Receive emails about upcoming NOVA programs and related content, as well as featured reporting about current events through a science lens. Email Address Zip Code Subscribe By the time either flight crew saw the other plane in the fog, it was too late to avert the disaster, which arose out of a series of miscommunications among both flight crews and the control tower. Support Provided By Learn More © WGBH Educational Foundation

Cockpit Recordings

Key to communications

APP—Air traffic control tower at Los Rodeos Airport

PA RT—Pan Am aircraft radio transmission

PA 1—Victor Grubbs, Pan Am CaptainPA 2—Robert Bragg, Pan Am First OfficerPA 3—George Warns, Pan Am Flight EngineerPA 4—Unidentified fourth person in Pan Am cockpit, likely one of two Pan Am employees who boarded in Tenerife and were sitting in the cockpit jumpseatsKLM RT—KLM aircraft radio transmissionKLM 1—Veldhuyzen (Jacob) van Zanten, KLM CaptainKLM 2—Klaas Meurs, KLM First OfficerKLM 3—Willem Schreuder, KLM Flight Engineer?—Unidentified

Note: The transcript below comes from the official Spanish accident report (see www.project-tenerife.com/engels/PDF/Tenerife.pdf) and has been slightly modified for clarity and ease of reading. Paragraphs preceding sections of the transcript, and also explanatory text attached to linked words or phrases, are NOVA annotations. Click on highlighted terms for a glossary.

The Final Minutes

At 4:58 p.m. 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 (see Figure 1 below). Some back-and-forth 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.

Figure 1 © Galaxie Production

1658:14.8 KLM RT: Approach KLM 4805 on the ground in Tenerife.

1658:21.5 APP: KLM—ah—4805, roger.

1658:25.7 KLM RT: We require backtrack on 12 for takeoff Runway 30.

1658:30.4 APP: Okay, 4805 ... 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.

1658:55.3 APP: Okay, KLM 80—ah—correction, 4805, 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: 4805, 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 it 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.

PA?: Three.

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.

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 4805 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.

1703:49.1 PA 2: Wing flaps?

1703:50.2 PA 1: Ten, indicate 10, leading edge lights are green.

1703:54.1 PA ?: Get that.

1703:55.0 PA RT: Clipper 1736.

1703:56.5 PA 2: Yaw damp and instrument?

1703:58.6 PA 1: Ah—Bob, we'll get a left one...

1703:59.3 PA 2: I got a left.

1704:00.6 PA 1: Did you?

1704:00.9 PA 2: And—ah—need a right.

1704:02.6 PA 1: I'll give you a little...

1704:03.8 PA 2: Put a little aileron in this thing.

1704:05.0 PA 1: Okay, here's a left and I'll give you a right one right here.

1704:09.7 PA 1: Okay, right turn right and left yaw.

1704:11.4 PA 2: Left yaw checks.

1704:12.4 PA 1: Okay, here's the rudders.

1704:13.6 PA 1: Here's two left, center, two right center.

1704:17.8 PA 2: Checks.

1704:19.2 PA 2: Controls.

1704:19.6 PA 1: Haven't seen any yet!

1704:20.3 PA 2: I haven't either.

1704:21.7 PA 1: They're free, the indicators are checked.

1704:24.6 PA 2: There's one.

1704:25.8 PA 1: There's one.

1704:26.4 PA 1: That's the 90-degree.

1704:28.5 PA ?: Okay.

1704:34.5 PA 2: Weight and balance finals?

1704:37.7: [Sounds similar to stabilizer trim]

1704:37.2 PA 1: We were gonna put that on four and a half.

1704:39.8 PA 3: We got four and a half and we weigh 534. [sound of stabilizer trim]

1704:44.6 PA 2: Four and a half on the right.

1704:46.8 PA 2: Engineer's taxi check.

1704:48.4 PA 3: Taxi check is complete.

Figure 2 © Galaxie Production

1704:50.5 PA 2: Takeoff and departure briefing?

1704:52.1 PA 1: Okay, it'll be standard. We gonna go straight out there till we get 3,500 feet, then we're gonna make that reversal and go back out to ... 14.

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]

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.

1705:40.0 PA ?: Huh.

1705:44.8 PA ?: I like this.

Figure 3 © Galaxie Production

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).

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.

Why Air Traffic Control would say "okay" after KLM has said it is taking off is unknown. Perhaps, the official investigation noted, the controller thought that KLM meant "we're now at takeoff position." But the problem is compounded in the moments immediately following, when both Air Traffic Control and Pan Am RT speak simultaneously. This causes a shrill noise in the KLM cockpit that lasts for almost four seconds and makes 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.

