Tenerife Airport Disaster (1977): What Happened & Its Safety Legacy
On 27 March 1977, in fog at Tenerife’s Los Rodeos airport, a KLM Boeing 747 (registration PH-BUF, callsign KLM 4805) began its take-off roll without an air-traffic take-off clearance and struck a Pan Am Boeing 747 (N736PA, Clipper 1736) that was still on the same runway. 583 people died — the deadliest accident in aviation history, per the Flight Safety Foundation. This is what happened, why, and the reforms it left behind.
In brief
- Two Boeing 747s collided on the runway at Los Rodeos (now Tenerife North); 583 of the 644 people aboard the two aircraft died, and 61 survived — all from the Pan Am jet.
- The official Spanish investigation, with Dutch and U.S. participation, found the probable cause to be the KLM aircraft taking off without a take-off clearance, in the mistaken conviction it had been given.
- Contributing factors included fog, a runway congested by diverted traffic, non-standard radio phraseology, and two radio transmissions blocking each other at the critical moment.
- The accident reshaped aviation safety: standard ICAO phraseology, strict readback/clearance discipline, and Crew Resource Management all trace much of their modern form to Tenerife.
What happened
A bomb explosion at Las Palmas (Gran Canaria) around midday closed that airport, and many flights — among them KLM 4805 from Amsterdam (Boeing 747-206B, PH-BUF) and Pan Am Clipper 1736 from Los Angeles via New York (Boeing 747-121, N736PA) — were diverted to the smaller Los Rodeos airport on Tenerife, where they parked on a congested apron. When Las Palmas reopened, the congestion meant departing aircraft had to taxi (backtrack) along the single active runway and turn at the end to depart.
KLM 4805 was cleared to backtrack runway 12 and turn; about three minutes later Pan Am 1736 was cleared to follow and to leave the runway at the third taxiway and report when clear. KLM reported ready and received a departure routing. Per the cockpit-voice-recorder transcript recorded by the Aviation Safety Network, the KLM crew read back the routing and added “We are now at take-off,” then released brakes and began the take-off roll while the Pan Am 747 was still on the runway ahead.
The tower — aware Pan Am was still on the runway — replied “OK … stand by for take-off, I will call you.” But that transmission coincided with Pan Am’s own call that it was “still taxiing down the runway.” The two simultaneous transmissions overlapped into a heterodyne squeal, so the critical warning was not heard clearly in the KLM cockpit. Seconds before impact the KLM crew saw the Pan Am jet and tried to climb away; its fuselage struck and sheared off the Pan Am aircraft’s upper deck and tail before crashing back onto the runway.
Conditions: fog and a single runway
Los Rodeos sits at about 2,000 ft (610 m), where hill fog can cut visibility quickly. The take-off began in low daylight visibility in which the tower and the two crews could not see one another on the runway. With taxiways congested by the diverted traffic, both aircraft were using the same strip of pavement — one departing, one backtracking — and the Pan Am crew, instructed to vacate at the third taxiway, had not identified and reached that exit when KLM began its roll.
The human toll
All 248 occupants of the KLM 747 were killed. Of the 396 aboard the Pan Am 747, 335 died or later died of their injuries and 61 survived. The combined 583 fatalities make Tenerife the deadliest accident in aviation history — the Flight Safety Foundation records it as “aviation’s worst disaster,” with 583 killed and 61 survivors. The figure refers to a single accident, not wartime or ground events.
Official cause & contributing factors
The official investigation is complete. As recorded by the Aviation Safety Network from the Spanish report, the probable cause was that the KLM aircraft took off without a take-off clearance, in the absolute conviction that the clearance had been obtained — a misunderstanding that arose from the mutual use of everyday terminology open to misinterpretation. In combination with other coinciding circumstances, the premature take-off led to the collision because the Pan Am aircraft was still on the runway, having missed its intersection.
SKYbrary summarises that the investigation attributed the accident primarily to the actions and inactions of the KLM captain — the operator’s chief flying instructor — with non-standard phraseology, the fog and the blocked radio transmissions among the coinciding factors. A separate ALPA / Flight Safety Foundation human-factors analysis emphasised time pressure (the “hurry-up syndrome”): the Foundation describes the accident as having “involved time pressure, which contributed to a disregard or a failure to recognize safety hazards by the flight crews.” That is contributory analysis rather than the formal probable cause, and the Dutch review placed more weight on mutual misunderstanding and system factors. (In keeping with our editorial policy, no flight-crew or controllers are named.)
