Pushkin. Did you know that the most deadly aviation accident in history happened on the ground? You might if you're a Pushkin Plus subscriber, because the episode you're about to hear has been available to those subscribers for a year. We thought that everyone else might enjoy it and the gripping sequel in a terrifying two part special on the nineteen seventy seven ten reef air disaster. And if you're a Pushkin Plus subscriber already, thank you. I hope you're
enjoying our special episodes about the Panama Canal. And there is another exclusive cautionary tale coming very soon on the cancer beating therrac Machine. But for now, we want everyone to enjoy this terrifying but fascinating cautionary tale about the fatal consequence of a simple miscommunication. Captain Jakob Veldhausen van Zanten opens up the throttles on his Boeing seven four seven. We're going, says Captain van Zanten in Dutch. The big
KLM plane starts to trundle down the runway. On board are two hundred and thirty five passengers looking forward to a package holiday on the Canary Islands off the coast of Morocco. But their holidays have not got off to a good start because they've had to land on the wrong Canary island. They've been hanging around in the airport all afternoon waiting to be able to take off for the short hop over to the right Canary island. Finally they're on their way. The crew were keen to get going,
it's been a long day. They just want to drop off their passengers, pick up the ones who are waiting, and get back home to Amsterdam. The seven four seven gathers pace. The runway is shrouded in thick fog. You can't see far ahead. The flight engineer says something. Captain Vanzantin doesn't catch it. What was that, he asked. It's not off yet. The Pan American off the runway. The
flight engineer means. There's another seven four seven, the Pan am that's also been hanging around all afternoon waiting to make the hop from one island to the other. The KLM plane taxied down the runway first, then turned around. The Pan American plane was going to taxi part of the way down the runway behind them, then turn off onto the first available exit. But was the pan American
plane definitely off the runway now, well, says Captain Vanzanten. Yes, well is the literal translation, but the senses Yes, of course, perhaps with a hint of annoyance. Of course, the PanAm plane is off the runway. Faster and faster goes the KLM plane. It passes one hundred and fifty miles an hour, too fast now to abort the takeoff. And then through the fog a shape begins to appear on the runway ahead of them. It's the PanAm plane. Oh God damn it,
says Captain van Zanten. I'm Tim Harford, and you're listening to cautionary tales. The Canary Islands are a group of volcanoes poking up above the Atlantic Ocean. They've been ruled from Spain since the fourteen hundreds, the colonial history of slavery and sugarcane. By nineteen seventy seven, the economy has shifted to tourism, and most Canary Islanders are happy enough to be part of Spain, which is just emerging into
democracy after decades of dictatorship. Most but not all, the movement for the Independence and self determination of the Canarias Archipelago doesn't have many followers, but the followers it has are zealous. On Sunday, March twenty seventh, nineteen seventy seven, two young supporters of the movement walk into the airport on Grand Canaria with a bomb in a suitcase. The two men leave the suitcase surreptitiously outside a florist's shop in the terminal building. Then they call the airport.
Switchboard evacuate the airport lanch. It bombs.
