- KLM Flight 4805 collision with Pan Am Flight 1736 at Tenerife
- Accident Overview
- Accident Board Findings
- Accident Board Recommendations
- Relevant Regulations / Policy / Background
- Prevailing Cultural / Organizational Factors
- Key Safety Issue(s)
- Safety Assumptions
- Resulting Safety Initiatives
- Airworthiness Directives (ADs) Issued
- Common Themes
- Related Accidents / Incidents
- Lessons Learned
- KLM Flight 4805 collision with Pan Am Flight 1736 at Tenerife
Photo of ramp area at Tenerife (North) airport – March 2005
Photo copyright Benedict Pressburger – used with permission
The KLM Boeing 747, registration PH-BUF, flight number 4805, took off from Amsterdam Schipol Airport at 0900 hours (local time) on March 27, 1977, en route to Las Palmas, Canary Islands.
The Pan Am Boeing 747, registration N73PA, flight number 1736, left Los Angeles International Airport at 1729 hours (local time) on March 26, 1977, arriving at New York JFK Airport at 0117 hours (local time) on March 27, 1977. After refueling and a crew change, the aircraft departed for Las Palmas, Canary Islands at 0242 hours (local time).
Terrorist Bombing at Las Palmas
While the aircraft were en route to Las Palmas, a bomb exploded in the passenger terminal building at the airport. Due to the threat of a second explosion, the terminal building was evacuated and the airport closed. Much of the traffic arriving at Las Palmas Airport was diverted to Los Rodeos (Tenerife) Airport on Tenerife Island. For this reason, the parking area at the latter airport was crowded with airplanes.
Approximate location of the five aircraft parked in the holding area for Runway 12. The KLM and Pan Am aircraft are at the top.
Photo of N736PA on the tarmac at Los Rodeos Airport on the day of the accident. PH-BUF is in the foreground.
Once the Las Palmas Airport had been reopened, the Pan Am crew prepared to proceed to Las Palmas. However, when they attempted to taxi to the runway, their path was blocked by the KLM airplane which, unlike the Pan Am airplane, had allowed its passengers to leave the aircraft during the delay time on the ground. All aircraft were also unable to use the parallel taxiway on account of the aircraft congestion on the main apron. The three other airplanes parked in front of the KLM airplane had already departed.
Approximately one hour later, KLM 4805 requested an estimated departure time. They said that they needed to refuel and that this would take approximately 30 minutes. They loaded 55,500 liters (approx. 14,700 gallons) of fuel. At 1656 the KLM aircraft called the tower requesting permission to taxi. A few minutes later, the Pan Am airplane called again in order to request clearance to start up its engines, and was cleared to do so.
The Tenerife-Las Palmas flight is approximately 25 minutes in duration, so the loading of 55,500 liters of fuel led investigators to believe that the KLM captain wished to avoid the difficulties of refueling in Las Palmas, with the resulting delay, because a great number of airplanes diverted from Tenerife would be arriving later. As a result, the aircraft could have returned to Amsterdam without refueling in Las Palmas.
Cockpit Voice Recorder Transmissions
At 1658 hours on March 27, 1977, when this transcript begins, the KLM and Pan Am 747s are both in queue to taxi down the runway and turn around for takeoff. The KLM aircraft is ahead of the Pan Am aircraft. Some back-and-forth communication occurs initially about what Air Traffic Control considers the best way to get the KLM plane into position for takeoff, but ultimately the controllers decide to send it taxiing straight down the runway. This portion of the transcript comes from the KLM cockpit voice recorder. (Note: In the following transcripts, RT signifies a radio transmission from the noted flight, while APP signifies a transmission from the tower controllers. If RT or APP does not appear, these statements were onboard communications between crew members, and not radio transmissions. Further, only pertinent sections have been included. Other sections not considered relevant to the events of the accident are omitted here, but may be found in the actual CVR transcript included in the accident report).
1658:14.8 KLM RT Approach KLM four eight zero five on the ground in Tenerife.
1658:21.5 APP KLM-ah-four eight zero five, roger.
1658:25.7 KLM RT We require backtrack on 12 for takeoff Runway 30.
1658:30.4 APP Okay, four eight zero five ... taxi ... to the holding position Runway 30.
