The copilot who drove a plane into the French Alps on March 24 may have practiced the control changes required for the crash on another flight earlier that day.
According to The New York Times, a 29-page report released by France's Bureau of Investigations and Analyses (BEA) states Andreas Lubitz programmed a flight from Düsseldorf to Barcelona to make sharp descents "several times" throughout the trip.
Lubitz did this while the captain was out of the cockpit, and he brought the controls back to normal when he returned. Some of the adjustments set the flight to drop as low as 100 feet above the ground.
The same crew that died on Germanwings Flight 9525, which left just two hours later from Barcelona, was also on this journey.
The director of BEA, Rémi Jouty, said,
The captain didn't realize at all, because the [copilot's] tests during the outgoing flight took place during a normal, preprogrammed descent and it never had an impact on the plane's trajectory.
Lubitz locked the captain out of the cockpit after he exited for an unconfirmed reason before making the fatal dive.
The sharp descent apparently went unnoticed because air traffic controllers gave the instruction to drop from 37,000 feet to 35,000 feet. Lubitz additionally set the engines to idle mode, The Huffington Post reports, making it easier for the plane to drop quickly.
To us, it is clear that this was some kind of rehearsal.
Lubitz reportedly suffered from depression, and he searched the Internet for ways to commit suicide in the days before the crash.
Investigators found torn-up doctors notes in his home saying he was unfit to fly that day.
Exactly what drove him to commit the catastrophic murder-suicide remains unknown.