UEBERLINGEN, Germany -- Swiss authorities said a collision-warning system was out of service in the Zurich tower when it took control of a Russian airliner and a cargo jet shortly before they collided at 35,000 feet, killing 71 people, mostly children headed for an end-of-school beach holiday.
As an international investigation began, Swiss air traffic control also acknowledged Wednesday that one of the two controllers on duty had broken regulations by being out of the tower for a break during the maintenance operation on the warning system -- which alerts controllers to the danger of a collision.
Patrick Herr, a spokesman for Swiss air traffic control, said it was "a purely theoretical question" whether the system alone could have prevented the disaster. "Many signs point to an exceptionally unlucky combination of circumstances."
Maintenance on the warning system typically is done during periods of light air traffic. Monday's collision happened shortly before midnight.
The Russian charter jetliner and a Boeing 757 cargo plane collided late Monday over Germany, leaving a 20-mile wide debris field near Ueberlingen, a vacation spot set in rolling hills and forests on Lake Constance across from Switzerland.
Russian investigators concentrated on a large section of the Russian Tu-154 aircraft's fuselage, which lay about 500 yards from where three engines from the tail of the aircraft were embedded in a charred corner of a golden barley field.
The children, standout students from the city of Ufa, were on their way to a Spanish beach resort near Barcelona. A travel agent who helped organize the trip said Wednesday that 45 of the 69 people on the Russian plane were known to be children, fewer than the 52 reported earlier by officials.
Sergei Kolesnikov, general director of the Kreks travel agency in Ufa, said it was discovered that seven other people also boarded the flight after buying last-minute tickets through a Moscow travel agency. Their ages were unclear.
Swiss officials were already facing criticism for not giving the Russian pilot enough time to lower the Tupolev 154 he was flying for Bashkirian Airlines out of the way of the Boeing 757 cargo jet. The Swiss officials insist the 50-second warning should have been sufficient, but a German pilot representative said pilots usually count on five to 10 minutes warning.
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