Apocalypse on the Runway: Revisiting the Tenerife Airport Disaster

Note: this accident was previously featured in episode 12 of the plane crash series on November 25th, 2017, prior to the series’ arrival on Medium. This article is written without reference to and supersedes the original.

The wreckage of Pan Am flight 1736 burns at Los Rodeos Airport as survivors scramble to safety. (Bureau of Aircraft Accidents Archives)

It was an event which shook the world: on a windswept island in the Atlantic Ocean, two Boeing 747s collided on a fog-shrouded runway, claiming the lives of 583 people. The story of the world’s worst air disaster has since been told and retold countless times: by the handful of lucky survivors; by the firefighters who ran into the fog, not realizing the scale of the catastrophe; by the investigators who pieced together the cause; by journalists and authors compelled to tell the world what happened; and by sociologists and behavioral scientists seeking to understand why humans make mistakes. The accuracy and nuance of these retellings varies, but the thrust of each is the same, reflecting upon the banality of disaster, the unfairness of coincidence, and the randomness of fate. Yet the events of the 27th of March, 1977 occurred in an environment that made this outcome possible, a series of misguided human decisions which established the rules of the game well before the two 747s ever arrived in the Canary Islands. And so, as we launch into yet another account of the Tenerife Disaster, it is worth stepping back from the glaring carnage and the accusations of guilt to consider more important questions. Was anything learned? How can the loss of so many lives be rendered less senseless? More than forty years later, the uncertain answers to these questions still draw us back to that fateful day on Tenerife.

A spectacular view along the coast of one of the Canary Islands. (Hotels.com)

Far to the southwest of Portugal, in the glistening subtropical waters off the coast of Morocco, lie the Canary Islands. A string of seven volcanic summits rising from the Atlantic, the Canaries have been a part of metropolitan Spain since the fifteenth century. Ever since the advent of air travel, their towering mountains, sun-blessed beaches, and active volcanoes have made the Canary Islands one of Europe’s top tourist destinations, a favorite among off-season travelers looking for a slice of summer during less pleasant times of year.

In 1975, around two million tourists visited the Canaries, but at that time it could not have been said that the islands were a major travel hub. Travel infrastructure in the archipelago was more suited to the reality of the 1960s, when the number of tourists had been ten times less, and the system frequently broke down under the strain. Nevertheless, when aviation experts in the 1970s expressed their concern about the inevitability of a fatal collision between two jumbo jets, they expected it to occur in New York or London or Los Angeles — not at a tiny single-runway airport on an island off the coast of Africa, so far from what were traditionally considered the world’s busiest airways.

N736PA, also known as “Clipper Victor,” the Pan Am plane involved in the accident. (Wikimedia user Aero Icarus)

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Believe it or not, the 27th of March, 1977 began as a normal day. At around 45 minutes after midnight, Captain Victor Grubbs, First Officer Robert “Bob” Bragg, and Flight Engineer George Warns reported for duty at New York’s John F. Kennedy International Airport in order to fly a Pan American Airways tourist charter service to the Canary Islands. Their double decker Boeing 747–100 was filled with 380 passengers, many of them retired couples embarking on a package cruise, along with 16 crew. For the pilots, the journey would have been utterly routine; there had doubtlessly been many others like it during their long careers, which had allowed the three men to rack up a combined 47,000 flying hours. When the 747, nicknamed Clipper Victor, took to the skies that night, the passengers could not have been in better hands.

PH-BUF, also known as “Rijn,” the KLM plane involved in the accident. (Wikimedia user clipperarctic)

An hour later and an ocean away, at Schiphol Airport in Amsterdam, the crew of a KLM Royal Dutch Airlines Boeing 747–200 also reported for duty in advance of a flight to the Canary Islands. Captain Jacob Louis Veldhuyzen van Zanten was a living legend at KLM, the face of the airline’s advertising campaign and the head of its Boeing 747 training program. These days, he spent most of his time training new pilots, and the trip to the island of Gran Canaria would be his first regular line flight in twelve weeks. His First Officer, Klaas Meurs, was also no rookie, but he had only just upgraded to the 747, accumulating a mere 95 hours since acquiring his type rating, which Captain van Zanten had personally granted to him. Finally, Flight Engineer Willem Schreuder was the most experienced of them all, with over 17,000 hours in the air. He was also the president and co-founder of the European Flight Engineer’s Organization, a major international trade union. Alongside this prestigious crew, there were also 11 flight attendants and 235 passengers, most of them younger Dutch families heading to the Canaries for a few days of sun and surf, courtesy of tour operator Holland International.

A banner promotes independence for the Canary Islands. (Unknown author)

The destination for both Pan Am flight 1736 and KLM flight 4805 was Gran Canaria Airport, located in the city of Las Palmas on the island of Gran Canaria. At the time this was the largest airport in the Canary Islands, and for tourists arriving from abroad it was the main port of entry. But, as it turned out, that also made it a target for those who were not satisfied with the way the islands were run.

Unlike most other North Atlantic archipelagoes, the Canary Islands were not uninhabited when Europeans and their armies first arrived in the 1400s. The islands have been home to the indigenous Guanches since the first millennium B.C., and even after 500 years of colonization some of their descendants have not forgotten the atrocities committed against their community. As the oppressive regime of dictator Francisco Franco began to unravel following his death in 1975, a pro-independence political party took advantage of the instability to launch an armed wing known as the Fuerzas Armadas Guanches, with the stated aim of winning self-government for the Canary Islands through terrorism. Although the group never directly killed anyone during its brief history, it would become most famous for setting in motion an unanticipated chain of events that went far beyond their modest terroristic ambitions.

