According to a preliminary report released by French investigators Wednesday, Germanwings pilot Andreas Lubitz had “practiced” the fatal descent that would lead to the crashing of an Airbus A320 and the killing of 149 people on an earlier flight that same day.

The report indicates that during an earlier flight on March 24 from Düsseldorf to Barcelona, Lubitz was left alone in the cockpit for about five minutes. During this time, he adjusted the plane’s autopilot settings to bring the plane down to an altitude of about 100 feet. Later that day, he is believed to have manipulated the doomed Germanwings Flight 9525’s autopilot settings to the same fatal altitude and then accelerated the plane’s crash into the French Alps.

“I can’t speculate on what was happening inside his head; all I can say is that he changed this button to the minimum setting of 100 feet and he did it several times,” Frances Bureau of Investigations and Analyses (BEA) director Remi Jouty told the Telegraph.

From the New York Times:

The French report indicates that Mr. Lubitz’s trial run was so fleeting that it went undetected by air traffic controllers, who had already given instructions for a moderate descent to 35,000 feet from 37,000 feet. The flight’s captain, Patrick Sondenheimer, also apparently did not notice the maneuvers, which occurred about 20 minutes into the flight and while the captain was out of the cockpit for roughly five minutes.

The report states that the co-pilot selected an altitude of 100 feet “several times” for durations ranging from a few seconds to up to three minutes during the captain’s absence.

Indeed, investigators confirmed to Reuters that the changes to autopilot setting at that point in the flight would have been difficult for passengers to notice because the plane was already descending.

The following chart, taken from the report, indicates when Lubitz entered altitudes during his time alone in the cockpit on the earlier flight:

While the report was completed by the BEA, their investigation is separate from any potential criminal lawsuit brought by French prosecutors, who are largely expected to indict Germanwings and its parent company, Lufthansa.

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