It's an anniversary today, thought not a good one.

Today marks 30 years since the deadliest airplane accident ever in Tenerife, Canary Islands, Spain, where 583 people died and scores of others were injured.

It's a prime example of links in the accident chain, and this accident is frequently quoted during cockpit resource management training, so let's take a quick look at it. This is just a blog post though, so it's kind of half-assed. For a full report on this, try Wikipedia,

The two Boeing 747 jumbo jets involved were initially headed to Las Palmas airport in the Canary Islands, but it had been closed due to a terrorist attack, so both jets were sent to Los Rodeos airport in Tenerife, which was a small airport that wasn't easily able to accomodate large passenger jets.

There was only 1 runway and 1 taxiway at the airport, and other diverted large jets were parked on the taxiway, so aircraft wanting to depart would have to go on the runway and taxi all the way down to the end before turning around and taking off.


A KLM Royal Dutch Airlines 747 was ready to go, so it was cleared to taxi down the runway to the end, turn around and wait there for further clearance. At the same time, a Pan Am 747 was given clearance to taxi down the runway behind the KLM 747, then to turn off the runway on a short taxiway so as to clear the runway for the KLM 747 to take off.

This sounds like a good time to add some thick fog, so let's do that. Fog started to form around the Los Rodeos airport, limiting the visual range to between 1/4 and 1/8th of a mile of visibility.

Now check out this diagram. It's a simplified drawing of the airport at Los Rodeos, and it sort of shows what happened.

The KLM plane taxied all the way down to the end of the runway and turned around. The Captain, perhaps wanting to make up some lost time, initially attempted to take off but was immediately stopped by the First Officer who pointed out that they didn't have clearance. So the plane sat at the end of the runway, in heavy fog, and waited for clearance.



Now the Pan Am 747 was told to taxi down the runway in the fog, and then to take the 3rd exit on the left so as to clear the runway. The runway charts weren't very detailed and there was some confusion on the part of the Pan Am plane - if you look at exit '3' on the drawing, you'll see that if you are planning on taking it, you need to turn sharply to get on it, and then turn sharply again to get off it. That's not an easy thing to do on a 747, so the crew assumed that the controller meant they were supposed to go to taxiway '4' and clear, which is a gentle turn and which would be a lot easier for the 747 to do.

(I cut n pasted this next paragraph from Wikipedia as their wording is perfect) "he KLM crew then received an ATC airways clearance; a clearance to fly a certain route after take-off, but not permission for the take-off itself. The captain may have mistaken this for a take-off clearance. He released the brakes of the aircraft and the co-pilot responded with a heavy Dutch accent with words that could either be "We are at take off" or "We are taking off". The control tower was confused by the message and asked for the KLM plane to stand by. However, simultaneous communication from Pan Am caused mutual interference. All that was audible was a heterodyne beat tone, making the tower response inaudible to the pilots. Coincidentally, Pan Am was reporting they had not finished taxiing. Either message, if broadcast separately, might have given the KLM crew time to abort its takeoff."

Because it was really foggy, the KLM plane couldn't see the Pan Am plane down the runway. The airport control tower couldn't see either aircraft, and unfortunately the airport didn't have ground radar either.

While the KLM crew had started its take-off run, the tower instructed the Pan Am crew to "report when runway clear". The crew replied: "OK, we'll report when we're clear". On hearing this, the KLM flight engineer expressed his concern about the Pan Am not being clear of the runway, repeating this concern a few seconds later, but he was overruled by the captain. The flight engineer did not explicitly challenge him on this decision.

How unfortunate that the company culture of KLM at the time was such that the captain's word was not to be questioned. The Captain on the KLM flight was one of the most senior and respected Captains, and had even appeared in KLM advertisements. If the flight engineer had felt more confident, perhaps his warnings would have been more forceful.

Anyway, the KLM plane rolled down the runway toward the Pan Am plane. Both Captains then saw each other's lights in the fog, which must have been...unpleasant. The Pan Am Captain immediately added full power in an attempt to make taxiway 4 in time. The KLM Captain was going too fast to stop before hitting the Pan Am 747, so he immediately started to pull the nose of his plane up in an attempt to fly over the Pan Am 747 and avoid a collision that way.

It didn't work out.

The bottom of the KLM plane slammed into the top of the Pan Am plane, which tore the Pan Am plane apart. The KLM plane continued for a few hundred feet, then crashed back down onto the runway, caught fire and exploded.

All 248 people aboard the KLM 747 died, as well as 326 passengers and 9 crew members aboard the Pan Am 747. 61 people aboard the Pan Am aircraft survived, including the cockpit crew.

So let's summarize:

1. The KLM 747 started to take off without a take-off clearance.
2. The KLM captain did not abort take-off when the Pan Am crew reported that they were still on the runway, as both the tower and the Pan Am plane were talking at the same time, which results in the radios broadcasting static instead of anything useful.
3. The Pan Am 747 continued to exit 4 instead of exiting at number 3 as directed by ATC.
4. The KLM Captain emphatically told the Flight Engineer that the Pan Am plane was clear of the runway when the Flight Engineer expressed concern.
5. There was use of non-standard phrases used by the KLM co-pilot ("We're at take off") and the Tenerife control tower ("O.K.").
6. Heavy ground fog prevented either plane from seeing each other on the runway until it was too late.

Those are just the most obvious links too.

As I think about this, I think about one of the most valuable things I have ever heard from a Transport Canada Inspector. This was years ago, and I was attending a Pilot Decision Making course. He said "Any time anything isn't totally routine on a flight, sit up and take notice. Double-check your procedures and double-check your checklists, because the first link in the accident chain has already been created, and your odds of crashing just went way up."

Words to live by.