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On This Day 1977: Runway collision kills 583

Los Rodeos Airport By Alex Castellá from Gavà, Spain (Flickr) [CC BY-SA 2.0]

Tenerife Disaster: The collision between KLM and PanAm Boeing 747's on Sunday, March 27, 1977, which happened years ago (feature for the 30th Anniversary on March 27, 2007), still attracts many readers every day.

Los Rodeos, now Tenerife-North Airport is, unfortunately, famous for the fateful accident which occurred on March 27, 1977, in which 583 people died when KLM and Pan Am 747s collided on a crowded, foggy runway in Tenerife. The incident remains the world's worst aviation accident in history. Many contributing factors lead up to the crash, but the probable cause, cited by Air Line Pilots Association (ALPA, 1978), was the KLM pilot taking off without take off clearance.

The wreckage of KLM Boeing 747 PH-BUF
What happened on the runway?

Simply put, the KLM attempted take off, even though the Pan Am was still on the runway and the KLM had not received clearance for take off. The Pan Am tried to get out of the way and the KLM tried to climb over, but the latter ended belly up after dragging it's tail on the ground. The lower fuselage of the KLM plane hit the upper fuselage of the Pan Am plane, ripping apart the centre of the Pan Am jet.

Pan Am 1736 ablaze after its collision with KLM 4805

Whilst I have no intention of quoting chapter and verse - you can check all the background information I've used to write this summary, via the links below - here is quick rundown of the various contributing factors:
  1. Neither plane should have been at Los Rodeos in the first place, which was not used to handling the traffic it had that day. They should have been in Gran Canaria, but a terrorist bomb attack by Canary Island separatists, The Canary Islands Independence Movement, closed the airport there.
  2. There was poor visibility from low cloud (at ground level) at Los Rodeos. That didn't help anyone, least of all the Pan Am who was looking for a suitable exit off the runway. The one they had been advised to take, seems an impossible turn for a 747.
  3. The pilot of the KLM, Captain van Zanten, seems to have been in some considerable hurry to get going and appears to have held a level of authority that subordinates did not dare challenge with the necessary strength.
  4. Analysis of the cockpit voice recorder (CVR) transcript showed that the KLM pilot was convinced that he had been cleared for takeoff, while the Tenerife control tower was certain that the KLM 747 was stationary at the end of the runway and awaiting takeoff clearance.
  5. Reading the transcript of the radio transmissions, exchanges between the tower and the planes were ambiguous at best. One contributing factor to the accident at Tenerife was the involved parties’ use of non-standard phraseology during the critical moments leading up to the accident.
  6. The crucial communication that might have prevented the KLM from taking off was lost in radio squelch. The congestion that results from using a single channel radiotelephone system can also lead to communications which are either missed or blocked by the transmissions of other users (Kerns, 1991, 1999). This problem of blocked transmissions was apparent in the runway collision at Tenerife, when the air traffic controller and the Pan Am pilot both tried to contact the KLM pilot at the same time.
Another article, from Wikipedia, which discusses the causes in more detail, also highlights one of the positive things to come out of the Tenerife air disaster: sweeping changes that were made to international airline regulations. With no small amount of irony, commercial aviation is safer today because of that terrible day in 1977, because, "It was made a worldwide rule that all control towers and pilot crews had to use English standard phrases."

The other positive move, of course, was building Reina Sofia (now Tenerife–South Airport) on the south of the island of Tenerife, which started operating in 1978. 

It is important to note, however, that it was already under construction when the Pan Am/KLM crash occurred and, therefore, was not built out of the aftermath. Previously, passengers had faced a very rough two hour journey by coach, so it was actually a tourism concern to build the south airport.

As with most information about Tenerife, there is more speculation, myth and legend published about this crash than there are plain, hard facts. Whilst I can't claim to know the full story (I wasn't there, but I've met people who were), I hope to distinguish between items that can be verified and those which cannot. What is certain is that Tenerife doesn't have a specially dangerous airport and, in any case, if you are arriving on a tourist charter flight you will arrive to the south airport, not the north one where the accident occurred.

Sources and media on the 1977 Disaster: