Tenerife airport disaster

KLM captain Veldhuyzen van Zanten featured in a 1977 advertisement for the airline.

KLM Flight 4805 was a charter flight for Holland International Travel Group and had arrived from Amsterdam Airport Schiphol, Netherlands.[8] Its cockpit crew consisted of captain Jacob Veldhuyzen van Zanten, age 50,[9] first officer Klaas Meurs, age 42, and flight engineer Willem Schreuder, age 48. At the time of the accident, Veldhuyzen van Zanten was KLM's chief flight instructor, with 11,700 flight hours, of which 1,545 hours were on the 747. Meurs had 9,200 flight hours, of which 95 hours were on the 747. Schreuder had 17,031 flight hours, of which 543 hours were on the 747.

The aircraft was a Boeing 747-206B, registration PH-BUF, named Rijn (Rhine). The KLM jet was carrying 14 crew members and 235 passengers, including 52 children. Most of the KLM passengers were Dutch; also on board were 4 Germans, 2 Austrians and 2 Americans. After the aircraft landed at Tenerife, the passengers were transported to the airport terminal. One of the inbound passengers, who lived on the island with her boyfriend, chose not to re-board the 747, leaving 234 passengers on board.[10][11]

Pan Am Flight 1736 had originated at Los Angeles International Airport, with an intermediate stop at New York's John F. Kennedy International Airport (JFK). The aircraft was a Boeing 747-121, registration N736PA, named Clipper Victor. Of the 380 passengers (mostly of retirement age, but including two children), 14 had boarded in New York, where the crew was also changed. The new crew consisted of captain Victor Grubbs, age 56, first officer Robert Bragg, age 39, flight engineer George Warns, age 46, and 13 flight attendants. At the time of the accident, Grubbs had 21,043 hours of flight time, of which 564 hours were on the 747. Bragg had 10,800 flight hours, of which 2,796 hours were on the 747. Warns had 15,210 flight hours, of which 559 hours were on the 747.

This particular aircraft had operated the inaugural 747 commercial flight on January 22, 1970.[8] On August 2, 1970, in its first year of service, it also became the first 747 to be hijacked: en route between JFK and Luis Muñoz Marín International Airport in San Juan, Puerto Rico, it was diverted to José Martí International Airport in Havana, Cuba.[12]

Rijn (foreground) and Clipper Victor (center) at Los Rodeos on the day of the accident

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.[13] 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.[4] The Pan Am crew indicated that they would prefer to circle in a holding pattern until landing clearance was given (they had enough fuel to safely stay in the air for 2 more hours), but they were ordered to divert to Tenerife.[14]

Los Rodeos was a regional airport that could not easily accommodate all of the traffic diverted from Gran Canaria, which included five large airliners.[15] 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.[4]

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).[10] 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.

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.[16] 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.[17]

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.[18]

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.[19] 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).[20]

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."[21] 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.[22]

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.[23]

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).[24]

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).[25]

Immediately after lining up, the KLM captain advanced the throttles and the aircraft started to move forward.[32] 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."[4] Captain Veldhuyzen van Zanten interrupted the co-pilot's read-back with the comment, "We're going."[4]

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",[4] indicating that he had not intended the clearance to be interpreted as a takeoff clearance.[33]

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.[34]

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.[4]

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.[35]

Computer graphics reconstruction of the moment immediately before the disaster: flight KLM 4805 (right) is about to collide with flight Pan Am 1736 (left). Part of the fog has been removed to give a clearer picture of the two planes.

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.[4] 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 22 m (72 ft) tailstrike.

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,[10] 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."[36]

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,[37] 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.[10]

Captain Veldhuyzen van Zanten was KLM's chief of flight training and one of their most senior pilots. About two months before the accident, he had conducted the Boeing 747 qualification check on the co-pilot of Flight 4805.[11] His photograph was used for publicity materials such as magazine advertisements, including the inflight magazine on board PH-BUF.[10][38] KLM had suggested initially that Veldhuyzen van Zanten should help with the investigation, not realising that he was the KLM captain who had perished in the accident.[39]

The investigation concluded that the fundamental cause of the accident was that captain Veldhuyzen van Zanten attempted to take off without clearance. The investigators suggested the reason for this was a desire to leave as soon as possible in order to comply with KLM's duty-time regulations (which went in place earlier that year) and before the weather deteriorated further.

