Tenerife: The Deadliest Aircraft Accident

On March 27, 1977, two 747 jumbo jets collided on the runway at an airport on Tenerife, one of the Canary Islands off the coast of Morocco. Of the 644 people on board the two planes, 583 were killed. The Tenerife collision still remains the deadliest aircraft accident in history.


A KLM Airlines Boeing 747.                        photo from WikiCommons

Located about 50 miles off the coast of Morocco, the Canary Islands have been a Spanish possession since the 15th century. In modern times, the tropical climate and good weather have made the islands a popular tourist destination.

On March 27, 1977, at about 1pm, a small bomb exploded in the terminal at the primary airport on the island of Las Palmas. Credit was quickly claimed by a small pro-independence group, which warned that other bombs had also been planted. As a precaution, the Las Palmas Airport was closed down, and all incoming air traffic was diverted to the smaller secondary Los Rodeos Airport, on the nearby island of Tenerife. Two of those diverted flights, that landed at Tenerife at around 2pm, were KLM Flight 4805 and Pan Am Flight 736. Both of these were Boeing 747 aircraft, which the Tenerife airport was just barely big enough to handle. Flight 4805 was piloted by Captain Jacob van Zanten, a supremely experienced pilot who was in charge of training for all of the Dutch airline’s 747 captains. Flight 736 was under the command of Captain Victor Grubbs, a veteran pilot with 21,000 hours of flying time.

At about 4pm, the Las Palmas Airport was reopened (no additional bombs had been found), and both 747s were cleared to taxi to the runway for takeoff from Tenerife to return to Las Palmas. KLM Captain van Zanten, however, requested additional fuel, and because of the small size of the airport (there was only one runway), the Pan Am 747 did not have enough room to get around them. Both jumbo jets waited as the fuel truck was rolled out. Then bad luck struck. As the KLM was being refueled, a heavy fog rolled in and shut down all flights leaving Tenerife. The planes were grounded again.

Shortly before 5pm, the fog began to lift, and it was decided to let both of the 747s go first. Because of all the rerouted planes crowded into the airport, the taxiway, which ran alongside the runway, was full, and there wasn’t enough room for the big jumbo jets to taxi. So the airport’s traffic controllers decided to let the 747s taxi down the main runway instead. Captain van Zanten on KLM 4805 was instructed to taxi all the way down the runway to the far end, turn around, and hold there. Captain Grubbs in Pan Am 736 was to follow partway down the runway, turn into one of the taxiways and wait there until KLM 4805 had taken off, then taxi back out onto the runway, turn around at the far end, and take off.

At 5:06pm, KLM Flight 4805 had completed its turnaround and was now waiting for clearance to take off. Pan Am 736, however, was still on the runway–the combination of low visibility in the fog and the unfamiliar airport had caused them to miss their turn, and they were forced to taxi further down the runway to another taxiway.

At about the same time, the Tenerife air traffic control tower gave KLM 4805 its “route clearance”, providing information on the heading and altitude it should take once airborne. This route clearance was normally given to pilots before they taxi’d to the runway, but now it was delayed by the chaotic conditions in the crowded foggy airport. At this point, however, Captain van Zanten made a lethal error–he mistook the tower’s route clearance for an actual takeoffclearance. Pushing the throttles forward, he began his takeoff run. “We are now at takeoff”, the copilot radio’d.

And now, a second fatal event. Hearing that the KLM pilot had started his takeoff, the tower radio’d to Captain van Zanten “Stand by for takeoff, I will call you.” But at the same instant, the copilot on Pan Am 736, Bob Bragg, also radio’d “We’re still taxiing down the runway!” But because both calls were made at the same time, the two radio signals interfered with each other, and the KLM crew heard only a burst of high-pitched static. Several seconds later, the tower told the Pan Am jet to “Report when runway clear”, followed by Bragg acknowledging “We’ll report when runway cleared.” And this time, the KLM crew heard it. The second officer on the KLM shouted to Captain van Zanten, over the roar of the engines, “Is he not clear? That Pan Am?” Van Zanten, inexplicably, shouted back, “Oh, yes.”

But the Pan Am 747 was not clear.

In the fog, Captain Grubbs can’t see the KLM jet at the end of the runway, but he now knows that it has begun its takeoff roll-directly at him. “Let’s get the fuck out of here,” he says, and begins to turn onto the grass at the side of the runway. Just seconds later, he sees the takeoff lights of the KLM 747 in the fog. “There he is!” he shouts. “Look at him! Goddamn, that son of a bitch is coming!” Copilot Bragg also shouts, “Get off! Get off!”

But it’s too late. In the KLM cockpit, Captain van Zanten desperately slams back on the control stick, pulling the nose of the plane up sharply to try to hop over the Pan Am jet. The KLM’s tail digs into the runway, and the landing gear and belly slams into the top of the Pan Am at over 100mph. The impact tears the top off the Pan Am 747 like a can opener. The KLM 747 drops back to the runway and explodes on impact. The Pan Am plane also bursts into flame.

On KLM Flight 4805, there are no survivors. On Pan Am Flight 736, 61 people survive–including the cockpit crew. A total of 583 people are killed.

Accident investigators concluded that although the accident had been compounded by the poor visibility and the garbled communications with the air traffic controller, the cause of the accident was pilot error–KLM Captain van Zanten’s takeoff without clearance, and his failure to abort that takeoff when he heard that the Pan Am plane was still on the runway.


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