On March 27, 1977, a Boeing 747-100 (registration N736PA) operated by Pan American World Airways - PAA was involved in an aviation accident near Tenerife-Norte-Los Rodeos, Spain while taxiing. 335 people were killed. Investigators recorded the probable cause as: The KLM aircraft took off without take-off clearance, in the absolute conviction that this clearance had been obtained, due to a misunderstanding between the tower and the KLM aircraft arising from the mutual use of usual terminology that gave rise to… This summary draws on records from the Bureau of Aircraft Accidents Archives (B3A); 14 related events involving the same aircraft type or operator are linked below.
On 27 March 1977, KLM Flight 4805 and Pan Am Flight 1736 collided at Los Rodeos Airport, Tenerife, after a bomb threat diverted both flights. The KLM aircraft took off without clearance, killing all 248 occupants and 335 of 396 on the Pan Am aircraft.
Background and Diversion to Tenerife On 27 March 1977, KLM Flight 4805, a Boeing 747 registered PH-BUF, departed Amsterdam Schiphol Airport at 0900 hours bound for Las Palmas de Gran Canaria. The flight was operated by KLM on behalf of the Holland International Travel Group (H.I.N.T.). Pan Am Flight 1736, a Boeing 747 registered N736PA, departed Los Angeles International Airport on 26 March 1977 at 0129Z, arriving at John F. Kennedy International Airport at 0617Z. After refueling and a crew change, it departed for Las Palmas at 0742Z. While both aircraft were en route, a bomb exploded in the Las Palmas passenger terminal. Due to the incident and a warning of a possible second bomb, the airport was closed. KLM 4805 was diverted to Los Rodeos (Tenerife) Airport, arriving at 1338Z on 27 March 1977. Pan Am 1736, for which Los Rodeos was its alternate, landed at 1415Z. ## Passenger and Aircraft Movements Initially, KLM passengers were not permitted to leave the aircraft. After approximately twenty minutes, they were transported to the terminal by bus and received transit cards for Flight KL 4805. All passengers later reboarded KLM 4805 except the H.I.N.T. company guide, who remained in Tenerife. Pan Am 1736 passengers remained on board throughout the aircraft's stay at the airport. When Las Palmas reopened, the Pan Am crew prepared to continue to its planned destination. While attempting to taxi on the taxiway leading to runway 12, where it had been parked with four other aircraft due to congestion from diverted flights, the crew found the taxiway blocked by KLM 4805, which was positioned between Pan Am 1736 and the entrance to the active runway. The first officer and flight engineer left the aircraft and measured the clearance, concluding it was insufficient for Pan Am 1736 to pass. They waited for the KLM aircraft to begin taxiing. ## Tower Communications and Take-Off KLM 4805 called the tower at 1656 requesting taxi permission and was authorized. At 1658, it requested to backtrack on runway 12 for take-off on runway 30. The tower controller initially cleared KLM 4805 to taxi to the holding position for runway 30 by taxiing down the main runway and leaving it via the third taxiway to its left. KLM 4805 acknowledged, stating it was taxiing on the runway and would leave by the first taxiway to proceed to the approach end of runway 30. The tower controller immediately issued an amended clearance, instructing KLM 4805 to continue taxiing to the end of the runway and backtrack there. KLM 4805 confirmed it would backtrack and was taxiing down the main runway. The tower signaled approval, after which KLM 4805 asked whether it should turn left on taxiway one. The tower replied in the negative and repeated the instruction to continue to the end of the runway and backtrack. At 1659, KLM 4805 replied, “O.K., sir.” At 1702, Pan Am 1736 called the tower to confirm it should taxi down the runway. The tower confirmed this and instructed it to leave via the third taxiway to its left. At 1703:00, in response to the tower's query about how many runway exits KLM 4805 had passed, KLM 4805 confirmed it was passing taxiway C4. The tower told KLM 4805, “O.K., at the end of the runway make one eighty and report ready for ATC clearance.” In response to a query from KLM 4805, the tower advised both aircraft that the runway centerline lights were out of service. The controller also reiterated to Pan Am 1736 that it should leave the main runway via the third taxiway to its left and report leaving the runway. ## Collision The following communications occurred between the tower and the two aircraft, with times taken from the KLM CVR: - 1705:44.6 KLM 4805: “The KLM four eight zero five is now ready for take-off and we are waiting for our ATC clearance.” - 1705:53.41 Tower: “KLM eight seven zero five you are cleared to the Papa Beacon, climb to and maintain flight level nine zero, right turn after take-off, proceed with heading four zero until intercepting the three two five radial from Las Palmas VOR.” - 1706:09.61 KLM 4805: “Ah - Roger, sir, we are cleared to the Papa Beacon, flight level nine zero until intercepting the three two five. We are now (at take-off).” - 1706:18.19 Tower: “O.K..... Stand by for take-off, I will call you.” - 1706:21.92 Pan Am 1736: “Clipper one seven three six.” - 1706:25.47 Tower: “Ah - Papa Alpha one seven three six report the runway clear.” - 1706:29.59 Pan Am 1736: “O.K., will report when we're clear.” - 1706:31.69 Tower: “Thank you.” KLM 4805 had released its brakes to begin the take-off run 20 seconds before this communication. It collided with the Pan Am aircraft. The control tower received no further communications from either aircraft. There were no eyewitnesses to the collision. ## Casualties All 248 occupants on board the KLM Boeing 747 were killed. Of the 396 people on board the Pan Am Boeing 747, 335 were killed, including nine crew members, and 61 others were injured.
Probable cause
The KLM aircraft took off without take-off clearance, in the absolute conviction that this clearance had been obtained, due to a misunderstanding between the tower and the KLM aircraft arising from the mutual use of usual terminology that gave rise to misinterpretation. In combination with other coinciding circumstances, the premature take-off resulted in a collision with the Pan Am aircraft, which was still on the runway because it had missed the correct intersection.
