On March 27, 1977, a terrorist group detonated a bomb in a flower shop in the airport terminal of Gran Canaria, Canary Islands. The blast injured eight people and following the incident the airport was closed to arriving aircraft while the terminal was secured.
The most tragic plane crash
The bombing set in motion a chain of events that by day's end led to the worst aviation accident in history, involving the collision of two Boeing 747s and the deaths of 583 people.
Aircraft involved
KLM Flight 4805 operated by a Boeing 747-200 was en route to Gran Canaria. At the wheel was Captain Jacob Veldhuyzen van Zantan, chief instructor at KLM, along with first officer Klaas Meurs and flight engineer Willem Schreuder. The KLM plane had 235 passengers and 14 crew members on board.
Pan Am Flight 1736, operated by a Boeing 747-100, was en route from Los Angeles with a stopover at New York JFK to Gran Canaria. The flight crew consisted of Captain Victor Grubbs, First Officer Robert Bragg, and Flight Engineer George Warns. There were 380 passengers and 16 crew members on board.
Upon learning that Gran Canaria's airport was closed, KLM and Pan Am crews diverted aircraft to Los Rhodeos Airport (now called Tenerife North Airport) on the neighboring island of Tenerife. The KLM Boeing 747 landed at 13:38 local time and the Pan Am Boeing 747 landed at 14:15.
Los Rhodeos Airport and the inability to handle air traffic
As a small regional airport, Los Rhodeos Airport was not used to handling the volume of traffic that was expected. The airport had a single runway with a single parallel taxiway. Due to the many diverted aircraft, the apron was full and aircraft had to park on the taxiway, making it unavailable for taxiing. The departing aircraft should therefore perform a backtrack, taxiing the length of the runway before lining up to take off in the opposite direction.
When Las Palmas airport reopened, the Pam Am crew was ready to leave immediately, but could not because of the KLM aircraft which was parked in front and blocking the taxiway. Also, the KLM crew had decided to refuel the aircraft, and the refueling of 55.500 liters of fuel took about 30 minutes.
Once fueled, controllers cleared the KLM aircraft to taxi to the runway and prepare for takeoff. As the KLM aircraft taxied onto the runway, the Pan Am crew was instructed to taxi to the runway but to stop at the third exit from the left, clearing the way for KLM.
Bad weather and fog made the situation worse
Instead the weather had worsened. Visibility dropped from 500 m (1600 ft) to less than 100 m (330 ft). The airport had no runway markings or operational runway lighting.
When KLM reached the end of the runway and completed its turn, the captain decided to accelerate for take-off, but the co-pilot informed him that they had not received clearance for take-off. The KLM crew then contacted the control tower, confirming that they were ready and waiting for ATC clearance, then the controller cleared KLM for departure and told them to wait for their signal, only that the KLM aircraft was already taxiing on the runway.
Pilot error and communication problems
The Pan Am aircraft had not reached the clearance area, and the situation makes the two aircraft come face to face. Unfortunately, while the controller reiterated to KLM to "hold for takeoff", the Pan Am crew simultaneously called to say "we are still taxiing", so no transmission was heard correctly.
Because of the fog, the controllers could not see the planes, nor could the planes see each other, and the airport had no ground radar to determine where both aircraft were located. Both crews saw each other two seconds before impact. As a result of the impact, 583 people died and 61 survived.
583 people died
A total of 234 passengers and 14 crew members died on the KLM plane. The extra fuel on board increased the severity of the fire that engulfed the aircraft and no one was able to escape. A single passenger, Robina van Lanschot, chose to remain in Tenerife, where she lived, rather than return to the aircraft, and thus was the sole survivor of KLM Flight 4805.
On the Pan Am flight, 317 passengers and nine crew members died, leaving only 61 survivors, most of whom were sitting at the front of the aircraft. Passengers escaped from the burning aircraft on the wing, before jumping to the ground and reaching safety.
Final accident report
The final report gave the direct cause of the accident as the KLM captain choosing to take off without authorization. However, it was recognized that there were a number of unfortunate factors and, absent just one of these elements, the accident could have been avoided.
The KLM crew's decision to refuel added extra weight and increased the required take-off distance. There was also the time required for refueling, during which the weather deteriorated. It was later determined that the aircraft had enough fuel to reach Gran Canaria and fly to Amsterdam without needing additional fuel.
In the wake of the disaster, changes were made in the industry, mandating the use of standard, concise and unambiguous language to improve safety. A radio call from the KLM co-pilot saying "we're about to take off" and the tower controller's reply saying "OK" were both misinterpreted by the receivers of the messages with disastrous consequences.
Departure clearances are now requested before taxiing and are encouraged to take place on a completely different radio frequency than the take-off clearance. In addition, the phrase "take-off" is now only used in the issuing and reading of a take-off clearance.