(Google + own work)

Early on the afternoon of March 27th, the Fuerzas Aramadas Guanches detonated an improvised bomb inside a florist’s shop inside the terminal at Gran Canaria Airport, wounding the shopkeeper. As police hurried to respond to the attack, the airport received a phone call warning of a second bomb, prompting the authorities to shut down the airport and evacuate the terminal. Hundreds of people were rushed to safety as bomb detection squads moved in to scour the premises for further explosive devices.

Up in the air, the crews of the Pan Am and KLM 747s received the unwelcome news that their destination airport was closed until further notice. All traffic, they were told, would be diverted to the neighboring island of Tenerife. The Pan Am crew protested, explaining that they had enough fuel to hold over Gran Canaria for several hours, but without any clear timeline for reopening the airport, the controller could not grant their request. Everyone would have to land on Tenerife, then make their way to Gran Canaria once the coast was clear — without exception.

Los Rodeos Airport (known today as Tenerife North). (Advartis Tenerife Properties)

In 1977, the island of Tenerife was served only by a small, single-runway airport called Los Rodeos, situated on a saddle between two mountain peaks at a height of more than 2,000 feet (600 meters) above sea level. The airport was not unaccustomed to international traffic, but it usually served smaller jets operating for private low-cost and holiday-focused airlines from Europe, and generally in small numbers. It certainly was not built to accommodate Boeing 747s; it had no radar, no runway visibility measuring system, and no taxiway markings; and the centerline lights were out of service. To make matters worse, today was Sunday, and the control tower was short-staffed.

Within minutes of the bomb explosion on Gran Canaria, planes started to arrive at Los Rodeos in a never-ending stream. KLM flight 4805 was among the first to arrive, touching down at 13:38. In anticipation of further arrivals, the controllers instructed it to park down at the end of the main taxiway where it intersected runway 12. Expecting a long delay, the KLM crew allowed their 235 passengers to disembark into the terminal, where they were given special ID cards so they could be found again at the end of the layover. Meanwhile, more planes quickly piled up behind it, including Pan Am flight 1736, which arrived at 14:15. By half past 14:00, the number of planes had become so large that the queue spilled all the way across the parking apron and into parts of the main taxiway.

A map of the airport, with the locations where the 747s were parked. (ALPA)

At 14:30, just 15 minutes after the arrival of the Pan Am 747 in Los Rodeos, bomb squads completed their sweep of Gran Canaria Airport. Finding no second bomb, the airport was promptly reopened. Upon receiving the good news, the Pan Am crew requested permission to start their engines and taxi to the runway for takeoff, as several smaller planes had already managed to do — only to be told by the controller that they probably wouldn’t fit past the KLM 747 still parked at the end of the taxiway. Furthermore, they couldn’t turn around and taxi in the other direction because there wasn’t enough room to pull a 180. Having been on duty all day, and with their passengers growing restless, the Pan Am pilots were itching to leave. First Officer Bob Bragg and Flight Engineer George Warns left the airplane to check whether they could fit past the KLM 747, only to return crestfallen: having paced out the distance between the KLM’s wing and the edge of the taxiway, they found it to be four meters too narrow.

Captain Jacob van Zanten, as featured in a KLM advertisement. (KLM)

As it turned out, the crew of the KLM 747 were in an even stickier situation. In 1974, the Netherlands had introduced a law which delineated strict new flight duty time limits, and allowed pilots to be held criminally liable for exceeding them. Possible penalties ranged from loss of license to outright imprisonment. Further compounding the situation, a 1976 law changed the way duty time limits were calculated, making the process so complex that pilots could only find out their limits by calling the company to ask. Understandably, the pilots of KLM flight 4805 were worried that they might not make it back to Amsterdam that night before their duty time expired, potentially incurring severe penalties. At Los Rodeos, a KLM dispatcher informed them that if they could leave Gran Canaria by 19:00, they should stay within limits, but that they should call again later to be sure. If they couldn’t make it, they would have to cancel the flight, and KLM would have to find enough empty hotel rooms to house all 235 passengers and 14 crew on a small island at the height of the tourist season.

An actual photo of the two 747s on the ground in Tenerife on the day of the accident. (FAA)

Unfortunately, they would not be leaving Los Rodeos in a timely fashion. The process of rounding up all the KLM passengers proved to be extraordinarily difficult, ultimately running until 16:00, an hour and a half after Gran Canaria reopened. On board the Pan Am plane, agitation grew as flight attendants struggled to attend to the passengers, who had mostly embarked at Los Angeles the previous evening and had by now consumed every ounce of food and drink aboard the 747. Frustrated that they couldn’t depart until the KLM plane cleared the taxiway, the Pan Am crew expressed their displeasure with the KLM pilots, but were unable to do anything to expedite the process.

In the end, the KLM cabin crew never managed to corral all 235 passengers. Robina van Lanschot, a Dutch tour guide based on Tenerife, decided to go against protocol and made her way home from the airport without permission, a minor act of disobedience which would save her life. She could not have known that out of 249 passengers and crew who flew into Tenerife on flight 4805, she would be the only survivor.

