27 March

The Tenerife airport disaster was a fatal runway collision between two Boeing 747s on this day in 1977, at Los Rodeos Airport (now Tenerife North Airport) on the Spanish island of Tenerife, one of the Canary Islands. The crash killed 583 people, making it the deadliest accident in aviation history. As a result of the complex interaction of organizational influences, environmental preconditions, and unsafe acts leading up to this aircraft mishap, the disaster at Tenerife has served as a textbook example for reviewing the processes and frameworks used in aviation mishap investigations and accident prevention.

A bomb explosion at Gran Canaria Airport, and the threat of a second bomb, caused many aircraft to be diverted to Los Rodeos Airport. Among them were KLM Flight 4805 and Pan Am Flight 1736 – the two aircraft involved in the accident. At Los Rodeos Airport, air traffic controllers were forced to park many of the airplanes on the taxiway, thereby blocking it. Further complicating the situation, while authorities waited to reopen Gran Canaria, a dense fog developed at Tenerife, greatly reducing visibility.

When Gran Canaria reopened, the parked aircraft blocking the taxiway at Tenerife required both of the 747s to taxi on the only runway in order to get in position for takeoff. The fog was so thick that neither aircraft could see the other, and the controller in the tower could not see the runway or the two 747s on it. As the airport did not have ground radar, the controller could not find where each airplane was, only having voice reports over the radio as a guide to location. As a result of several misunderstandings, the KLM flight tried to take off while the Pan Am flight was still on the runway. The resulting collision destroyed both aircraft, killing all 248 aboard the KLM flight and 335 of 396 aboard the Pan Am flight. Sixty-one people aboard the Pan Am flight, including the pilots and flight engineer, survived the disaster.

As the accident occurred in Spanish territory, Spain was responsible for investigating the accident. Investigators from the Netherlands and the United States also participated. The investigation revealed that the primary cause of the accident was the captain of the KLM flight taking off without clearance from Air Traffic Control (ATC). The investigation specified that the captain did not intentionally take off without clearance; rather he fully believed he had clearance to take off due to misunderstandings between his flight crew and ATC. Dutch investigators placed a greater emphasis on this than their American and Spanish counterparts, but ultimately KLM admitted their crew was responsible for the accident, and the airline financially compensated the victims’ relatives.

The accident had a lasting influence on the industry, particularly in the area of communication. An increased emphasis was placed on using standardized phraseology in ATC communication by controllers and pilots alike, thereby reducing the chance for misunderstandings. As part of these changes, the word “take off” was removed from general usage, and is only spoken by ATC when clearing an aircraft to take off or when cancelling that same clearance. Less experienced flight crew members were encouraged to challenge their captains when they believed something was not correct, and captains were instructed to listen to their crew and evaluate all decisions in light of crew concerns. This concept was later expanded into what is known today as Crew Resource Management (CRM), in which training is now mandatory for all airline pilots.