Safety legacy: phraseology & clearance discipline
Tenerife reshaped how pilots and controllers talk. Standard ICAO radiotelephony phraseology was reinforced worldwide, and the word “take-off” is now reserved strictly for issuing or cancelling a take-off clearance; in every other context controllers and crews say “departure” or “airborne,” so the word can never be mistaken for a clearance. Readback and “hearback” discipline was strengthened too: a take-off clearance and its readback must be unambiguous, and an incorrect readback must be caught and corrected by the controller.
Procedures now clearly separate “line up and wait” from an actual take-off clearance, and conditional phrasing is restricted to line-up rather than departure. A blocked or garbled frequency — exactly what masked the warning at Tenerife — is treated as a warning sign in its own right: controllers intervene to clarify, and crews are trained to query rather than assume a clearance.
Safety legacy: CRM & runway-incursion defenses
Tenerife is a foundational case for Crew Resource Management. The steep cockpit authority gradient — the captain was the airline’s chief flying instructor — and the decision to proceed without a confirmed clearance pushed the industry toward training that empowers junior crew members to voice and escalate doubts. The Flight Safety Foundation’s analysis ties the accident to a recognised pattern in which crew coordination is used to counter time pressure and high workload during taxi and pre-take-off. The accident is also catalogued as a runway-incursion archetype, underpinning the clearance-confirmation discipline, controller vigilance and unambiguous hold-short procedures still taught today.
Almost every time you fly today, three Tenerife-born defences are working quietly in the background: the controller reserves the word “take-off” for a clearance, your crew reads it back so any error is caught, and Crew Resource Management means the most junior person on the flight deck is expected to speak up. A single fog-bound misunderstanding rewired how the whole industry communicates. For how rare such events now are, see is flying safe?
Tenerife Disaster — Frequently Asked Questions
Common search queries answered with current status, FIR codes, and source citations.
- How many people died in the Tenerife disaster?
- 583 of the 644 people aboard the two Boeing 747s were killed — all 248 on the KLM aircraft and 335 of the 396 on the Pan Am aircraft. 61 people survived, all from the Pan Am jet. It remains the deadliest accident in aviation history.
- What caused the Tenerife airport disaster?
- The official investigation found the probable cause was the KLM aircraft beginning its take-off without an air-traffic take-off clearance, in the mistaken conviction that clearance had been given. Fog, a runway congested by diverted traffic, non-standard radio phraseology, and two radio transmissions blocking each other were contributing factors.
- Were there any survivors of the Tenerife disaster?
- Yes — 61 people survived, all of them from the Pan Am Boeing 747 (registration N736PA). Everyone aboard the KLM aircraft was killed. The combined death toll of 583 makes it the deadliest accident in aviation history.
- Why were two Boeing 747s on the same runway?
- A bomb at nearby Las Palmas airport had closed it, diverting many aircraft to the smaller Los Rodeos, whose taxiways were too congested to use normally. Departing aircraft had to taxi along the single active runway, so a taxiing 747 and a departing 747 ended up on the same pavement in fog.
- What safety changes resulted from the Tenerife disaster?
- It drove standardised ICAO radio phraseology (the word "take-off" reserved only for issuing or cancelling a clearance), stricter readback and hearback discipline, the clear separation of "line up and wait" from a take-off clearance, and the rise of Crew Resource Management training that empowers crew members to question unsafe decisions.
- Where and when did the Tenerife disaster happen?
- At Los Rodeos airport (now Tenerife North) in the Canary Islands, Spain, on 27 March 1977. The two Boeing 747s collided on the airport’s single runway in hill fog at approximately 17:06 UTC.
Related Pages
Sources
- SKYbrary — “B742 / B741, Tenerife Canary Islands Spain, 1977” (accident summary), with “Takeoff without ATC Clearance” and “Line Up” articles and the official final report (bookshelf)
- Aviation Safety Network — accident records for KLM PH-BUF (wikibase 329178) and Pan Am N736PA (19770327-0), and the KLM 4805 / Pan Am 1736 CVR transcript
- Flight Safety Foundation — Human Factors & Aviation Medicine, Vol. 40 No. 5, Sept/Oct 1993 (“Hurry-up Syndrome,” citing the ALPA Tenerife report)
A factual reference account compiled from official investigation findings and recognised aviation-safety sources, written to inform — with respect for those who died. It is not legal or investigative commentary. See Terms of Service.