Tenerife 1977: the Los Rodeos disaster and what it changed in the cockpit

Some accidents changed aviation so fundamentally that you can still hear their traces in every radio call today. The Tenerife air disaster of March 27, 1977 is the best known of them. At Los Rodeos Airport, two Boeing 747s collided in fog, and 583 people died. This article explains how the collision came about, what happened on the radio, how the investigations assigned responsibility and why aviation radio and crew training have worked differently ever since.

Tenerife 1977: the short answer

On March 27, 1977, two jumbos were stranded at the small Los Rodeos airport in the north of Tenerife: KLM flight 4805, a Boeing 747-200 from Amsterdam, and Pan Am flight 1736, a Boeing 747-100 from Los Angeles via New York. Both had been diverted because of a bomb attack on Gran Canaria. When they were allowed to continue in the late afternoon, both had to taxi along the only runway to the departure point. Around 5:06 p.m. local time, the KLM began its takeoff roll in dense fog – without takeoff clearance and while the Pan Am was coming toward it on the same runway.

The KLM crew saw the Pan Am only when it was too late to stop. The captain pulled the aircraft up early, the tail struck the runway, but the landing gear and the underside of the fuselage hit the Pan Am in the area of the upper deck. The KLM crashed onto the runway a few hundred meters further on and burst into flames. None of the 248 people on board survived. On the Pan Am, 335 of the 396 occupants died.

The two aircraft and their crews

Both aircraft were examples of the first jumbo generation, which had been in scheduled service since 1970. How the early versions differ is shown in our overview Boeing 747-100 to 747-8; the origins of the type are described in the history of the Boeing 747.

Feature	KLM 4805	Pan Am 1736
Type	Boeing 747-200 (747-206B)	Boeing 747-100 (747-121)
Registration / name	PH-BUF “Rijn”	N736PA “Clipper Victor”
Origin	Charter flight from Amsterdam	Charter flight from Los Angeles via New York
Occupants	248 (234 passengers, 14 crew)	396 (380 passengers, 16 crew)
Fatalities	248	335
Captain	Jacob Veldhuyzen van Zanten	Victor Grubbs

The KLM captain was no ordinary line pilot. Jacob Veldhuyzen van Zanten headed his airline’s 747 training and was among the best-known pilots at KLM. Many colleagues had earned their type rating under him, and the first officer that day had also been checked by him. This constellation plays an important role in the later analysis. The Pan Am aircraft was one of the airline’s very first jumbos; you can find more about the company’s history in the article on Pan Am.

The backstory: an attack on Gran Canaria

Both flights were actually supposed to land on Gran Canaria, today’s Gran Canaria Airport. At midday on March 27, a bomb planted by the separatist movement for the independence of the Canary Islands exploded in the terminal there. Eight people were injured. Because a second bomb had been announced, the authorities closed the airport.

Inbound aircraft were diverted to Los Rodeos, then the main airport of Tenerife and today’s Tenerife North Airport. The field had not been built for this volume of traffic: one runway, a parallel taxiway, a small apron. On top of that, it sits at about 630 meters elevation in a saddle between mountains, where low-hanging clouds quickly turn into dense fog.

A clogged airport

Because the apron was soon full, the diverted aircraft also parked on the taxiway. In the end the two jumbos stood in such a way that the Pan Am could not get past the KLM. When Gran Canaria reopened in the afternoon, the Pan Am was ready to go but had to wait: the KLM crew had decided to refuel completely on Tenerife so they could depart again faster from Gran Canaria. The refueling took a good half hour and made the aircraft considerably heavier.

Time pressure added to this. In the Netherlands, stricter rules for crew duty times had recently come into force, and exceeding them would have meant the KLM crew being stuck on Gran Canaria – with a full jumbo and hundreds of passengers needing a hotel. The Spanish investigation saw this as an important reason for the later haste.

Taxiing in fog

Because the taxiway was blocked, the tower instructed both aircraft to taxi along the runway – a procedure specialists call a backtrack. The KLM was to proceed to the end, turn 180 degrees there and wait for takeoff clearance. The Pan Am followed it and was supposed to leave the runway via the third exit to clear the way.

