583 Lives Lost in the Fog at Tenerife

The fog came in patches, drifting across the runway in thick, blinding banks. One moment the pilots could see; the next, nothing. At Los Rodeos Airport on the Spanish island of Tenerife, on the afternoon of Sunday, March 27, 1977, two fully loaded Boeing 747s were stuck in exactly the wrong place at exactly the wrong time.

Neither plane was supposed to be there. Both had been bound for Gran Canaria Airport, on a neighboring island — the KLM flight, a charter from Amsterdam carrying Dutch vacationers, and the Pan Am flight, a charter that had begun in Los Angeles and picked up more passengers in New York, carrying Americans on their way to a Mediterranean cruise. But that afternoon, a bomb planted by separatists exploded in the terminal at Gran Canaria, injuring eight people. With the airport closed over fears of a second bomb, incoming flights were diverted to tiny Los Rodeos.

Los Rodeos was never meant to hold this much traffic. Diverted airliners crammed the ramps and spilled onto the single taxiway, blocking it entirely. That meant departing planes had to taxi down the runway itself — a slow, awkward procedure called a back-taxi — and then turn around to take off. And all the while, fog kept rolling across the field.

By late afternoon, Gran Canaria had reopened, and both 747s were preparing to leave. The KLM jet, Flight 4805, taxied the length of the runway and turned for takeoff. Behind it, the Pan Am jet, Flight 1736, was instructed to follow down the same runway, then exit onto the taxiway. But the Pan Am crew, peering into the murk, couldn't find the correct turnoff — the taxiways were unmarked, and visibility had dropped below a hundred meters in places.

What happened next took seconds. At 17:06 GMT, the KLM captain, Jacob Veldhuyzen van Zanten — one of the airline's most senior pilots, its chief flight instructor — advanced the throttles and began his takeoff roll, believing he had been cleared. He had not been. The tower had given him a route clearance, not a takeoff clearance, and the Pan Am jet was still on the runway ahead, invisible in the fog. When the KLM crew finally saw the Pan Am's lights looming through the mist, the captain hauled the giant jet into the air as desperately as he could — but it was too late. The KLM plane's landing gear tore through the Pan Am's fuselage.

All 248 people aboard the KLM flight were killed. On the Pan Am flight, 335 of the 396 aboard died; 61 people, most seated toward the front, survived. The total — 583 dead, 61 injured — made it the deadliest aviation accident in history, a record it still holds.

The investigation found no single cause, but a chain of them: the diversion, the congestion, the fog, the unmarked taxiways, the ambiguous radio calls. The Dutch investigators emphasized a tragic misunderstanding between the KLM crew and air traffic control; the Spanish report placed the blame squarely on the KLM captain's decision to take off. In the end, KLM admitted its crew was responsible and compensated the victims' families.

Out of the wreckage came changes that have saved countless lives since. Aviation authorities around the world standardized the language of the cockpit: the word "takeoff" may now be spoken only when actual takeoff clearance is given — until then, crews say "departure." Controllers require pilots to read back critical instructions. And cockpit culture itself was transformed, with the creation of crew resource management — the principle that a captain is not infallible, and that any crew member must be able to speak up.

The fog lifted that evening over Los Rodeos. What it left behind changed the way every pilot in the world talks, listens, and flies.

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