Tenerife airport disaster

Tenerife disaster
	File:Tenerife Disaster Collision aftermath 27 March 1977.jpg Pan Am 1736 ablaze after its collision with KLM 4805
Occurrence
Date	March 27 1977
Summary	Runway collision
Site	Tenerife, Canary Islands
Aircraft type	Boeing 747-121
Operator	Pan American World Airways
Registration	N736PAdisaster
Passengers	382
Crew	14
Fatalities	583
Injuries	61
Survivors	61

The Tenerife disaster took place at 17:06 local time on March 27, 1977, when two Boeing 747 airliners collided at Los Rodeos Airport on the island of Tenerife, Canary Islands, killing 583 people. The accident had the highest number of fatalities of any single accident in aviation history.

The aircraft involved were Pan Am Flight 1736, named Clipper Victor, under the command of Captain Victor Grubbs, and KLM Royal Dutch Airlines Flight 4805, named Rijn (Rhine River), under the command of Captain Jacob Veldhuyzen van Zanten. KLM 4805, taking off on the only runway of the airport, crashed into the Pan Am aircraft which was taxiing on the same runway.

Los Rodeos Airport (then TCI, now TFN) is situated in the northern part of Tenerife, and is used mainly for flights within the Canary Islands and flights from the Spanish mainland.

Terrorist bomb threat

Pan Am Flight 1736 had taken off from Los Angeles International Airport with an intermediate stop at New York's JFK International Airport. The aircraft was a Boeing 747-121, registration N736PA. KLM Flight 4805, a charter flight from the Netherlands, had taken off four hours before from Amsterdam Schiphol Airport. The destination of both planes was Las Palmas on Gran Canaria.

Upon contacting Gran Canaria International Airport, the Pan Am flight was told that the airport was temporarily closed due to a terrorist bomb attack by Canary Island separatists. A bomb had exploded in the airport concourse, injuring several persons, and a threat of a second bomb had been received. Although the Pan Am crew indicated that they would prefer to circle until landing clearance was given, the plane was ordered to divert to Los Rodeos airport on the nearby island of Tenerife, together with many other planes. The KLM aircraft was also given instructions to divert to Los Rodeos.

In all, at least five large aircraft were diverted to Los Rodeos, a regional airport that could not easily accommodate them. The airport consisted of one runway and one major taxiway parallel to it, as well as several small taxiways connecting them. The diverted aircraft were parked on the long taxiway, meaning that it could not be used for taxiing. Instead, departing aircraft would have to taxi along the runway to position themselves for takeoff.

Chain of events leading to disaster

Refueling

On investigation, the terrorist threat at Las Palmas turned out to be false and the authorities reopened the airport. The Pan Am aircraft was ready to depart, but the KLM plane and a refueling vehicle obstructed the way to the active runway. Captain van Zanten had decided to refuel at Los Rodeos instead of Las Palmas, apparently to save time, even if the fuel costs were higher at Los Rodeos.

Taxiing and weather conditions

Following the tower's instructions, the KLM aircraft was cleared to taxi to the end of the only runway and make a 180 degree turn (in aviation terms this is called a 'backtaxi', or 'backtrack', and is difficult with a 747 on the narrow runway). While KLM 4805 was backtaxiing on the runway, the controller asked the flight crew to report when it was ready to copy the ATC clearance. Because the flight crew was performing the checklist, copying this clearance was postponed until the aircraft was lined up in the direction of takeoff on Runway 30. During taxiing, the weather deteriorated. Fog had limited the visual range to 1000 feet (305 meters).

Pan Am was instructed to taxi along the same runway and take the third exit on their left, leaving the main runway, and head to the parallel taxiway. There was a degree of confusion in the Pan Am cockpit as to whether the control tower meant exit C3 or literally the third exit on their left, as when this instruction had been received, the 747 was already past exit C1. Upon viewing their airport maps and then visual recognition once C3 had been reached, the crew realized that the aircraft would have to make a 135° left turn onto the exit, and a 135° right turn onto the taxiway (for a simplified map of the runway and exits see Collision).

Since this maneuver is an almost impossible task for a 747 on an undersized airport, analysis of the CVR recording suggests that the crew assumed that Tenerife ATC must have ordered them to turn at the next exit, C4, which was only 45°. They reasoned that the control tower must have realized the greater ease with which this turn could be made, and combined with their belief that the tower meant them to turn on the third exit on their left from their current position, that exit being C4, were led to the belief that they were intended to take exit C4.

