History's A Disaster

Crash at Tenerife

• Andrew

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On a foggy March day in 1977, the tiny Los Rodeos Airport on Tenerife in the Canary Islands became an unintended host to multiple diverted jumbo jets after a terrorist bombing closed their intended destination. Among them were two Boeing 747s: KLM Flight 4805 and Pan Am Flight 1736. What happened next would claim 583 lives and revolutionize aviation safety forever.

The KLM aircraft was piloted by Captain Jacob Veldhuyzen van Zanten, the airline's chief flight instructor and the face of their advertising—a man whose authority went virtually unquestioned. Under pressure from looming duty-time restrictions and deteriorating weather, van Zanten made a fateful decision to take off without proper clearance, despite his flight engineer's hesitant questions. Meanwhile, the Pan Am jet was still taxiing on the same runway, invisible in the thick fog that had enveloped the airport. Without ground radar, the control tower was blind to the impending disaster, and a cruel radio interference blocked the final warnings that might have saved hundreds of lives.

The collision was catastrophic—all 248 aboard KLM perished instantly, while only 61 of the 396 people on Pan Am survived. From this tragedy emerged fundamental changes that have shaped modern aviation: Crew Resource Management training that encourages all cockpit personnel to speak up regardless of rank, standardized communication protocols that eliminate ambiguity, and technological improvements like mandatory ground radar at major airports.

Listen as we dissect this tragic chain of events that reminds us how fragile our systems can be when communication breaks down and assumptions go unchallenged. Follow History's A Disaster on social media and share your thoughts at historysdisaster@gmail.com. Because understanding yesterday's disasters helps prevent tomorrow's tragedies.

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Special thank you to Lunarfall Audio for producing and doing all the heavy lifting on audio editing since April 13, 2025, the Murder of Christopher Meyer episode https://lunarfallaudio.com/


SPEAKER_00:

March 27th, 1977 was a shitty day to take a vacation. First, a terrorist bombing closes the airport you're flying into, causing your flight to get diverted to a much smaller regional airport with a single runway over a half hour away. Foggy conditions on the ground would end up causing delays, and add to that, limited technology means no one can see a damn thing. And that sounds like a recipe for disaster. And such a disaster it would be, it would go down as the worst air disaster in history. So what happened? I'm Andrew, and this is History's A Disaster. Tonight we are going to the Canary Islands, which is a collection of seven large islands and several smaller ones, considered an autonomous region of Spain, even though it's way fucking south of Spain, just off the coast of Morocco. And despite being volcanic in origin, it is a tourist destination for mostly Europeans on holiday. Being somewhat tropical, it has a ton of beaches and coastlines that draw the crowds in. And in 1977, the largest of the Canary Islands would be the site of the worst aviation accident in history. And tonight's episode is brought to you by the Flying Ace Can Opener Company. For those hard to open cans, nothing slices through the top of a can like a hot knife through butter, quite like a flying ace. The morning of March 27th, 1977, began with the routine hum of two Boeing 747s on their respective long haul journeys. On the tarmac at Amsterdam's Schiphol Airport, and I know I did not pronounce that right. KLM Royal Dutch Airlines Flight 4805, a Boeing 747, prepared for a charter flight to the Canary Islands. At the helm was Captain Jacob Veldehousen van Zatten, an experienced and well-respected pilot, known informally as KLM. He was not only a captain, but the company's chief flight instructor for their entire 747 fleet. This guy was so trusted that his face was all over KLM's advertising campaigns. Aboard this flight were 248 passengers and crew, and most of them were Dutch tourists and 52 of them were children. Meanwhile, flying over the Atlantic, PM Flight 1736, which was another Boeing 747, was on its final leg from New York's JFK Airport to the same destination. Ran Canaria Airport on the island of Las Palmas. Flying the jet was Captain Victor Grupps, a veteran pilot with over 21,000 hours of flight time. The Pan Am Jumbojet carried 396 people. 380 of them were passengers and 16 crew members. It was a long and boring flight, and most of them were looking forward to being off the plane after being stuck on it for over 13 hours. These fucking shitheads were really showing the Spanish how serious they were about standing up to them in open conflict to gain independence for the islands from Spain. Cause you know, there's nothing that says ready to fight to the last man in open conflict than trying to kill innocent civilians with a bomb, the fucking cowards. Anyways, civilian aviation authorities, in an act of caution, immediately closed the airport, forcing all incoming traffic to divert. A number of large aircraft, including the two Boeing 747s, were rerouted to the smaller regional airfield of Los Rodos on the neighboring island of Tenerife. The PNAM crew asked for permission to fly a holding pattern. They had plenty of fuel to spare, and after having flown from LA with only a single stopover in New York, they were really not looking forward to spending any more time on the plane than possible. Their request unfortunately got denied and they were forced to divert to Tenerife. Los Rodeos was ill-equipped to handle this sudden surge of heavy international traffic. The airport featured a single runway, designated runway 1230, and one main taxiway running parallel to it. When the diverted aircraft, which included five large airliners, arrived, they took up so much space on the main apron and taxiway that ran parallel to the runway that they effectively blocked it for its intended purpose. This forced a highly unusual and inherently dangerous procedure known as back taxiing or backtracking, which means instead of using the dedicated taxiway, departing planes were forced to use the active runway itself as a taxiway, moving in the opposite direction of the designated takeoff traffic before having to turn the plane around to take off. The delay on the ground at Los Verdeos really fucked with the KLM crew, particularly on Captain Jacob Van Zanten. As KLM's chief flight instructor for the 747, Van Zanten held a position of near unquestionable authority, a culture of seniority that meant the captain was basically a god within the cockpit. And in the documentary I watched, he was kind of a dick too. With this culture of the captain is always right, no one in the cockpit felt they could question his choices, which really put First Officer Klaus Moors in a bad position. Captain Van Zanten could make or break his career at any time. So doing anything to piss him off was probably not a good idea. Beyond his professional standing, Van Zanten was also under a more immediate personal burden. New Dutch government regulations limiting crew duty time had recently been enacted. These restrictions were very strict and carried the threat of criminal prosecution if exceeded, creating a looming deadline for the crew. He knew that with the day's complications and worsening weather, his window of opportunity to get out of Tenerife before an overnight stay was closing, and he desperately wanted to get the fuck out of there. This sense of urgency culminated in a shitty decision to refuel the aircraft at Los Rodeos. This despite the fact that normal procedure is to only take enough fuel to make the scheduled flight plus a little extra in case of emergencies. The KLM flight, a short 25-minute hop to Los Palmas, did not require the 55 tons of fuel that was being loaded. Van Zanten chose to do this to avoid the inevitable delays of refueling in a newly reopened and congested Las Palmas airport. The refueling process took approximately 35 minutes. Passengers on the KLM flight were allowed to de-plane and reboard. So instead of sitting in a cramped plane, the passengers got to enjoy sitting in a cramped terminal with all the other people that were stuck there. Delaying the plane even longer, they managed to lose a few passengers, which is a switch. Normally airlines lose your luggage. KLM apparently loses whole people. A family of four had yet to make it to the plane when reboarding started. The two kids had run off to explore, so they had to run around searching for them to round them up. There was also a fifth person that would not make it to the plane. Rabina Van Lanshot was one of three tour guides returning to Teneriff, and she chose not to return to the plane. The three of them were going to Teneriff anyways, so getting back on the plane meant they would be flying back to Gran Canaria just to turn around and come back to Tenerife. And she was ready to be done with the flight and see her boyfriend. After discussing it with her friends who were getting back on the plane, she snuck off, going against KLM's request that everyone get back on the plane. Back on the tarmac, while the Pan Am jet was ready to go, it was now trapped. Its path to the runway completely blocked by the stationary KLM plane and its refueling vehicle. The 747 being over 200 feet in width didn't have the clearance to make it around. They were short by just 12 feet, so they had to wait on KLM to get their act together and find the people they misplaced and take on fuel they didn't need. As the KLM crew finally finished its preparations and requested permission to taxi, the weather went to shit rapidly. A thick low-lying fog, which is a hallmark of the Tenerife Airport's unique microclimate, rolled in and enveloped the airfield. Visibility dropped to less than a thousand feet, far below the normal required minimums for takeoff. And it was so dense that the control tower, which had no ground radar, could no longer see the runway. So now both crews were now operating completely blind, forced to rely entirely on a system of verbal communications that was already under significant stress. As the KLM 747 back taxi down the runway, the Pan Am jet followed at a distance behind it. At 1702, the Tenerife Control Tower instructed the Pan Am crew to taxi into the runway and take the third taxiway. This instruction, however, was pretty unclear and pretty problematic. The third taxiway, designated Charlie 3, required a difficult 150-degree turn for 747. And since shit really wasn't marked that great, it was difficult to see in the fog. The Pan Am crew was confused and concerned, discussed the matter in the cockpit, debating whether the tower had meant the first or third exit, and ultimately decided to continue taxiing to the fourth exit, Charlie 4, which offered a more standard 45 degree turn and made more sense to the crew. The critical breakdown in communication occurred between the KLM cockpit and the control tower. After completing the back taxi and turning 180 degrees to face the end of the runway, KLM First Officer Moores received and read back their ATC clearance for their flight path. Now this clearance is only telling them their flight path after takeoff. Permission for takeoff is a completely separate event. However, in a fatal edition, the co-pilot ended his transmission with the non-standard phrase, we are now at takeoff. The controller, who had not yet issued a takeoff clearance, responded with okay, immediately followed by the crucial instruction, stand by for takeoff, I will call you. But in shithead Van Zanten's mind, the mind of a jackass that was in a hurry and thought he could do no wrong, the okay was a confirmation of his co-pilot's statement and the clearance he was waiting for. He immediately pushed the throttles forward and began the takeoff roll. A split second later, in a moment of tragic irony, the system's final defense was rendered useless. As the tower said standby for takeoff, the Pan Am crew transmitted, and we are still taxiing down the runway. The two messages sent at the same time overlapped, creating a high-pitched whistling sound that blocked both transmissions in the KLM cockpit. The final warning, a clear statement that could have saved 583 lives, was completely inaudible due to a simple technical limitation. In the KLM cockpit, the flight engineer William Schroeder felt something was wrong and actually twice questioned the captain, asking, is he not clear then? Van Zanden, with the blind conviction of a man under pressure, replied, Oh yeah. His unchallenged authority and the culture of deference in the cockpit silenced any further questioning, and the fatal takeoff run continued. From within the dense blinding fog, the crews of both aircraft were suddenly confronted with a horrific reality. In approximately 1706, the Pan Am crew, whose frantic cockpit chatter revealed their growing unease, saw the landing lights of the KLM 747 emerging from the mist just 2,000 feet away and closing fast. Captain Grubbs yelled into the cockpit voice recorder, pushed his throttles to full power, and desperately tried to veer the massive jet off the runway. In the KLM cockpit, Van Zanton, having committed to the takeoff, saw the lights of the Pan Am jet ahead too late. They were going way too fast to stop and not quite fast enough for takeoff. He pulled back on the yoke with full force, trying to get his aircraft airborne and clear the obstacle, but the attempt was too late and too violent. The aircraft tail dragged for over 60 feet along the runway due to its high angle of attack. The KLM 747 barely got off the ground. When it did leave the ground, its nose landing gear cleared the Pan Am, but its left side engines, lower fuselage, and main landing gear struck the upper right side of the Pan Am's fuselage, ripping apart the middle of the Pan Am jet almost directly above the wing. The right side engines crashed through the Pan Am's upper deck immediately behind the cockpit, instantly killing all of the passengers seated there. The KLM plane remained briefly airborne, but the impact had sheared off the number one engine, caused significant amounts of shredded material to be ingested by the number two engine and damaged the wings. The plane immediately went into a stall, rolled sharply, and hit the ground approximately 500 feet past the collision, sliding down the runway for another thousand feet. Upon impact with the runway, the full load of fuel, which Van Zanten just had to have, went up immediately into a fireball that could not be contained for several hours. The destruction was total. All 248 people on board the KLM flight were killed. Their fresh fuel load turning the wreckage into an incinerating pyre. Robina would be the lone survivor from the KLM flight who had chosen to stay behind in Tenerife. On the Pan Am jet, 61 people survived, all from the front section of the aircraft, which remained relatively intact after the impact. The remaining 335 people on board died. In total, 583 souls were lost. The tower, blinded by the fog, heard the explosions but could not see what had happened. Sending rescue crews initially to the KLM wreckage without knowing a second aircraft had been involved. It would be another 20 minutes after crews got to the KLM plane before they knew there was a second plane burning. 