The families of victims killed last year when a suicidal pilot flew an airliner into a mountainside in the French Alps filed a lawsuit Wednesday against the U.S. flight school where the pilot was trained, alleging the school failed to properly screen his medical background.

The suit was filed in U.S. District Court in Phoenix against the Airline Training Center of Arizona. It's owned by Lufthansa, which is also the parent company of Germanwings, a regional Europe carrier that employed pilot Andreas Lubitz.

On March 24, 2015, Lubitz locked Germanwings Flight 9525's captain out of the cockpit and deliberately set the plane on a collision course with the mountainside. All 150 people aboard, including Lubitz, were killed.

While training in Europe with Lufthansa, Lubitz had been suspended from his academic course work for nearly 10 months while he sought treatment for depression. In 2010, after returning to Lufthansa with letters from his doctors that he was no longer depressed or taking medication, he was sent to the U.S. for flight training.

German authorities had twice turned down applications from Lubitz for a pilot medical certificate because of his history of depression before issuing him a medical certificate in July 2009 that included a restriction stating it would become invalid if he had a relapse, the suit said.

Had the Arizona school screened Lubitz, the restriction on his German medical certificate would have tipped officials that he'd been previously hospitalized for severe depression and treated with medications that would have prohibited him from flying, according to the suit, which was filed on behalf of more than 80 families.

Lubitz's behavior while at the flight school should also have caused officials to inquire further, the suit said, without providing details of that behavior.

The flight school's president, Matthias Kippenberg, and Lufthansa didn't immediately respond to requests for comment.

"Lubitz's particular history of depression and mental instability made him a suicide time bomb, triggered to go off under the ordinary stresses of life, particularly the kind of stresses a commercial pilot routinely faces," said attorney Marc S. Moller of the New York law firm Kreindler & Kreindler, which represents the families. It's well known that cases of depression frequently recur, although when they will recur is unpredictable, he said.