Other major factors contributing to the accident were:

• The sudden fog greatly limited visibility. The control tower and the crews of both planes were unable to see one another.
• Interference from simultaneous radio transmissions, with the result that it was difficult to hear the message.

The following factors were considered contributing but not critical:

• Use of ambiguous non-standard phrases by the KLM co-pilot ("We're at take off") and the Tenerife control tower ("OK").
• The Pan Am aircraft had not left the runway at the third intersection.
• The airport was forced to accommodate a great number of large aircraft due to rerouting from the terrorist incident, resulting in disruption of the normal use of taxiways.[47]

The Dutch authorities were reluctant to accept the Spanish report blaming the KLM captain for the accident.[48] The Netherlands Department of Civil Aviation published a response that, while accepting that the KLM captain had taken off "prematurely", argued that he alone should not be blamed for the "mutual misunderstanding" that occurred between the controller and the KLM crew, and that limitations of using radio as a means of communication should have been given greater consideration.

In particular, the Dutch response pointed out that:

• The crowded airport had placed additional pressure on all parties, including the KLM cockpit crew, the Pan Am cockpit crew, and the controller;
• Sounds on the CVR suggested that during the accident the Spanish control tower crew had been listening to a soccer match on the radio and may have been distracted;[49]
• The transmission from the tower in which the controller passed KLM their ATC clearance was ambiguous and could have been interpreted as also giving take-off clearance. In support of this part of their response, the Dutch investigators pointed out that Pan Am's messages "No! Eh?" and "We are still taxiing down the runway, the Clipper 1736!" indicated that captain Grubbs and first officer Bragg had recognized the ambiguity (this message was not audible to the control tower or KLM crew due to simultaneous cross-communication);
• The Pan Am had taxied beyond the third exit. Had the plane turned at the third exit as instructed, the collision would not have occurred.[5][50]

Although the Dutch authorities were initially reluctant to blame captain Veldhuyzen van Zanten and his crew,[5][50] the airline ultimately accepted responsibility for the accident. KLM paid the victims' families compensation ranging between $58,000 and $600,000 (or $245,000 to $2.5 million today, adjusted for inflation).[6] The sum of settlements for property and damages was $110 million (or $464 million today),[51] an average of $189,000 (or $797,000 today) per victim, due to limitations imposed by European Compensation Conventions in effect at the time.

This was one of the first accident investigations to include a study into the contribution of "human factors".[52] These included:

• Captain Veldhuyzen van Zanten, a KLM training captain and instructor for over ten years, had not flown on regular routes during the twelve weeks prior to the accident.[53]
• The apparent hesitation of the flight engineer and the first officer to challenge Veldhuyzen van Zanten further. The official investigation suggested that this might have been due not only to the captain's seniority in rank, but also to his being one of the most respected pilots working for the airline.[10][54] This view is questioned by Jan Bartelski, a former KLM captain and the president of the International Federation of Air Line Pilots' Associations (IFALPA), who knew both officers and believes this explanation to be inconsistent with his knowledge of their personalities. The first officer had intervened when Veldhuyzen van Zanten first opened the throttles, but had then failed to do so on the second occasion. Although the flight engineer had indeed asked the captain whether or not the Pan Am was clear of the runway, he seemed reassured by the captain's answer. The co-pilots had clearly challenged the captain's decisions, but were not insistent enough to convince him to abort the attempted takeoff.[55]
• The flight engineer was the only member of the KLM's flight crew to react to the control tower's instruction to "report when runway clear"; this might have been due to him having completed his pre-flight checks, whereas his colleagues were experiencing an increased workload, just as the visibility worsened.[56]
• The ALPA study group concluded that the KLM crew did not realize that the transmission "Papa Alpha one seven three six, report when runway clear" was directed at the Pan Am, because this was the first and only time the Pan Am was referred to by that name. Previously, the Pan Am had been called "Clipper one seven three six", using its proper callsign.[57]

The extra fuel taken on by the KLM added several factors:

• Takeoff was delayed by an extra 35 minutes, allowing time for the fog to settle in;
• Over forty tons of additional weight was added to the aircraft,[58] increasing the takeoff distance and making it more difficult to clear the Pan Am when taking off;
• The increased severity of the fire caused by the crash led ultimately to the deaths of all those on board.[59][60]