World’s Worst Air Disaster:
Pan Am 1736 and KLM 4805, Tenerife, 1977

Tenerife is one of the Spanish Canary Islands a few hundred miles off the coast of Morocco. The big town on Tenerife is Santa Cruz, and its airport, beneath a set of cascading hillsides, is called Los Rodeos. There, on 27^th March 1977, two Boeing 747s, one belonging to KLM, the other to Pan Am, collided on a foggy runway. 583 people were killed in what remains the biggest air disaster in history.

Setting the Scene

Both of the 747s at Tenerife were charters. Pan Am 1736 came from Los Angeles, after a stopover in New York, KLM 4805 from its home base in Amsterdam. As it happens, neither plane was supposed to be on Tenerife. They were scheduled to land at Las Palmas, on the nearby island of Gran Canaria, where many of the passengers were on their way to meet cruise ships. After a bomb planted by Canary Island separatists exploded in the Las Palmas airport flower shop, they were diverted to Los Rodeos, along with several other flights, arriving around 2 pm. The normally lazy Los Rodeos was packed with diversions. The two 747s were adjacent to each other at the southeast corner of the apron, their wingtips almost touching. Finally at around four o’clock, Las Palmas began accepting traffic again. The Pan Am was quickly ready for departure, but the lack of room and the angle at which the jets faced each other required the KLM to begin to taxi first.

Pan American World Airways
Koninklijke Luchtvaart Maatschappij N.V. (Royal Dutch Airlines)

The weather was fine until just before the accident, and if the KLM had not requested extra fuel at the last minute, both would have been on their way sooner. During the delay, a heavy blanket of fog swept down from the hills and enveloped the airport. That fuel also meant extra weight, affecting how quickly the 747 was able to become airborne. That was critical.

Because of the tarmac congestion, the normal route to runway 30 was blocked. Departing planes needed to taxi down on the runway itself. Reaching the end, they made a 180° turn before taking off in the opposite direction. This procedure, rare at commercial airports, is called a “back-taxi”. At Tenerife in 1977, it put two 747s on the same runway at the same time, invisible not only to each other, but to the control tower as well. The airport had no ground tracking radar.

KLM and Pan Am Aircraft Taxi and KLM Begins its Take-off

The KLM captain was Jacob Van Zanten, the airline’s top 747 instructor pilot and a KLM celebrity. The KLM flight taxied ahead and onto the runway, with the Pan Am ambling several hundred yards behind. Captain Van Zanten steered to the end, turned round, then held in position until authorized for takeoff. Pan Am’s instructions were to turn clear along a left-side taxiway to allow the other plane to depart. Once safely off the runway, they would report so to the tower. Unable to differentiate the taxiways in the low visibility, the Pan Am pilots missed their assigned turnoff. Continuing to the next one was no big problem, but now they were on the runway for several additional seconds.

At the same time, having wheeled into position at the end, Van Zanten came to a stop. His first officer, Klaas Meurs, took the radio and received the ATC route clearance. This is not a takeoff clearance, but rather a procedure outlining turns, altitudes, and frequencies for use once airborne. Normally it is received well before an aircraft takes the runway, but the pilots had been too busy with checklists and taxi instructions until then. They were tired, annoyed, and anxious to get going. The irritability in the pilots’ voices, Van Zanten’s in particular, had been duly noted by the control tower and other pilots.

Mistaken Instructions and Heterodynes

There were still a couple of dominos yet to fall, but now the final act was in motion – literally. Because the route clearance came where and when it did, it was mistaken for a takeoff clearance as well. First officer Meurs, sitting to Van Zanten’s right, acknowledged the altitudes, headings and fixes, then finished off with an unusual, somewhat hesitant phrase, backdropped by the sound of accelerating engines. “We are now, uh, at takeoff”. Van Zanten released the brakes. “We gaan” he was heard saying on the cockpit voice recorder. “Let’s go”. And with that, his mammoth machine began trundling down the fog-shrouded runway, completely without permission. “At takeoff” is not standard phraseology among pilots. But it was explicit enough to grab the attention of the Pan Am crew and the control tower. It was hard for either party to believe the KLM was actually moving, but both reached for their microphones to make sure. “And we’re still taxiing down the runway” relayed Bob Bragg, the Pan Am first officer.

