Tenerife Runway Collision

On March 27th, 1977, two Boeing 747s, **KLM Flight 4805** and **Pan Am Flight 1736**, collided on the runway of Los Rodeos Airport (now Tenerife North Airport), on the Spanish island of Tenerife. The incident killed 583 people, making it the deadliest aviation accident of all time.

## Disaster

Both flights were supposed to land at Gran Canaria Airport, until a terrorist bomb by the Canary Islands Independence Movement exploded at around 13:15 caused both flights to be diverted to Los Rodeos Airport. 1736 asked if they could circle until it reopened, but were denied.

Los Rodeos was a regional airport that couldn't easily accomadate the large amount of traffic, as it only had one runway and taxiway running parallel, along with no Ground Radar. While waiting for Gran Canaria airport to reopen, the diverted airplanes took up so much space that they were having to park on the long taxiway, making it unavailable for the purpose of taxiing. Instead, departing aircraft needed to taxi along the runway to position themselves for takeoff, a procedure known as a backtaxi or backtrack.

The KLM crew were worried as a new company policy meant they couldn't be late, and could possibly lose their jobs. They decided to refuel, hoping they could make up time. However this backfired when the airport reopened a few minutes later, meaning they would lose more time. The Pan Am flight also tried to go past it, but was unable to as there wasn't enough space.

After they stopped refueling, it started raining and the control tower asked the KLM to "backtrack," which involves using the runway as a taxiway, a passenger also left the KLM at this point. While the KLM was backtaxiing on the runway, the controller asked the flight crew to report when it was ready to copy the ATC Clearence. Because the flight crew was performing the checklist, copying this clearance was postponed until the aircraft was in takeoff position on Runway 30.

Shortly afterwards, the Pan Am was asked to followed the KLM down the same runway, and turn to "C3." The crew initally couldn't understand wether he said "C1" or "C3," but eventually understood it was "C3." At this point the airport was getting very foggy, meaning the ATC had to relie on the crew's word. According to the ALPA report, as the Pan Am aircraft taxied to the runway, the visibility was about 500 m (1,600 ft). Shortly after they turned onto the runway it decreased to less than 100 m (330 ft).

The Pan Am identified "C1" and "C2," but the discussion never mentioned "C3," until they reached "C4." The report later stated that it would require two 148-degree turns, which would be "practically impossible," for a 747, while C4 would only require two 45-degree turns. The official report from the Spanish authorities explains that the controller instructed the Pan Am aircraft to use the third taxiway because this was the earliest exit that they could take to reach the unobstructed section of the parallel taxiway.

Immediately after the KLM lined up, the captain advanced (pushed foward), the throttle, making the aircraft move foward. The first officer advised him that the ATC didn't give him clearence, and captain Veldhuyzen van Zanten responded: "No, I know that. Go ahead, ask." Meurs then radioed the tower that they were "ready for takeoff" and "waiting for our ATC clearance". The KLM crew then received instructions that specified the route that the aircraft was to follow after takeoff. The instructions used the word "takeoff," but did not include an explicit statement that they were cleared for takeoff.

When Meurs told the flight clearence after completing the readback with the statement: "We are now at takeoff." Captain Veldhuyzen van Zanten interrupted the co-pilot's read-back with the comment, "We're going."

The controller initally responded "OK" (terminology that is nonstandard), which reinforced the KLM captain's misinterpretation that they had takeoff clearance. The controller's response of "OK" to the co-pilot's nonstandard statement that they were "now at takeoff" was likely due to his misinterpretation that they were in takeoff position and ready to begin the roll when takeoff clearance was received, but not in the process of taking off. The controller then immediately added "stand by for takeoff, I will call you", indicating that he had not intended the clearance to be interpreted as a takeoff clearance.

A simultaneous radio call from the Pan Am crew caused mutual interference on the radio frequency, which was audible in the KLM cockpit as a 3-second-long shrill sound, (or heterodyne). This caused the KLM crew miss the (crucial) latter portion of the tower's response. The Pan Am crew's transmission was "We're still taxiing down the runway, the Clipper 1736!" This message was also blocked by the interference and inaudible to the KLM crew. Either message, if heard in the KLM cockpit, would have alerted the crew to the situation and given them time to abort the takeoff attempt.

After the KLM plane had started its takeoff roll, the tower instructed the Pan Am crew to "report when 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?" Veldhuyzen van Zanten emphatically replied "Oh, yes" and continued with the takeoff.

According to the Cockpit Voice Recorder, the Pan Am captain saw the KLM and said, "There he is!," just as they were approaching C4. When it became clear the KLM was at V1 Speed (Rotation/Lift Off Speed), the captain exclaimed. "Goddamn, that son-of-a-bitch is coming!", while first officer Robert Bragg yelled, "Get off! Get off! Get off!". The Pan Am crew appiled full power and started turning sharply to "C4" while the KLM crew started pulling back on their control sticks to try and take off, scrapping the tail in the process.

The KLM 747 was within 100 m (330 ft) of the Pan Am and moving at approximately 140 knots (260 km/h; 160 mph) when it left the ground. Its nose landing gear cleared the Pan Am, but its left-side engines, lower fuselage, and main landing gear struck the upper right side of the Pan Am's fuselage, ripping apart the center of the Pan Am jet almost directly above the wing. The right-side engines crashed through the Pan Am's upper deck immediately behind the cockpit.

The KLM plane was briefly airbourne, before crashing back into the ground around 150m (500ft) past the Pan Am, igniting a massive fire that lasted hours. Both planes were destroyed soon, with all 248 people on the KLM and 335 people on the Pan Am dying. 61 people inside the Pan Am survived the collision, including the entire cockpit crew, with many of the people leaving on the intact left wing. The Pan Am survivors waited for help to arrive, but it took a little due to the thick fog as the firefighters were unaware there were two planes.

## Timeline

* **13:15** - Bomb explodes at Gran Canaria
* **Around** **16:30** - Photographer takes this picture
* **16:56** - Dense fog rolls in reducing visibility to 300m
* **16:58** -  KLM asks for permission clearance for enter the runway.
* **17:02** -  Pan Am starts taxiing and asks what taxiway to taxi to
* **17:03** - Tower Controller asks what taxiway Pan Am is passing
* **17:04** - KLM turns 180 degrees, lining up with the runway.
* **17:06** - KLM captain advances the throttle and releases the brakes.
* **17:06:16** - The tower controller the KLM to wait, but a miscommunication causes the KLM think they're ready to take off.
* **17:06:45** - The crew of the Pan Am sees the KLM coming, and start turning onto "C4."
* **17:06:50** - The KLM collides with the top section of the Pan Am at 290 km/h, and crashes further down the runway.

## Trivia

* The Pan Am 747 involved was the first 747 put into service.