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.

However, before the controller could inform the pilots of their full clearance, according to Dutch investigators, the KLM Boeing 747 had already started its take-off run. While Pan Am’s crew heard the conversation and informed ATC that they were still “taxiing down the runway.” The controller confirmed that he heard the message and asked the pilots to “report runway clear.”

Further strain was put on the controller due to the fact that heavy fog had set in: without any ground radar present at the airport, the controller was essentially blind to what was happening on the runway, just 30 seconds before disaster struck.

When the Pan Am crew replied “okay, will report when we are clear,” the KLM crew then began discussing their reply as the message was audible up in the Dutch cockpit. While the first officer and flight engineer discussed whether the Pan Am exited the runway, the captain of the flight emphatically said “Oh, yes,” continuing the take-off.

The investigators also noted that “perhaps influenced by his great prestige, making it difficult to image an error of this magnitude on the part of such an expert pilot, both the co-pilot and the flight engineer made no further objections.”

The lasting legacy of the accident

The investigators concluded that the KLM captain was at fault for taking off without proper clearance and not aborting the take-off after the Pan Am crew reported that they were still on the runway. Moreover, when his flight engineer asked whether the other Boeing 747 left the runway, he emphatically confirmed that it left the runway.

The Tenerife disaster further enhanced the view from several studies that concluded that the majority of accidents happened due to human error, rather than a mechanical failure or weather difficulties. Research into the dynamics of human error within the cockpit resulted in a highly influential NASA paper in 1980 that resulted from a workshop held in June 1979, titled “Resource management on the Flight Deck.” The paper was the start of crew resource management – training procedures for pilots to “emphasize increased awareness and the use of available resources by aircrews under high workload conditions.”

One of the attendees of the NASA workshop concluded that “the justification for resource management training is, I think, abundantly clear.”

Thus, crew resource management was “born”. Emphasis was put on using all available resources to flight crews, including people. Younger pilots were now able to speak up and suggest solutions to a pressing issue, reducing the chance of a human error leading to an accident, no matter fatality-free or such deadly incidents like the one in Tenerife in 1977.

Further legacy is the clearing up of Air Traffic Control and flight crew communication. The investigation into the Tenerife disaster recommended the “use of standard, concise and unequivocal aeronautical language.” This resulted in the standardization of language, as the Air Line Pilot Association (ALPA) conducted their own investigation into the accident and heavily emphasized the usage of “rigid standards” to staff that are involved in “commercial aeronautical communications.”

However, changes only came in 2001 when the International Civil Aviation Organization (ICAO) presented a set of recommendations called the Proficiency Requirements in Common English (PRICE). ICAO adopted the Standards and Recommended Practices (SARPs) in 2003, which became applicable only in March 2008.

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