At the same instant, the tower radioed a message to KLM. “Okay” said the controller. “Standby for takeoff. I will call you”. There was no reply. This silence was taken as a tacit, if not exactly proper, acknowledgment. Either of these transmissions would be, should have been, enough to stop Van Zanten cold in his tracks. He still had time to discontinue the roll. The problem was, because they occurred simultaneously, they overlapped.

Pilots and controllers communicate via two-way VHF radios. The process is similar to speaking over a walkie-talkie: a person activates a microphone, speaks, then releases the button and waits for an acknowledgment. It differs from using a telephone, for example, as only one party can speak at a time, and has no idea what his message actually sounds like over the air. If two or more microphones are clicked at the same instant, the transmissions cancel each other out, delivering a noisy occlusion of static or a high-pitched squeal called a heterodyne. Rarely are heterodynes dangerous. But at Tenerife this was the last straw.

Van Zanten heard only the word “Okay” followed by a five-second squeal. He kept going. Ten seconds later there was one final exchange, clearly and maddeningly audible on the post-crash tapes. “Report when runway clear”, the tower said to Pan Am. “We’ll report when we’re clear” acknowledged Bob Bragg. Focused on the takeoff, Van Zanten and his first officer apparently missed this. But the second officer, sitting behind them, did not. Alarmed, with their plane now racing forward at a hundred knots, he leant forward. “Is he not clear?” he asked. “That Pan American?” “Oh, yes” Van Zanten answered emphatically.

In the Pan Am cockpit, nose-to-nose with the still unseen, rapidly approaching interloper, there was a growing sense that something wasn’t right. “Let’s get the fuck out of here” Captain Victor Grubbs said nervously. A few moments later, the lights of the KLM 747 emerged out of the greyness, dead ahead, 2,000 feet away and closing fast. “There he is!” cried Grubbs, shoving the thrust levers to full power. “Look at him! Goddam, that son of a bitch is coming!” He yanked the plane’s steering tiller, turning left as hard as he could, toward the grass at the edge of the runway. “Get off! Get off! Get off!” shouted Bob Bragg.

A Laden 747 Can’t Do Leapfrogs

Van Zanten saw them, but too late. Attempting to leapfrog, he pulled back on the elevators, dragging his tail along the tarmac for 70 feet in a hail of sparks. He almost made it, but just as his plane broke ground, its undercarriage and engines sliced into the ceiling of the Pan Am plane, instantly demolishing its midsection and setting off a series of explosions. Badly damaged, the KLM settled back to the runway, skidded hard on its belly for another thousand feet, and was consumed by fire before a single one of its 248 occupants could escape.

Remarkably, of 396 passengers and crew aboard the Pan Am jumbo, 61 of them survived, including all five people in the cockpit – the three-man crew and two off-duty employees riding in the jumpseats. Once on the ground, the survivors of the Pan Am plane faced a deafening roar. The plane had pancaked into the grass, but because the cockpit control lines were severed, the engines were still running at full power. It took several moments before the motors began coming apart. One of the engines’ huge forward turbofans detached from its shaft, falling forward onto the ground with a thud. The fuselage was engulfed by fire. A number of passengers, most of them seated in forward portions of the cabin, had made it onto the craft’s left wing, and were standing at the leading edge, about 20 feet off the ground. Bragg ran over, encouraging them to jump. A few minutes later, the plane’s centre fuel tank exploded, propelling a plume of flames and smoke a thousand feet into the sky.

The airport’s ill-equipped rescue team, meanwhile, was over at the KLM site, the first wreckage they’d come to after learning there’d been a crash. They hadn’t yet realized that two planes were involved, one of them with survivors. Eventually, authorities opened the airport perimeter gates, urging anybody with a vehicle to drive toward the crash scene to help. Bob Bragg tells the cracked story of standing there in fog, surrounded by stunned and bleeding survivors, watching his plane burn, when suddenly a taxicab pulled up out of nowhere.

The new Tenerife South airport, opened in 1978, is now used for most international flights.