Mid-air crash: Focus of inquiry

A policeman and his dog sift through the debris

UEBERLINGEN, Germany -- Russian, German and Swiss officials are trading accusations over who was to blame for a mid-air collision at 36,000 feet that killed 71 people, many of them of Russian teenagers.

The aircrafts' voice and data recorders have all been recovered and will be analysed. At the moment, the investigation into the tragedy is focussing on a number of areas:

Air traffic control

The focus of the inquiry is increasingly on Swiss Air Traffic Control after it was revealed that the automatic system alerting air traffic controllers if two planes are on a collision course was switched off at the time of the accident.

The Swiss tower, which monitors air traffic in southern Germany, had been shut down for routine maintenance -- normally carried out at night.

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Skyguide, the Swiss air traffic controllers' body monitoring the flights, said it was "purely hypothetical" that the alarm system could have prevented the crash.

A spokesman for the body added the air traffic controller reacted 50 seconds before the collision of the passenger and cargo planes -- enough time for remedial action to be taken.

Earlier Swiss air traffic controllers had said three warnings in two minutes had been directed at the Russian pilot of the Tupolev Tu-154 to reduce altitude.

German officials said that was far less time than usual, saying pilots usually counted on five to 10 minutes' warning.

Swiss air controllers had taken over both planes from their German counterparts only a few minutes before the crash happened.

A controller was working alone with an assistant as his partner took a break because of the light air traffic. Five planes were in the sector over southern Germany which they were monitoring at the time, including the two doomed planes.

Early warning system

Both planes, DHL's Boeing 757 and the Russian Tupolev 154, were equipped with anti-collision radar, but pilots flying at more than 500mph may be required to react within seconds.

The Russian pilot finally lowered his altitude after warnings from air traffic control at the same point the internal warnings system on the DHL cargo plane activated, instructing the pilots to descend as well.

Distance

The collision came less than six months after European air traffic controllers reduced the minimum height between aircraft by half as part of the Reduced Vertical Separation Minimum, or RVSM, programme.

The change is designed to increase capacity in the skies by 20 percent and was introduced simultaneously in 41 countries in Europe and north Africa.

Eurocontrol, the Brussels-based European air safety organisation, said the changeover took four years to plan and that 9,300 aircraft were modified to handle the alteration.

Under RVSM, airlines flying above 29,000 feet in Europe can fly 1,000 feet apart instead of 2,000 feet previously.

The change almost doubles the number of flight levels between 29,000 and 41,000 feet.

Pilot error

Swiss Air Traffic Control said the Russian pilots had time to change their altitude to avoid the collision with the DHL cargo jet.

The Russian airline, Bashkirian Airlines, defended its pilots, saying they were fluent in English and had 15,000 hours of flight time between them.

The captain of the cargo plane was British and the co-pilot was Canadian.

German officials said pilots are used to between five and 10 minutes response time.

The Tu-154 had just made a stop in the German city of Munich before the collision.

Technical problems

The Tupelov, known as the workhorse of the Russian air fleet, has had a history of problems, but the 1995-built Tupelov-154 involved in the accident had been fitted with the necessary equipment required for flights to Europe in December 2000, Russia's First Deputy Minister for Air Transport, Alexander Neradko, said.