Meanwhile, KLM Captain Jacob van Zanten made another calculated decision which would further delay their departure from Tenerife but might reduce their overall time on duty. Once all the passengers were on board, he decided to fill up with an additional 55,500 liters of fuel — enough to fly not just to Gran Canaria but all the way back to Amsterdam as well. Van Zanten expected to face long lines at the pump in Gran Canaria as diverted planes streamed back to the airport, potentially delaying their departure; therefore it made more sense to fuel up at Tenerife. Later reports would come to contradictory conclusions about whether this was necessary.

Fog rolls over a mountain on Tenerife. (TenerifePhotos)

Throughout the afternoon, the weather at Los Rodeos continuously deteriorated. Tenerife rises directly into the path of oceanic winds blowing off the Atlantic, which results in unpredictable conditions on the upwind slope of the island. This problem becomes particularly acute on the saddle between the island’s two main mountain ranges, where the terrain funnels clouds directly over Los Rodeos Airport at a high rate of speed. By the time KLM flight 4805 began refueling sometime after 16:00, clouds were already streaking over the airport, creating intermittent conditions of low visibility. Both crews were acutely aware that if the visibility dropped below the minimums for takeoff, they would be stuck on Tenerife overnight.

A map of the movements of the two planes. Note the locations of the four exits. (Wikimedia user Mtcv)

Finally, at 16:51, KLM flight 4805 finished refueling and requested clearance to start its engines, and Pan Am flight 1736 followed suit 20 seconds later. After performing final checks and running up the engines, the KLM 747 taxied out onto runway 12.

Due to the prevailing wind out of the west, both planes would have to take off from runway 30 — the same runway, but in the other direction. This meant that they would have to taxi down to the far end of the runway before turning around, a process which was rapidly increasing in complexity due to shrinking visibility and the large number of planes still parked on the various taxiways. The controller was also struggling to figure out how best to handle the massive 747s. After some initial waffling over which route to use, he eventually instructed the KLM crew to “back-taxi” up the runway in the wrong direction, then make a 180-degree turn at the far end. Four minutes later, he cleared the Pan Am 747 to follow the KLM up the runway, then turn off at the third exit, the nearest one which was not blocked by parked airplanes. Captain Grubbs expressed his displeasure with taxiing on the runway before the KLM plane had taken off, but decided not to press the point with a controller whose grasp of English appeared to be shaky.

Confusion is evident as the Pan Am crew tries to figure out where to exit the runway. (ALPA)

As both 747s crawled along the runway amid blowing fog, the controller and the two crews all lost sight of one another. With no ground radar at the airport, the controller had to rely on pilot reports to keep track of the locations of the 747s. But for the pilots, figuring out where they were and where they were going was easier said than done. Visibility oscillated between about 100 and 900 meters on a very rapid interval, and the taxiways were not marked with any sort of sign or painted number. And as if that wasn’t enough, the controller’s thick Spanish accent made it hard for the Pan Am crew to understand what he was saying. When the controller said “Leave the runway third one your left” [sic], the pilots spent the next two minutes trying to figure out whether he said “first” or “third.”

Meanwhile, the controller asked the KLM crew, “KLM four eight zero five, how many taxiways did you pass?”

“I think I just passed Charlie four now,” First Officer Meurs said, observing what appeared to be the fourth and final taxiway angling off to his left.

“Okay — at the end of the runway make one-eighty and report, ah, ready for ATC clearance,” said the controller.

Now, after several confusing exchanges, Pan Am First Officer Bragg finally asked, “Would you confirm that you want the Clipper one seven three six to turn left at the THIRD intersection?”

“The third one sir, one two three, third, third one,” the controller replied.

“That’s what we need, right?” said Captain Grubbs.

“Uno, dos, tres,” Flight Engineer Warns affirmed.

As the Pan Am crew ran through their taxi checklist, the KLM 747 arrived at the end of the runway and began its delicate 180-degree turn. Captain van Zanten had to give the maneuver his utmost concentration, because the 747 requires 42 meters to turn around, and the runway was only 46 meters wide.

An ALPA diagram explains why the 747 could not have entered the main taxiway from exit 3. (ALPA)

The Pan Am crew, still taxiing down the runway, were struggling to find the third taxiway. According to their charts, the third exit was a narrow strip angling sharply back the way they came, requiring two successive 148-degree turns to get onto the main taxiway, which paralleled the runway. Later analysis would show that a Boeing 747 could not make the second turn because the taxiways were too narrow. The Pan Am crew instinctively knew this, but the controller, who was unfamiliar with the capabilities of the 747, did not.

“That’s two,” Captain Grubbs said, spotting the second exit drifting past them through the dense fog. For the next minute, the crew struggled to figure out which exit was in fact the third one.

“Yeah, that’s the forty-five there,” said Flight Engineer Warns.

“Yeah.”

“That’s this one right here.”

“Yeah I know.”

“Next one is almost a forty-five, but huh, yeah.”

“But it goes — yeah, but it goes ahead, I think it’s gonna put us on the taxiway.”

“Yeah, just a little bit, yeah.”

“Maybe he — maybe he counts these [as] three.”

Considering that a 747 could not negotiate the third taxiway, the crew considered whether the controller started counting up to three from the position they were in when the message was sent, by which time they had already passed the first one. That would mean they should leave the runway via the fourth and final exit, which was easy for a 747 to use. But nobody knew for sure.

“I like this,” someone drily commented. It did not take the power of hindsight to see that they were in a dangerous position.

A critical excerpt from the CVR transcript reveals the moment the KLM crew almost avoided their mistake, but did not. (ALPA)

On board KLM flight 4805, the crew finished the last takeoff checklist item, and First Officer Meurs called the checklist complete. Visibility at that point was 900 meters, but another wave of dense cloud could be seen headed toward them down the runway at a speed of about six meters per second. With a minimum takeoff visibility of 300 meters, they knew they needed to start rolling before the cloud enveloped them again.

