What happened
On 27 March 1977, an explosion in the passenger terminal at Amsterdam Schiphol Airport led to the closure of the facility. As a result, KLM flight 4805, a Boeing 747 with registration PH-BUF, was diverted to Los Rodeos Airport in Tenerife. Simultaneously, Pan Am flight 1736, a Boeing 747 with registration N736PA, also diverted to the same airport.
The congestion at Los Rodeos caused significant taxiway obstructions. The crew of the Pan Am aircraft found their path blocked by the KLM jet, necessitating a wait until the KLM flight began its movement. During the taxiing process, several communications occurred between the tower and both aircraft regarding runway exits and instructions to backtrack on runway 12 for takeoff on runway 30.
The tower controller informed both crews that the runway centerline lights were non-functional. While the Pan Am crew was instructed to exit the runway via a specific taxiway, the KLM flight requested clarification on its path. At approximately 17:05, the KLM crew indicated they were ready for takeoff and received departure instructions. Shortly thereafter, the KLM aircraft began its takeoff roll. Approximately 20 seconds after releasing the brakes, the Boeing 747 belonging to KLM collided with the Pan Am aircraft, which was still occupying the runway. The collision resulted in 248 fatalities on the KLM flight and 335 fatalities on the Pan Am flight, with 61 survivors reported from the latter aircraft.
Findings
Investigations concluded that the primary factor was a critical misunderstanding between the tower and the KLM crew regarding takeoff clearance. The KLM pilot proceeded with the takeoff run under the mistaken belief that permission had been granted. This error was compounded by the use of ambiguous terminology during radio communications and the fact that the Pan Am aircraft remained on the runway after missing its intended exit.