Communication problems

While lined up and holding, the KLM captain pushed the throttle for take-off but the co-pilot immediately advised the captain that ATC clearance had not been given and takeoff was aborted instantly. The KLM crew then received an ATC airways clearance; a clearance to fly a certain route after take-off, but not permission for the take-off itself. The captain probably mistook this for a take-off clearance. He released the brakes of the aircraft and the co-pilot responded with a heavy Dutch accent with words that could either be "We are at take off" or "We are taking off"[1]. The control tower was confused by the message and asked for the KLM plane to stand by. However, simultaneous communication from Pan Am caused a heterodyne, making the tower response inaudible to the pilots. Coincidentally, Pan Am was reporting they had not finished taxiing. Either message, if broadcast separately, might have given KLM crew time to abort its takeoff.

Due to the fog, the KLM crew was not able to see the Pan Am 747 taxiing on the runway ahead of them. In addition, neither of the aircraft could be seen from the control tower, and the airport was not equipped with ground radar.

While the KLM crew had started its take-off run, the tower instructed the Pan Am crew to "report when runway clear". The crew replied: "OK, we'll report when we're clear". On hearing this, the KLM flight engineer expressed his concern about the Pan Am not being clear of the runway, repeating this concern a few seconds later, but he was overruled by the captain. The flight engineer did not explicitly challenge him on this decision.

Final radio transmissions

This section of the radio transmission is taken exactly from the original CVR Transcript.

1706:20.08
TENERIFE TOWER Stand by for take-off, I will call you.
1706:20.3
PanAm Radio(c/p) And we're still taxiing down the runway, the clipper one seven three six.
1706:19.39-  1706:23.19  
RDO and TENERIFE TOWER communications caused a shrill noise in KLM cockpit - 
messages not heard by KLM crew .
1706:25.6
TENERIFE TOWER Roger alpha one seven three six report when runway clear
1706:29.6
PanAm Radio(c/p) OK, we'll report when we're clear.
TENERIFE TOWER Thank you
1706:32.43
KLM FLT ENGR Is hij er niet af dan? {Is he not clear then?}
1706:34.1
KLM CAPTAIN Wat zeg je? {What do you say?}
1706:34.15
KLM-? Yup.
1706:34.7
KLM FLT ENGR Is hij er niet af, die Pan American? {Is he not clear that Pan American?}
1706:35.7
KLM CAPTAIN Jawel. {Oh yes. - emphatic}
1706:40.0
PanAm captain sees landing lights of KLM Boeing at approx. 700m
1706:44.0
PH-BUF started rotation

Collision

According to the CVR (Cockpit Voice Recorder), Captain Grubbs, captain of the Pan Am plane, spotted the KLM's landing lights just as the plane approached exit C4. The Pan Am crew applied full power and took a sharp left turn onto the exit to avoid a collision. The KLM plane attempted to avoid a collision by climbing away, scraping the tail of the plane along the runway for 20 metres (65 ft). The lower fuselage of the KLM plane hit the upper fuselage of the Pan Am plane, ripping apart the center of the Pan Am jet nearly directly above the wing. The KLM plane slammed into the ground belly-up 150 m past the point of collision and slid down the runway.

All 234 passengers and 14 crew members in the KLM plane were killed, and 335 of the 396 aboard the Pan Am flight (326 passengers and 9 crew members) perished, primarily due to the fire and explosions resulting from the fuel spilled in the impact. The Pan Am Captain, First Officer, and Flight Engineer were among the survivors (56 passengers and 5 crew members).

File:Tenerife collision.jpg

A computer generated image of the impact

Investigation

About 70 crash investigators from Spain, the Netherlands, the United States, and the two airline companies were involved in the investigation. Facts showed that there had been misinterpretations and false assumptions. Analysis of the cockpit voice recorder (CVR) transcript showed that the KLM pilot was convinced that he had been cleared for take-off, while the Tenerife control tower was certain that the KLM 747 was stationary at the end of the runway and awaiting takeoff clearance.

Probable cause

While there is debate about their relative importance, the general conclusion is that the disaster was caused partly by:

the fact that the KLM captain did not interrupt take-off when Pan Am reported that they were still on the runway.
In reply to the KLM flight engineer's query as to whether the Pan Am plane had already left the runway, KLM captain replied emphatically in the affirmative.
squelched radio messages (calls between a plane and the control tower canceled each other because they happened to be at precisely the same instant)
the use of non-standard phrases used by the KLM co-pilot ("We're at take off") and the Tenerife control tower ("O.K."),
the fact that the Pan Am crew continued along the runway instead of turning at exit C3, as directed.
the fact that the two plalnes were surrounded by thick fog and they could not see each other.

