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Sat Mar 27, 2021, 12:13 PM

44 Years Ago Today; The Tenerife Air Disaster

https://en.wikipedia.org/wiki/Tenerife_airport_disaster



On March 27, 1977, two Boeing 747 passenger jets, KLM Flight 4805 and Pan Am Flight 1736, collided on the runway at Los Rodeos Airport (now Tenerife North Airport), on the Spanish island of Tenerife, Canary Islands, killing 583 people, making it the deadliest accident in aviation history.

A terrorist incident at Gran Canaria Airport had caused many flights to be diverted to Los Rodeos, including the two aircraft involved in the accident. The airport quickly became congested with parked airplanes blocking the only taxiway and forcing departing aircraft to taxi on the runway instead. Patches of thick fog were drifting across the airfield, so that the aircraft and control tower were unable to see one another.

The collision occurred when the KLM airliner initiated its takeoff run while the Pan Am airliner, shrouded in fog, was still on the runway and about to turn off onto the taxiway. The impact and resulting fire killed everyone on board KLM 4805 and most of the occupants of Pan Am 1736, with only 61 survivors in the front section of the aircraft.

The subsequent investigation by Spanish authorities concluded that the primary cause of the accident was the KLM captain's decision to take off in the mistaken belief that a takeoff clearance from air traffic control (ATC) had been issued. Dutch investigators placed a greater emphasis on mutual misunderstanding in radio communications between the KLM crew and ATC, but ultimately KLM admitted that their crew was responsible for the accident and the airline agreed to financially compensate the relatives of all of the victims.

The disaster had a lasting influence on the industry, highlighting in particular the vital importance of using standardized phraseology in radio communications. Cockpit procedures were also reviewed, contributing to the establishment of crew resource management as a fundamental part of airline pilots' training.



Disaster
Diversion of aircraft to Los Rodeos


Both flights had been routine until they approached the islands. At 13:15, a bomb planted by the separatist Canary Islands Independence Movement exploded in the terminal of Gran Canaria International Airport, injuring eight people. There had been a phone call warning of the bomb, and another call received soon afterwards made claims of a second bomb at the airport. The civil aviation authorities had therefore closed the airport temporarily after the explosion, and all incoming flights bound for Gran Canaria had been diverted to Los Rodeos, including the two Boeing 747 aircraft involved in the disaster. The Pan Am crew indicated that they would prefer to circle in a holding pattern until landing clearance was given, but they were ordered to divert to Tenerife.

Los Rodeos was a regional airport that could not easily accommodate all of the traffic diverted from Gran Canaria, which included five large airliners. The airport had only one runway and one major taxiway running parallel to it, with four short taxiways connecting the two. While waiting for Gran Canaria airport to reopen, the diverted airplanes took up so much space that they were having to park on the long taxiway, making it unavailable for the purpose of taxiing. Instead, departing aircraft needed to taxi along the runway to position themselves for takeoff, a procedure known as a backtaxi or backtrack.

The authorities reopened Gran Canaria airport once the bomb threat had been contained. The Pan Am plane was ready to depart from Tenerife, but access to the runway was being obstructed by the KLM plane and a refueling vehicle; the KLM captain had decided to fully refuel at Los Rodeos instead of Las Palmas, apparently to save time. The Pan Am aircraft was unable to maneuver around the refueling KLM, in order to reach the runway for takeoff, due to a lack of safe clearance between the two planes, which was just 3.7 meters (12 ft). The refueling took about 35 minutes, after which the passengers were brought back to the aircraft. The search for a missing Dutch family of four, who had not returned to the waiting KLM plane, delayed the flight even further. A tour guide had chosen not to reboard for the flight to Las Palmas, because she lived on Tenerife and thought it impractical to fly to Gran Canaria only to return to Tenerife the next day. She was therefore not on the KLM plane when the accident happened, and she would be the only survivor of those who flew from Amsterdam to Tenerife on Flight 4805.

Taxiing and takeoff preparations
The tower instructed the KLM to taxi down the entire length of the runway and then make a 180-degree turn to get into takeoff position. While the KLM 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 in takeoff position on Runway 30.


Simplified map of runway, taxiways, and aircraft. The red star indicates the location of impact. Not to scale.

