A doctor referred Germanwings co-pilot Andreas Lubitz to a psychiatric clinic two weeks before he deliberately crashed a plane into the French Alps, killing 150 people, according to newly released report by French air accident investigators.

The BEA investigation agency, in releasing its report Sunday on the March 2015 crash, said multiple doctors who treated Lubitz in the weeks before the crash did not inform authorities of concerns about his mental health.

Because Lubitz didn't inform anyone of his doctors' warnings, the BEA said "no action could have been taken by the authorities or his employer to prevent him from flying."

Arnaud Desjardin, leading the BEA investigation, told reporters that experts found Lubitz's symptoms at that time "could be compatible with a psychotic episode."

He says this information "was not delivered to Germanwings."

"It wasn't a psychiatrist who was concerned here, it was a general practitioner who was also the co-pilot's referral consultant on a fairly regular basis, but it is this doctor who diagnosed possible psychosis and recommended admittance to a psychiatric hospital," Desjardin told reporters.

Investigators found that Lubitz intentionally crashed Flight 9525 en route from Barcelona to Duesseldorf.

The BEA investigation is separate from a manslaughter investigation by French prosecutors seeking to determine eventual criminal responsibility for the crash.

The investigators say the pilot certification process failed to identify the risks presented by Lubitz.

French air accident investigators are recommending that world aviation bodies define new rules to require that medical professionals warn authorities when a pilot's mental health could threaten public safety.

Lubitz had been treated for depression in the past, and the investigation found that he had consulted dozens of doctors in the weeks before the crash.

German privacy rules strict

French aviation investigators say one factor leading to the Germanwings plane crash might have been a "lack of clear guidelines in German regulations on when a threat to public safety outweighs" patient privacy.

At a news conference Sunday in Le Bourget, Arnaud Desjardin, leading the investigation for the BEA agency, described Germany's privacy rules as being especially strict. He said doctors fear losing their jobs if they unnecessarily report a problem to authorities.

"That's why I think clearer rules are needed to preserve public security," Desjardin said.

The BEA report also recommends measures to remove the fear of losing a job that many pilots face for mental health issues. It says "the reluctance of pilots to declare their problems and seek medical assistance ... needs to be addressed."

But Desjardin says the investigators determined that systematic, deep psychological tests every year for all pilots would be "neither effective nor beneficial."

No change for cockpit rules

BEA investigators say airplane cockpit rules should not be changed, even though a suicidal Lubitz locked his pilot out of the control room before taking the plane into its deadly descent.

The agency said Sunday that it's still just as important to protect the cockpit from attackers elsewhere in the plane. Current cockpits are equipped with a code
system to prevent the kind of hijackings that occurred on Sept. 11, 2001, in the United States.

BEA investigator Arnaud Desjardin said "a lockage system cannot be created to prevent threats coming from outside and inside the cockpit."

Many airlines and regulators have issued changes since the March 2015 Germanwings crash in the French Alps and now require at least two people to be in the cockpit at any given time to prevent similar crashes.

Allow antidepressants for pilots

French air accident investigators are recommending that European aviation authorities adopt a more American-style system on mental health issues to encourage pilots to come forward about what medications they are taking.

The investigation agency says authorities in the U.S., Britain, Australia and Canada allow pilots to continue to fly while taking specific medications to treat depression as long as they are under clear medical supervision. Currently this is not done in Europe.

The French agency, in a report on the Germanwings crash, said Lubitz was using several antidepressants when he crashed the plane, but the airline said it had no knowledge of his illness, and BEA said the many doctors who treated him did not bring any concerns about his mental health issues to authorities.

Union supports recommendations

A union representing German pilots is welcoming the report's recommendations, while stressing the need to protect patient confidentiality.

Markus Wahl, a spokesman for the Cockpit union, said in a statement Sunday that BEA's safety recommendations are "a balanced package of measures" and should be implemented in full.

The agency has urged that laws be changed so medical workers must report concerns about pilots' mental health to authorities.

Cockpit said patient confidentiality must be protected and that "strict data protection standards" should be applied in drawing up checklists of criteria setting out what illnesses doctors must report. It said there needs to be a "careful balance" that secures "an improvement that is reliable for all sides without damaging the trust between a doctor and their patient.