Speculations

There has been speculation of other, albeit unverifiable, possible contributing factors.

Van Zanten was known as a first-class pilot, and was even the preferred pilot for publicity, such as KLM magazine ads. The flight was one of his first after spending six months training new pilots on a flight simulator. Some experts suggest he may have developed some kind of governance attitude as a consequence of having been in charge of everything at the simulator (including simulated ATC), which is another reason suggested for van Zanten not confirming the instructions from the tower.
The flight engineer apparently hesitated to further challenge van Zanten, possibly because van Zanten was not only senior in rank, but also one of the most able and experienced pilots working for the airline.
The possibility that Captain van Zanten was in a hurry to commence the delayed flight due to Dutch regulations on exceeding crew duty hours.
The deteriorating weather conditions could prevent the flight from taking off at all, and the airliner would be forced to stay on Los Rodeos, with financial consequences for KLM.
The use of an unsafe procedure: An Air Traffic Control clearance by a control tower issued under no-visibility conditions is not a safe procedure as such a clearance is based on visual contact. However, most authorities allowed control to continue based entirely on reports from pilots, who do not have visual contact either. Although this procedure still goes on in some countries, the practice is increasingly being abandoned and superseded by the installation of Surface Movement Radar. It has been also revealed that some countries do not conform entirely with international standards under poor visibility conditions. Some Tower units accept it under the strict condition that only one aircraft alone is operating on the runway, while taxiing to and from it is done by using a vehicle called "follow-me car" moving slowly ahead of the plane, leading the pilot. The unsafe nature of the procedure that caused the accident in Tenerife was verified in a bitter way some 25 years later in what became known as the Linate Airport disaster at Milano Linate International Airport on October 8, 2001, when Flight SAS686, an MD-87 airliner, was cleared for take-off based on the report of a private jet plane (a German Cessna Citation) pilot that erroneously followed a different taxiway under zero visibility conditions, which did not allow a visual verification by the Tower. The MD-87 collided with the Cessna that was crossing the runway and came down on aerodrome buildings, causing the deaths of some 130 people. [2]

Safety response

As a consequence of the accident, there were sweeping changes made to international airline regulations and to aircraft. Aviation authorities around the world introduced requirements for standard phrases and a greater emphasis on English as a common working language. For example, ICAO calls for the phrase "line up and wait" as an instruction to an aircraft moving into position but not cleared for take-off. The FAA equivalent is "taxi into position and hold". Air traffic instruction should not be acknowledged solely with a colloquial phrase such as "OK" or even "Roger", but with a read back of the key parts of the instruction, to show mutual understanding. Additionally the phrase "take-off" is only spoken when the actual take-off clearance is given. Up until that point both aircrew and ATCOs should use the phrase "departure" in its place (e.g., "ready for departure").

Cockpit procedures were also changed. Hierarchical relations among crewmembers were played down. More emphasis was placed on decision-making by mutual agreement. This is known in the industry as crew resource management, and is now standard training in all major airlines.

Due to the frequent and dangerous fogs that cover the area around Los Rodeos airport in the North of the island, a second airport was built in the South of the Island: the new Reina Sofía Airport. This airport serves the majority of Tenerife's domestic and international commercial flights.

Memorial

A memorial and final resting place for the victims of the KLM plane is located in Amsterdam, at Westgaarde cemetery.

Trivia

The Pan Am plane was the first 747 to carry fare-paying passengers, on a flight from New York to London on 21 January 1970.

Well-known people who were killed in the disaster were:

Eve Meyer, a pin-up model, film actress and producer and former wife of Russ Meyer.
A. P. Hamann, the former city manager of San Jose, California, and his wife Francis Hamann.

Sources

External links

BBC report with news report
ICAO document mentioning phrasing used in the accident
Comprehensive account of collision
1001 Crash - A complete story of the Tenerife disaster : This story includes DFDR transcriptions, and pictures taken the day of the tragedy
Airmanship Online - a detailed account of the tragedy

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^ "FAA Registry (N736PA)". Federal Aviation Administration.
^ "Civil aircraft register (PH-BUF)". Inspectie Leefomgeving en Transport.

[1] "FAA Registry (N736PA)". Federal Aviation Administration.

[2] "Civil aircraft register (PH-BUF)". Inspectie Leefomgeving en Transport.

[1]