Civil proceedings following the 2015 Germanwings plane crash which killed 150 people are set to begin in the German city of Essen on Wednesday. The co-pilot is believed to have locked the pilot out of the cockpit and to have deliberately flown the plane into a mountain, killing everyone on board.

The lawsuit has been brought by the relatives of passengers who died in the crash against the Lufthansa Group, which owns the low-cost Germanwings airline. Also accused is a Lufthansa training school in the US, the flight school where the co-pilot trained.

The plaintiffs say that the flight school and Lufthansa failed to prevent the crash by adequately supervising the medical condition of the co-pilot. They are demanding more compensation than the money which has already been paid out.

The co-pilot, Andreas Lubitz, suffered from depression and is believed to have deliberately steered the plane into a mountain in the French Alps on March 24 2015. The pilot was locked out of the cabin, having left to go to the toilet, when Lubitz crashed it.

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Company responsible, or the government?

His history of depression and pyschiatric treatment emerged after the crash, prompting an intense debate on whether some professions were too sensitive for typical patient confidentiality norms in Germany.

Lubitz had been declared "unfit to work" by a doctor in February, with the note still valid on the day of the crash. He had previously been diagnosed as having suicidal tendencies. The risk his mental health issues could pose to his career, if unearthed, was listed by Lubitz as one of his sources of concern. It emerged after the crash that Lubitz had not passed on this sick note, or others in the past, to his employer.

The Essen court will seek to determine whether any party had more responsibility to monitor Lubitz's mental health. The court has suggested that the German state may be held responsible for this, in which case Lufthansa and the flight school might not be liable.

The plane was traveling from Barcelona to Düsseldorf. Seventy-two of the passengers aboard were German, including 16 school students and their two teachers from a high school in the town of Haltern am See in the state of North Rhine-Westphalia. The town's mayor described the crash as "the darkest day in the town's history."

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No court decision is expected on Wednesday.

ed/msh (AFP, dpa)

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