Figure 4 © Galaxie Production

The following messages are audible in the KLM cockpit, causing the KLM flight engineer, even as the KLM plane has begun rolling down the runway, to question the 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]

Perhaps because of the KLM pilot's very senior position, neither the copilot nor flight engineer questions the pilot again, and the impact occurs 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 seconds before impact. The Pan Am captain says "There he is ... look at him! Goddamn, that [expletive deleted] is coming!" and his copilot yells "Get off! Get off! Get off!" The Pan Am pilot guns the engines but it's too late. At 1706:47.44, the KLM pilot screams, and the collision occurs.

Glossary

Runway 12/30

In the transcript, both Runway 12 and Runway 30 are mentioned. Both are actually the same runway; the difference lies in which direction a plane is facing as it travels along the runway. The KLM plane, for example, taxis along Runway 12 (short for 120°, the direction it is then facing), then turns 180° and attempts takeoff in the opposite direction on what for it has then become Runway 30 (short for 300°).

1658:14.8

The transcript uses standard aviation notation to represent time. 1658:14.8 signifies 4:58 p.m. and 14.8 seconds.

KLM 4805

This aircraft is a Boeing 747 carrying 234 passengers and 14 crew. It is a chartered flight bound from Amsterdam to Las Palmas in the Canary Islands. Like the other airplane involved in the crash, it is diverted to Tenerife's airport when the Las Palmas airport suddenly closes. All those onboard this plane when it crashes die. (One passenger, a tour guide, got off the plane in Tenerife.)

backtrack

Backtracking means using the same runway for both taxiing and takeoff, i.e., taxiing down it in one direction then turning around and taking off in the opposite direction.

12 for takeoff Runway 30

See Runway 12/30

holding position

As Los Rodeos Airport fills up on this day with an uncommon number of large aircraft, Air Traffic Control orders the planes to line up at the end of the landing runway (see number 2 on the diagram).

Charlie 1

The transverse taxiways are identified as Charlie 1, 2, 3, and 4, as shown in the diagram.

Clipper 1736

Pan Am 1736 carries 378 passengers, 16 crew, and two Pan Am employees, who boarded in Tenerife and are sitting in the cockpit jumpseats. It departed from Los Angeles bound for the same intended destination as KLM 4805—Las Palmas's Gran Canaria International Airport—but was diverted to Tenerife. Sixty-one people on this plane will survive the impending collision, though nine of these later die from their injuries.

takeoff minimums

Every airport has its own minimum visibility requirement for takeoffs. Here, the Pan Am captain, noticing the thickening fog, surmises that the poor visibility will not meet the takeoff minimums and therefore no planes will be cleared to take off until the visibility improves.

They put a bomb (in) the terminal

At Gran Canaria International Airport, the intended destination for both aircraft, Canary Island separatists exploded a bomb in the concourse earlier that day, injuring several people. They also called in a threat of a second bomb. Gran Canaria shut down for several hours, causing the temporary diversion of KLM 4805 and Pan Am 1736 to Los Rodeos Airport on Tenerife.

90-degree turn

The Pan Am copilot has a small map of the airport, which shows that the first taxiway is a 90-degree turn. But as the plane taxis down the runway, the flight crew apparently can't decide whether Air Traffic Control considers this a taxiway proper.

it's a 45

Still looking at his map, the Pan Am copilot is probably referring to either Charlie 2 or Charlie 3 taxiways here, both of which lie at roughly 45° angles to the runway. For them, however, they would each represent roughly 135° turns, hence their eventual decision to turn on Charlie 4, which is a much easier turn because of the angle.

That's the 90-degree

The Pan Am flight crew now sees taxiway Charlie 1, which they're now just passing on their journey up the runway.

That's two.

The Pan Am pilot sees Charlie 2, which his plane is now passing in the fog. But from the transcript it's unclear what the flight crew subsequently considers the proper taxiway to turn on, Charlie 3 or Charlie 4. In the end, its decision to take the fourth rather than the third taxiway did contribute to the accident.

you are cleared

Air Traffic Control gives the KLM crew clearance, but, crucially, not to begin takeoff but only to fly a certain route after takeoff. Captain van Zanten on the KLM plane apparently mistakes the meaning of "clearance" here.

we're now at takeoff

This phrase used by the KLM copilot is nonstandard, as is the tower's vague "okay" after the captain starts powering up and says "Let's go." The copilot is apparently announcing that KLM is now taking off, yet the tower does not understand his comment this way, evidenced by its instruction moments later to stand by and wait for its clearance. In the aftermath of the disaster at Tenerife, officials implemented standard aviation phrasing worldwide to avoid similar confusion in the future.