At that moment, Captain van Zanten began to move the throttle levers forward, but First Officer Meurs said, “Wait a minute, we do not have an ATC clearance.”

Van Zanten pulled the throttles back to idle again. “No, I know that,” he said. “Go ahead, ask.”

ATC clearance, it must be said, is not the same thing as takeoff clearance. An ATC clearance is a description of the route which the plane will fly after departure, but does not give an aircraft permission to actually depart.

“The KLM four eight zero five is now ready for takeoff, and uh, we are waiting for our ATC clearance,” First Officer Meurs said over the radio.

“KLM four eight zero five, you are cleared to the Papa beacon, climb to and maintain flight level niner zero, right turn after takeoff, proceed with heading zero four zero until intercepting the three two five radial from Las Palmas VOR,” the controller replied.

First Officer Meurs started to read back the clearance. “Roger sir, we are cleared to the Papa beacon, flight level nine zero…”

At that moment, Captain van Zanten pushed the throttles to takeoff power and announced, “We’re going!”

This section of the transcript approximates what was audible on the KLM CVR. (ALPA)

Apparently taken by surprise, First Officer Meurs hastily finished his transmission: “…right turn out zero four zero until intercepting the three two five. We are now (at takeoff).”

Even after countless hours of post-facto analysis, no one would be able to say for sure whether Meurs said “at takeoff” or “eh, taking off.” But whatever he meant, one thing was clear: no one understood him to mean that KLM flight 4805 was already rolling. The controller thought he meant they were at the takeoff position, but he seemed to have a moment of doubt. He said “Okay,” then paused, as though trying to formulate a directive which would cover all contingencies. After two seconds, he continued, “Standby for takeoff, I will call you.”

At that exact moment, First Officer Bragg on the Pan Am, believing that the pause indicated the end of the transmission, keyed his mic and said, “And we’re still taxiing down the runway, the Clipper one seven three six.”

In what can only be considered a horrible coincidence, the simultaneous transmissions on the same frequency caused interference which manifested in the KLM cockpit as a loud squeal, partially drowning out the words underneath. If they had been paying close attention the pilots probably could have understood what was said, but such concentration is not normally needed and in this case was not applied. The only word the KLM pilots definitely heard was the controller’s “Okay,” which they mistakenly took for confirmation that the controller understood their intentions. Thus the controller’s instruction to wait for takeoff clearance, and the Pan Am First Officer’s position report, both passed unnoticed by precisely those people who most needed to hear them. And so KLM flight 4805 accelerated down the runway toward the dark wall of fog, unaware of the danger which lurked within.

This incredible animation of the crash appeared in the TV show “Mayday”. Unlike with most animations, no disclaimer about accuracy is needed; as far as anyone knows, this is pretty much what the collision looked like. (Mayday)

Seconds later, the controller said to the Pan Am crew, “Papa Alpha one seven three six, report the runway clear.”

“Okay, we’ll report when we’re clear,” First Officer Bragg replied.

“Thank you,” said the controller.

“Let’s get the hell out of here,” Captain Grubbs said, eliciting a round of nervous chuckles.

“Yeah, he’s anxious isn’t he,” said First Officer Bragg.

“Yeah, after he held us up for an hour and a half, that bastard,” said Flight Engineer Warns, “now he’s in a rush!”

On the KLM, Flight Engineer Schreuder, having overheard the conversation between the Pan Am and the tower, said, “Is he not clear then?”

“What did you say?” asked Captain van Zanten.

“Is he not clear, that Pan American?” Shreuder repeated.

“Oh yes!” van Zanten emphatically replied. The 747 continued to accelerate, barreling directly toward the Pan Am jet still searching for the fourth exit.

“V one,” First Officer Meurs called out. It was now impossible to abort the takeoff.

At that moment, Pan Am Captain Victor Grubbs spotted the landing lights of the KLM 747 hurtling out of the fog. “There he is, look at him!” he shouted. “Goddamn, that son of a bitch is coming!” Grubbs swung the tiller hard to the left and accelerated the engines to max power, attempting to force his plane onto the grass. So abrupt was his input that an alarm sounded, warning that they were taking off in an improper configuration.

Over the blare of the warning horn and the scream of the engines, First Officer Bragg yelled, “Get off, get off, get off, get off!” But it was already too late. All Bragg could do was duck.

On the KLM, the Pan Am 747 also appeared suddenly through the fog, its white bulk looming dead ahead. “Oh shit,” Captain van Zanten exclaimed, pulling the control column back as far as it would go in a desperate attempt to lift off. The tail slammed into the runway in a shower of sparks as the fully laden 747, its engines straining, fought heroically to become airborne. At the last moment, the wheels left the runway and the plane lurched into the air, but it was too late. The time was 17:06 and 49 seconds.

This artist’s impression by Matthew Tesch in Macarthur Job’s Air Disasters: Volume 1 also captures fully the horror of the collision.

Flying in a nose high position with its tail about two meters off the ground, KLM flight 4805 slammed broadside into Pan Am flight 1736 at a speed of 260 kilometers per hour. The four engines, landing gear, and rear fuselage tore through the right side of the Pan Am jet in a dozen places simultaneously. Engines, pieces of fuselage, and burning jet fuel flew in every direction. The KLM’s number four engine sliced off the Pan Am’s fully occupied upper deck and hurled it down the runway, instantly killing everyone inside. In the main cabin, the roof opened up to reveal a sky of blazing orange.

