KLM-Pan Am collision – Worst air disaster in history

On March 27, 1977, a KLM Boeing 747 passenger aircraft collided with a Pan Am Boeing 747 passenger aircraft on the runway at Los Rodeos Airport on Tenerife island.

The collision occurred when the KLM aircraft initiated a takeoff run in dense fog while the Pan Am aircraft was still on the runway.

The impact and resulting fire killed all 248 people on board the KLM aircraft and 335 of the 396 people on board the Pan Am aircraft. The 61 survivors were in the front section of the Pan Am aircraft. The accident, with a total of 583 fatalities, is the worst air disaster in aviation history.

KLM Flight 4805, operated by a Boeing 747-206B, originated at Amsterdam Schiphol Airport and carried 14 crew members and 234 passengers.

Pan Am Flight 1736, operated by a Boeing 747-121 aircraft, originated at Los Angeles International Airport with an intermediate stop at New York's JFK airport and carried 380 passengers and 16 crew members.

Both the Pan Am and KLM flights were destined for Gran Canaria Airport (GCA) on the tourist island of Gran Canaria, one of the Canary Islands.

As both flights approached the GCA, a bomb planted by the separatist Canary Islands Independence Movement exploded in the GCA terminal injuring eight people.

After the initial explosion, a threat of a second bomb caused authorities to close the airport. All inbound flights to GCA were diverted to Los Rodeos Airport.

Los Rodeos airport, with only one runway and one long parallel taxiway, had to accommodate all aircraft diverted by the terrorist incident requiring parking on the long taxiway, making it unusable for taxing. Consequently, departing aircraft had to backtrack along the runway to the takeoff position.

After the bomb threat was contained, GCA was reopened. The Pan Am aircraft was ready to depart Tenerife for GCA.

However, access to the runway was obstructed by the refuelling of the KLM aircraft as the KLM captain decided to fully refuel at Los Rodeos Airport to save time.

After the KLM aircraft was ready for departure, the tower instructed the KLM aircraft to backtrack along the runway and then make a 180-degree turn to get into takeoff position.

Air Traffic Control (ATC) then instructed Pan Am to follow KLM down the same runway and turn off at the third exit and use the parallel taxiway.

There were no markings or signs to identify the runway exits. With poor visibility, the Pan Am crew identified the unmarked exits using an airport diagram and mistakenly ended up at exit C-4

The KLM aircraft completed its 180-degree turn and after lining up on Runway 30, the KLM captain advanced the throttles and the aircraft began to move forward.

The co-pilot advised him that ATC clearance had not yet been given and the captain responded: "I know that. Go ahead, ask."

The co-pilot then radioed ATC that they were "ready for takeoff" and "waiting for our ATC clearance."

ATC radioed the clearance to KLM aircraft, but did not clear them for takeoff. The co-pilot read the flight clearance back to the controller, completing the read-back with the statement: "We are now at takeoff."

A simultaneous radio call from the Pan Am crew, "We're still taxiing down the runway, Clipper 1736!" caused interference and became inaudible to the KLM crew.

Audibility of the messages in the KLM cockpit would have alerted the crew to the situation giving time to abort the takeoff.

Due to the fog, neither crew was able to see the other aircraft on the runway and both aircraft could be seen from the control tower. Also, the airport was not equipped with ground radar.

After the KLM aircraft started its takeoff roll, the tower instructed the Pan Am crew to "report the runway clear." The Pan Am crew replied: "OK, will report when we're clear." On hearing this, the KLM flight engineer expressed his concern about the Pan Am not being clear of the runway by asking the pilots in his own cockpit, "Is he not clear that Pan American?" The captain replied "Oh, yes" and continued with the takeoff.

According to the cockpit voice recorder (CVR), the Pan Am captain said, "There he is!" when he spotted the KLM's landing lights through the fog just as his aircraft approached exit C-4.

When it became clear that the KLM aircraft was approaching at takeoff speed, the Pan Am captain applied full power to the throttles and made a sharp left turn towards the grass in an attempt to avoid the impending collision.

When the KLM pilots saw the Pan Am aircraft, they had already exceeded their decision V1 speed and were moving too fast to stop. In desperation, the KLM pilots prematurely rotated the aircraft nose upward and attempted to clear the Pan Am aircraft by lifting off. The nose landing gear cleared the Pan Am aircraft, but the left-side engines, lower fuselage, and main landing gear struck the upper right side of the Pan Am's fuselage, ripping apart the centre of the Pan Am aircraft almost directly above the wing. The right-side engines crashed through the Pan Am's upper deck immediately behind the cockpit, instantly killing all of the passengers seated there.

The KLM aircraft remained briefly airborne, but the impact had sheared off the outer left engine, caused significant amounts of shredded materials to be ingested by the inner left engine, and damaged the wings. The aircraft immediately went into a stall, rolled sharply, and hit the ground 500 ft past the collision point, sliding down the runway for another 1,000 ft.

Upon impact with the runway, the KLM aircraft, with a full load of fuel, ignited into a fireball.

The accident was investigated by Spain's Civil Aviation Accident and Incident Investigation Commission.

Analysis of the CVRs transcript showed that the KLM pilot thought he had been cleared for takeoff, while the Los Rodeos control tower believed that the KLM 747 was stationary at the end of the runway, awaiting takeoff clearance.

The investigation concluded that the probable cause of the accident was the KLM captain attempted takeoff without ATC clearance.

As a consequence of the accident, sweeping global regulatory changes were made to aircraft operations procedures and the use of standard aviation phraseology by pilots and ATCs.