The switchboard operator is still getting the message to airport security when the bomb goes off, glass shatters, plaster falls from the ceiling. Could have been worse. When the smoke clears, only a few people have been injured. But did the voice on the phone say they'd planted a bomb or bombs? They'd better get everyone out of the airport and conduct a thorough search. Up in the air Captain Jakob Veeldhausen van Zanten is preparing to land his seven four seven,
filled with expectant holidaymakers. Vanzanten has just turned fifty. At KLM, he's something of a celebrity. He's the head of the flight training department. He drives a yellow Ferrari Dino. The Airlines magazine adverts feature an image of Van Zanten at the cockpit controls, looking back over his shoulder, silver haired, sun tanned and confident with a gleaming white smile. At KLM. The advert promises, you'll find your trust sincerely reciprocated thanks
to that singular Dutch ability for doing things well. Van zanton hasn't been flying much these days. He's mostly been training others. Later in the week, he's due in Ireland to oversee exams for trainee pilots on the seven four seven, and in Zurich for an international meeting on aviation safety. But he knows he needs to keep his hand in with actual flights, so he's taken this one. It should be straightforward from Amsterdam to Grand Canaria, then straight back home,
hopefully in time for dinner. But then comes the message from Grand Canaria airport. Don't land. A bomb's gone off circle above us while we figure out what to do. Then we think there might be another bomb. We have to clear the airport and search. It'll take a while. Land in tena Reef wait there till we give the all clear. Ten a Reef is the next island over
from Grand Canaria, about fifty miles away. The airport is tiny, it's not really set up for seven four sevens, and Vanzantin's KLM flight isn't the only one that's been diverted to ten Reef because of the bomb. They're soon followed by another seven four seven, the Pan American, and a lot of smaller planes. They all land taxi off the runway and find a place to park as best they can. The tarmac's getting crowded and nobody knows how long the
delay is going to be. For Captain vanzanton that presents a headache. KLM has rules on how long a flight crew is allowed to be on duty inneed. Rules like that you don't want tired and overworked pilots in charge of a plane, But the rules have recently changed. Before they were more like company guidelines. The captain could use discretion if they went a bit over the limit, with a good enough excuse, they'd be forgiven. Not anymore, Pilot
overtime rules have been written into Dutch law. That's not all With the old guidelines, there'd been a simple way to calculate the maximum hours the crew could work. It out themselves. With the new law, it's more complicated. Kalm's headquarters in the Netherlands have to apply a formula to work it out. Van Zanton walks to the control tower and asks to use the phone. He calls headquarters, explains the situation and says, by when will I have to
leave Grand Canaria? If I want to be sure I can make it back to Amsterdam without exceeding the time limit, good question. Say if you can get off Tenerif in the next hour or so, he'll probably be fine. If not, HM, we'll figure it out and send you a telex In Grand Canaria. So Van Zanton doesn't yet know how much time he's got, but he does know that if he gets home a minute too late, he'll be in trouble, maybe serious trouble. The captain now has personal legal responsibility
for not exceeding the crew's maximum duty time. In the cockpit, the crew discuss what all these recent changes mean. What are the repercussions you'll face the judge.
Is it a question of fines or of prison?
Van Zanton joins the conversation.
At any rate, he says, it would mean revocation of your license for quite a while.
And that means money.
The clock ticks on, there's still no word from Grand Canaria Airport on how they're bomb sweep is going. Vanz Anton really doesn't want to be stuck on Tenerif or Grand Canaria for the night. He's got a busy, weakerhead, and besides, wherever they're going to magic up last minute hotel rooms for a planeload of stranded passengers, but he can't afford to risk his license. He starts to think about what will happen when they finally get to Grand Canaria.
How long will it take to turn the plane around for Amsterdam. He'd been planning to refuel there for the journey home, but after all the delays and diversions, the airport's bound to be manic. Maybe he should try to save time by refueling here in Tenerif. Instead, he calls the control tower and makes the order. Fifteen thousand gallons fuel trucks arrive, and wouldn't you know it, No sooner has the nozzle gone into the airplane. The news comes
through from Grand Canaria. They've finished the search, no more bombs, the airport's open again. Well, they've started refueling. Now they may as well finish. Some other smaller planes start to taxi pass and make their takeoffs for Grand Canarrea. But further down the tarmac there's one plane that can't get past Vanzanton. It's too big. It's the other seven four seven, the Pan American. Its pilot comes on the radio in Van Zanton's cockpit.
How much longer are you going to be with that refueling?
About twenty minutes, says van Zanten. The two big planes sit and wait, and as they do, the weather changes. The island of Tenerif is a twelve thousand foot volcano poking up above the ocean. The airport is on the side of the mountain two thousand feet above sea level. Sometimes clouds form quickly higher up the slopes and roll down towards the airport. That happens now. By the time the ALM plane has been fueled up, thick fog is all around. Cautionary tails will be back after the break.
In the nineteen nineties, academic researchers ask their students to imagine a hypothetical plane crash on a national border with debris strewn on both sides. They wanted to know what the students thought should happen next. Where should the survivors be buried? If they were mostly European, what if they were traveling circus performers of no fixed abode. About half the students thoughtfully engaged with the question of the most appropriate burial site. Only half said, hold on, you asked
whether survivors should be buried, You don't bury survivors. They're still alive. The researchers were trying to learn more about a curious phenomenon known as the Moses illusion. It had been discovered a few years earlier by the social scientist Thomas Erickson and the psychologist Mark Matson. How many animals of each different kind did Moses take onto the ark? The answer, of course, is that it wasn't Moses, it
was Noah. Still, when Ericson and Matson asked experimental subjects to this question, they found roughly half gave the confident answer too. It's not that these people didn't know who took the animals on the ark. When asked afterwards, they were well aware that Noah was the arc guy and Moses was the one who parted the Red Sea and brought down the Ten Commandments. So why hadn't they noticed that the question was wrong. Ericson and Matson were intrigued.
