Two years ago - a tremendous tragedy.
July 1, 2004 2:15 AM   Subscribe

On 1 July 2002 at 21:35:32 hrs a collision between a Tupolev TU154M, which was on a flight from Moscow/Russia to Barcelona/ Spain, and a Boeing B757-200, on a flight from Bergamo/Italy to Brussels/ Belgium, occurred north of the city of Ueberlingen (Lake of Constance). Investigation Report as of May 2004, PDF. Very detailed, intelligibly written.

71 people were killed in one of Europe's worst peacetime air accidents. The report comes the the conclusion that human error was the main cause. The TCAS system (PDF) which should have prevented the collision worked, but the Tupolew crew followed the ATC instructions. It turned out that the air traffic controller missed a key warning on his radar screen in one of a chain of errors. ATCs from nearby airports realized what was going on but weren't able to contact the responsible Skyguide controller because the telephone network did not work: the main telephone line was switched off because of work being done on the telephone network, and the collision warning system was temporarily shut down for maintenance.
The ATC in charge was stabbed to death in February 2004 by a Russian man who lost his wife, son and daughter in the plane crash.
posted by tcp (9 comments total) 1 user marked this as a favorite
That is very, very sad. Good post.
posted by scarabic at 2:20 AM on July 1, 2004

I would like to echo scarabic, an excellent post cheers.
posted by johnnyboy at 2:47 AM on July 1, 2004

Relevant mefi threads can be found here and here.
posted by tcp at 2:54 AM on July 1, 2004

Sad story. It's incredible how much effort is put into investigating such accidents. Kudos to dhartung for pretty much nailing the causes, two years before the official report.
posted by cbrody at 3:36 AM on July 1, 2004

Good post indeed tcp, thanks!

I saw a documentary about this on tv a short while ago when the ATC was killed. (In the next village from where I am working). This gives a lot more background.
posted by sebas at 3:42 AM on July 1, 2004

One of the ugly points of this chain of errors -- despite the ATC error, the crash would have been avoided, except:

The Tupolev crew, flying for Aeroflot, had been told that in case of conflicting instructions from the controllers and TCAS, they should follow the controller. The other crew had been told, in the same situation, to follow TCAS.

One thing most people don't generally know. In route, commercial air traffic doesn't fly under Visual Flight Rules, instead, above 18,000 feet* (in the US and Canada) all aircraft fly under Instrument Flight Rules. The key difference. In VFR, the pilots are responsible for maintaining separation between the planes. In IFR, the ground controllers are.

Thus, the conflict. Both planes were being told to turn to turn away from a crash by ATC -- who is responsible for keeping the planes safely apart. Both were getting instructions from TCAS to turn away from a crash -- but they were contradictory.

The Russians, for historical (the Soviets were big on central control) and technological (they had many false alarms with their early TCAS gear) were taught to follow the controller above all. Everyone else on the planet was taught to trust TCAS over a controller.

* The problem with "feet", or for that matter, "meters." Aircraft altimeters, by and large, are barometric. This means that what it reads depends on what the air pressure is at ground level.

The problem comes with long flights at high altitude. The ground pressure between Chicago and London may be vastly different, leading a plane, flying at 21,000 feet (Chicago) to be at the same level as a plane flying at 23,000 feet (London). So, planes above 18,000 fly at "Flight Levels". Flight levels are measured in thousands of feet (FL310-31,000 feet), but with the altimeter set to a common setting (29.92 inHg, or 1013.2 mBar) This means that an aircraft at FL310 may or may not be at 31,000 feet above mean sea level -- but it *will* be at a different altitude than a plane at FL320.
posted by eriko at 6:22 AM on July 1, 2004

The Russians, for historical (the Soviets were big on central control) and technological (they had many false alarms with their early TCAS gear) were taught to follow the controller above all. Everyone else on the planet was taught to trust TCAS over a controller.

eriko, that sounds plausible but I can't believe the pilot's behaviour was russian policy.

From the TCAS PDF:

TCAS II altitude data is better than ATC’s [...] Therefore, for aircraft in close proximity, the TCAS II knowledge of the vertical situation is much better than the ATC one. It can be considered to be at least 4 times more accurate, and 4 times more up-to-date. [...] It is important that pilots follow all RAs even when there is an opposite avoiding instruction by the controller. If the RA is not followed, it can adversely affect safety when the other aircraft responds to a coordinated RA.

The commander of the Tupolev was under supervision by an instructor, one report I have read assumed that the instructor possibly gave the order to obey the ATC although the commander first decided to listen to the TCAS, but I have no evidence to sustain this version.
posted by tcp at 7:11 AM on July 1, 2004

Eriko, I thought about it again. You seem to know what you're talking about and maybe there was such as an internal arrangement not to trust TCAS. Where did you hear about that?

Heck, planes crashed because some french ATCs refused to speak english so why shouldn't russian pilots deny to listen to TCAS.
posted by tcp at 7:26 AM on July 1, 2004

I just saw a TV show about air safety that discussed this. They said that at the time of the crash there hadn't been a set standard on whether to follow the TCAS or the ATC. The TCAS was just supposed to be a back-up system when the ATC made an error; no one had considered how to deal with a conflict. Now all pilots are taught to do what the TCAS directs. I suppose at that point, the ATC has lost his credibility!
posted by loafingcactus at 7:16 AM on July 3, 2004

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