On March 28, 1977, two jumbo jets — a Pan American 747 and a KLM Royal Dutch Airlines 747 — collided on the runway as they were attempting to take off from Tenerife airport in the Canary Islands off the west coast of Africa. The Pan Am 747 had 378 passengers on board and the KLM 747 was transporting 235 passengers. The death toll of 583 makes the Tenerife runway collision one of the worst accident in aviation history. The circumstances of the disaster suggest human failure, and not technical failure, as the cause of the disaster.
The two aircraft were diverted with many others to Los Rodeos because a bomb had exploded at Gran Canaria Airport their original destination. Due to the size of Tenerife‘s airport the Air Traffic Controllers were forced to park many of the airplanes on the taxiway, thereby blocking it. Further complicating the situation, a dense fog developed greatly reducing visibility. With fog rolling in and no ground radar the only way the controllers could know the location of aircraft was by radio communication. As a result of several misunderstandings in communications the KLM flight attempted to take off while the Pan Am aircraft was still on the runway. When Gran Canaria, reopened the aircraft at Los Rodeos were given permission to begin preparations for takeoff. To begin the process KLM and Pan Am were both given permission to taxi out onto the runway. KLM, was cleared to taxi to the end of the runway and hold until the Pan AM aircraft turned off the runway at taxiway number 3. In the fog Pan Am missed taxiway 3 and mistook taxiway 4 as their turnoff point. The Captain onboard KLM misunderstood the tower communication telling Pan Am to clear the runway as clearance for him to takeoff. KLM 4805 rolled down the runway and did not see Pan Am 1736 until it was too late to abort. The Captain did his best to clear the Pan AM 747 pulling back so hard on the stick that the tail struck the ground as they tried to climb. The landing gear of the KLM 747 took the Upper Deck Lounge off, and caused the right wing off Pan AM 1736 to burstinto flame.
Language-related misunderstandings of various kinds have been a critical contributing the fatal accident in Tenerife from misunderstanding of the phrase at takeoff, which was used by the flight crew to indicate that they were in the process of taking off‘‘, but was understood by the tower controller as meaning “at the takeoff point‘‘. So, the pilot was not warned that another Boeing 747, shrouded in fog, was already on the runway. It seems that the reason for the wrong usage on the part of the Dutch pilot was his code-switching between Dutch and the English language, translating the Dutch idiom (preposition “at‘‘ + the infinitive) instead of using the present continuous tense of the English language.
Several different factors contributed to the crash, no single one being enough to have triggered the accident.
- Unexpected conditions: there was a terrorist threat that caused one of the planes to divert from the airport in the Canary Islands to a smaller airport at Tenerife (this was necessary for refuelling, and the threat ended up being incorrect). There were also poor weather conditions that prevented the 2 aircraft on the runway from seeing each other and the control tower from seeing these planes. The taxing and takeoff runways at the regional Tenerife airport were the same.
- Both aircraft crews had been on duty for a long time period.
- The KLM crew was concerned about duty time and was worried about not being able to return to Amsterdam without changing crews and putting passengers up in (insufficient) hotel space.
- The weather was closing in fast.
- The Pan Am flight was ready to go an hour before KLM, but had to wait because it couldn’t clear the taxi-way until the KLM plane moved out of the way.
- The pilot of the KLM flight was the chief pilot of KLM, with strong opinions about flying, but who had few duty hours as an operational pilot (he was mostly involved in training). The KLM co-pilot had been recently checked out for the 747, by the pilot.
- The communication with Air Traffic Control (ATC) was not optimum and there is evidence that the Pan American flight gave up trying to change its runway assignment because of this problem.
- There was confusion as to the point at which the Pan Am aircraft should leave the runway (to a taxi strip, thereby permitting the KLM plane to take off). The ATC said the third exit, but this was not
possible (the required turn was too sharp), and so Pan Am, after several attempts at clarification, evidently assumed it was the fourth exit that was meant.
- Miscommunication: the KLM aircraft crew did not all speak English as their first language. Arguably, misinterpretation of the communication, which was in English, was a factor, including the KLM captain who mistook clearance for a takeoff route for the Pan Am jet as permission for takeoff for the KLM jet. There was also simultaneous communication between the airliners and the tower that prevented the communication from the tower from being heard by the pilots.
- Lack of preparation: there was no runway radar.
- Change in protocol: the Pan Am jet was taxiing to an exit but went past the exit they were instructed to use, assuming that the next exit (offering a less difficult maneuver) was the one that was really their intended exit.
- Authority: the KLM flight engineer questioned that the communication from the Pan Am jet from the tower meant that the Pan Am crew would report when the runway was clear. This was overruled by the captain saying that the runway was clear, with no challenge by the appropriate individuals. This was an experienced, well-respected pilot.
- Fog prevented the KLM plane and the Pan Am plane from seeing each other, or the tower from seeing either plane.
These factors all intermixed to cause the incident. No single one was responsible. The probability of all these factors coming together was remote, but still happened.
Aircraft crews are highly structured, mechanistic groups known to be capable of failures of communication and decision-making. The Tenerife air disaster is a clear example of that. Mechanistic groups typically perform very well if the tasks are fairly predictable and routine. However, during crisis situations, these trained responses tend to break down. Nowhere is this more evident than in the air transportation industry. Accidents due to equipment failures are now thought to constitute just three to five percent of all airline accidents. The remaining accidents are attributable solely to human error.
Authorities at the U.S.A, National Aeronautics and Space Administration’s Ames Aerospace Human Factors Research Division also reports that up to 80 percent of all aircraft accidents are due to a lack of adequate coordination or utilization of available resources. We must continue looking for ways to reduce subjective decisions on the part of pilots. We can’t take the human factor out unless we want a system that is completely rigid and inflexible. Research, study of lessons learned, and application of the knowledge gained will help reduce the chances of another Tenerife disaster in the future.