The crash of two Boeing 747s at Los Rodeos Airport (now Tenerife North Airport) on March 27th,
1977 was the deadliest in aviation history. The planes collided on the runway after the departing
KLM aircraft started its take-off run before the taxiing Pan Am aircraft had vacated the strip. 583
lives were lost. But… How did this tragedy come to pass? And what has changed in aviation since then?
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The crash involved two heavily loaded passenger 747s colliding on the runway,
operated by KLM and Pan American World Airways. Both aircraft had diverted to the airport that day
and were preparing to depart to continue their journeys to Gran Canaria.
The KLM aircraft was a 747-200, registration PH-BUF. It entered service with KLM in October
1971, just six years prior. That day, it was operating KLM Flight 4805 from
Amsterdam Schiphol to Gran Canaria. It was flown by Captain Jacob Veldhuyzen
van Zanten and First Officer Klaas Meurs. Also on board was Flight Engineer Willem Schreuder.
It carried 14 crew and 234 passengers on departure from Tenerife.
The Pan Am aircraft was a 747-100, with registration N736PA,
and named Clipper Victor. It entered service in January 1970 and was operating Pan Am Flight 1736
from Los Angeles to New York JFK and on to Gran Canaria.
It was piloted by Captain Victor Grubbs and First Officer Robert Bragg,
with Flight Engineer George Warns also in the cockpit. It carried 16 crew and 380 passengers.
There were several unfortunate contributing factors that day.
The first was the fact that neither aircraft was originally intended to be at that airport. Along
with several other planes, they had both diverted from nearby Gran Canaria Las Palmas Airport
due to a terrorist alert. A bomb had exploded in the terminal,
injuring eight people. The Canary Islands Independence Movements claimed the attack,
and there was a warning about a second bomb at the site.
All incoming aircraft were diverted to the much smaller Los Rodeos Airport. The
airport only had one runway, one parallel taxiway, and limited aircraft parking.
The diverted aircraft were forced to park on the main taxiway,
meaning departing aircraft had to taxi into position using the runway.
A second contributing factor was the weather. While the diversions
had been due to the bombing and not environmental conditions,
the weather in Tenerife was not ideal, especially for the increased aircraft traffic.
Los Rodeos Airport sits at an altitude of 610 meters (or about 2,000 feet) and
is frequently subject to clouds and foggy conditions. This was the case on the day of
the accident, with drifting clouds quickly reducing the visibility at the airport.
The crash report estimated that the Pan Am aircraft had less than 100 meters of visibility
on the runway. The KLM aircraft, at the other end of the runway, had good visibility when it
started its take-off roll, but clouds were moving towards it down the runway. These
conditions affected the aircraft’s visibility of each other, and also the tower’s view.
Both 747s were departing the airport when the collision occurred. By that time,
Gran Canaria airport had reopened, and they were set to continue their flights. The Pan
Am flight was ready to depart first as its passengers had not left the aircraft.
But Pan Am was blocked from entering the runway by the KLM flight and had to wait
for it to be ready. The flight engineer and first officer actually left the aircraft to
measure the clearance but determined they could not pass, so would have to wait.
This was further delayed by the KLM flight fully refueling before departure
(a fateful decision) and then having to wait for missing passengers who had deplaned.
At 4:56 PM, the tower gave the KLM aircraft clearance to taxi the length of the runway
and line up for takeoff at the other end. And at 5:02 PM, it gave the Pan Am aircraft
instructions to start its taxi along the runway, and to vacate at the third exit. So far, nothing
unusual for a busy airport area that was having to use the runway for taxi and flight departures.
The Pan Am aircraft did not, however, take the third
exit. This would have required two 148 degree turns to reach the main taxiway.
It is not clear why this was instructed, but with reduced visibility and unclear instructions,
Pan Am continued to taxi along the runway towards the fourth exit.
The real problems began when the tower gave KLM 4805 departure instructions.
Four minutes after the tower instructed the Pan Am flight to taxi, at 5:06 PM,
the tower gave departure and routing instructions but not takeoff clearance. KLM 4805 read this back
and finished with “… we are now at takeoff.” The captain released the brakes and applied power.
The response from the tower (which could not see the runway end due to the cloud) was,
“stand by for takeoff. I will call you.”
The KLM crew likely missed part of this communication due to radio interference.
At the same time, the Pan Am crew radioed, “We’re still taxiing down the runway,
Clipper 1736.” The overlap led to the KLM crew hearing neither critical message.
And again, due to the fog, the two aircraft could not see each other.
There was one final opportunity to abort the takeoff: The tower asked the Pan Am
aircraft to report when it was clear of the runway. This was heard in the KLM cockpit,
and the flight engineer twice asked the pilots if the other aircraft was clear. It was not acted on.
The KLM aircraft accelerated down the runway towards the Pan Am flight,
which was approaching the fourth taxiway. Based on the cockpit recording,
it was the Pan Am captain who first saw the aircraft approaching.
He applied full throttle and attempted to turn the aircraft left towards the grass.
When the KLM crew saw the other aircraft, they attempted to rotate early, as it was already
too late to stop the roll. The Boeing 747 left the ground but struck the central upper fuselage
of the Pan Am aircraft. With its full load of fuel, the resulting fire was devastating.
583 people died in the collision. All passengers and crew on the KLM aircraft were killed.
There were 61 survivors on the Pan Am aircraft, including the flight deck crew.
Following the incident, the Spanish Civil Aviation Accident and
Incident Investigation Commission (CIAIAC) opened an investigation.
It determined that the main cause of the accident was the KLM aircraft taking off without clearance.
Investigators agreed that the captain believed he had clearance,
and that the tower thought the aircraft was still waiting at the end of the runway.
The report described several other contributing factors, including:
The cloud, fog, and variable visibility conditions...
Radio interference and difficulty hearing two simultaneous messages...
Use of non-standard phrases by both the KLM crew and air traffic control...
The increased volume of aircraft at the airport... The Pan Am aircraft not leaving the runway
at the third taxiway as instructed... There was also discussion about the interaction
between the KLM crew. Captain Veldhuyzen van Zanten was a senior figure at KLM and the head
of pilot training. Investigators suggested that this could have impacted any intervention the crew
could have made. They questioned the Captain’s take-off decision but were not insistent.
Dutch authorities pushed against the KLM Captain taking full responsibility.
They argued that the other factors were highly relevant (particularly, the missed communications
and the Pan Am aircraft continuing beyond where it was instructed to leave the runway).
Though KLM did not accept responsibility, it did pay compensation to the victims’ families.
In the wake of the accident and subsequent investigation,
there were many safety changes and recommendations made. The most significant was strengthening
the regulations for standard radio communications and English language,
as well as requirements for readback of instructions received. Phrases including
“We’re at take-off” and the ATC response of “OK” were considered contributing factors to the crash.
There were also changes to crew training and management. Crew were now encouraged
to work together, regardless of seniority, and to challenge decisions when appropriate.
There were changes at the airport in Tenerife too. Ground radar was soon installed at Los
Rodeos Airport, and a second, lower altitude airport opened at Tenerife South (TFS).
The events of March 27, 1977, at Los Rodeos Airport in Tenerife were no doubt tragic,
but aviation has made many changes to avoid such incidents in the future. Did you know
about the Tenerife airport disaster? What do you think of the changes instituted afterward?
Feel free to share your thoughts in the comments.