Here lies one of the many crux points. The exits were barely visible in the fog, and visibility temporarily dropped below 100 meters while taxiing. The Pan Am crew counted the turnoffs but did not find the third one, or considered it unsuitable: it would have required a very sharp angle that a 747 can hardly manage. A later study by the US pilots’ association concluded that the maneuver would have been practically impossible there. The Pan Am therefore kept going toward the fourth exit. How exits and holding points are named and signed today is explained in our article on taxiways and signs.

There was no ground radar at Los Rodeos that would have let the tower see the aircraft in the fog. The controllers relied entirely on the crews’ position reports. What the individual lights on runways and taxiways mean is shown in the article on runway and taxiway lighting.

The decisive seconds on the radio

At the runway end the KLM turned and stopped. Shortly afterward the captain pushed the thrust levers forward. The first officer pointed out that they did not have clearance yet. The captain pulled the power back and asked him to obtain the clearance. What followed is one of the most analyzed radio exchanges in aviation.

The tower first transmitted the route clearance – the route the aircraft is to fly after departure. The word “takeoff” did not appear in it as a permission, but to a crew that wanted to depart, the clearance sounded like the last missing piece of the puzzle. While the first officer was still reading it back, the captain began to accelerate. The first officer ended his transmission with an unclear phrase usually rendered in the transcripts as “We are now at takeoff” – roughly “We are now at the start.” Whether he said “at takeoff” or “uh, taking off” has never been established clearly.

The controller apparently understood this to mean that the KLM was waiting in takeoff position. He replied with “OK,” a brief pause, and then, roughly: “Stand by for takeoff, I will call you.”

Shortly afterward the tower asked the Pan Am to report when the runway was clear. The Pan Am acknowledged. The KLM crew could hear this exchange. The flight engineer then asked whether the Pan Am was not clear of the runway yet. The captain answered emphatically with yes and continued the takeoff. A few seconds later the Pan Am’s lights appeared in the fog.

The Pan Am crew saw the KLM’s landing lights coming toward them and tried to steer left off the runway onto the grass. The KLM had already passed decision speed, and an abort was no longer possible. The captain pulled the aircraft up, but it could no longer clear the Pan Am.

The investigations: who bore responsibility?

Investigators from Spain, the Netherlands and the US evaluated flight recorders, radio recordings and witness statements. The results differed in their weighting.

• Spain, as the state of occurrence, saw the fundamental cause in the KLM captain taking off without takeoff clearance and not aborting the takeoff even after the flight engineer’s query. As contributing factors, the investigation named the sudden fog, the radio overlap, non-standard phrases such as “OK” and “at takeoff,” the Pan Am’s missed exit and the overcrowded airport.
• The Netherlands accepted that the KLM had taken off too early but put more emphasis on a mutual misunderstanding. In their view the tower’s messages were ambiguous and the Pan Am should have left the runway earlier.

KLM ultimately accepted responsibility and paid compensation to the victims’ families. For aviation, though, the question of blame was less important than the realization that no single person had failed here. A highly experienced captain, a qualified first officer, an attentive flight engineer and a tower that wanted to act correctly – and still a chain of small deviations led to the catastrophe.

Consequence 1: stricter radio language

The most visible change concerned radiotelephony. ICAO rules were made more precise, and airlines and air traffic control services enforced them more strictly. The most important points:

Common before Tenerife	Standard since
“Takeoff” in various contexts	“Takeoff” only in the takeoff clearance or its cancellation, otherwise “departure”
“OK” or “Roger” as acknowledgment	Clearances and safety-relevant instructions are read back word for word
Clearances to aircraft on the runway without a clear lead-in	Clearances to an aircraft in takeoff position begin with “Hold position”
Local colloquial language and mixed forms	Fixed phrases, English as the common working language

When you listen to aviation radio today, this is exactly what you notice: a crew in takeoff position hears “Line up and wait,” and only the actual clearance contains “cleared for takeoff.” Anyone who gets the route clearance beforehand hears the word “departure” there. This discipline is a direct result of Los Rodeos. The basics are explained in our article on radio phraseology, and the question of the working language is covered in the post English or German on aviation radio.

