Eight air traffic controllers have gone on trial in Switzerland on charges of manslaughter and negligence over an air crash in 2002 that killed 71 people.
The children on board were going on holiday to Spain
A Russian passenger jet collided with a cargo aircraft. Most of the victims were schoolchildren from Russia.
The eight accused were all employed by the air traffic control firm Skyguide at the time of the incident.
They are all charged with manslaughter and negligence, and face jail sentences of up to 15 months if found guilty.
All eight deny responsibility. Seven of them are still working for Skyguide.
The Russian charter flight carrying children on holiday to Spain collided with the DHL plane in Swiss airspace in July 2002. The wreckage came down in Germany.
The court heard that crucial telephone and radar systems were not functioning at the time of the crash because of maintenance work.
Skyguide also had a practice of having only one air traffic controller on duty at night.
The single air traffic controller who was working on the night of the crash was subsequently stabbed and killed by the father of two of the children who died.
German and Swiss investigations into the crash have already found what are described as significant organisational deficiencies within Skyguide which, it is said, contributed to the accident, says the BBC's Imogen Foulkes in Berne.
Skyguide has already provided financial compensation to some of he bereaved families, our correspondent says.
But she says many more are still waiting for compensation and for an admission of responsibility for the crash.
Some relatives are expected to come to Switzerland for the trial, which will last two weeks.