Aviation experts are calling for more rigorous psychological testing for pilots, after Tuesday's Germanwings plane crash in the French Alps that killed all 150 people on board.
Investigators believe the co-pilot of the Lufthansa- owned budget carrier deliberately brought the Airbus A-320 down.
While it is common for airlines to conduct some form of psychological screening before pilots are hired, standards vary and there are no global guidelines, said Mr Michael Daniel, a retired air accident investigator with the United States Federal Aviation Administration.
"There are no psychological standards set by the International Civil Aviation Organisation, only medical," he said.
"We need global standards for mental fitness, beginning with stress, duress and depression."
Dr Philip Scarpa Jr, president of the US-based Aerospace Medical Association, said: "Most airlines do not perform any periodic mental health assessments after an initial screening during the hiring process.
"In addition to screening, though, education of the pilots, their families and others in the aviation community on what to look for in mental wellness and how to report it are also important measures the airlines can take."
Dr Hsin Chen Chung, an aviation expert and the director of Nanyang Technological University's Air Traffic Management Research Institute, said: "Many airlines will say they have all the rules and screening in place, but what is crucial is the degree of implementation."
Singapore Airlines (SIA) pilots told The Straits Times that the carrier's pre-hiring assessment, which typically takes several hours, is "quite intense".
Former pilot and current head of the diploma in aviation management programme at Republic Polytechnic, Mr H. R. Mohandas, said: "It's all quite scientific and calibrated, designed to pick up personal traits and characteristics.
"Different scenarios and situations are presented to test your logic, intellect and other skills."
One SIA pilot told The Straits Times: "Examiners also assess your body language and mannerisms."
Once hired, annual or twice-yearly reviews are conducted, but these mainly focus on physical rather than mental health, he added.
Some airlines also have mechanisms in place for pilots to voluntarily disclose emotional and mental stress.
Said an SIA captain with more than 30 years of flying experience: "Pilots are trained to operate under pressure and stress and, being senior, we also look out for the younger ones.
"On rare occasions, I've had co-pilots tell me they are a little tired or troubled by family affairs, but at no time did this affect their flight performance.
"In all my years of flying, I've never offloaded a fellow pilot because I did not think he was fit to fly."
The Germanwings crash is likely to trigger airline operational reviews.
But no test or screening can guarantee that a similar incident will never occur, said Dr Hsin.
"The root of the problem is the human being, and unless everyone is a saint or has absolute peace of mind, there is no foolproof assurance."
This article was first published on March 28, 2015.
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