On March 27, 1977, two Boeing 747 passenger jets collided on a runway at Los Rodeos Airport on the Spanish island of Tenerife, killing 583 people and injuring 61 others in the deadliest accident in aviation history.
The incident occurred at 17:06 GMT (UTC +0) in dense fog, when KLM Flight 4805 initiated its takeoff run, colliding with the right side of Pan Am Flight 1736, which was on the runway. The impact and the resulting fire killed all 248 people on board the KLM plane and 335 of the 396 people on board the Pan Am plane, with all 61 survivors being in the front section of the aircraft.
The two aircraft had landed at Los Rodeos earlier that Sunday and were among a number of aircraft diverted to Los Rodeos due to a bomb explosion at their intended destination of Gran Canaria Airport. Los Rodeos had become congested with parked planes blocking the only taxiway, forcing departing aircraft to taxi on the runway. Patches of thick fog were drifting across the airfield, so visibility was greatly reduced for pilots and the control tower.
An investigation by Spanish authorities concluded that the primary cause of the accident was the KLM captain's decision to take off believing that air traffic control (ATC) had issued takeoff clearance and that the Pan Am Boeing had cleared the runway, despite the latter radioing that they would "report when clear of the runway". Dutch investigators placed a greater emphasis on a mutual misunderstanding in radio communications between the KLM crew and ATC, but ultimately KLM admitted that its crew was responsible for the accident and the airline agreed to financially compensate the relatives of all of the victims.
The accident had a lasting influence on the industry, highlighting in particular the vital importance of using standard 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. The captain is no longer considered infallible, and combined crew input is encouraged during aircraft operations.
Background
Tenerife was an unscheduled stop for both flights. Their destination was Gran Canaria Airport (also known as Las Palmas Airport or Gando Airport), serving Las Palmas on the nearby island of Gran Canaria.
KLM Flight 4805
KLM Flight 4805 was a charter flight for Holland International Travel Group and had arrived from Amsterdam Airport Schiphol, Netherlands. Its cockpit crew consisted of Captain Jacob Veldhuyzen van Zanten (age 50), First Officer Klaas Meurs (42), and Flight Engineer Willem Schreuder (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 and the three employees from Holland International who lived on the different islands in the Canaries. Most of the KLM passengers were Dutch; also on board were four Germans, two Austrians, and two Americans. After the aircraft landed at Tenerife, the passengers were transported to the airport terminal. One of the inbound passengers, Robina van Lanschot, a tour guide who worked at Holland International, lived on the island with her boyfriend and chose not to re-board the 747, leaving 234 passengers on board.
Pan Am Flight 1736
Pan Am Flight 1736 was also a charter flight, by the Greek shipping company Royal Cruise Line. It had originated at Los Angeles International Airport, with an intermediate stop at New York City's John F. Kennedy International Airport. The aircraft was a Boeing 747-121, registration N736PA, named Clipper Victor. Of the 380 passengers, who were mostly of retirement age but including two children, plus the two Royal Cruise Line employees, 14 had boarded in New York, where the crew was also changed. All but five passengers onboard the aircraft were Americans; the non-American passengers were all Canadian nationals. They were on their way to board the cruise ship Golden Odyssey for a 14-day trip across the Mediterranean.
The new crew consisted of Captain Victor Grubbs (age 56), First Officer Robert Bragg (39), Flight Engineer George Warns (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.
Clipper Victor was a historic plane, as it was the first Boeing 747 to operate a commercial airline flight when it flew from John F. Kennedy Airport to London Heathrow on 21 January 1970. On 2 August 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.
Accident
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 Airport, injuring eight people. Due to the threat of a second bomb, the civil aviation authorities closed the airport temporarily after the initial explosion, and all incoming flights bound for Gran Canaria were diverted to Los Rodeos, including the two 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 (they had enough fuel to safely stay in the air for two more hours), 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 planes took up so much space that they had 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 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, where the two Dutch children were in the runway who had not returned to the waiting KLM plane, delayed the flight even further. Additionally, Robina van Lanschot, a tour guide from Holland International, 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 was the only survivor of those who flew from Amsterdam to Tenerife on Flight 4805.
Taxiing and takeoff preparations
The Los Rodeos tower instructed the KLM plane to taxi down the entire length of the runway and then make a 180° 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 the clearance was postponed until the aircraft was in takeoff position.
Shortly afterward, the Pan Am was instructed to follow the KLM down the same runway, exit it by taking the third exit on the 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 (C1 and C2), but their discussion in the cockpit indicated that they had not sighted the third taxiway (C3), 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 (C4).
The angle of the third taxiway would have required the plane to perform a 148° turn, which would lead back toward the still-crowded main apron. At the end of C3, the Pan Am would have to make another 148° turn to continue taxiing toward the start of the runway, similar to a mirrored letter Z; taxiway C4 would have required two 35° turns instead. A study carried out by the Air Line Pilots Association (ALPA) after the accident concluded that making the second 148° turn at the end of taxiway C3 would have been "a practical impossibility". The official report from the Spanish authorities explained 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. These instructions issued by the airport controllers indicated their lack of familiarity with the difficulty of handling large aircraft such as the 747. In an interview years later, First Officer Bragg said he believed that the airport controllers saw the plane pass the first taxiway and their instructions to turn on the third taxiway were intended to mean the third taxiway they saw after the first one, which would have been taxiway C4.
Weather conditions at Los Rodeos
Los Rodeos airport is at 633 meters (2,077 ft) above sea level, which gives rise to weather conditions that differ from those 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 legal minimum 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 toward 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 toward 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. Meurs advised him that ATC clearance had not yet been given and 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". ATC radioed the KLM aircraft (addressing them by the wrong call sign, although the KLM still interpreted the transmission as theirs), providing instructions that specified the route that the aircraft was to follow after takeoff, but did not clear them for takeoff. To add to the confusion, the controller had used the word "takeoff" in his clearance, potentially convincing Veldhuyzen van Zanten that a takeoff clearance had been issued.
Meurs read the flight clearance back to the controller, completing the readback with the statement "We are now at takeoff", although it is still not known whether "We are at takeoff" or "We are taking off" was said. Veldhuyzen van Zanten interrupted the first officer's readback with the comment "We're going."
The controller, who could not see the runway due to the fog and did not have any ground radar to use at the airport, 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 first officer's non-standard statement that they were "now at takeoff" was likely due to his misinterpreting that the aircraft was 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 instruction 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 three-second-long shrill sound (or heterodyne). This caused the KLM crew to miss the latter portion of the tower's response. The Pan Am crew's transmission was "We're still taxiing down the runway, 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.