French investigators urged new rules for the medical screenings of pilots on Sunday, after their inquiry found that a doctor had recommended hospital treatment for Germanwings co-pilot Andreas Lubitz two weeks before he deliberately downed a passenger plane.
The troubled 27-year-old was on two separate antidepressants and a sleeping medication when he steered the Dusseldorf-bound plane into a mountainside in the French Alps, the country's civil aviation authority (BEA) said in its final report on the crash that killed all 150 people on board.
Investigators for the safety agency said they were unable to interview Lubitz's physicians or relatives - who exercised their privacy rights - and could therefore not reach a definitive conclusion on his mental health.
"The limited medical information available may be consistent with the co-pilot having suffered from a psychotic depressive episode that started in December 2014, which lasted until the day of the accident," their report said.
"Other forms of mental ill-health cannot be excluded and a personality disorder is also a possibility," it added.
Privacy concerns over medical confidentiality also likely stopped the doctor who recommended hospital treatment - and diagnosed possible psychosis - from approaching the authorities. Neither that doctor nor another psychiatrist informed the aviation agency or any other officials, the report said.
Scrutiny throughout the unravelling of the case has focused on why someone with health problems could have ended up alone in the cockpit of a commercial jet.
"The Lufthansa group hired and trained a psychologically sick pilot candidate, with terrible consequences," said Christof Wellens, a lawyer for some of the victims' families.
Lufthansa is the parent company of budget airline Germanwings, which has since been rebranded under the name Eurowings.
"For Lufthansa and the airlines of the Lufthansa group, the greatest possible flight safety was and remains our highest priority," a spokesman for the company said. "The company will continue working closely with the authorities and supporting the implementation of concrete measures."
The BEA, a safety agency that does not weigh in on judicial or criminal proceedings, said there was "lack of clear guidelines in German regulations" on when the interests of public safety should overrule medical confidentiality.
It added that neither Germanwings nor the authorities could have prevented Lubitz from entering the cockpit in Barcelona on March 24, 2015, the day of the accident, because information about his medical conditions had not been provided to them.
This lack of shared knowledge is one of the factors that remains most troubling to some of the victims' families. "These sick notes that were given, they were not forwarded to Lufthansa's aeromedical service," said one family member, who did not want to be named.
Recommendations issued by the BEA tried to grapple with that oversight, while stopping short of recommending regular psychiatric tests for all pilots. It said that there should be rules on follow-up checks for pilots who have a history of psychological troubles.
Lubitz, who had been flying for Germanwings since 2014, was issued a class 1 medical certificate in 2008. The following year, the certificate was not revalidated twice due to depression and the medication Lubitz was taking. When he received a new certificate in July 2009, it was with restrictions and had to be renewed annually.
Some investigators have suggested that Lubitz may have kept his illness a secret out of fear of not passing a medical certificate renewal due in the August following the crash.
There is evidence that he researched suicide methods and cockpit door-locking mechanisms online during the week prior to the accident.
The BEA recommended making sure that pilots struggling with depression would not be afraid of seeking help, including taking medication under supervision. It also urged clearer rules for balancing public safety with medical confidentiality, and recommended programmes to ensure grounded pilots would have other forms of income.
Germany's cockpit union welcomed the report, and said aviation workers with mental health problems should not fear the consequences of seeking out support.
"It is important that this package is implemented in its entirety and not only in the places that seem easy to implement," Markus Wahl, a spokesman for the pilots' union, said.