Forty years ago last March what remains the greatest disaster in aviation history occurred at Tenerife in the Canary Islands.  Human error was the primary cause.


583 people were killed (61 survived, or a 90% fatality rate) when two Boeing 747s – one belonging to KLM, trying to take off and the other to Pan Am, taxiing – collided on Los Rodeos Airport’s single runway. Pan Am flight 1736 had originated in Los Angeles and KLM Royal Dutch Airlines flight 4805 in Amsterdam.

As usual with serious aviation or industrial accidents, several things went wrong in a sort of Faustian cascade that ultimately led to the disaster:  But there was one overwhelming primary cause, which we’ll get to.

The lesser but still highly material problems:

  • Thanks to a separatist bomb being set off in the terminal at the far larger Las Palmas Airport on Gran Canaria, Tenerife was pressed into service to accept diverted planes and the small airport was seriously overcrowded, its aprons and taxiways full of parked aircraft.  This meant the runway itself  had to do double duty as a taxiway.
  • A dense fog descended shortly before the accident, limiting visibility to 1,000 feet or so at best.
  • Air traffic control (ATC) terminology and phraseology had not yet been fully standardized.
  • And “crew resource management” training did not yet exist.

A brief word on the last point, not self-explanatory to the uninitiated.  Before Tenerife–and the following  year’s crash of a United DC-8 holding on approach into Portland, Oregon which ran out of fuel while the crew was trouble-shooting balky landing gear–this concept was unknown.  Cockpits were authoritarian environments where the captain’s word and judgment ruled.  It was out of bounds for a co-pilot or first officer to so much as point out contrary instrument readings, much less ask the pilot if he were certain in his judgment or, God forbid, disagree.  

The story of the United/Portland crash is instructive on how “crew resource management” was introduced into aviation.

United 173 left Denver about 2:47 pm with 189 people on board; the estimated flying time was 2 hours and 26 minutes.  The total amount of fuel required was 31,900 pounds, and 46.700 pounds were on board the DC-8 at Denver gate departure.

The cockpit crew was highly experienced: Captain Malburn McBroom (52), had been with United for 27 years and was one of the most senior pilots at the airline; First Officer Roderick Beebe (45) (13 years at United) and Flight Engineer Forrest Mendenhall (41) (11 years).

As the landing gear was being lowered on approach into Portland, there was a strange vibration and the aircraft yawed; the indicator light for “gear locked” also failed to come on. The crew requested a holding pattern to diagnose the problem.  With flaps down at 15° and the gear lowered, fuel consumption rose to abnormal levels during the hour-long holding maneuver. Meanwhile, none of the three in the cockpit monitored fuel levels.  As they finally entered their final approach for an emergency landing at Portland International, they lost the ##1 and 2 engines to flameout and, flying low and slow, crashed into a heavily wooded suburban area six nautical miles short of the airport; there was no fire. Mendenhall died but Beebe and McBroom survived, albeit with serious injuries, as did the majority of the passengers (8 killed, 21 seriously injured).

The NTSB’s determination was that the primary cause was McBroom’s failure to properly monitor the fuel level and failure to respond to the other cockpit officers’ advisories about critically low fuel, because he was preoccupied with the landing gear malfunction and preparing for an emergency landing. The first officer and engineer was also criticized for not “successfully communicat[ing] their concern to the captain.”

Here are some excerpts from the cockpit voice recorder (emphasis mine).  If you could write a more compelling real-world-dialogue study in miscommunication, you may be the next Elmore Leonard.

About 1750 [25 minutes before the crash], the captain asked the flight engineer to “Give us a current card on weight. Figure about another fifteen minutes [before landing].” The first officer responded, “Fifteen minutes?” To which the captain replied, “Yeah, give us three or four thousand pounds on top of zero fuel weight.” The flight engineer then said, “Not enough. Fifteen minutes is gonna — really run us low on fuel here.”

At 1806 [9 minutes before the crash], the first officer told the captain, “We’re going to lose an engine….” The captain replied, “Why?” At 1806.49, the first officer again stated, “We’re losing an engine.” Again the captain asked, “Why?” The first officer responded, “Fuel.

1808:42 [six minutes before the crash]- Captain: “You gotta keep ’em [the engines] running….”

Flight Engineer: “Yes, sir.”

1808:45 – First Officer: “Get this…on the ground.”

Flight Engineer: “Yeah. It’s showing not very much more fuel.”

At 1813:38, the captain said, “They’re all [four engines] going. We can’t make Troutdale.” [a small airport on the final approach to PDX] The first officer said, “We can’t make anything.”

Back to “CRM:”  Its primary goal is to develop situational and self-awareness, flexibility, adaptability, and communication.  It:

aims to foster a climate or culture where authority may be respectfully questioned. It recognizes that a discrepancy between what is happening and what should be happening is often the first indicator that an error is occurring. This is a delicate subject for many organizations, especially ones with traditional hierarchies,

The human factor I mentioned back at Tenerife?  The human in question was the KLM captain, Jacob Veldhuzen van Zanten, described as “a seasoned pilot so popular and photogenic” that KLM featured him in its promotional campaigns, he was KLM’s most experienced pilot.  In fact, when news of the disaster reached KLM headquarters, they tried to reach van Zanten to get him to the scene to investigate.

