TENERIFE AIRPORT DISASTER M. Mustafin- Dpl-11 R.Anayatova-Supervisor The Tenerife airport disaster occurred on Sunday, March 27, 1977, whentwo Boeing 747 passenger aircraft collided on the runway of Los Rodeos Airport(now known as Tenerife North Airport) on the Spanish island of Tenerife, one ofthe Canary Islands. With a total of 583 fatalities, the crash is the deadliest accidentin aviation history. After a bomb exploded at Gran Canaria Airport, many aircraft were diverted toTenerife. Among them were KLM Flight 4805 and PanAm Flight 1736 – the twoaircraft involved in the accident. The threat of a second bomb forced the authoritiesto close the airport while a search was conducted, resulting in many airplanesbeing diverted to the smaller Tenerife airport where air traffic controllers wereforced to park many of the airplanes on the taxiway, thereby blocking it. Furthercomplicating the situation, while authorities waited to reopen Gran Canaria, adense fog developed at Tenerife, greatly reducing visibility. When Gran Canariareopened, the parked aircraft blocking the taxiway at Tenerife required both of the747s to taxi on the only runway in order to get in position for takeoff. Due to thefog, neither aircraft could see the other, nor could the controller in the tower seethe runway or the two 747s on it. As the airport did not have ground radar, the onlymeans for the controller to identify the location of each airplane was via voicereports over the radio. As a result of several misunderstandings in the ensuingcommunication, the KLM flight attempted to take off while the Pan Am flight wasstill on the runway. The resulting collision destroyed both aircraft, killing all 248aboard the KLM flight and 335 of 396 aboard the Pan Am flight. Sixty-one peopleaboard the Pan Am flight, including the pilots and flight engineer, survived thedisaster . As the accident occurred in Spanish territory, that nation wasresponsible for investigating the accident. Investigators from the Netherlands andthe United States also participated. The investigation revealed that the primarycause of the accident was the captain of the KLM flight taking off withoutclearance from Air Traffic Control (ATC). The investigation specified that thecaptain did not intentionally take off without clearance; rather he fully believed hehad clearance to take off due to misunderstandings between his flight crew andATC. Dutch investigators placed a greater emphasis on this than their Americanand Spanish counterparts, but ultimately KLM admitted their crew was responsiblefor the accident, and the airline financially compensated the victims. Events on both planes had been routine until they approached the islands. Then,at 1:15 pm, a bomb (planted by the separatist Fuerzas Armadas Guanches)exploded in the terminal of Gran Canaria International Airport, injuring one person. It had been preceded by a phone call warning of the bomb, and soon afteranother call came in claiming a second bomb was at the airport. The civil aviationauthorities closed that airport after the bomb detonated and diverted all of itsincoming flights to Los Rodeos, including the two Boeing 747 aircraft involved inthe disaster. Upon contacting Gran Canaria airport, the Pan Am flight was
informed of the temporary closure. Although the Pan Am crew indicated that theywould prefer to circle in a holding pattern until landing clearance was given, theplane was ordered to divert to Los Rodeos, along with the KLM flight. This led tothe critical cramped aircraft conditions within the smaller airport. There were congestions at Los Rodeos. In all, at least five large aircraft werediverted to, a regional airport that could not easily accommodate them. The airporthad only one runway and one major taxiway parallel to it, as well as several smalltaxiways connecting the main taxiway and the runway. While waiting for GranCanaria airport to reopen, the diverted aircraft took up so much space that theywere parked on the long taxiway, meaning that it could not be used for taxiing.Instead, departing aircraft would have to taxi along the runway to positionthemselves for takeoff, a procedure known as a runway backtrack. After the threat at Gran Canaria International Airport had been contained,authorities reopened the airport. The Pan Am aircraft was ready to depart, but theKLM plane and a refueling vehicle obstructed the way to the active runway. ThePan Am aircraft was unable to manoeuvre around the fueling KLM, reach therunway and depart due to a lack of just 12 ft (3.7 m) of clearance. CaptainVeldhuyzen van Zanten had decided to fully refuel at Los Rodeos instead of LasPalmas, apparently to save time. The refueling took about 35 minutes . Following the towers instructions, the KLM aircraft was cleared to backtaxithe full length of runway 30 and make a 180° turn to put the aircraft in takeoffposition. While KLM 4805 was backtaxiing on runway 30, the controller asked theflight crew to report when it was ready to copy the ATC clearance. Because