On this day in 1977, the worst air disaster in aviation history* took place at Tenerife in the Canary Islands. The appropriately named Tenerife Airport Disaster occurred when two Boeing 747 passenger jets–then the largest airliner in the world–collided with each other on a runway at Los Rodeos Airport. 583 people were killed and only 61 survived. The sequence of events which led to the accident demonstrate how a catastrophe can occur when a seemingly unrelated set of decisions come together at the worst possible time. The accident and the subsequent investigation fundamentally changed how airline crew and air traffic control (or ATC) communicate and how airline cockpit crews interact with each other.



In the early afternoon of March 27, Pan Am Flight 1736 and KLM Flight 4805 were both making a normal landing approach to Gran Canaraia Airport on the island of Gran Canaria. At 1:15pm local time, a bomb planted by local insurgent group Fuerzas Armadas Guanches exploded in a flower shop in the terminal of Gran Canaria airport, injuring one person. An anonymous phone call had warned of the first bomb before it went off and subsequently another anonymous caller warned that a second bomb was planted at the airport and would explode soon as well. Airport and municipal officials immediately decided to close the airport and reroute all incoming flights. Both Pan Am 1736 and KLM 4805 were waived off from their approaches to Gran Canaria and ordered to land, along with five other large airliners, at the nearby Los Rodeos Airport.



Los Rodeos was, at the time, a much smaller regional airport that was unaccustomed with and unprepared to handle large airliners, let alone several of them landing in order. There was a limited airport apron to park all of the airliners, including the two massive Boeings, which could not be parked near the terminal. Instead, the ATC ordered both onto the taxiway that ran parallel to the airport’s single runway. This prevented any other aircraft from using the taxiway, instead the two 747s would have to taxi along the edge of the main runway and take off first, thus allowing the smaller airliners parked on the apron to use the taxiway for their own takeoffs.



After a short delay at Los Rodeos, officials at Gran Canaria reported that the airport was swept and no further bombs discovered; flights were cleared to begin landing at Gran Canaria again. Pan Am 1736 reported to ATC that they were immediately ready for takeoff, but they were hemmed in by KLM 4805 and a refueling truck. The captain of KLM, who was the airline’s chief flight instructor at the time, had decided to refuel while on the ground in Tenerife, a process which took 35 minutes. After KLM 4805 was refueled and all of its passengers re-boarded–except for one tour guide who lived on Tenerife and decided not to take the next leg to Gran Canaraia–ATC ordered them to taxi down the main runway and then position itself for takeoff. Pan Am 1736 was to follow and then exit the runway at the third exit to the left in order to allow KLM 4805 to takeoff.



While both planes taxied, an immensely dense fog swept over the airport. ATC lost visual contact with both aircraft and, having no ground radar to track them electronically, was forced to reply on radio calls from each cockpit in order to plot where they were on the runway. Once positioned at the end of the runway KLM 4805 was to ready for takeoff but, following standard procedure, waited for official clearance from ATC. In a confused exchange which followed the Dutch captain throttled up his four engines in preparation for takeoff while the co-pilot radioed their readiness to ATC. In response ATC issued instructions for the route KLM 4805 was to take in order to reach Gran Canaria but this instruction included the word “takeoff” which the Dutch crew interpreted as clearance to throttle down the runway. Meanwhile, Pam Am 1736 reported to ATC that they would radio when they were clear of the runway.



Neither KLM 4805, Pan Am 1736, nor ATC were in visual contact with one another due to the fog. But upon hearing Pan Am’s communication which indicated that they had not cleared the runway yet, the KLM crew, which was already moving down the runway at full throttle, became immediately concerned. The co-pilot of Pan Am 1736 spotted KLM 4805′s landing lights breaking through the fog as it roared down the runway. The pilot immediately throttled up his engines and tried to steer into the grassy area next to the runway while the KLM pilot, realizing his mistake, attempted a premature rotation in order to clear the Pan Am aircraft. The actions of both pilots were of no avail and KLM 4805 suffered a severe tailstrike which dragged it along the runway for 72 feet where it collided with Pan Am 1736. The engines, lower fuselage, and main landing gear of the KLM airliner collided with the upper right fuselage of Pan Am 1736 at 140 knots, ripping both aircraft apart before the KLM plane slung directly into the ground where it exploded into a fireball.



All 234 passengers and 14 crew of KLM 4805 perished in the accident along with 326 passengers and 9 crew on Pan Am 1736. 62 passengers and 7 crew, including all 3 cockpit crew on Pan Am 1736 survived. Passengers on the left side of the aircraft, which was not struck, were able to simply walk out onto the wing of the crippled airplane and then onto the ground where they awaited rescuers.



Since the accident, communications between airliner crews and ATC have been more thoroughly standardized and airlines have trained their crews to communicate more clearly with one another; e.g., ATC’s no longer use the word “Takeoff” unless a takeoff is specifically cleared or cancelled. The installation of ground radar at all major airports has also become standard. Los Rodeos Airport would remain closed until April 3 after all of the wreckage was finally cleared by the Spanish Army.







*The four airplanes involved in the September 11, 2001 attacks constitute the worst disaster in aviation history if you count those killed on the ground. The Tenerife Airport Disaster’s fatalities were solely from the two aircraft involved.