Shortly afterward, the Pan Am was instructed to follow the KLM down the same runway, exit it by taking the third exit on their left and then use the parallel taxiway. Initially, the crew was unclear as to whether the controller had told them to take the first or third exit. The crew asked for clarification and the controller responded emphatically by replying: "The third one, sir; one, two, three; third, third one." The crew began the taxi and proceeded to identify the unmarked taxiways using an airport diagram as they reached them.

The crew successfully identified the first two taxiways (C-1 and C-2), but their discussion in the cockpit never indicated that they had sighted the third taxiway (C-3), which they had been instructed to use. There were no markings or signs to identify the runway exits and they were in conditions of poor visibility. The Pan Am crew appeared to remain unsure of their position on the runway until the collision, which occurred near the intersection with the fourth taxiway (C-4).

The angle of the third taxiway would have required the plane to perform a 148-degree turn, which would lead back toward the still-crowded main apron. At the end of C-3, the Pan Am would have to make another 148-degree turn, in order to continue taxiing towards the start of the runway, similar to a mirrored letter "Z". Taxiway C-4 would have required two 35-degree-turns. A study carried out by the Air Line Pilots Association (ALPA) after the accident concluded that making the second 148-degree turn at the end of taxiway C-3 would have been "a practical impossibility." The official report from the Spanish authorities explains that the controller instructed the Pan Am aircraft to use the third taxiway because this was the earliest exit that they could take to reach the unobstructed section of the parallel taxiway.

Weather conditions at Los Rodeos
Los Rodeos airport is at 633 meters (2,077 ft) above sea level, which gives rise to cloud behavior that differs from that at many other airports. Clouds at 600 m (2,000 ft) above ground level at the nearby coast are at ground level at Los Rodeos. Drifting clouds of different densities cause wildly varying visibilities, from unhindered at one moment to below the minimums the next. The collision took place in a high-density cloud.

The Pan Am crew found themselves in poor and rapidly deteriorating visibility almost as soon as they entered the runway. According to the ALPA report, as the Pan Am aircraft taxied to the runway, the visibility was about 500 m (1,600 ft). Shortly after they turned onto the runway it decreased to less than 100 m (330 ft).

Meanwhile, the KLM plane was still in good visibility, but with clouds blowing down the runway towards them. The aircraft completed its 180-degree turn in relatively clear weather and lined up on Runway 30. The next cloud was 900 m (3,000 ft) down the runway and moving towards the aircraft at about 12 knots (14 mph; 22 km/h).

Communication misunderstandings
Immediately after lining up, the KLM captain advanced the throttles and the aircraft started to move forward. First officer Meurs advised him that ATC clearance had not yet been given, and captain Veldhuyzen van Zanten responded: "No, I know that. Go ahead, ask." Meurs then radioed the tower that they were "ready for takeoff" and "waiting for our ATC clearance". The KLM crew then received instructions that specified the route that the aircraft was to follow after takeoff. The instructions used the word "takeoff," but did not include an explicit statement that they were cleared for takeoff.

Meurs read the flight clearance back to the controller, completing the readback with the statement: "We are now at takeoff." Captain Veldhuyzen van Zanten interrupted the co-pilot's read-back with the comment, "We're going."

The controller, who could not see the runway due to the fog, initially responded with "OK" (terminology that is nonstandard), which reinforced the KLM captain's misinterpretation that they had takeoff clearance. The controller's response of "OK" to the co-pilot's nonstandard statement that they were "now at takeoff" was likely due to his misinterpretation that they were in takeoff position and ready to begin the roll when takeoff clearance was received, but not in the process of taking off. The controller then immediately added "stand by for takeoff, I will call you", indicating that he had not intended the clearance to be interpreted as a takeoff clearance.

A simultaneous radio call from the Pan Am crew caused mutual interference on the radio frequency, which was audible in the KLM cockpit as a 3-second-long shrill sound, (or heterodyne). This caused the KLM crew to miss the crucial latter portion of the tower's response. The Pan Am crew's transmission was "We're still taxiing down the runway, the Clipper 1736!" This message was also blocked by the interference and inaudible to the KLM crew. Either message, if heard in the KLM cockpit, would have alerted the crew to the situation and given them time to abort the takeoff attempt.

