The crash of two Boeing 747s at Los Rodeos Airport (now Tenerife North Airport) in 1977 was the deadliest in history. They 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. The crash was primarily due to pilot error and departure without clearance, but there were several contributing factors.
The two 747s involved
The crash involved two heavily loaded passenger 747s colliding on the runway. The 747s involved were operated by KLM and Pan American World Airways (Pan Am). 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, and named Rihn (meaning Rhine). It had entered service with KLM in October 1971. That day, it was operating KLM Flight 4805 from Amersterdam 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. That day, it 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.
March 27th, 1977 – diversions to Tenerefire
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 aircraft, 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 Rodeia 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. The diversions had been due to the bombing, not weather conditions. But the weather was not ideal in Tenerife, especially for the increased aircraft traffic.
Los Rodeos Airport is at an altitude of 610 meters and frequently suffers from cloud and fog conditions. This was the case on the day of the accident, with drifting cloud 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 run, 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.
Collision on takeoff
Both 747s were departing the airport when the collision occurred. Gran Canaria airport had re-opened, and they were both continuing their flights. The Pan Am flight was ready to depart first as its passengers had not left the aircraft. The KLM passengers disembarked.
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.
At 16:56, 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 17:02, 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. You can see a full transcript of the conversations between the two aircraft and the tower in this FAA animation:
At 17:06, 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 then followed one more chance for the takeoff to be aborted. The next communication from 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 aircraft, 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 aircraft. The aircraft left the ground but struck the central upper fuselage of the Pan Am aircraft. The right engine detached and hit the upper deck. Fuel leaks caused a fire, which claimed most lives.
With the low airspeed and loss or damage to its engines, the KLM aircraft stalled and hit the runway around 150 meters beyond the Pan Am aircraft. With its full load of fuel, the resulting fire was devasting.
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. Both aircraft were completed destroyed.
Passengers and crew from the Pan Am aircraft escaped onto the intact left wing and jumped to the ground. Fire and accumulated metal wreckage prevented escape from the center and rear sections of the cabin. All passengers on the upper deck were killed. Emergency services took survivors to Santa Cruz hospital.
The airport remained closed for two days. On March 29th, a US Air Force C-130 aircraft landed and transported many casualties to Las Palmas for further treatment. The Spanish Army assisted with clearance and runway repairs at the airport, and it reopened fully on April 3rd.
Investigation and causes
The Spanish Civil Aviation Accident and Incident Investigation Commission (CIAIAC) investigated the crashes.
The investigation 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 (although it was not as certain for the first officer) and that the tower thought the aircraft was still waiting at the end of the runway.
The crew’s anxiety over a delayed return to Amsterdam was a significant factor in the early departure. KLM had recently introduced new duty time regulations, and the cockpit recording showed how the crew were concerned about this. It was also a contributor to the fateful decision to fully refuel the aircraft in Tenerfife to speed its stopover at Gran Canaria. This increased its takeoff weight and, of course, led to the devasting fire.
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 having left the runway at the third taxiway.
- 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 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). KLM did accept responsibility, however, and it paid compensation to the victims’ families.
Changes made to aircraft communication
There were many safety changes and recommendations made following the investigation. The most significant was strengthening the regulations for standard radio communications and English language, and 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.
Changes were also brought in for crew training and management. Crew began to be encouraged to work together, regardless of seniority, and to challenge decisions. However, this continues to be a problem, with other accidents (including Korean Air 801 in 1997) having similar contributing factors.
There were also airport changes in Tenerife. Ground radar was soon installed at Los Rodeos Airport, and a second, lower altitude airport opened at Tenerife South (TFS).
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