Taxi into the runway and-ah-leave runway (third) to your left.
1658:47.4 KLM RT Roger, sir, (entering) the runway at this time and the first (taxiway) we, we go off the runway again for the beginning of Runway 30.
Aerial photo of Tenerife (North) Airport
Photo copyright Gabe Basco – used with permission
1658:55.3 APP Okay, KLM 80-ah-correction, four eight zero five, taxi straight ahead-ah-for the runway and-ah-make-ah-backtrack.
1659:04.5 KLM RT Roger, make a backtrack.
1659:10.0 KLM RT KLM 4805 is now on the runway.
1659:15.9 APP four eight zero five, roger.
1659:28.4 KLM RT Approach, you want us to turn left at Charlie 1, taxiway Charlie 1?
1659:32.2 APP Negative, negative, taxi straight ahead-ah-up to the end of the runway and make backtrack.
1659:39.9 KLM RT Okay, sir.
With the KLM aircraft now taxiing down Runway 12, Air Traffic Control turns its attention to Pan Am 1736. The controllers instruct the plane to travel down the runway and then exit using one of the transverse taxiways. This would clear the way for the KLM plane to take off. This portion of the transcript comes from the Pan Am cockpit voice recorder.
1701:57.0 PA RT Tenerife, the Clipper 1736.
1702:01.8 APP Clipper 1736, Tenerife.
1702:03.6 PA RT Ah-we were instructed to contact you and also to taxi down the runway, is that correct?
1702:08.4 APP Affirmative, taxi into the runway and-ah-leave the runway third, third to your left, [background conversation in the tower].
1702:16.4 PA RT Third to the left, okay.
1702:18.4 PA 3 Third, he said.
1702:20.6 APP [Th]ird one to your left.
1702:21.9 PA 1 I think he said first.
1702:26.4 PA 2 I'll ask him again.
1702:32.2 PA 2 Left turn.
The situation deteriorated further when low-lying clouds reduced visibility to the point at which neither airplane taxiing on the main runway, nor some of those located in the parking area, were visible from the tower.
Photo of Tenerife Tower – January 2004
Photo copyright Gustavo Bertran – used with permission
1702:33.1 PA 1 I don't think they have takeoff minimums anywhere right now.
1702:39.2 PA 1 What really happened over there today?
1702:41.6 PA 4 They put a bomb (in) the terminal, sir, right where the check-in counters are.
1702:46.6 PA 1 Well, we asked them if we could hold and-uh-I guess you got the word, we landed here...
1702:49.8 APP KLM four eight zero five how many taxiway-ah-did you pass?
1702:55.6 KLM RT I think we just passed Charlie 4 now.
1702:59.9 APP Okay ... at the end of the runway make 180 [degree turn] and report-ah-ready-ah-for ATC clearance. [background conversation in tower]
1703:09.3 PA 2 The first one is a 90-degree turn.
1703:11.0 PA 1 Yeah, okay.
1703:12.1 PA 2 Must be the third ... I'll ask him again.
1703:14.2 PA 1 Okay.
1703:16.6 PA 1 We could probably go in, it's ah...
1703:19.1 PA 2 You gotta make a 90-degree turn.
1703:21.6 PA 1 Yeah, uh.
1703:21.6 PA 2 Ninety-degree turn to get around this ... this one down here, it's a 45.
1703:29.3 PA RT Would you confirm that you want the Clipper 1736 to turn left at the third intersection? ["third" drawn out and emphasized]
1703:35.1 PA 1 One, two.
1703:36.4 APP The third one, sir, one, two, three, third, third one.
1703:38.3 PA ? One two (four).
1703:39.0 PA 1 Good.
1703:39.2 PA RT Very good, thank you.
1703:40.1 PA 1 That's what we need right, the third one.
1703:42.9 PA 3 Uno, dos, tres.
1703:44.0 PA 1 Uno, dos, tres.
1703:44.9 PA 3 Tres-uh-si.
1703:46.5 PA 1 Right.
1703:47.6 PA 3 We'll make it yet.
1703:47.6 APP ...er 7136 [sic] report leaving the runway.
1704:26.4 PA 1 That's the 90-degree.
1704:28.5 PA ? Okay.