theflight crew was performing the checklist, copying this clearance was postponeduntil the aircraft was in takeoff position on Runway 30.Shortly afterward, Pan Am 1736 was also instructed to backtaxi, to follow theKLM aircraft down the same runway, to exit the runway by taking the third exit ontheir left and then use the parallel taxiway. Initially, the crew was unclear as towhether the controller had told them to take the first or third exit. The crew askedfor clarification and the controller responded emphatically by replying: "The thirdone, sir; one, two, three; third, third one" . The crew began the taxi andproceeded to identify the unmarked taxiways using an airport diagram as theyreached them.Based on the chronology of the cockpit voice recorder (CVR), the distancesbetween the taxiways, and the location of the aircraft at the time of the collision,the crew successfully identified the first two taxiways (C-1 and C-2), but theirdiscussion in the cockpit never indicated that they had sighted the third taxiway (C-3), which they had been instructed to use. There were no markings or signs toidentify the runway exits and they were in conditions of poor visibility. The PanAm crew appeared to remain unsure of their position on the runway until thecollision, which occurred near the intersection with the fourth taxiway (C-4).The angle of the third taxiway would have required the plane to perform a turn ofapproximately 148°, which would lead back toward the still-crowded main apron.At the end of C-3, another 148° turn would have to be made, in order to continuetaxiing towards the start of the runway. Taxiway C-4 would have required two
turns of just 35°. A study carried out by the Air Line Pilots Association after theaccident concluded that making the second 148° turn at the end of taxiway C-3would have been "a practical impossibility". Subsequent performance calculationsand taxi tests with a B747 turning off on an intersection comparable to the C-3 atTenerife, as part of the Dutch investigation, indicate that in all probability the turnscould have been made. The official report from the Spanish authorities did notexplain why the controller had instructed the Pan Am aircraft to use the thirdtaxiway, rather than the easier fourth taxiway. Tenerife / Los Rodeos airport is at 633 metres (2,077 feet) above sea level,which accounts for cloud behaviour that differs from that at most other airports.Clouds at 600 m (2,000 ft) above ground level at the nearby coast, are at groundlevel at Los Rodeos / Tenerife North. Drifting clouds from different densities causewildly varying visibilities, from unhindered at one moment to below the minimumsthe next. The collision took place in a high density cloud . The Pan Am Aircraft found themselves in poor and rapidly deterioratingvisibility almost as soon as they entered the runway. According to the ALPAreport, as the Pan Am Aircraft taxied to the runway, the visibility was about 500 m(1,600 ft). Shortly after they turned onto the runway it decreased to less than 100 m(330 ft). Meanwhile, the KLM aircraft was still in good visibility, but with cloudsblowing down the runway towards them. The KLM aircraft completed its 180degree turn in relatively clear weather and lined up on Runway 30. The next cloudwas some 900 m (3,000 ft) down the runway and moving towards the aircraft atabout 12 knots (6 meters per second). Immediately after lining up, the KLM captain, the most senior pilot working forKLM, advanced the throttles (a standard procedure known as "spool-up", to verifythat the engines are operating properly for takeoff) and the co-pilot advised thecaptain that ATC clearance had not yet been given. Captain Veldhuyzen vanZanten responded, "I know that. Go ahead, ask." Meurs then radioed the tower thatthey were "ready for takeoff" and "waiting for our ATC clearance". The KLMcrew then received instructions which specified the route that the aircraft was tofollow after takeoff. The instructions used the word "takeoff," but did not includean explicit statement that they were cleared for takeoff.Meurs read the flight clearance back to the controller, completing the readbackwith the statement: "We are now at takeoff." Captain Veldhuyzen van Zanteninterrupted the co-pilots read-back with the comment, "Were going."The controller, who could not see the runway due to the fog, initially respondedwith "OK" (terminology which is nonstandard), which reinforced the KLMcaptains misinterpretation that they had takeoff clearance. The controllersresponse of "OK" to the co-pilots nonstandard statement that they were "now attakeoff" was likely due to his misinterpretation that they were in takeoff positionand ready to begin the roll when takeoff clearance was received, but not in theprocess of taking off. The controller then immediately added "stand by for takeoff,I will call you," indicating that he had not intended the clearance to be interpretedas a takeoff clearance. Here we see communication misunderstanding.