The collision itself only lasted a split second; and then KLM flight 4805 was in the air, but falling, crippled beyond hope of recovery, back to the runway. 150 meters on, it crashed to the ground and broke into three pieces. The full load of fuel ignited, and the wreckage slid down the runway for another 300 meters, consumed in flames.

Survivors flee for their lives as Pan Am flight 1736 burns to the ground. (Bureau of Aircraft Accidents Archives)

On board the Pan Am 747, a number of people had been killed by the collision itself, but most of the 396 passengers and crew were still alive. First Officer Bragg, having felt only a mild impact, reached up to flip the fuel shutoff switches, only to find that the entire overhead panel was gone, and so was the roof it had been attached to. He turned around to discover that the first class lounge was missing, and the entire upper half of the plane, from cockpit to tailfin, had been sliced open “like a can of sardines.”

From the moment it began, the evacuation was conducted in a rush of pure desperation. The back of the economy class cabin was so choked with debris that few, if any, of those seated there managed to escape; one must presume that they burned to death as the fire ripped through the plane. Near the front, however, passengers managed to escape via several avenues. Many found their way out through a hole in the tangled metal and emerged on top of the left wing, from which they jumped to the ground. Others braved the equally long drop from a hole near the first class cabin and from the L2 door, the only emergency exit that anyone managed to open. Those who made it out described scenes that would have been at home in Dante’s Inferno: a cabin filled with fire, smoke, and debris, where row upon row of people sat frozen in their seats, utterly stunned, staring into some interminable distance. All around them, explosions burst forth in every direction; fire surged in through the shattered windows and up through the riven floor. A younger crowd might have fared better, but the average age of those on the flight was well north of 50, and many, it seemed, never even tried to escape.

The fog clears over Los Rodeos to reveal the burning Pan Am 747. (Bureau of Aircraft Accidents Archives)

In the cockpit, all three pilots survived the collision, but the stairs to the lower deck had vanished along with the lounge, and they were forced to jump down into the first class cabin. Captain Grubbs apparently fell all the way through into the cargo hold, as did a flight attendant; both managed to escape through a hole in the bottom of the plane. Other flight attendants hurried to the left wing, where they estimated that around 50 passengers were standing directly above the still-spinning engines. One woman bravely jumped first, only for everyone else to jump on top of her. Many broke limbs, or worse, during the fall. As the crew urged the survivors to run away from the burning plane, a damaged engine exploded, throwing debris in all directions and killing a flight attendant. Moments later, the fuel in the right wing ignited, and an even bigger explosion tore through the plane from end to end, sending the remains of its twisted fuselage toppling inward into a fiery void.

Pieces of KLM flight 4805 lie scattered across the runway. (The Telegraph)

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In the control tower, the dense fog obscured the controllers’ view of the wreckage and fire, but the sound of two explosions was unmistakable. With the earlier bomb blast at Gran Canaria still fresh on their minds, the controllers’ first thought was that the terrorists had struck again. The pilot of a plane parked on the apron soon reported that fire was visible through the fog, but its location was uncertain, as was its source. Only when the controllers attempted to contact the two 747s, without receiving a reply from either, did they realize that something truly horrible had occurred.

As airport firefighters hurried toward the dim glow of the flames, they came upon the fuselage of KLM flight 4805 lying on the runway, completely engulfed in a raging inferno. They immediately set about fighting the fire, but hope for survivors appeared dim. It was not until several minutes later that the fog cleared enough for them to discern another fire located about 450 meters back up the runway, which they assumed was another part of the KLM. Only upon arriving at the scene did they realize, to their immense horror, that the second fire was nothing less than another burning 747, the remains of Pan Am flight 1736. And all around its shattered remnants were strewn the survivors, crying out for help before a panorama of utmost devastation.

After the fire was extinguished, this was all that remained of Pan Am flight 1736. (PA Images)

The rescue of the survivors was chaotic but swift. The five ambulances which had reached the airport quickly filled up, and a number of people were taken to hospital in private cars. A call went out on the radio for more vehicles, but by the time people started to arrive at the airport, all the survivors had already been evacuated. There were, unfortunately, far fewer of them than those who sent out the call were expecting. Of the 248 people on board KLM flight 4805, none survived; investigators would later conclude that the impact itself was “not especially violent,” but that the fire consumed the plane so quickly that hardly anyone even managed to leave their seat, let alone open an exit door. On Pan Am flight 1736, where fire was also the primary killer, loss of life was even heavier. Initially, 327 of the 396 on board were said to have died, but this soon grew to 335 as several badly burned victims succumbed to their injuries. In the end, only 61 survived, including all the Pan Am pilots. The death toll would ultimately be pinned at 583, but in the chaotic days after the disaster, reported numbers ranged from 530 to more than 600 as authorities struggled to reconcile the vast number of missing people with the sea of remains laid out in the hangar at Los Rodeos.

A full page spread from Macarthur Job’s Air Disasters: Volume 1 features a collection of newspaper headlines from the day after the accident.