Perhaps they thought it's because Moses and Noah sounds so what are like They're both two syllable names. They picked another two syllable name and ran an experiment. How many animals did Nixon take on the arc? This time? Nobody answered to Everyone said Nixon, and they tried another old Testament name instead, one that sounds nothing like Noah. How many animals did Abraham take on the arc? Again? A
lot of people answered too. Language scientists are still investigating exactly what's going on when people make this kind of error. They run experiments scanning people's brains as they listened to different sentences that might trigger the illusion. But the basic problem seems clear enough. Sometimes the brain fills in the gaps. It hears what we expect to hear rather than what's actually said something something arc animals. How many another word
in the sentence sounds incongruous like Nixon. We pay attention and the illusion breaks. But when all the other words sound conceptually related arc animals, some dude from the Bible, we often don't notice the mistake. The researchers who asked students about burying survivors of a plane crash found something similar. They wanted to test how variations on phrasing the question would affect how many people fell for the illusion. But
they also tested a question without that conceptual link. Instead of asking about a plane crash, they asked about a bicycle accident. Where should we bury the survivors? Nobody suggested location, apparently because survivors isn't a word you usually hear. With bicycle accident, we notice straight away that something's wrong, but survivors and plane crash they often go together, so the brain might not flag up that the sentence makes no sense.
We just hear something something plane crash, bury ware, and we fill in the blanks for ourselves. At the airport in Tenerif, at long last, the final drop of the fifteen thousand gallons of fuel has been deposited in the tank of the KLM plane. An airport employee comes into the cockpit to give Captain van Zanten the good news. Is Captain van Zanten so stressed by the delay that he can't think straight. If he is, he's doing a good job of hiding it. The airport staff said that
he was kind, polite and easy going. He gets on the radio to the control tower.
Tenerif Kalem four eight zero five is ready to start.
The controller instructs him to taxi down the runway. Usually a plane will use a separate taxiway to get themselves to the right end of the runway, but that's not an option. Here in the cockpit, the KLM crew can also hear everything that's being said between the control tower and the pan And plane called Clipper Victor. They're using the same radio frequency.
Tenerif Clipper are one seven three six Clipper one seven three six ten reef, we were instructed to contact you, and also taxi down the runway.
Is that correct?
Affirmative? Taxi into the runway and leave the runway third third to your left, third third to the left.
Okay, So Captain van Zanton knows that the pan AM plane, the Clipper one seven three six, is going to taxi down the runway behind him. The clouds are coming and going. The fog thickens and easies and thickens again. At times you can barely see more than three hundred meters ahead, less than a tenth of the length of the runway from the control tower. The controller can't see the planes on the runway. He has to ask where they are, and in the fog, it's not always easy for the
pilots to be sure. How many of those exits to the left they've gone past?
Kalemn four eight zero five? How many taxiways did you pass?
I think we just passed Charlie four.
Now, okay, at the end of the runway, make it one to eighty and report ready for EIGHTC clearance.
Okay, sir.
EIGHTC clearance. That's air traffic control. Before they can depart, planes need two kinds of clearance. There's clearance for the takeoff itself, and there's ATC clearance that's for where to go after you've taken off their separate things. In the KLM cockpit, another conversation between the pan and plane and the control tower comes over the radio.
Would you confirm that you want the clipper one seven three six to turn left at the third intersection.
Third one, sir one two three third third one, Very good, Thank you, clipper one seven three six. Report leaving the runway.
Report leaving the runway. The controller is asking them to report on the radio when they're leaving the runway. Is it possible Captain van Zanten misheard and thought they were reporting they were leaving the runway. Maybe Captain Vanzanton gets to the end of the runway and turns his plane around. That isn't easy. The seven four seven is a big plane with a wide turning circle, but he manages appointing
the right way. Now in the cockpit, the first officer is going through the last of the formalities.
