Aviation experts from the United States, Russia and Germany are searching for the cause of a mid-air jetliner collision over southern Germany that killed 71 people. Evidence suggests the pilots may have been warned too late to avoid the crash.

As relatives of many of the crash victims arrived in Germany from Russia to claim the bodies of loved ones, the technical inquiry into what happened in those final minutes before the crash began to produce some answers, and raise more questions.

Sixty-nine of the victims, most of them children, were on the Bashkirian airlines Tupolev 154 that was flying from Moscow to Barcelona, Spain. The Russian airliner collided with a Boeing 757 cargo plane flying to Brussels. Only the pilot and co-pilot were aboard the cargo plane.

The flight data recorders and cockpit voice recorders of both aircraft have been found. That will allow the international experts to begin their detailed examination of those final minutes in the air and listen to the exact timings of the conversations between the pilots and Swiss air-traffic controllers.

But even before the experts get to work, the Zurich-based controllers have admitted that the pilot of the Russian aircraft was first told to take evasive action only 50 seconds before the collision. The German pilots' union says that normally, a warning would be expected five to 10 minutes before a possible collision, which would be ample time for pilots to adjust their flight paths.

Also, there was only one controller at his desk in Zurich at the time, because a colleague was taking a break. And a collision warning system at the Zurich airport was out of action for routine maintenance work at the time of the crash.

It has also emerged that the Russian pilot took 25 seconds to react, and when he did he tried to take the plane sharply downwards to avoid the cargo plane. At the same time, the automatic safety system on the cargo plane directed its pilots to lose altitude.

The two planes collided in mid-air and exploded in a ball of fire that scattered bodies and wreckage for many kilometers along the shores of Lake Constance in southern Germany. Miraculously, officials say, no one was killed on the ground.

One school was hit by flying debris and set afire, but at that time of night, the building was empty. Other large pieces of metal landed within a few meters of homes, but no one was hit.