An early warning system used by Swiss air traffic controllers was out of action at the time of Monday night's mid-air collision.This content was published on July 3, 2002 - 23:26
Carlo Bernasconi, head of operations at the Swiss air traffic control body, Skyguide, said a collision warning system at Zurich airport was out of action for maintenance checks.
But he refused to speculate on whether the accident could have been prevented if the system - which sounds an alarm if there is danger of a collision - had been fully operational.
"The system is really a safety net, an airbag for the controller if everything goes wrong and he fails to detect and solve the conflict...but as the transcript has shown, the controller did detect the conflict," Bernasconi told swissinfo.
The controller on duty at the time of the accident is currently being treated for shock and has so far been unable to make a statement to investigators.
The mid-air collision occurred late on Monday night in Swiss-controlled airspace at a height of over 11,000 metres when a Boeing 757 cargo jet and a Russian TU-154 passenger aircraft dived to avoid each other.
Aviation and safety experts on the ground are continuing their search for clues to the crash of the two jets close to the Swiss-German border on Monday night.
On Wednesday, investigators combing the crash site - spread over some 30 kilometres near Lake Constance - said they had recovered all four black box flight recorders from the aircraft.
Internal guidelines broken?
But even before the black boxes had been located and sent for analysis, questions were being asked about the role of Swiss air traffic controllers in the minutes leading up to the mid-air crash.
According to Skyguide, five planes were in the air when the two aircraft crashed. Only one air traffic controller was on duty at the time because his colleague was away on a break.
Anton Maag, head of air traffic controllers at Skyguide, said internal guidelines - which stipulate that two controllers should always be on duty when maintenance work is being carried out on the alarm system - had been broken.
But one of his aides, Philipp Seiler, said later this rule does not apply at night. Skyguide confirmed afterwards that all working rules had been properly followed.
After initial reports suggested the first warning had been issued 90 seconds before the crash, Skyguide later revised this figure, admitting the air traffic controller in charge had given the first instruction to descend just 50 seconds before the crash.
By the time the Russian plane began to descend, the Boeing 757 - operated by the freight company, DHL - was also diving, apparently instructed to do so by its on-board collision avoidance system.
But Bashkirian Airlines - the company which operated the TU-154 jet - denied its crew had failed to react to warnings issued by air traffic control authorities.
"It is the opinion of our company," said airline director, Nikolai Odegov, "that the air traffic control was at fault."
Instruction to dive
Skyguide insists the Russian pilot had been given ample warning to react, but a German pilot representative said the instruction to dive should have been received earlier.
"Of course, we must ask why the two planes were not brought apart earlier," said pilots' union spokesman, George Fongern.
"That would have been the usual thing to do," he added.
Skyguide spokesman, Urs Ryf, said the warning had been "tight but sufficient".
"The controllers gave several instructions and it's up to the investigations to reveal everything else," he said.
Hundreds of recovery workers continued on Wednesday to sift through the wreckage and have so far found 38 bodies, some of which were still strapped into seats of the Russian plane.
Russian investigators sent by President Vladimir Putin arrived on Tuesday evening to join the recovery efforts, while the United States National Transportation Safety Board said it was sending five investigators at the request of German authorities.
Officials are currently working to fly in relatives of the 45 Russian children who died in the crash. Some families have already arrived at the scene of the tragedy.
swissinfo with agencies
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