Due to the fog, neither crew was able to see the other plane 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.

After the KLM plane had started its takeoff roll, the tower instructed the Pan Am crew to "report when runway clear." The Pan Am crew replied: "OK, will 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 by asking the pilots in his own cockpit, "Is he not clear, that Pan American?" Veldhuyzen van Zanten emphatically replied "Oh, yes" and continued with the takeoff.

Collision
According to the cockpit voice recorder (CVR), the Pan Am captain said, "There he is!", when he spotted the KLM's landing lights through the fog just as his plane approached exit C-4. When it became clear that the KLM aircraft was approaching at takeoff speed, captain Grubbs exclaimed, "Goddamn, that son-of-a-bitch is coming!", while first officer Robert Bragg yelled, "Get off! Get off! Get off!". Captain Grubbs applied full power to the throttles and made a sharp left turn towards the grass in an attempt to avoid the impending collision. By the time the KLM pilots saw the Pan Am aircraft, they were already traveling too fast to stop. In desperation, the pilots prematurely rotated the aircraft and attempted to clear the Pan Am by lifting off, causing a severe tailstrike for 22 m (72 ft).

The KLM 747 was within 100 m (330 ft) of the Pan Am and moving at approximately 140 knots (260 km/h; 160 mph) when it left the ground. Its nose landing gear cleared the Pan Am, but its left-side engines, lower fuselage, and main landing gear struck the upper right side of the Pan Am's fuselage, ripping apart the center of the Pan Am jet almost directly above the wing. The right-side engines crashed through the Pan Am's upper deck immediately behind the cockpit.

The KLM plane remained briefly airborne, but the impact had sheared off the outer left engine, caused significant amounts of shredded materials to be ingested by the inner left engine, and damaged the wings. The plane immediately went into a stall, rolled sharply, and hit the ground approximately 150 m (500 ft) past the collision, sliding down the runway for a further 300 m (1,000 ft). The full load of fuel, which had caused the earlier delay, ignited immediately into a fireball that could not be subdued for several hours.

One of the 61 survivors of the Pan Am flight, John Coombs of Haleiwa, Hawaii, said that sitting in the nose of the plane probably saved his life: "We all settled back, and the next thing an explosion took place and the whole port side, left side of the plane, was just torn wide open."

Both airplanes were destroyed in the collision. All 248 passengers and crew aboard the KLM plane died, as did 335 passengers and crew aboard the Pan Am plane, primarily due to the fire and explosions resulting from the fuel spilled and ignited in the impact. The other 61 passengers and crew aboard the Pan Am aircraft survived, including the captain, first officer, and flight engineer. Most of the survivors on the Pan Am walked out onto the intact left wing, the side away from the collision, through holes in the fuselage structure. The Pan Am's engines were still running for a few minutes after the accident despite first officer Bragg's intention to turn them off. The top part of the cockpit, where the engine switches were located, had been destroyed in the collision, and all control lines were severed, leaving no method for the flight crew to control the aircraft's systems. Survivors waited for rescue, but it did not come promptly, as the firefighters were initially unaware that there were two aircraft involved and were concentrating on the KLM wreck hundreds of meters away in the thick fog and smoke. Eventually, most of the survivors on the wing dropped to the ground below.

Captain Veldhuyzen van Zanten was KLM's chief of flight training and one of their most senior pilots. He had given the co-pilot on Flight 4805 his Boeing 747 qualification check about two months before the accident. His photograph was used for publicity materials such as magazine advertisements, including the inflight magazine on board PH-BUF. Before realising that Veldhuyzen van Zanten was the KLM captain who had been killed in the accident, KLM suggested that he should help with the investigation.

Aftermath
The following day, the Canary Islands Independence Movement, responsible for the bombing at Gran Canaria that started the chain of events that led to the disaster, denied responsibility for the accident.