No matter the exact toll, it was apparent from the beginning that the crash was by far the worst in aviation history, easily surpassing the 346 who died in the 1974 crash of Turkish Airlines flight 981. And unlike many large accidents, where the victims frequently hail from all over the world, almost everyone who died in the Tenerife Disaster came from just two places: California, and the Netherlands. Both were united in shock and grief, as were the residents of the Canary Islands, who lost almost none of their own but were left in disbelief that such a tragedy could have occurred in their community. Statements issued by the Fuerzas Armadas Guanches, whose crude bomb had set the whole sequence of events in motion, expressed genuine horror at the scale of the accident and denied that they had intended to cause such destruction, although this was later undermined by the group’s leader, who reported from exile in Algeria that the deceased tourists should never have come to the islands during a time of “armed struggle.”

An aerial photo captures the wreckage of both aircraft. (CORR/Stringer)

As investigators from Spain, the Netherlands, and the United States converged on the island of Tenerife, they faced the aviation industry’s greatest nightmare made manifest: the fatal collision of two heavily loaded jumbo jets. They also faced a crash scene which could only be described as apocalyptic. From the smoldering wreck of the Pan Am jet, its left wing jutting out from a pile of charred metal, pieces of both planes lay strewn down the runway for several hundred meters, including some of the KLM’s engines and numerous pieces of the right side of the Pan Am, some of which were found as far away as the second wreckage site. It was there that the KLM plane lay split into several pieces, the burnt out shell of its fuselage rising ghost-like above a field of blackened debris. How could this have happened? Who was to blame? The world wanted to know, but there would be no simple answers.

Wreckage of KLM flight 4805. (Unknown author)

The chain of events which led to the crash turned out be absurdly long. Neither plane was supposed to be on Tenerife in the first place; they diverted there after the closure of Gran Canaria. The way the KLM plane was parked prevented the Pan Am jet from taxiing past, even though they were ready to leave much earlier. The efforts to find all the KLM passengers and take on more fuel delayed the departure of both planes until after the arrival of the island’s notorious fog, which restricted visibility and forced all parties to rely on radio communications to coordinate their movements. And then a long series of misunderstandings occurred, as the Pan Am crew, convinced that they would not be ordered onto a taxiway too narrow for a 747, missed their expected exit, and the KLM captain, apparently mishearing a clearance, initiated his takeoff without permission. Two simultaneous warnings that could have revealed his mistake cancelled each other out, causing him to hear neither. That was what happened, but explaining why it happened would prove to be a much more difficult and controversial endeavor.

A gendarme approaches the remains of KLM 4805. (Tony Comiti)

The question at the heart of the inquiry was why KLM Captain Jacob van Zanten took off without clearance. He was one of the most respected pilots at KLM, the head of the airline’s Boeing 747 training program, a man so revered that when the airline first heard of the crash they tried to recruit him to lead the investigation, not realizing he was dead. How could van Zanten, of all people, commit such a basic error?

The problem with van Zanten was that for the past ten years, he had almost exclusively conducted training flights, performing only the bare minimum number of real flights needed to maintain his type rating. Prior to the accident, he hadn’t flown a regular line flight for twelve weeks. Significantly, during a training flight in the simulator the instructor will play the roles of both pilot and air traffic controller, issuing clearances to the trainee on an as-needed basis. In a typical simulator session, the trainee would arrive at the runway threshold, van Zanten would announce “cleared for takeoff,” and they would go without any delay. Although he obviously knew that in real life a clearance from a controller was needed, his time as an instructor had conditioned him to the point that his basic instinct, were he to for some reason revert to it, was to take off without clearance. Investigators believed that he nearly did so before First Officer Meurs told him to “wait a minute.”

Some of the KLM’s engines came to rest in the grass alongside the runway. (PA Images)

A second factor could be seen in the ambiguity of certain communications. When Meurs contacted the controller, he appeared to ask for both takeoff clearance (“now ready for takeoff”) and ATC clearance (“and we are waiting for our ATC clearance”) in the same transmission. Both pilots, having no particular reason to believe that the Pan Am plane was still on the runway, expected to receive both clearances immediately. Instead, the controller only granted the ATC clearance. Critically, however, he used the word “takeoff” in the transmission (“right turn after takeoff”), precisely the cue which Captain van Zanten was primed to expect. Although First Officer Meurs perhaps realized that something was not right about van Zanten’s decision to initiate the takeoff, his doubt was presumably dispelled when the controller responded “Okay” to his hurried report that they were “now at takeoff/taking off.”

An aerial view of the Pan Am wreckage. (CORR/Stringer)

The controller, for his part, interpreted the situation rather differently. Having no good reason to believe that the KLM would take off without clearance, he considered Meurs’s transmission to mean that they had assumed the takeoff position. However, the message possessed sufficient ambiguity to unnerve him, and he decided to add additional clarification. When he said “Okay,” he did not intend to express approval, but was simply filling air as he gathered his thoughts and worked out an instruction that would make sense regardless of whether the plane was stationary or rolling. The Pan Am pilots, also unsettled by the situation, decided to make their position clear as well, and interpreted the pause after “Okay” as an opportunity to do so. Because they were broadcasting, not receiving, neither the Pan Am crew nor the controller were aware of the resulting interference. The KLM crew, hearing distorted voices underneath a shrill squeal, probably thought that an irrelevant transmission had slipped through from a different frequency and made no attempt to clarify its contents.

Recovery crews examine the tail section of KLM flight 4805. (The Telegraph)

Moments later, another exchange between the Pan Am crew and the controller presented a second opportunity to avoid the accident. When First Officer Bragg said “We’ll report when we’re clear,” he was effectively stating that he was still on the runway, but a number of factors contributed to the KLM crew’s failure to assimilate this critical information.

