Relatives of those who died last year when a Germanwings pilot deliberately crashed a plane in the French Alps filed a wrongful death suit on Wednesday against the United States flight school that trained him.

'Andreas Lubitz, the suicidal pilot, should never have been allowed to enter' the training program at Airline Training Center Arizona, Inc (ATCA), said Brian Alexander, an attorney who filed the suit in federal court in Phoenix, Arizona.

It was filed on behalf of 80 people whose relatives perished in the March 15, 2015 crash of a Germanwings' Flight A320.

Alexander's firm, Kreindler and Kreindler, was joined in the suit by attorneys in Britain, Germany and the Netherlands.

The crash took 150 lives, including that of Lubitz, a troubled pilot who had struggled for years with mental health problems.

The 28-year-old locked the pilot out of the cockpit and while alone at the controls, steered the jetliner into the side of a mountain, killing all 144 passengers and six crew.