Swiss air traffic control officials have conceded that they told the pilot of a Russian charter jet to reduce altitude and avert a mid-air collision before it smashed into an oncoming cargo plane.
It has emerged the two planes which crashed over southern Germany last night, killing 71 people, were both diving at the time of impact.
The Russian passenger plane from Bashkirian Airlines with 69 people on board was en route to Barcelona from Moscow when it crashed into a Boeing 757 cargo jet carrying two pilots at about 36,000 feet above Lake Constance.
Fifty-two of the victims were top-of-the-class students who had won trip for outstanding performance in school. They were between the ages of 12 and 18, police said.
The two planes both were making a fatal descent from 36,000 feet to 35,000 feet when the accident happened.
The Russian plane in response to urgent orders from Swiss air traffic control and the cargo plane in response to its on-board collision avoidance system.
Skyguide, the Swiss air traffic control body, initially insisted that it had given the Russian crew between 90 seconds' and two minutes' warning to descend and that the crew had only begun the descent on the third request.
But, Skyguide officials were forced to confirm what German authorities were saying: that there was only 50 seconds' warning and that the Russian plane complied with instructions on the second request.
Swiss air traffic controllers took over responsibility for the cargo plane at about 22:23 p.m. and for the Russian plane at about 22:30 p.m.
The accident occurred at 22.35 p.m. - at a time when just one air traffic controller was on duty in Zurich because his colleague was on a break.
The controller, described as an experienced member of staff, was being treated for shock today and had not been questioned.
Mr Sepp Moser, one of Switzerland's best known aviation experts, criticised the Swiss for reacting too late, given that they could predict at what altitude the two planes would be flying 15 minutes beforehand.
"I think that the behaviour of Swiss air traffic authorities should be examined on a second-by-second basis," he said.
Emergency services crews have so far recovered 26 bodies in the area near Lake Constance on the Swiss-German border. Wreckage and bodies were spread over a 30-kilometre area comprised mainly of farmland. Police sealed off much of the area while recovery teams used dogs and helicopters to locate the dead.
Some 1,200 police officers, firefighters and rescue workers were combing the terrain for clues to the cause of the incident. Recovery operations were to continue until sunset and continue tomorrow at sunrise.
Two Tornado jets from the German air force were to assist with the search. Up to 12 Russian crash experts are expected in Germany tomorrow to assist in the investigation.
Federal Transport Minister Mr Kurt Bodewig told a news conference that it was "nearly a miracle" that no casualties were reported on the ground. He pledged a swift and complete investigation of the crash.
Russian Prime Minister Mikhail Kasyanov quickly urged against pointing the blame at either ground control officials or the pilots of the two jets.
"It is difficult to find the cause for such a tragedy until the black boxes are discovered and read," Mr Kasyanov was quoted as saying during a visit to Paris.
Witnesses near Lake Constance reported hearing a loud explosion and seeing flaming pieces of wreckage crashing towards the ground.
Ms Uta Otterbein, a spokeswoman for German Air Traffic Control, said the planes went down over Ueberlingen, close to the lake had 80 passengers and 13 crew aboard.
The cargo plane, flying for the DHL delivery service on a trip from Bahrain to Brussels, had two pilots on board. One of them was British father-of-three Mr Paul Phillips.
Reuters adds:The collision of a Tupolev jet with the Boeing cargo jet over southern Germany last night was the first in the history of Bashkirian Airlines (BAL), a small airline based in the Russian republic of Bashkortostan.
The company, based in the capital Ufa, specialises in internal flights and flights to other former Soviet republics, but also offers links to holiday destinations in countries such as Turkey, Greece, Germany, China and Iran.
The doomed Tupolev Tu-154 was one of eight owned by the company. The airline, which employs nearly 2,000 people, owns other Russia-built planes such as Antonov-24s and Tupolev Tu-134s.
PA & AFP