1704:58.2 APP [KLM] 8705 [sic] and Clipper 1736, for your information, the centerline lighting is out of service. [APP transmission is readable but slightly broken]
Takeoff Visibility for Tenerife
Photo of Transmissometer
- for determining runway visual range
Runway visibility at Tenerife was determined from several sources. An individual was located in a weather observation tower about 400 meters (1300 feet) southwest of the approach end of runway 30. (There was a similar tower at the opposite end of the runway.) This person would take weather readings and also determine both the horizontal and slant visibility he could see as he looked toward the approach path of an airplane as it landed. This person would also determine runway visibility if it exceeded the limits of the automated visibility instrument. The tower would report those values to the pilot.
The automated visibility instrument is known as a transmissometer. It was located 70 meters (200 feet) south of the runway 30 approach. This device measures the maximum horizontal distance, in kilometers or meters, at which a pilot could see either the runway surface or runway lights while rolling down the runway. Some runways have additional transmissometers at the midpoint of the runway and the far end. At Tenerife, the transmissometer visibility value at the departure end of the runway controlled the visibility required by the pilot for takeoff. If runway lights are inoperative, the required visibility value for takeoff increases. (For example, since the runway centerline lights were out of service, the Pan Am pilot required 800 meters visibility to takeoff, or about 2600 feet.)
Located near the transmissometer was a ceilometer, which measures the ceiling, or the height of the lowest layer of clouds. It uses triangulation to determine the height of a spot of light projected onto the base of a cloud.
Following the communication from the control tower regarding the inoperative runway centerline lighting, the flights acknowledged the information:
1705:05.8 KLM RT I copied that.
1705:07.7 PA RT Clipper 1736.
1705:09.6 PA 1 We got centerline markings (only) [could be "don't we"] they count the same thing as ... we need 800 meters if you don't have that centerline ... I read that on the back (of this) just a while ago.
1705:22.0 PA 1 That's two.
1705:23.5 PA 3 Yeah, that's 45 [degrees] there.
1705:25.7 PA 1 Yeah.
1705:26.5 PA 2 That's this one right here.
1705:27.2 PA 1 [Yeah], I know.
1705:28.1 PA 3 Okay.
1705:28.5 PA 3 Next one is almost a 45, huh, yeah.
1705:30.6 PA 1 But it goes...
1705:32.4 PA 1 Yeah, but it goes ... ahead, I think (it's) gonna put us on (the) taxiway.
1705:35.9 PA 3 Yeah, just a little bit, yeah.
1705:39.8 PA ? Okay, for sure.
1705:40.0 PA 2 Maybe he, maybe he counts these (are) three.
Photo of incoming fog bank at Tenerife (North) Airport
Photo copyright Manual Luis Ramos Garcia – used with permission
In the final minute before the collision, key misunderstandings occur among all the parties involved. And in the end, the KLM pilot initiates takeoff even though Air Traffic Control has not issued the proper clearance.
1705:41.5 KLM 2 Wait a minute, we don't have an ATC clearance.
KLM 1 No, I know that. Go ahead, ask.
1705:44.6 KLM RT Uh, the KLM 4805 is now ready for takeoff and we're waiting for our ATC clearance.
1705:53.4 APP KLM 8705 [sic] uh you are cleared to the Papa beacon. Climb to and maintain flight level 90 ... right turn after takeoff proceed with heading 040 until intercepting the 325 radial from Las Palmas VOR.
1706:09.6 KLM RT Ah, roger, sir, we're cleared to the Papa beacon flight level 90, right turn out 040 until intercepting the 325, and we're now (at takeoff).
When the Spanish, American, and Dutch investigating teams heard the tower recording together for the first time, no one, or hardly anyone, understood that this transmission meant that they were taking off.
1706:11.08 [Brakes of KLM 4805 are released.]
1706:12.25 KLM 1 Let's go ... check thrust.
1706:14.00 [Sound of engines starting to accelerate.]
1706:18.19 APP Okay.
Investigators questioned why Air Traffic Control would say "okay" after KLM had said that it was "at takeoff." The investigation noted that the controller may have thought that KLM meant "We're now at takeoff position." This confusion was compounded in the moments immediately following when both Air Traffic Control and Pan Am transmitted simultaneously. This caused a shrill noise in the KLM cockpit that lasted for almost four seconds and made the following three communications hard to hear in the KLM cockpit:
1706:20.08 APP Stand by for takeoff ... I will call you.
