people on board the two flights.
The crash was caused for multiple reasons.
The KLM captain wanted to takeoff quickly so that he could return to Amsterdam as soon as possible. Because of a radio heterodyne, this made him misunderstand a partly garbled transmission into thinking that he was cleared by the Air Traffic Controller to takeoff, and so he began his takeoff roll, not knowing that the Pan American 747 was still on the runway.. At that time, the Tenerife North Airport did not have ground radar, so the controllers could not know that the KLM flight was taking off.
Another reason was the fog surrounding the airport. The bad weather reduced the visibility, meaning both pilots and the controllers could not see. Because of the fog, the pilots only saw each other at the last minute, when prevention of the crash was impossible. If there was no fog, the KLM crew would have seen the Pan Am plane on the runway and would not have taken off.
During the takeoff roll of KLM 4805, the crew of the Pan Am radioed that they were still taxiing down the runway. The KLM flight crew heard this and asked themselves if the Pan American was still on the runway, to which the captain then replied "oh yes".
A few seconds later, the crew of both aircraft spot each other, the captain of the Pan Am exclaiming, "there he is, that goddamn son of a bitch is coming, he's coming", and "get off, get off, get off", as full thrust was applied in an attempt to get his aircraft off the runway out of the way of the oncoming KLM.
In an attempt to leave the ground before collision, the captain rotates his aircraft, causing a tailstrike that lasts a few hundred feet. Just as the KLM leaves the ground, both 747s collide and explode, dealing major damage to the almost stationary Pan Am airplane. The KLM, without engines and main landing gear, descends back down to the runway and crashes, skidding along the pavement and explodes, killing everyone on board.
It was the worst accident in the history of aviation.