Aviation agencies around the world should draw up new rules requiring medical workers to warn authorities when a pilot's mental health could threaten public safety, French investigators have recommended in their report on the Germanwings plane crash.
Germanwings co-pilot Andreas Lubitz had been treated for depression in the past, and the investigation found that he had consulted dozens of doctors in the weeks before he deliberately crashed a jet into the French Alps on March 24, 2015, killing all 150 people on board.
But the doctors did not tell authorities of any concerns about Lubitz's mental health, France's BEA air accident investigation agency said, even though one even referred Lubitz to a psychiatric clinic just two weeks before the crash.
"Experts found that the symptoms (two weeks before the crash) could be compatible with a psychotic episode," said Arnaud Desjardin, leader of the BEA investigation. This information "was not delivered to Germanwings".
As Lubitz did not 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".
Germanwings and parent company Lufthansa have strongly denied any wrongdoing in the crash, insisting that the 27-year-old was certified fit to fly. There was no immediate comment from Lufthansa on Sunday after the report was released.
But relatives of those killed have pointed to a string of people they say could have raised the alarm and stopped Lubitz, going back to the days when he began training as a pilot in 2008.
The BEA investigation is separate from a manslaughter investigation by French prosecutors seeking to determine eventual criminal responsibility for the crash of Flight 9525 from Barcelona to Duesseldorf. The focus of its report was recommendations to avoid such events in the future, notably about pilot mental health issues and better screening before a pilot gets certified.
The agency found that the certification process failed to identify the risks presented by Lubitz. It said one factor leading to the crash might have been a "lack of clear guidelines in German regulations on when a threat to public safety outweighs" patient privacy.
Germany's confidentiality laws prevent sensitive personal information from being widely shared, though doctors are allowed to suspend patient privacy if they believe there is a concrete danger to the person's safety or that of others.
Mr Desjardin described Germany's privacy rules as being especially strict, and 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," he told reporters at a press conference in the French city of Le Bourget.
The BEA recommendations also included peer support groups and other measures to remove the stigma and fear of losing a job that many pilots face for mental health issues.
"The reluctance of pilots to declare their problems and seek medical assistance ... needs to be addressed," the BEA said.
Doctors who treated Lubitz for depression and mental illness refused to speak with the BEA investigators, according to victims' family members who were briefed on Saturday on the report.
Half an hour into the Germanwings flight, Captain Patrick Sondenheimer handed the controls to Lubitz and went to the restroom. When he returned, Sondenheimer found the cockpit locked from the inside. Lubitz, it seems, had disabled the safety code that would have allowed the pilot to open the door.
Shortly afterward, the Airbus A320 hit the ground near the French village of Le Vernet.
Lubitz had previously been treated for depression and suicidal tendencies, and documents seized by prosecutors show he partly hid his medical history from employers.
Lubitz interrupted his Lufthansa training for several months due to psychological problems. He was allowed to return in 2009, having received the "all clear" from his doctors - though his aviation record now contained the note "SIC" meaning "specific regular examination."
Lufthansa said after the crash that it was aware of Lubitz's depressive episode, but Germanwings, which he joined in 2013, said it had no knowledge of his illness.
The French investigators determined that systematic, deep psychological tests every year for all pilots would be "neither effective nor beneficial," Desjardin said.
Instead, the BEA recommended tougher monitoring of pilots who had mental health issues in the past.
It also said that cockpit security rules shouldn't be changed because it was still very important to protect the cockpit from outside attackers. Current cockpits are equipped with a code system to prevent the kind of hijackings that occurred on September 11, 2001, in the United States, where planes full of passengers were turned into weapons.
"A lockage system cannot be created to prevent threats coming from (both) outside and inside the cockpit," Mr Desjardin said.
After the Germanwings crash, many airlines and aviation regulators began to require at least two people in the cockpit at any given time to prevent such crashes.
Many of the relatives of the Germanwings victims were still upset after hearing about the report Saturday from BEA officials.
"People were not happy at all with some of the explanations. Some of the family members felt as if these BEA representatives were Lubitz' lawyers - making excuses as to why Germanwings didn't take action knowing what they knew," said Robert Tansill Oliver, whose son died in the crash.
"How is it possible Germanwings would let a crazy guy fly a plane? He was mentally unbalanced, tremendously unbalanced," Mr Oliver said.
For many victims' families, the biggest hope of holding someone to account lies in taking Lufthansa to court. Their frustration is heightened by the fact that the company has offered little more than the standard compensation required under German law - 25,000 euros (£19,000) for each victim - plus 10,000 euros (£7,700) to each of the victims' immediate relatives.
Since the crash, the airline has replaced its Germanwings brand with the name Eurowings.
Investigators also revealed that Lubitz was using antidepressants at the time of the crash.
Traces of Citalopram and Mirtazapine were found in Lubitz's system as well as the sleeping aid medication Zopiclone.
The US National Library of Medicine notes on its entry for Citalopram that children and young adults who take the drug can become suicidal "especially at the beginning of your treatment and any time that your dose is increased or decreased".
BEA chief Remi Jouty acknowledged that it is possible for pilots to be flying while using antidepressants that they have not declared to their employers.