(Adds Skyguide comment)

By Erich Buergler

BUELACH, Switzerland, Sept 4 (Reuters) - A Swiss court found four air traffic control managers guilty of manslaughter on Tuesday over a 2002 mid-air accident that killed 71 people, most of them Russian children.

"The accused is guilty of multiple cases of manslaughter," said Judge Rainer Hohler as he read out each ruling.

On trial were eight employees of air traffic control firm Skyguide, charged with manslaughter for contributing to circumstances that caused two planes to crash in Swiss-controlled airspace above southern Germany.

A single controller was on duty shortly before midnight on July 1, 2002, when a Russian charter and a freight plane operated by logistics company DHL collided in Swiss-controlled airspace over southern German town of Ueberlingen.

Most of the victims were Russian children on holiday.

The court sentenced three managers to 12-month suspended terms and one was fined. The remaining four Skyguide employees on trial were acquitted, the court said.

"Staffing the entire ACC (Zurich air control) at night with only one controller goes completely against air traffic security principles," said the judge.

Wealthy Switzerland, a country as well known for public order and quality services as for the beauty of its landscape, has struggled to come to terms with the disaster, one of Europe's worst-ever peacetime air accidents.

The controller on duty that evening, Peter Nielsen, was later stabbed to death by a Russian man who lost his wife, son and daughter in the collision.

The head of Skyguide later asked for forgiveness and the Swiss president offered an official state apology to Russia.

"We, for our part, are convinced that this tragedy is attributable primarily to systemic causes in the interplay between people, technology and procedures," said interim Skyguide chief executive Francis Schubert in a statement.

BOTH PLANES DIVED

The Russian Tupolev holiday charter flight had 57 passengers, mostly children, and 12 personnel on board. The Boeing 757 flight operated by DHL had two pilots aboard.

The Russian plane obeyed Nielsen's order to dive at the same time as the DHL freight flight obeyed its on-board anti-collision system, which told it to dive as well, leading the two aircraft to collide at an altitude of 11,000 metres (35,000 feet).

Both the main telephone and the backup telephone were out of order, the radar software that displays flight coordinates was in a restricted mode and Nielsen's only backup colleague was on a coffee break when the two planes collided.

During trial proceedings, defendants said they had no reason to think that Skyguide's practice -- now banned -- of leaving controllers alone on night shifts could prove dangerous. Defendants also largely blamed Nielsen for poorly handling the events that led up to the crash.

But the judge said that Skyguide managers could have averted the disaster by prohibiting the second controller from taking a coffee break, leaving Nielsen alone.

"A simple ban on coffee breaks would have been enough (to prevent the accident)," he said. "All three of the accused had the authority to ensure that two air controllers were present".

The public prosecutor had requested suspended jail sentences ranging from 6 to 15 months.

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