As investigators probe why a young German pilot deliberately crashed an Airbus A320 passenger jet into the French Alps on Tuesday, pilots and psychologists warn there is no foolproof way to prevent similar incidents in the future.
All 150 people on board Germanwings flight 4U9525 died after 27-year-old first officer Andreas Lubitz locked the cockpit door, took control of the plane and veered it down from cruising altitude at 3,000 feet per minute.
German tabloid Bild reported on Friday that Lubitz received psychiatric treatment for a "serious depressive episode" six years ago, and the crash has prompted calls for more rigorous mental health and stress tests for pilots.
Students of Joseph-Koenig-Gymnasium high school hold a minute of silence outside their school in Haltern am See, Germany. The deaths of 16 teenage students and two young teachers in the Germanwings plane crash in the French Alps left the lakeside town of Haltern am See in a state of shock. (Reuters)
The International Civil Aviation Organization (ICAO), the UN body that sets global aviation standards, recommends that someone with depression should not fly a plane. But it also states in its Manual of Civil Aviation Medicine that psychological tests of aircrew are "rarely of value" and not "reliable" in predicting mental disorders.
Rescue workers at the Germanwings passenger plane crash site near Seyne-les-Alpes, France. (AP Photo)
Asian airlines including Cathay Pacific, Japan Airlines, Qantas Airways and Singapore Airlines said potential pilots undergo a rigorous medical that includes a psychological test. Pilots must then pass a medical check-up, which includes some psychological tests, at least once a year. They also have access to confidential counselling services, the airlines added.
These may not be enough, analysts and pilots say.
"People are afraid they won't be able to resume their jobs" if they self-report, said Gail Saltz, a professor of psychiatry at Weill Cornell Medical College in New York.
An experienced captain with an Asian airline added: "They ask about your mental health, about events that could affect you psychologically. But who willingly admits to anything that could lead to a suspension of their license? I won't. I need my job."
Pilots are encouraged to assess colleagues during flights and simulator training sessions, and speak up if they spot any potential issues, said an A320 captain with an Asian carrier. But he added that this is a delicate issue.
A German police officer enters the house believed to belong to crashed Germanwings flight 4U 9524 co-pilot Andreas Lubitz in Montabaur. (Reuters)
"Do you want to work in an office where your colleagues are snitching on you? That's why this happens so rarely," he said.
"Everyone has problems and some deal with it better than others. Not everyone will deal with it by crashing a plane. That's an extreme reaction and nobody can predict it."
David Powell, an aviation medicine specialist in New Zealand, said there were only 10 air crashes involving medical issues in an ICAO study of 20 years of global incidents.
"Could you reliably ensure that you'll never have an airline pilot suddenly, deliberately crash aircraft?" he said. "Pilots are a highly screened population and highly scrutinised, but who can totally predict the behaviour of human beings?"
Several airlines have responded by requiring a second crew member to be in the cockpit at all times - already compulsory in the United States.
"Never leave a person alone - that's probably the most effective suicide prevention technique there is," said Tony Catanese, a clinical psychologist at Glen Iris Psychology in Melbourne.