WASHINGTON — The German pilot who deliberately flew his airliner into a mountainside last year had struggled with learning to fly and had failed a key test of his skills during training in the U.S., according to FBI interviews with his flight instructors.

Andreas Lubitz was promoted anyway. But his training difficulties were one more “red flag” that should have caused Lufthansa and the airline’s Arizona flight school to take a closer look and discover his history of depression, asserted attorneys representing families of crash victims.

Lubitz was a co-pilot for Germanwings, a regional airline owned by Lufthansa, when he locked Flight 9524’s captain out of the cockpit and set the plane on a collision course with a mountain in the French Alps last year. All 144 passengers and six crew members, including Lubitz, were killed.

One instructor described Lubitz as “not an ace pilot,” and said he failed one flight test because of a “situational awareness issue.” In aviation, loss of situational awareness usually means a pilot becomes absorbed in something and loses track of what else is happening with the plane.

Another instructor said that Lubitz lacked “procedural knowledge” and had trouble with splitting his attention between instruments inside the plane and watching what was happening outside. But while Lubitz struggled with training, he would achieve passing scores.

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