Tenerife Air Disaster 1977

Next Tuesday sees the release of our next Airbus A320 Cadet Training Program module. We meet this time at euroJet’s crew room in Berlin, for a lengthy slog down to Tenerife. It's long flight for an A320-sized aircraft and can routinely take over five hours. It’s an even longer day for the operating crew, who usually perform the return flight also, giving rise to the nickname ‘ten hours of grief’ for the Tenerife sector. But jokes aside, our flight to Tenerife is one that follows in the footsteps of an aviation tragedy of almost unimaginable proportions.


Located in the Atlantic Ocean off Morocco in northwest Africa, Tenerife is the largest of Spain’s eight Canary Islands. A popular tourist destination, the island attracts more than five million tourists each year. Tenerife has two airports, the North airport (Los Rodeos) and the South airport (Reina Sofia).

On March 27th 1977, two Boeing 747 passenger jets, KLM Flight 4805 and Pan Am Flight 1736 collided on the runway at Los Rodeos Airport resulting in 583 fatalities, an accident considered the worst in aviation history.


The Boeing 747 was only in its eighth year of service, yet it was already revered as the most prestigious commercial airliner ever built. As happens disturbingly often in deadly air disasters, a series of fateful coincidences, combined with human error, ultimately led to the collision.


Tragically neither 747 was even supposed to be on the island of Tenerife that day, let alone on the same runway. Both had been scheduled to fly into nearby Las Palmas airport on the neighbouring island of Gran Canaria.

On that fateful Sunday morning, shortly before their scheduled arrival at 13:15, a small bomb planted by a separatist movement exploded in the terminal building of Las Palmas, resulting in several casualties. A phone call claimed responsibility and warned of a secondary device. The airport authorities had no choice but to temporarily close the airport. All incoming flights were cancelled or diverted.

While the subsequently fruitless search for a second bomb was performed, a dozen incoming aircraft, including the Pan Am and KLM 747s, were temporarily diverted to Tenerife, where they waited for Las Palmas officials to give them the all-clear. The airport was ill-equipped to deal with so many large aircraft, struggling with the limitations of one runway, plus one main taxiway, running parallel to it.

Whilst waiting on the tarmac, Captain Grubbs and First Officer Brag of the Pan Am flight decided to keep passengers entertained by inviting them up to look at the 747s cockpit. As an orderly queue of eager travellers formed through the upstairs lounge, the KLM crew chose to let their passengers disembark, encouraging them to stretch their legs by wandering around the Terminal building. 


Fretting about breaking the strict Dutch government rules limiting overtime for flight crews, Captain Van Zanten of the KLM flight made an operational decision to use the time constructively to refuel his jet. Just as refuelling began, the announcement came that Las Palmas airport was about to reopen. Stuck mid-refuelling, the KLM airliner blocked the path of other aircraft wishing to depart, the smaller of which subsequently manoeuvred carefully around the 747. The Pan Am 747, however, was parked on the apron behind the KLM plane and was too large to get past.

To add to the tragic domino effect, the additional fuel now on board the KLM flight made it significantly heavier, meaning it required more speed and additional runway to get off the ground. Meanwhile, the fog got thicker and visibility rapidly decreased. 

As the KLM passengers began making their way to the bus waiting to be transported back to the aircraft, one lady changed her mind. Robina van Lanschot, worked for a tour group based on Tenerife. She thought it somewhat futile leaving the island, only to have to come back, so she asked a friend to collect her luggage and headed for the payphone in the terminal to ring her boyfriend to collect her. Robina said in a 2017 interview that she struggled with survivor’s guilt for many years over that spontaneous decision which ultimately saved her life.


Just before 17:00, air traffic control granted KLM permission to start its engines, enter the runway at the northwest end, then move down the runway taking the third turnoff, C-3. Pan Am was about to start its engines, and would be given exactly the same instructions, following KLM.

Neither airline crew was sure if the ground controller had told them “first” or “third” runway exit, the two words have an identical sound to them, which is perhaps where the confusion began. Adding to the uncertainty, leaving at the third exit required turning the 747 at an angle of 135 degrees. By comparison, the fourth turnoff was only 45 degrees from the direction of their taxiing - a significantly easier manoeuvre.

After several clarification calls between the KLM cockpit and the control tower, the controller eventually changed his mind and instructed Dutch Captain Van Zanten to simply continue to the end of the runway and do a “backtrack” - completing a 180 degree turn so that the jet was facing the direction from which it had just come.