20 minutes survivors had to wait, praying for rescue. The scene was utter chaos. The left wing was destroyed and the entire top half of the airplane was ripped off. Doors were crumpled or smashed closed, survivors struggled to escape, one door would eventually be forced open. The passengers used any means necessary to escape, whether by the single open door or any hole in the plane they could find. Without a ladder or any other means of getting down, passengers were faced with jumping down nearly 20 feet to the debris-filled ground below. The survivors gathered near the left wing of the plane, which had remained intact, sitting by helplessly, unable to do anything for anyone that was still trapped in the wreckage, as they had to wait for the first responders. The fire was just burning too intensely for them to get anywhere near it. In the post-crash investigation that followed, the Spanish investigative authority, Subsecretaria de Aviation Civil, concluded that the fundamental cause was the KLM captain's actions, his decision to take off without clearance, his failure to obey the standby for takeoff instructions, and his emphatic denial that the Pan Am aircraft was on the runway. The Dutch investigation, while acknowledging the captain's role, placed a greater emphasis on the mutual miscommunications between the KLM crew and air traffic control. The KLM co-pilot's non-standard phrase, we are now at takeoff, and the tower's bag okay were considered examples of inadequate language that contributed to the misunderstanding. Even though initially they desperately tried to push the blame onto anyone else, blaming the air traffic controllers listening to the radio and not paying enough attention. Then they blamed it on their bad English, confusing the pilots. When that didn't quite pan out, they blamed the Pan Am pilots for not following orders and turning off. Which, none of which really matters, since they never got permission to take off, anyways. Ultimately, KLM admitted its crew was responsible and financially compensated the victims' families. The crash at Tenerife became the catalyst for complete overhaul of modern aviation safety. The sheer scale and complexity of the accident provided an undeniable lesson. Safety could not be guaranteed by the brilliance of individual pilots alone. The paradigm shifted from a culture that sought to pinpoint a single culprit to one that looked at the entire system for points of failure. The 583 people who perished that day became the unfortunate founders of a new era of safety. And their deaths led to some significant changes that are felt today and making air travel safer. The first and most significant change was the establishment of crew resource management as a mandatory component of pilot training. The investigation into the KLM cockpit revealed a profound psychological failure, a steep authority gradient where the flight engineers' correct and crucial question was easily dismissed by his captain, the supposedly legendary Mr. KLM. The aviation industry recognized that a cockpit environment where subordinates fear challenging a superior's decision is a critical vulnerability. The CRM was designed to dismantle this rigid hierarchy. It promotes a flanner command structure fostering open communication, mutual support, and shared decision making among all crew members. Pilots are now explicitly trained to be assertive, to speak up if they have a concern, and to ensure that safety decisions are a product of two-way communication, not a single individual's assumption. Second, the accident highlighted the deadly ambiguity of language. The KLM co-pilot's non-standard phrase we are now at takeoff and the controller's vague okay demonstrated that a lack of standardized terminology could have serious consequences. As a result, the airline industry adopted a universal set of concise, aeronautical phrases. Most critically, the word takeoff is now used exclusively to issue a clearance for takeoff. All other instructions use the word departure to avoid any confusion. This single global standard has eliminated the possibility of a pilot mistaking a route clearance for a takeoff clearance. Finally, the crash led to fundamental changes in airport infrastructure and procedures. The fact that the Tenerife control tower was blind to the aircraft on its own runway was a serious technological vulnerability. In the wake of the crash, the widespread installation of ground radar at major airports became standard. This technology provides air traffic controllers with a visual representation of all aircraft on the ground, which greatly improved situational awareness, especially in shitty weather conditions. Additionally, the non-standard practice of using an active runway for taxiing was re-evaluated, with strict guidelines now in place to lower the risk of such operations. And that was the Tenerife Air Disaster. Thanks for listening, and if you like the show, please consider leaving a rating or review on your app of choice. And you can reach out to the show at historiesandisaster at gmail.com with questions, comments, or suggestions. As well as follow the show on social media, like Facebook, Instagram, TikTok, YouTube, whatever. And share the episodes with your friends. They'll love it. Take care of yourself out there. Chase that dream. Live for today. Because tomorrow is never guaranteed. Thanks and goodbye.