Russian pilots given contradictory instructions

The Russian pilots were ordered to descend while their own systems were telling them to go the other way Keystone Archive

Voice recorders from last week's air disaster show that the Swiss traffic air controller unwittingly set the two planes on a collision course.

The recorders show the Swiss air traffic controller contradicted the Russian jet’s cockpit warning systems. Seconds earlier the pilots had been told to gain altitude because the oncoming Boeing 757 cargo plane had been ordered to descend by its own warning systems.

The Russian pilots obeyed the air traffic controller, and began to descend, not realising that the Boeing was doing the same.

Swiss aviation analyst, Sepp Moser, said the Russian pilots were wrong to listen to the controller, and should have followed the instructions of their own system.

“Both traffic collision avoidance systems were working properly, and the Russian pilots made a mistake because in such cases it is common, and standard procedure, that the pilot obeys the computer and not the air traffic controller,” he told swissinfo.

Russians sceptical of computers

“However, we have to take into account that this was a Russian pilot, and Russian pilots have a tendency to obey the computers less than humans because their computers usually are not very reliable.”

Moser added that “the prime responsibility rests with [Swiss air traffic control] Skyguide because the warning system is just a supplementary system – an added safety net.”

The voice recorders also indicated that the Russian pilots failed to respond immediately to the instructions and the Swiss controller repeated the command 14 seconds later.

The Russian pilot then responded, and 30 seconds later the planes crashed at 11,000 metres, killing 71 people.

Germans issued alert

Earlier on Monday, German aviation officials said they tried to warn Swiss controllers ahead of last week’s mid-air collision.

German controllers in the southern city of Karlsruhe say they telephoned the Zurich tower two minutes before the fatal accident but could not get through because the only available line was busy.

Axel Raab, spokesman for the Karlsruhe control centre, said staff tried to get in touch with the lone controller after receiving an automatic radar warning that the Russian passenger jet and the Boeing 757 were on a collision course.

At the time, the Swiss controller was using a back-up line while routine maintenance work was being carried out on the main telephone system, according to the German Federal Bureau of Aircraft Accidents Investigations (BFU).

The revelations have added further weight to growing criticism of the role of Skyguide, the Swiss air traffic control agency, in the disaster, which left 71 people, including 45 children, dead.

Technical problems

German investigators said the Swiss controller on duty in Zurich on Monday was battling with technical problems.

They said on Friday that Skyguide was working on its telephone and radar systems on the night that the two aircraft slammed into each other high above Lake Constance.

According to the Germans, Skyguide’s air traffic controller was not only without his main telephone line, but around the same time Skyguide’s radar data processing system momentarily went out of action.

The problems meant the air traffic controller was simultaneously monitoring two frequencies and two radar monitors.

Control system discrepancies

Between 23:25 and 23:33, the air traffic controller repeatedly attempted to contact an aircraft that was landing at the German port of Friedrichshafen.

Shortly afterwards, at 23:34, the controller made contact with the Tupolev – just 44 seconds before it collided.

The Russian pilot began to lose altitude 30 seconds prior to impact – around the same time as the Boeing pilot began to initiate a descent after his in-flight warning system warned of the oncoming Tupolev.

Funerals

Meanwhile, Russian President Vladimir Putin made an unannounced visit on Monday to Ufa, capital of the country’s Bashkortostan region where most of the victims came from.

Thousands of people turned out to pay an emotional farewell to the children who died in the crash.

Crowds thronged the airport at Ufa, as the remains of 22 children and 11 adults were flown in from Germany.

swissinfo with agencies