On March 27, 1977, a chain of events began that would eventually result in the deadliest aviation accident. 583 people were fatally injured on the day and only 61 passengers from the Pan American World Airways Boeing 747 survived the accident, including the Pan Am flight crew.

KLM Flight 4805 that began its journey that day from Amsterdam Schiphol Airport, Netherlands (AMS) and Pan Am Flight 1736 that started its day in Los Angeles International Airport (LAX) via John F. Kennedy International Airport (JFK) in New York, both were destined for Gran Canaria Airport (LPA) in Spain. Gran Canaria and Tenerife, where the accident did happen, are part of Canary Islands, a Spanish archipelago in the Atlantic Ocean, just off the coast of Africa. A popular tourist spot throughout the years, the islands long ago established themselves as one of the major tourist spots in the world.

And while they were both en route to Gran Canaria, a bomb exploded in the passenger terminal at Las Palmas Airport. Subsequently, all incoming traffic to LPA was diverted elsewhere, with a lot of aircraft going towards Los Rodeos Airport (TFN) in Tenerife, Spain, just 69 miles (112 kilometers) northwest of Gran Canaria. Los Rodeos, as it was known back then and is now named Tenerife North, is a fairly small airport with a single runway and a parallel taxiway next to it.

And with the bomb explosion in Las Palmas, the chain of events that would eventually lead to 583 fatalities and KLM taking responsibility for the accident was set off.

Crowded airport

After Las Palmas Airport (LPA) was closed off in the aftermath of the explosion, a fair few aircraft landed in the small airport, which was also manned by a single tower controller. Later on, Dutch investigators (Netherlands Aviation Safety Board, succeeded in 1999 by the Dutch Transport Safety Board) noted that he worked for the whole day with “an unusually high traffic load.”

As the aircraft landed at Tenerife, they were parked anywhere where they could fit, from the taxiway to the various aprons. Thus, when Gran Canaria was reopened, quite a lot of traffic was on the ground. For aircraft to depart, they had to taxi on the runway, take a 180-degree turn on the runway and prepare for take-off. With KLM’s 747 lined up in front of Pan Am’s Queen, as traffic started to move, the 747 operated by KLM moved onto the runway, with the Pan Am following suite. However, Pan Am was set to exit the runway on the third taxiway exit to allow the KLM to continue its journey to Las Palmas.

At this point, the weather turned for the worse. Spanish investigators highlighted that three minutes before the disaster occurred, the Dutch flight crew, which operated KLM Flight 4805, asked whether the runway center lights were in service in connection with the minimum required take-off conditions.

TFN, which is located 2,077 feet (633 meters) above sea level, is very prone to deteriorating weather conditions, including fog, which was also one of the contributing factors on the day of the accident.

The controller responded that runway center lights were out of service. He also reiterated the information to the Pan Am crew.

Miscommunication on all fronts

When the KLM Boeing 747 stopped at the end of the runway and finished its take-off checklist, the first officer noted that “we [KLM crew – ed. note] do not have an ATC clearance.” The captain responded with “No, I know, go ahead, ask.”

The controller, when the first officer stated that the 747 is ready for take-off, responded that the flight is cleared for “Papa Beacon [a VOR interception for Las Palmas Airport – ed. note], climb to and maintain flight level nine zero,” with a right turn after take-off. The Dutch captain responded with a short yes, while the first officer repeated the instructions from the Air Traffic Control tower. The controller responded with an “ok,” and added to “stand-by for take-off” as he would call the KLM crew to give full clearance.