Both 747 captains were eager to get going and off Tenerife, including Capt. Victor Grubbs at the helm of the Pan Am jumbo, who had already flown for eight hours (the flight had originated in LA and he took over at a New York stopover) but more importantly van Zanten; he and his crew were running out of time in terms of their permitted period of duty and he was in a hurry to get to his destination.  Also, as separately reported, “Van Zanten knew that every moment the fog got worse made it that much likelier that the Tenerife tower would shut down the airport. He saw that his window of opportunity to get out of Tenerife before an overnight stay was closing. It was now or never–time to go.”

He had taxied to the start of the runway and turned the plane 180 degrees to prepare for takeoff as Grubbs’ Pan Am 747  was also on the runway looking in the dense fog for a taxiway turnoff (as instructed by the control tower).

Unfamiliar with the airport, Grubbs missed the first turnoff and was headed for a second when the fateful exchange of messages came between the tower and KLM. Here’s the full story, and forgive the comprehensiveness but it’s essential, I believe, to understanding who did what when and why.:

KLM taxis ahead and onto the runway, with the Pan Am Clipper ambling several hundred yards behind.  Captain Van Zanten will steer to the end, turn around, then hold in position until authorized for takeoff.  Pan Am’s instructions are to turn clear along a left-side taxiway to allow the other plane’s departure.  Once safely off the runway, they will report so to the tower.


Unable to differentiate the taxiways in the low visibility, the Pan Am pilots miss their assigned turnoff.  Continuing to the next one is no big problem, but now they’re on the runway for several additional seconds.


At the same time, having wheeled into position at the end, Van Zanten comes to a stop.  His first officer, Klaas Meurs, takes the radio and receives the ATC route clearance.  This is not a takeoff clearance, but rather a procedure outlining turns, altitudes, and frequencies for use once airborne.  Normally it is received well prior to an aircraft taking the runway, but the pilots have been too busy with checklists and taxi instructions until now.  They are tired, annoyed, and anxious to get going.  The irritability in the pilots’ voices, Van Zanten’s in particular, has been duly noted by the control tower and other pilots.  First officer Meurs, sitting to Van Zanten’s right, reads back the altitudes, headings and fixes, then finishes off with an unusual, somewhat hesitant phrase, backdropped by the sound of accelerating engines.  “We are now, uh, at takeoff.”


Van Zanten releases the brakes.  “We gaan,” he is heard saying on the cockpit voice recorder.  “Let’s go.”


“At takeoff” is not standard phraseology among pilots.  But it’s explicit enough to grab the attention of the Pan Am crew and the control tower.  It’s hard for either party to believe KLM is actually moving, but both reach for their microphones to make sure.


“And we’re still taxiing down the runway,” relays Bob Bragg, the Pan Am first officer.


At the same instant, the tower radios a message to KLM.  “Okay,” says the controller.  “Standby for takeoff.  I will call you.”


Ten seconds later there is one final exchange, clearly and maddeningly audible on the post-crash tapes.  “Report when runway clear,” the tower says to Pan Am.


“We’ll report when we’re clear,” acknowledges Bob Bragg.


Focused on the takeoff, Van Zanten and his first officer apparently miss this.  But the second officer, sitting behind them, does not.  Alarmed, with their plane now racing forward at a hundred knots, he leans forward.  “Is he not clear?” he asks.  “That Pan American?”


“Oh, yes,” Van Zanten answers emphatically.


In the Pan Am cockpit, nose-to-nose with the still unseen, rapidly approaching interloper, there’s a growing sense that something isn’t right.  “Let’s get the fuck out of here,” Captain Victor Grubbs says nervously.


A few moments later, the lights of the KLM 747 emerge out of the grayness, dead ahead, 2,000 feet away and closing fast.


“There he is!” cries Grubbs, shoving the thrust levers to full power.  “Look at him!  Goddam, that son of a bitch is coming!”  He yanks the plane’s steering tiller, turning left as hard as he can, toward the grass at the edge of the runway.


“Get off! Get off! Get off!” shouts Bob Bragg. [Bob Bragg died of natural causes in February of this year.–Bruce]

When van Zanten saw the Pan Am Clipper, he used the only option he had at that point–too late to stop–and tried to take off at suboptimal speed.  It didn’t work.  Although the nose of his 747 cleared the Pan Am, the tail had been dragging along the runway for a few hundred yards and the rear of the KLM took the top off all but the front of the Pan Am plane; indeed, the 61 survivors at Tenerife, including the cockpit crew, were all in the front of the Pan Am.  The KLM plane cartwheeled and exploded, freshly refueled, with no survivors at all.

Van Zanten was as fine and as experienced a pilot as KLM, or any of the world’s airlines, had at the time.  His skill, training, credentials, and expertise were impeccable, and he had the years and years of flying time that are required to achieve the highest level of excellence.  But he still was the proximate cause of the greatest aviation disaster of all time.  Process was ignored, subordinates were ignored, checklists were ignored, contrary information was ignored. He knew, implacably, best.

So endeth today’s parable.



The Tenerife story is my distilled compendium of several sources, including:

NTSB Investigation into United Flight 173,

Wikipedia (inevitably) on Flight 173:

Crew resource management:

The Tenerife disaster:

The Telegraph, “The true story behind the deadliest air disaster of all time” (by Patrick Smith, author and pilot: March 27, 2017):

Wired, “March 27, 1977: The worst air disaster ever” (March 26, 2009):

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