Buddy gave dis Armed landing lights on, checklists.
Completed, Vanzanten releases the brakes and starts to move forward.
Wait a minute, we don't have an eighty SE clearance.
No I know that, says van Zanten. Go ahead and ask hmm did Vanzanton know that or had he forgotten? Vanzanton was the head of KLM's flight training department. It had been twelve weeks since he had been in charge of an actual plane. He's more used to instructing trainees in the simulator and as the instructor, he also plays the role of the controller. He's the one who gives clearances to the trainee pilot. Has he got too accustomed
to not needing clearance from anyone else? Perhaps the first officer gets on the radio.
The KLM for eight zero or five is now ready for takeoff, and we're waiting for our eighty C clearance.
Remember, they need two types of clearance from the control tower, the eighty C clearance for their route after takeoff and the clearance for takeoff itself. The first officer has asked for both types of clearance, Explicitly we're waiting for our ATC clearance and implicitly we're ready for takeoff. In response, the controller gives him the ATC clearance, but doesn't tell him that he can take off yet.
Kalem eight seven zero five, you are clear to the PAPA beacon. Climb to and maintain flight level nine zero right turn after takeoff, proceed with heading zero four zero until intercepting these three to two five radio from Las Palmas.
By the way, what's the KLM flight's number? In that last message, the controller messed it up. He said eight seven zero five, not four eight zero five?
Did you notice? Why should you?
It doesn't matter. There's only one KLM plane here. Everyone knew what he meant. Maybe that's why our brains evolved to be susceptible to the Moses illusion. Most of the time, when we hear what we expect to hear, it's also what the person we're talking to intended to say. It's our brain helpfully filtering out a misspeak. But the Moses illusion can be deadly. Captain van Zanten was expecting to
hear that he was cleared for takeoff. He got only the air traffic control clearance, but the sentence did also contain the word takeoff and a bunch of other words that are all conceptually related. It seems that all he heard was something something cleared take off. We're going, said Captain van Zanten. He opened the throttles and the plane began to move. The calamity could still have been averted.
We'll hear why it wasn't. After the break. When Captain van Zanten said we're going, his first officer was just finishing reading back the air traffic control clearance to the controlled.
Roger, Sir, we are clear to the PAPA Beacon flight level nine zero right turnout zero for zero until intercepting the three two five, and we're now at takeoff.
Is that what he said at takeoff? That's what most of the investigators heard. Some think he said we're now taken off. But the controller seems to have heard at takeoff and understood it to mean we're in position ready for takeoff. Okay, said the controller.
Stand by for a takeoff. I will call you.
But then a tragic coincidence, both the KLM plane and the pan AM plane. Remember are using the same frequency to talk to the control tower. In the cockpit of the PanAm plane, they've also heard the KLM first officer say we're now at takeoff, and they think they'd better make sure everyone knows where They are still moving slowly along the runway trying to count the exit. It's in the fog.
And we're still taxiing down the runway.
But both transmissions happen at the same time, and that causes interference. In the KLM cockpit, all they hear.
Is step back, I will call you.
They might just have made out what was being said if they'd been listening closely. They weren't. Captain van Zanten was pushing the big plane down the runway faster and faster through the fog. But then another transmission on the radio between the controller and the PanAm plane, and this one was perfectly clear.
About a fore six, report runway clear. Okay, we'll report when we're clear.
Captain Vanzanton doesn't respond to this, nor does the first officer. The flight engineer has heard the exchange and he speaks up, Is he.
Not off yet?
Then? What was that?
It's not off yet?
The Pan American y?