PA1 No, uh.
PA RT And we are still taxiing down the runway, the Clipper 1736.
File Photo of burning Pan Am 747
The following messages were audible in the KLM cockpit, causing the KLM flight engineer, even as the KLM plane had begun rolling down the runway, to question the KLM pilot:
1706:25.47 APP Ah-Papa Alpha 1736 report runway clear.
1706:25.59 PA RT Okay, we'll report when we're clear.
1706:31.69 APP Thank you.
1706:32.43 KLM 3 Is he not clear, then?
1706:34.10 KLM 1 What do you say?
1706:34.15 PA ? Yup.
1706:34.70 KLM 3 Is he not clear, that Pan American?
1706:35.70 KLM 1 Oh, yes. [emphatically]
The accident report noted that perhaps influenced by the KLM captain's ".....great prestige, making it difficult to imagine an error of this magnitude on the part of an expert pilot, both the co-pilot and the flight engineer made no further objections." Impact occurred about 13 seconds later. Based on the Pan Am cockpit voice recording, investigators determined that the Pan Am flight crew saw the KLM coming at them out of the fog about nine and a half seconds before impact. The Pan Am captain said, "There he is ... look at him! [expletives deleted] is coming!" and his copilot yells, "Get off! Get off! Get off!" The Pan Am pilot accelerates the engines but not in sufficient time to avoid the collision. At 1706:47.44, the collision occurred.
Duty Time and Rest Regulations
At the time of the accident, investigators learned that the Dutch rules regarding duty time limits had recently been changed. Prior to this, the captain had a great deal of discretion in extending his crew's duty time in order to complete the scheduled service. However, new rules imposed absolute rigidity with regard to duty time limits. The captain was forbidden to exceed these limits and, in the event that duty times were exceeded, could be prosecuted under the law.
Moreover, until December 1976, it was relatively easy to adjust the duty time by taking only a few factors into account. The investigation concluded that the new calculation methods were so complicated that, in practice, it was impossible for a flight crew to calculate adjustments in the cockpit. For this reason, KLM management strongly recommended that they be contacted in order to determine the adjusted duty time.
This was the situation on the day of the accident. The investigators noted that during the delay at Tenerife, the KLM captain, using HF radio, contacted the company's operations office in Amsterdam. He was told that if he was able to takeoff before a certain time it seemed that there would be no problems with duty time. However, if there was any risk of exceeding the limit, the company would send a telex to Las Palmas. This uncertainty of the crew as to their duty time limit was found by the accident investigation to be an important psychological factor.
Photo of KLM Flight 4805 wreckage
The investigation noted a number of factors that may have influenced the decisions made by the KLM crew. These are listed in the report as: (quoted directly from the report, as indicated.)
'...from a careful listening to the KLM CVR that although cockpit operation was correct and the check-lists were adequately kept, there was some feeling of anxiety regarding a series of factors, which were: the time margin remaining to them, to the point of straining the allowable limit of their duty time; the poor and changing visibility which, especially as the runway centre lights were not operative, might prevent the possibility of take-off within the weather limits required by the company; the inconvenience for the passengers, etc.'
'It is also observed that, as the time for take-off approached, the captain - perhaps on account of all these worries - seemed a little absent from all that was heard in the cockpit. He enquired several times, and after the co-pilot confirmed the order to backtrack, he asked the tower if he should leave the runway by C-l, and subsequently asked his co-pilot if he should do so by C-4. On arriving at the end of the runway, and making a 180-degree turn in order to place himself in take-off position, he was advised by the co-pilot that he should wait as they still did not have an ATC clearance. The captain asked him to request it, which he did, but while the co-pilot was still repeating the clearance, the captain opened the throttle and started to take off.'