In an environment where multiple people are talking to one another, the human brain tends to search for key words that indicate a statement’s relevance to the listener. Such key words might be a person’s name or an aircraft callsign. In this case, having spent a good chunk of the afternoon coordinating with the Pan Am plane, the KLM crew would have been primed to pay attention upon hearing the callsign “Clipper.” But in his final transmission to Pan Am 1736, the controller — for the first time that day — used the NATO alphabet callsign “Papa Alpha” instead, thus failing to capture the KLM pilots’ attention. Flight Engineer Shreuder was the only one listening closely enough to discern what was said. But Bragg’s promise to “report when clear” was not so straightforward as “we are still on the runway,” and Shreuder was probably wondering, “clear of what?” Captain van Zanten’s emphatic response that the Pan Am had indeed cleared the runway was apparently sufficient to convince him that nothing was wrong.

A section of what appears to be the Pan Am’s fuselage skin lies next to the wreckage of the KLM. (Tony Comiti)

One possible factor shaping the junior crewmembers’ judgment about the location of the Pan Am was a simple unwillingness to believe that van Zanten would make such an egregious mistake as to take off while another plane was still on the runway. This steep authority gradient would have been reinforced by the fact that van Zanten had recently given Meurs his Boeing 747 type rating, and by the fact that Shreuder was apparently a proponent of a limited role for flight engineers, believing that they should stick to aircraft systems and not involve themselves in operational decision-making. The result was a crew who were receptive to the idea that, in times of uncertainty, van Zanten was probably right and they were probably wrong.

But even highly experienced pilots can and do make mistakes under pressure. And that day, the pressure on van Zanten would have been particularly acute. It cannot be emphasized enough that this had long since ceased to be a normal flight — the number of considerations and ad-hoc decisions facing the two crews was highly abnormal. The KLM crewmembers were worried about compliance with draconian duty time laws, worsening weather, and mounting delays; and van Zanten even expressed concern that his wife would worry about him if she heard about the bomb explosion on the evening news. On top of that, they had been on duty all day and were doubtlessly suffering from fatigue. All in all, there were several sources of stress pressing in upon van Zanten from all sides.

All that remained of the KLM’s center fuselage section was a burnt out shell. (Bureau of Aircraft Accidents Archives)

When a person is under stress, their perception narrows and their ability to handle multiple simultaneous tasks is impaired. From the KLM’s cockpit voice recording, it was evident that Captain van Zanten was not closely following the conversations between First Officer Meurs and air traffic control during taxi and takeoff; in fact, he had to ask repeatedly for clarification. This was a sign that he had become more narrowly focused on taxiing, which due to the fog, the lack of taxiway markings, and the extremely tight turn at the end of the runway was a task requiring careful concentration. This would have increased his reliance on certain key words to draw his attention to the contents of ATC communications, which he would otherwise tune out. And this in turn would have made him more likely to interpret these transmissions in a way that conformed with his expected scenario.

Another symptom of stress is a reversion to deeply ingrained habits at the expense of conscious decision-making. Because van Zanten had spent the last several years in a training environment, where he would always grant takeoff clearance as soon as the trainee was positioned on the runway, his ingrained expectation would have been to receive clearance immediately.

These two stress-related phenomena combined to ensure that when Captain van Zanten heard the controller use the word “takeoff,” he became completely convinced that he had been cleared to start rolling.

A man stands inside one of the surviving engines of Pan Am 1736. (The Telegraph)

In their final report, Spanish investigators placed most of the blame on van Zanten for taking off without clearance, in the process doing away with much of the nuance. The Dutch reply to the report took an equally dubious stance, casting van Zanten as completely blameless. The Dutch comments on the report included a number of extremely questionable takes, including that there was no evidence of stress, nothing wrong with the authority gradient, and no errors by the KLM crew, preferring to put the blame on a series of unfortunate misunderstandings. Their report also suggested that the controllers had been listening to a football match and that this fact had been covered up by Spain. However, contrary to popular belief, the Dutch investigators concluded that this likely had no effect on the sequence of events and chose not to place any blame on the controller or the Pan Am crew. The system itself, they said, was at fault in the crash. Although their characterization of the KLM pilots induced vigorous eye-rolling, the Dutch investigators were essentially right when they explained that the causes of the crash went way beyond Captain van Zanten’s mistaken decision to take off without clearance.

Coffins line the floor in a hangar where the wreckage and victims were brought after the crash. (Ullstein Bild)

Four systemic problems in fact set the stage for the Tenerife Disaster. First, the criminalization of procedural violations placed undue stress and fear on the KLM crew, causing them to make decisions which were suboptimal. The Dutch flight duty time laws were only part of a broader trend, spurred by pressure from a public with no understanding of aviation safety, to criminalize errors and violations that should be handled internally by an airline.

Second, cockpit hierarchies were dangerously one-sided. The prevailing culture was one of deference to the captain, in which junior crewmembers did not feel empowered to assert themselves if they thought the captain was making a mistake. In the case of the Tenerife disaster, this manifested in the form of self-doubt that prevented the First Officer and Flight Engineer from fully exploring or articulating their own concerns, laboring under a mistaken assumption that the Captain had a better understanding of the situation than they did.

Panorama of the KLM wreckage. (History of Yesterday)

Third, imprecise terminology allowed the air crews and controllers to develop conflicting mental models of the traffic situation. In addition to the use of the word “takeoff” in an ATC clearance and the unexpected use of the callsign “Papa Alpha” instead of “Clipper,” statements such as “we are now at takeoff,” “we’ll report when we’re clear,” and “okay” contributed to repeated misunderstandings that led directly to the crash. Furthermore, the controller’s thick accent and lack of knowledge of the 747’s maneuvering capabilities contributed to the Pan Am plane remaining on the runway longer than expected. The effect of so much imprecise language was that all involved parties could find ways to interpret the others’ statements in a manner which reinforced their pre-existing expectations.