A simultaneous radio call from the Pan Am crew caused mutual interference onthe radio frequency, which was audible in the KLM cockpit as a three second longwhistling sound (or heterodyne). This made the crucial latter portion of the towersresponse audible only with difficulty by the KLM crew. The Pan Am crewstransmission, which was also critical, was reporting, "Were still taxiing down therunway, the Clipper 1736!" This message was also blocked by the interference andinaudible to the KLM crew. Either message, if heard in the KLM cockpit, wouldhave given the KLM crew time to abort the takeoff attempt.Due to the fog, neither crew was able to see the other plane on the runway ahead ofthem. In addition, neither of the aircraft could be seen from the control tower, andthe airport was not equipped with ground radar. After the KLM plane had startedits takeoff roll, the tower instructed the Pan Am crew to "report when runwayclear." The Pan Am crew replied: "OK, well report when were clear." On hearingthis, the KLM flight engineer expressed his concern about the Pan Am not beingclear of the runway by asking the pilots in his own cockpit, "Is he not clear, thatPan American?" Veldhuyzen van Zanten emphatically replied "Oh, yes" andcontinued with the takeoff. Look at the diagram of collision . Simplified map of runway, taxiways, and aircraft. The red star indicates the location of impact. According to the CVR, Captain Grubbs, captain of the Pan Am plane, said,"There he is", when he spotted the KLMs landing lights through the fog just as hisplane approached exit C-4. But he was mistaken. The KLM was coming towardsthem at takeoff speed. The only way was to get off the RW as quick as possible!The Pan Am crew applied full power to the throttles and took a sharp left turntowards the grass in an attempt to avoid a collision. By the time CaptainVeldhuyzen van Zanten noticed the Pan Am on the runway ahead, his aircraft wasalready traveling too fast to stop. In desperation he prematurely rotated his aircraftand attempted to clear the Pan Am by climbing away, causing a tail strike for 20 m(100 ft). The KLM was within 100 m (330 ft) of the Pan Am when it left theground. As it did so, its excessively steepangle of attack allowed the nose gear toclear the Pan Am but the engines, lower fuselage and landing gears struck theupper right side of the Pan Ams fuselage at approximately 140 knots (260 km/h;160 mph), ripping apart the center of the Pan Am jet almost directly above thewing. The right side engines crashed through the Pan Ams upper deckimmediately behind the cockpit. The KLM plane remained briefly airborne following the collision, but theimpact with the Pan Am had sheared off the #1 (outer left) engine, and the #2
(inner left) engine had ingested significant amounts of shredded materials from thePan Am. The KLM pilot quickly lost control, and the 747 went into a stall, rolledsharply, and hit the ground at a point 150 m (500 ft) past the collision, sliding afurther 300 m (1,000 ft) down the runway. The full load of fuel, which had causedthe earlier delay, ignited immediately. A survivor of the Pan Am flight, John Coombs of Haleiwa, Hawaii, said thatsitting in the nose of the plane probably saved his life: "We all settled back, and thenext thing an explosion took place and the whole port side, left side of the plane,was just torn wide open ." Both airplanes were destroyed. All 234 passengers and 14 crew members in theKLM plane died, while 326 passengers and 9 crew members aboard the Pan Amflight were killed, primarily due to the fire and explosions resulting from the fuelspilled and ignited in the impact. The other 56 passengers and 5 crew membersaboard the Pan Am aircraft survived, including the pilots and flight engineer. Mostof the survivors on the Pan Am aircraft walked out onto the left wing, the sideaway from the collision, through holes in the fuselage structure. The Pan Amsengines were still running at takeoff power for a few minutes after the accidentdespite First Officer Braggs intention to turn them off. The top part of the cockpit,where the engine switches were located, had been destroyed in the collision, andall control lines were severed, leaving no method for the flight crew to control theaircrafts systems. After a short time running at full power, the Pan-Ams enginesbegan to disintegrate, throwing engine parts at high speed that killed a flightattendant who had escaped the burning plane. Survivors waited for rescue, but itdid not come promptly, as the firefighters were initially unaware that there weretwo aircraft involved and were concentrating on the KLM wreck some distanceaway in the thick fog. Eventually, most of the survivors on the wings dropped tothe ground below. In conclusion, the accident had a lasting influence on the industry,particularly in the area of communication. An increased emphasis was placed onusing standardized phraseology in ATC communication by both controllers andpilots alike, thereby reducing the chance for misunderstandings. As part of thesechanges, the word "takeoff" was removed from general usage, and is only spokenby ATC when actually clearing an aircraft to take off. Less experienced flight crewmembers were encouraged to challenge their captains when they believedsomething was not correct, and captains were instructed to listen to their crew andevaluate all decisions in light of crew concerns. This concept would later beexpanded into what is known today as Crew Resource Management. CRM trainingis now mandatory for all airline pilots. As a result of several misunderstandings in the ensuing communication, theKLM flight attempted to take off while the Pan Am flight was still on the runway.The resulting collision destroyed both aircraft, killing all 248 aboard the KLMflight and 335 of 396 aboard the Pan Am flight, primarily due to the fire andexplosions resulting from the fuel spilled and ignited in the impact. The other 56passengers and 5 crew members aboard the Pan Am aircraft survived, including thepilots and flight engineer.