Los Rodeos airport, the only operating airport on Tenerife in 1977, was closed to all fixed-wing traffic for two days. The first crash investigators to arrive at Tenerife the day after the crash travelled there by way of a three-hour boat ride from Las Palmas. The first aircraft that was able to land was a United States Air Force C-130 transport, which landed on the airport's main taxiway at 12:50 on March 29. The C-130 transport was arranged by Lt. Col Dr. James K. Slaton, who arrived before the crash investigators and started triaging surviving passengers. Slaton was dispatched from Torrejon Air Base just outside of Madrid, Spain. Slaton, who was a flight surgeon attached to the 613th Tactical Fighter Squadron, worked with the local medical staff and remained on scene until the last survivor was air lifted to awaiting medical facilities. The C-130 transported all surviving and injured passengers from Tenerife to Las Palmas; many of the injured were taken from there to Air Force bases in the United States for further treatment.

Spanish Army soldiers were tasked with clearing crash wreckage from the runways and taxiways. By March 30, a small plane shuttle service was approved, but large jets still could not land. Los Rodeos was fully reopened on April 3, after wreckage had been fully removed and engineers had repaired the airport's runway.

Investigation
The accident was investigated by Spain's Comisión de Investigación de Accidentes e Incidentes de Aviación Civil (CIAIAC). About 70 personnel were involved in the investigation, including representatives from the Netherlands, the United States, and the two airline companies. Facts showed that there had been misinterpretations and false assumptions before the accident. Analysis of the CVR transcript showed that the KLM pilot thought that that he had been cleared for takeoff, while the Tenerife control tower believed that the KLM 747 was stationary at the end of the runway, awaiting takeoff clearance. It appears that KLM's co-pilot was not as certain about take-off clearance as the captain.



Legacy of the disaster
As a consequence of the accident, sweeping changes were 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.

Air traffic instruction should not be acknowledged solely with a colloquial phrase such as "OK" or even "Roger" (which simply means the last transmission was received), but with a readback of the key parts of the instruction, to show mutual understanding. The phrase "take off" is now spoken only when the actual takeoff clearance is given or when cancelling that same clearance (i.e. "cleared for take-off" or "cancel take-off clearance". Up until that point, aircrew and controllers should use the phrase "departure" in its place, e.g. "ready for departure". Additionally, an ATC clearance given to an aircraft already lined-up on the runway must be prefixed with the instruction "hold position".

Cockpit procedures were also changed. Hierarchical relations among crew members were played down. More emphasis was placed on team decision-making by mutual agreement. 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), training which is now mandatory for all airline pilots.

In 1978, a second airport on the island was opened: the new Tenerife–South Airport (TFS). This airport now serves the majority of international tourist flights. Los Rodeos, renamed to Tenerife North Airport (TFN), was then used only for domestic and inter-island flights. In 2002, a new terminal was opened and Tenerife North once again carries international traffic.

The Spanish government installed a ground radar at Tenerife North Airport following the accident.



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Reply 44 Years Ago Today; The Tenerife Air Disaster (Original post)
Dennis Donovan Mar 27 OP
dalton99a Mar 27 #1
NNadir Mar 27 #2
Klaralven Mar 27 #3
Bo Zarts Mar 27 #4

Response to Dennis Donovan (Original post)

Sat Mar 27, 2021, 12:26 PM

1. A survivor's story:

https://www.news-journalonline.com/news/20181001/mama-im-alive-incredible-story-of-survival
‘Mama, I’m alive:’ An incredible story of survival
By Pat Rice @newsjournaledit
Posted Oct 1, 2018

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Response to Dennis Donovan (Original post)

Sat Mar 27, 2021, 12:30 PM

2. I was visiting a young woman friend when the phone rang...

...and in that call she learned that the neighbors in the house where she grew up were in that accident. (I was living in the LA basin at the time, and the Pan Am flight had originated out of LAX.)

She broke down crying.

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Response to Dennis Donovan (Original post)

Sat Mar 27, 2021, 12:38 PM

3. One of at least 15 airliner crashes with passenger loss of life in 1977

I think that we forget how frequently airliners crashed in the '50s through '70s.

https://en.wikipedia.org/wiki/List_of_accidents_and_incidents_involving_commercial_aircraft#1977

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Response to Dennis Donovan (Original post)

Sat Mar 27, 2021, 12:52 PM

4. The Pan Am captain, Victor Grubbs, was from my home town in Georgia.

When I went through airline accident investigation training, years after this, the KLM/Pan Am runway accident was a case study in the curriculum.

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