Technology plays a part too. Two simultaneous transmissions cannot be separated physically, which is why the rule is to transmit only when the frequency is free. Modern radios and procedures reduce the risk, but it cannot be eliminated entirely to this day. Which frequencies at an airport serve which purpose is shown in the article Delivery, Ground, Tower, Approach, Center.

Consequence 2: crew resource management

The second big lesson concerned how people work together in the cockpit. The flight engineer had voiced his doubts, but only as a cautious question. The first officer had already corrected the captain once shortly before and did not object a second time. In a hierarchy in which the captain is also the chief instructor, it was hard to stop a takeoff forcefully.

Tenerife was not the only accident of this kind. In the late 1970s several crashes showed that crews were having accidents with fully functional aircraft because information in the cockpit did not get through or was not taken seriously. At a NASA workshop in 1979, the psychologist John Lauber coined the term cockpit resource management. United Airlines was the first airline to introduce a comprehensive training program in 1981. Later “cockpit” became “crew,” because cabin crew, dispatchers and ground staff were also included.

The basic ideas of CRM:

• Everyone may and should voice concerns – clearly, directly and, if necessary, repeatedly, regardless of rank.
• The captain decides, but not alone: He gathers information and listens before acting.
• Clear division of work: One pilot flies, the other monitors and speaks up about deviations.
• Confirm instead of assume: Anyone unsure whether a clearance has been given asks instead of assuming.

Today CRM training is mandatory for airline pilots under the major aviation authorities such as the American FAA and the European EASA. The principles have meanwhile also spread to medicine, firefighting and shipping.

Other lessons: technology and airports

Besides radio and cockpit culture, Tenerife also brought practical changes. After the disaster, Spain equipped Los Rodeos with ground radar. Worldwide, the topic of runway incursion – an aircraft or vehicle on a runway where it should not be – became a safety priority of its own. Stop bars, stop bar lighting and special warning systems are part of it.

It is often said that Tenerife South Airport was built in response to the disaster. That is not quite right: according to the operator Aena, plans for a new airport in the weather-favored south of the island had been under way since the late 1960s, because Los Rodeos was considered problematic due to its weather. Tenerife South opened in fall 1978, a good year and a half after the disaster. Since then, most of the international leisure traffic has gone through it.

How important clean communication between air traffic control and crews is was shown again 25 years later in the midair collision at Überlingen in 2002. The development of controller work as a whole is described in the history of air traffic control.

Remembering the victims

On the 30th anniversary, March 27, 2007, an international memorial was dedicated on Mesa Mota hill near La Laguna, not far from the airport. The Dutch artist Rudi van de Wint designed a spiral staircase that seems to lead into the sky. Relatives from the Netherlands and the US took part in the dedication. In Amsterdam a monument at Westgaarde cemetery commemorates the victims, and there are further memorial sites in California.

Whether and how you may listen in on aviation radio in Germany is covered in the post on the legal situation of listening to aviation radio. How to follow the radio via web stream is shown in listening to aviation radio online, and how call signs and numbers are pronounced is explained in the ICAO phonetic alphabet.

Experiencing Tenerife as a spotter today

Anyone traveling to Tenerife today usually lands in the south. The airport in the north is still worth a visit, especially given its history – and because clouds and fog still often drift across the runway there. Which spots exist on the islands and when a detour is worthwhile is summarized in our plane spotting guide to the Canary Islands. At the Mesa Mota memorial, please remember that it is a place of mourning and not a photo spot like any other.

Conclusion

The Tenerife disaster was not an accident with a single cause. An attack, an overcrowded diversion airport, fog, time pressure, a hard-to-find exit, an unclear radio call and three seconds of overlap came together. Aviation drew two lasting conclusions from it: a radio language with no room for interpretation and a cockpit in which doubts are spoken aloud. Every “Line up and wait” you hear on the scanner is a piece of this legacy.