Well, of course, the PanAm plane off the runway. Why is van Zanton so sure? Perhaps because he mistakenly believes he's been cleared for takeoff and he knows the controller wouldn't have given him that clearance if the runway was still blocked. But hasn't he just heard that exchange on the radio with the controller saying report when runway clear, and PanAm replying we'll report when we're clear. Maybe he wasn't listening, or maybe he half heard and it was
another Moses illusion something something runway clear. Van Zanten heard what he expected. After every accident, there are some causes you just have to file under one of those things. There isn't much of a lesson we can draw from the strange sequence of the bomb, the diversion, the refueling and the fog. But sometimes there are causes you can
learn from and they change how things are done. Nowadays, all members of a flight's crew are training to speak up respectfully but forcefully when they think the captain is making a mistake. There's room to wander if the first officer and the flight engineer felt too timid to contradict Captain Jakob Veldhausen van Zanten, the celebrity pilot whose face
beamed from the KLM adverts. Some investigators think the first officer said we're now taken off in a tone of surprise, trying to alert the controller that Van Zanten had jumped the gun. Maybe, but just a few moments earlier he had reminded van Zanten that they didn't have air traffic control clearance. That doesn't sound like he was too overawed to point out when his boss was messing something up. If he'd realized they weren't cleared for takeoff, he'd surely
have mentioned that too. What about the flight engineer. Was he genuinely reassured by van Zanton's emphatic javelle assuming the cap must have access to information he doesn't know, or did he spend the last few seconds of his life thinking should I insist he aborts the takeoff? Paddled a layers and I'll get the blame. Would he have been more insistent if it had the kind of training flight
crews get today. We'll never know. But something else changed too as a result of what happened that day on Tenerif let's pick up our copy of a Guide to Phraseology for General aviation Pilots in Europe and turn to page seven.
Listen carefully to make sure you understand what.
Is said to you.
It is easy to hear what you expect rather than what is actually said.
It is easy to hear what you expect rather than what is actually said. A perfect warning not to succumb to the Moses illusion. Pilots are now trained to be aware of the risk. But apart from asking people to listen more carefully, what can we do if we want to minimize the chance that someone might fall prey to the illusion. One approaches simply not to say the words that might lead to confusion. Turn to page seventeen of our Guide to Aviation Phraseology.
To avoid confusion. The word cleared is only used in connection with a clearance to take.
Off or land.
The words take off are only used when an aircraft is cleared for takeoff or when canceling a takeoff clearance.
Pilots and controllers are now taught to use different words in different situations. Instead of ready for takeoff, say ready for departure. Instead of after takeoff, say wants airborne. If you want to make sure nobody hears something something cleared take off, don't say the words cleared or take off at all. The KLM plane is hurtling down the fog bound runway in Tenerif, and there's the PanAm plane still
searching for the right exit. Captain van Zanton is going over one hundred and fifty miles an hour, too quickly to stop. But is he going quickly enough to get into the air. He yanks on the controls. If the nose points up, the tail slams down into the runway. It leaves a streak of metal and the tarmac twenty meters long. At last, the plane starts to lift off the runway, but it struggles. If only it didn't have
those extra fifteen thousand gallons of fuel on board. The nose clears the top of the PanAm plane, but the rest isn't going to make it.
Oh God, damn it.
The bottom of the plane clips the top of the other. It crashes back onto the tarmac and careens along the runway. The collision ruptures the fuel tanks. The fifteen thousand gallons explode into a fireball hot enough to melt the fuselage. Flames rise high in the air. Everyone on board is killed instantly. Forty four of the bodies are so badly burned they can never be identified. Among them, Captain Jakob Veldhausen van Zanten, a few hundred meters back from the fireball,
stands what's left of the PanAm plane. Some of its passengers have also been killed already. Others are still alive, but many of these survivors will end up being buried. They don't have long before fire will begin to consume their plane. We'll hear what decides who makes it out and who doesn't in the next episode of Cautionary Tales. An important source for this episode was Collision on tenna Reef for How and Why of the World's worst aviation
disaster by John Ziamec and Caroline Hopkins. For a full list of our sources, see the show notes at Timharford dot com. Cautionary Tales is written by me Tim Harford with Andrew Wright. It's produced by Alice Fines with support from Marilyn Rust. The sound design and original music is the work of Pascal Wise. Sarah Nix edited the scripts. It features the voice talents of Ben Crowe, Melanie Guttridge,
Stella Harford, Jemmy Saunders and Rufus Wright. The show also wouldn't have been possible without the work of Jacob Weisberg, Ryan Dilly, Greta Cohne, Betal Mollard, John Schnaz, Eric's handler, Carrie Brody, and Christina Sullivan. Details is a production of Pushkin Industries. It's recorded at Wardour Studios in London by
Tom Berry. If you like the show, please remember to share, rate and review, tell your friends and if you want to hear the show ad free, sign up for Pushkin Plus on the show page in Apple Podcasts or at pushkin dot fm, slash plus