Photo of wreckage (KLM Flight 4805 in the foreground)
'Then the co-pilot, instead of requesting take-off clearance or advising that they did not yet have it, added to his read-back, "We are now at take-off." The tower, which was not expecting the aircraft to take off as it had not given clearance, interpreted the sentence as, "We are now at take-off position"(1) and the controller replied: "Okay, ... stand by for take-off ... I will call you." Nor did the Pan Am on hearing the "We are now at take-off", interpret it as an unequivocal indication of take-off. However, in order to make their own position clear, they said, "We are still taxiing down the runway." This transmission coincided with the "Stand by for take-off ... I will call you", causing a whistling sound in the tower transmission and making its reception in the KLM cockpit not as clear as it should have been, even though it did not thereby become unintelligible.'
‘The communication from the tower to the PAA requested the latter to report when it left the runway clear. In the cockpit of the KLM airplane which was taking off, nobody at first confirmed receiving these communications (Appendix 5) until the Pan Am airplane responded to the tower's request that it should report leaving the runway with an "Okay, we'll report when we're clear." On hearing this, the KLM flight engineer asked: "Is he not clear then?" The captain didn't understand him and he repeated: "Is he not clear that Pan American?" The captain replied with an emphatic "Yes" and, perhaps influenced by his great prestige, making it difficult to imagine an error of this magnitude on the part of such an expert pilot, both the co-pilot and the flight engineer made no further objections. The impact took place about thirteen seconds later.'
"(1) When the Spanish, American and Dutch investigating teams heard the tower recording together and for the first time, no-one, or hardly anyone, understood that this transmission meant that they were taking off."
Another factor identified in the investigation was the low-lying clouds that descended upon the airport just prior to the accident. Visibility both before and during the accident was variable. While runway visibility was reported to be 2 to 3 kilometers 17 minutes prior to the accident, visibility reduced to just 300 meters 12 minutes later. Just after the accident, visibility had improved to one kilometer. The investigators concluded that the changing visibility caused "...an increase in subconscious care to the detriment of conscious care, part of which was already focused on takeoff preparation (completing of checklists, taxiing with reduced visibility, etc.)."
The investigation also concluded that the KLM crew also had a "...fixation on what was being seen (increasing fog) with a consequent diminished capacity to assimilate what was heard." The crew was also fixated "...on trying to overcome the threat posed by a further reduction of the already precarious visibility. Faced with this threat, the way to meet it was either by taking off as soon as possible, or by testing the visibility once again and possibly refraining from taking off (a possibility which certainly must have been considered by the KLM captain)."
The investigation also concluded that the KLM crew probably felt a certain level of relaxation following the execution of a "...difficult 180 degree turn, which must have coincided with a momentary improvement in the visibility (as proved by the CVR, because which shortly before arriving at the approach end of the runway they turned off the windshield wipers), the crew must have felt a sudden feeling of relief which increased their desire to finally overcome all of the ground problems: the desire to be airborne."
Photo of wreckage of KLM 4805 (left) and Pan Am Flight 1736 (right)
Photo of International Tenerife Memorial
On March 27, 2007, 30 years after the disaster, a first time ever official international memorial service for the largest aviation disaster in history was held on the initiative of the Foundation for the Surviving Relatives of the Tenerife Disaster.
The international commemoration consisted of two parts: a memorial service at the Auditorio de Tenerife in the capital Santa Cruz; and the unveiling of an international monument on Mount Mesa Mota in the municipality of San Cristóbal de La Laguna. The ceremonies were attended by Dutch and American next of kin and survivors, as well as Spanish aid workers and others who were involved in the disaster. The monumental art work, designed by renowned Dutch artist Rudi van de Wint, is an 18-meter spiral stair case, named Stairway to Heaven, of which the steps appear to move endlessly upward into infinity, but are cut off suddenly.
Photo of Captain Robert Bragg
The FAA wishes to thank Captain Robert L. Bragg, First Officer on Pan American Flight 1736, for his assistance in the preparation and review of this "Lessons Learned from Transport Airplane Accidents" material. Captain Bragg began his flying career with the United States Air Force in 1959, and transitioned to a commercial pilot in 1964 with Pan American, and in 1987 with United Airlines. During his flying career, he has flown many different types of airplanes ranging from the DC-6, to the B747-400. He logged more that 33,000 hours, and after leaving flying duties in 2000, continued giving lectures and providing aviation consultant services to several major networks. For his efforts in assisting fellow crew members and passengers of the Tenerife crash, he received the United States President's Award for heroism, FAA's Achievement Award, and the Flight Safety Foundations Award for actions during an accident.