PARIS • A doctor had recommended that the German pilot who crashed a Germanwings jet into the Alps last year should be treated in a psychiatric hospital two weeks before the disaster, French investigators said.

Prosecutors believe co-pilot Andreas Lubitz, 27, who had a history of severe depression, barricaded himself in the cockpit and deliberately propelled his Airbus jet into a mountainside on March 24 last year, killing all 150 people on board.

The French aviation investigation agency BEA, in its final report, said Lubitz had begun to show symptoms that could be consistent with a psychotic depressive episode in December 2014, and consulted several doctors over the following months.

Under German law, none of the doctors was able to alert his employers to his state of mind, and he was allowed to continue flying. The probe recommended more stringent medical checks for pilots in its conclusions published yesterday.

"Clearer rules are needed to establish when it is necessary to lift medical confidentiality," investigator Arnaud Desjardins said at the release of the BEA report.

"Several doctors in private practice had the information (that Lubitz) was ill," he said. "This information was not passed on to aeronautical authorities or to his employer Germanwings."

On the black-box voice recorder recovered at the crash site, all that is heard from Lubitz is regular breathing but there is no explanation from him for his murderous course of action.

The European Aviation Safety Agency has already recommended stepping up medical testing for pilots, including more psychological tests.

BEA chief Remi Jouty said the French investigation had sought to identify the "systematic failures which led to this accident".

As a result of the Germanwings crash, European aviation authorities have already recommended making it compulsory to have two people in the cockpit at any time during flights. Some countries are opposed to the measure, however, with Germany's pilots' union saying it poses "risks that outweigh any supposed improvements in security".

The death toll in the Germanwings disaster included 72 Germans, including a group of 16 high school students, and 50 Spaniards.

A German lawyer for some of the families of the dead said this month that they intended to sue the training school in Phoenix, Arizona, which Lubitz attended, saying it should have flagged his psychological problems.

"The co-pilot interrupted his training there for a while, due to psychological problems," said lawyer Christof Wellens. "He shouldn't have been allowed to resume his training," he added.

Lufthansa, which owns the budget airline, has paid €50,000 (S$76,600) for each victim in an initial payment, and offered an additional €25,000 to each of the families, plus €10,000 to each immediate relative, including parents, children and spouse.

REUTERS, AGENCE FRANCE-PRESSE