The crew did as directed, completing their pivot turn as Pan Am was entering the runway at the opposite end. As with KLM, the Pan Am crew were instructed to leave the runway on the difficult C-3 turnoff. The voice transcripts showed that pilots Grubbs and Bragg had trouble believing they weren’t supposed to leave at the easier angle of exit C-4.

With both crews struggling to understand their instructions, thick fog drastically reducing visibility, an impatient KLM crew keen to avoid overtime penalties, and no ground radar in place, the tragic line-up of fateful coincidences were now in place.

As passengers packed away belongings and fastened their seatbelts, a final catastrophic miscommunication sealed the fate of both aircraft. Pan Am’s crew informed the tower it was still on the runway. The transmission should have been audible in KLM’s cockpit, but at that exact moment an electronic buzz (known as a heterodyne) impeded transmission. Captain van Zanten never heard the announcement.

As Pan Am began slowly taxiing down the runway, the crew consulted their airport map struggling to find their assigned turnoff to move across onto the adjacent taxiway. Bragg, the first officer, later said the fog was so heavy that they taxied past the third exit without even realising.


Just before the Pan Am passed exit 3, KLM’s captain began his takeoff roll before getting permission from the controller. As First Officer Klaas Meurs was finishing a radio confirmation with the tower of their post-takeoff flight instructions, van Zanten pushed the throttles and began rolling down the runway.

“Stand by for takeoff. I will call you,” the controller said. Apparently van Zanten heard only the word “takeoff.” Second officer Schreuder didn’t like what he (correctly) thought he’d heard on the radio. “Is Pan Am still on the runway?” he asked van Zanten, speaking in Dutch, as KLM gained pace.

Van Zanten didn’t hear him clearly, and crucial seconds were lost. “What did you say?” the pilot asked his flight engineer. “Is he not clear, the Pan American?” “Oh, yes!” van Zanten responded.

The last sentence recorded in the KLM cockpit, just before the impact at 17:06:49, was a horrified curse, when Pan Am startlingly appeared through the dense fog in front of them: “Oh, Godverdomme” (literally meaning “God dammit, may God damn”. It expresses the wish that God damns something.)


Van Zanten pulled hard on the yoke and increased power in a futile attempt to clear the Pan Am 747. He managed to get the aircraft partially airborne, in the process carving a deep groove in the runway with the plane’s tail.

Computer Generated Reconstruction

Some sections of the Pan Am jet weren’t as damaged as those that had taken the full impact of KLM’s engines and lower fuselage. More than one hundred passengers attempted to flee the blazing debris. What followed was the next phase of this disaster, a frantic few minutes of evacuation by some of the passengers, and a bewildered paralysis by others.

The Tenerife air disaster killed every passenger on board KLM 4805 and all but 61 passengers on the Pan Am flight.


As a consequence of the crash, sweeping changes were made to international airline regulations and aircraft. Aviation authorities globally introduced strict requirements for standard phrases and a greater emphasis on English as a common working language.

As a result, air traffic instruction must not be acknowledged solely with a colloquial phrase such as “okay” or “Roger”, but rather with a read back of the instruction’s essential parts to show mutual understanding. The word “takeoff” is now used only when the actual takeoff clearance is given. Up until that point, aircrew and controllers should use the word “departure” in its place.

CRM or crew resource management - whereby junior members of the crew are encouraged to speak up to their Commander if they feel that an unsafe situation is developing - is now prevalent in airline culture. Both the First and Second Officers on the KLM 747 were uncomfortable with the situation but in 1977 would have been reluctant to speak up to the highly experienced Captain Van Zanten - the pin up of KLM's own advertising for the 747 fleet. 

Although ultimately the KLM Captain's actions sealed his fate and that of 582 others, an entire catalogue of fateful events begining with a terrorist bomb, fog, a poorly equipped airport, language difficulties and finally the Pan Am crew missing their turn in the low visibility all played a deadly role. This is known in aviation as 'the Swiss cheese' effect, whereby the holes line up one by one to allow a fatal accident. Were any one of the holes to be plugged, the accident would not have occured.

Many aviation safety commentators believe that the Tenerife accident would be unlikely to happen again, such are the lessons learned from that fateful day. We can only hope so.....

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