Two colliding Boeing 747s is probably the biggest catastrophe one could think of! On March 27, 1977, the Los Rodeos Airport (now known as Tenerife North Airport) was the scene of such a nightmare: one KLM 747-260B and one Pan Am 747-121 collided on the runway of the airport. There were 583 fatalities and just 61 survivors. Here’s the story of the deadliest crash in aviation history.

Both planes shouldn’t be at Los Rodeos Airport. Their final destination was the Gran Canaria International Airpot, which has been closed after a terrorist bomb exploded in the terminal. After that incident, on March 27, 1977, the authorities decided to close to divert all the flights to the Tenerife North Airport. More than five large aircraft were diverted that day to the Tenerife North Airport, a regional an relatively small airport that could not easily accommodate such an amount of passengers.

Pan Am flight 1736 had taken off from the LA International Airport and it had a stop at New York’s John F. Kennedy International Airport. 14 of the 380 passengers boarded from NY and the crew, consisting of 14 members, also changed here. The Boeing 747-121, with the N736PA registration, was the first 747 delivered to Pan Am.

KLM Flight 4805 was a charter flight for the Holland International Travel Group and it had taken off 4 hours before from the Amsterdam Schiphol Airport. The 747-260B Boeing, with the PH-BUF registration, had 235 passengers and 14 crew members. After landing at Tenerife, one local woman decided not to re-board the plane, leaving 234 passenger on board.

While both of the planes were at Los Rodeos Airport, the authorities reopened the Gran Canaria airport. The Pan Am was ready to take off, but due to the limited size of the airport, it did not manage to do this, since the KLM 747 decided to refuel. This was another decisive coincidence, since Pan Am had to wait for the KLM aircraft departure before taking off. The KLM captain decided to save time by fuelling at Tenerife, but all the new fuel added more weight, that slightly decreased the lift-off power and the accident escape ability.

When finished, the 747 KLM taxied to the runway, being aware that the Pan Am aircraft was back-taxiing behind them, on the same runway. Both of the planes had to back-taxi the whole runway, in order to make a 180 degree turn to put the aircraft in the take off position. During all this time the weather deteriorated and the low clouds limited the visibility to only 300 m (1,000 ft). The legal visibility range for a take off was 700 m (2,300 ft) back then.

The ATC instructed the Pan Am aricraft to back-taxi as well and eventually to exit the runway through the “third exit”. Based on the recordings, the Pan Am flight crew identified the first and the second exit but nobody knows if they have sighted the third one, since these taxiways were not clearly marked. Investigations conducted after the accident concluded that exiting through the third taxi-way would be practically impossible, due to the traffic congestion at the airport, that day.

The accident was caused by a communication misunderstanding. When lined up, the captain of the KLM aircraft spined-up the engines (advancing the throttles in order to check if the engines are operating properly) and the co-pilot, surprised, asked for the ATC clearance. The ATC gave a clearance that specified the route to be followed by the KLM plane after taking off. Still, there was no specific statement regarding the “take off clearance”. The captain started rolling for taking off, the co-pilot completed the read-back at the ATC by saying “we’re now at take off… we’re now, uh, taking off” (exact citation) and the Spanish controller replied “OK”, although this is a non-standard terminology.

Due to the fog, neither crew was able to see the other plane on the runway. Neither of the aircraft was seen from the control tower, as well. The Pan Am captain spotted the KLM’s taking off lights right when the 747 was approaching. The Pan Am applied full power and attempted a sharp left turn, but the KLM’s aircraft lower fuselage hit the upper right side of the Pan Am plane, at 140 knots (160 mph). The Pan Am was ripped apart and the KLM right engines crashed on the upper deck of the Pan Am. The KLM was briefly airborne, but then the captain lost control and crashed 150 m (500 ft) after the collision, sliding another 300 m on the runway.

234 passengers and 14 crew members in the KLM plane died and 326 passengers and 9 crew members from the Pan Am jet also were killed. The 56 passengers and 5 crew members of the Pan Am flight escaped by walking onto the left wing. The fire-fighters were initially unaware that there was another plane involved in the accident. Investigation that followed this tragedy concluded the fact that KLM’s captain was the main responsible for the accident, by deciding to take off without a clearance.

The authorities installed a ground radar at the Tenerife North Airport after the accident and in 1978, Tenerife’s second and larger airport was opened. The latter serves now as the main airport of the island, although the ex-Los Rodeos Airport is still functional, serving as a low-cost carrier destination. If you’re looking for cheap flights to Tenerife, it’s most likely to land at the Tenerife Nort Airport, but do not worry. The ATC new radars, the progress of the technology and the new rigorous training methods for the cockpit crews are now considerably improved, therefore the flight safety and respecting the ground procedure is not a question of option, but a “has to” for every aircraft. Studies revealed nowadays air travel is still the safest way to travel, the human errors are causing less fatal aircraft accidents than in the past and the number of air accidents is on a decreasing trend, both in America and Europe.