The Germanwings co-pilot thought to have deliberately caused the French Alps plane disaster "rehearsed" his plan on an earlier flight on the day of the crash, an accident report is expected to say.
All 150 people on the Airbus A320, including three Britons, were killed when it crashed while flying from Barcelona to Dusseldorf on March 24.
Recovered voice recorder evidence points to the plane's co-pilot Andreas Lubitz, 27, locking the captain out of the cockpit and putting the plane into a steady descent.
According to German newspaper Bild, an interim report from French air accident bureau the BEA will say that Lubitz had practised reducing flight altitude on the outbound flight from Dusseldorf to Barcelona on March 24.
Bild said the BEA report would talk about a "controlled descent that lasted for minutes and for which there was no aeronautical justification".
Lubitz suffered from severe depression in the past and a computer found in his home showed he had used the internet to research ways of committing suicide in the days leading up to the crash.
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Prosecutors also found torn-up sick notes at his home, indicating he should not have flown on the day of the flight.
One of the Britons who died in the disaster was Paul Bramley, 28, who was originally from Hull. He was studying hospitality and hotel management at Cesar Ritz College in Lucerne and was about to start an internship.
Another of the Britons killed was father-of-two Martyn Matthews, 50, a senior quality manager from Wolverhampton.
Also killed was seven-month-old Julian Pracz-Bandres, from Manchester, was died alongside his mother, Spanish-born Marina Bandres Lopez-Belio.