And fourth, the crash would not have been possible without the severe lack of infrastructure at Los Rodeos airport. Ground radar, which detects the position of airplanes on the airport surface, had not been installed even though Los Rodeos was prone to fog. There were not enough controllers to deal with the increased traffic, and they did not have enough experience to appropriately handle Boeing 747s. The airport was not large enough to accommodate the number of diverted airplanes, forcing the controllers to use unusual taxi procedures, including the inherently risky “back-taxiing” maneuver, to get planes around the logjam. Despite frequent spells of low visibility, the airport also didn’t have any taxiway markings or a reliable means of measuring runway visibility range. All of these factors helped create a situation in which unambiguous radio communications were essential to safety.

Another closeup view of the remains of the Pan Am. (C. Mulder)

There were, of course, several links in the chain of events which could only be put down to coincidence (or, if you prefer, fate). Nobody had control over the fog, without which the accident would not have occurred. The crash also would have been avoided if the gap next to the KLM 747 was four meters wider, or if the controller and the Pan Am crew had not picked up their microphones to broadcast warnings at exactly the same time. And perhaps most cruelly, were it not for the extra weight of the newly added fuel, the KLM plane probably would have become airborne in time to clear the Pan Am. But this vulnerability to coincidences is one of the inherent dangers of an unstable complex system. The large number of interconnected decisions influencing the events at Los Rodeos created a system where no one was completely in control. Unintended consequences propagated outward from every decision, affecting the course of events in unexpected ways. Insidiously, this type of increasing complexity also increases stress, causing a narrowing of perception that further hinders an individual’s ability to understand how all aspects of the system are interconnected. It is easy to see how this could create a feedback loop which builds up to the point of catastrophic collapse of the system, which is what occurred at Tenerife.

The center wing section of the KLM. (Bureau of Aircraft Accidents Archives)

The Tenerife Disaster did catalyze several major changes in the aviation industry. The most direct changes were to radio communications, where the crash prompted increased standardization of terminology around the world. Most notably, the word takeoff is no longer used by controllers except when giving a takeoff clearance; and ATC clearance, now called “route clearance” for clarity, is usually granted before a plane even leaves the gate so as to prevent confusion. The crash also spurred the more widespread installation of taxiway markings, which were sometimes lacking at small airports in 1977 but are standard at every airport today.

The Tenerife Disaster is also frequently cited as the progenitor of crew resource management, or CRM, the now-universal set of strategies intended to ensure open communication and optimal task distribution in airline cockpits. However, the truth is not nearly so clear-cut. Tenerife was merely one of dozens of accidents which collectively led to the development of CRM, a program which coalesced out of research conducted both before and after the accident. Although the scale of the disaster did cause experts to accelerate their efforts to fix cultural problems in the cockpit, the existence of the issue and its possible solutions were already known well before KLM flight 4805 began its fateful takeoff roll. The disaster simply added another 583 deaths to the growing pile of evidence that testified against the existing system.

Aerial view of the center section of KLM 4805. (Bureau of Aircraft Accidents Archives)

The country which did the least to prevent a recurrence of the horror at Tenerife was undoubtedly Spain. Despite the fact that poor infrastructure made the accident possible, the ability to exclusively blame Captain van Zanten appeared to give Spanish authorities cover to avoid taking any action of their own. The only significant change was the construction of a new airport on the dry side of Tenerife, which was already planned before the accident. The now-infamous Los Rodeos Airport was thus largely unchanged when in 1980 a British airliner crashed, killing 146, while attempting to land there. Radar could have prevented that crash too, but despite recommendations to do so following Tenerife, none had been installed. Inadequate taxiway markings would also contribute to another runway collision in Madrid six years later, which killed 93 people. In the end, it would take 20 years for Spain to make the improvements needed to stop the bloodshed.

A memorial park, monument, and plaque in three languages were installed in honor of the victims on the 30th anniversary of the disaster. (TripAdvisor)

In some accidents it can be said that the resulting changes ensured that the victims did not die in vain. But the sheer number of deaths and the somewhat diluted response make it difficult to say the same about Tenerife. How can the loss of 583 lives in a matter of moments ever be rationalized? How can we observe so much destruction because of four meters, because of a noise, because of a word, and be at peace with the world?

As time passes, the industry and the public have largely dealt with these unsettling questions by mythologizing the disaster, lending it an aura of fatefulness, perhaps even predestination, which belies the senselessness and preventability of the errors which led to it. This has also involved the construction of Captain Jacob van Zanten as a sort of folk villain, creating an archetype of an angry, self-aggrandizing blowhard who took off out of sheer recklessness. In reality, there has never been any evidence to justify such a portrayal; while van Zanten may have overestimated his own ability, by all accounts he was not mean or vindictive. Many summaries of the accident today would have the reader believe van Zanten took off knowing he had not received clearance, even though this couldn’t be further from the truth. The villainization of a captain who made a mistake is not necessarily an indictment of our collective humanity, but as a coping mechanism it is less than ideal. Most plane crashes are the result of normal people making decisions based on incorrect information, and Tenerife was no different. How strange it is that the spectacle of mass death can so easily distract us from that fundamental truth.

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