The disturbing realization that one of the co-pilots of the Germanwings jetliner orchestrated its deadly descent into a French mountainside has travelers asking: How do we know if a pilot is mentally fit to fly?
The problem, aviation experts say, is that there's no uniform consistency across the industry to know for sure. The United Kingdom's Civil Aviation Authority, for instance, says its commercial pilots must have their mental health assessed during each medical exam, which is typically done every year.
In the United States, the Federal Aviation Administration requires captains to have a first-class medical certificate renewed every year if the pilot is under 40 and every six months if the pilot is 40 or older. But psychological checks aren't required, although concerned doctors could order pilots to undergo testing for "emotional stability and mental state."
So, a pilot who doesn't raise any obvious red flags will keep flying.
"The system relies on pilots self-declaring, so unless a pilot is honest about an alcohol problem or a psychiatric disorder, there’s no guarantee a problem would be spotted," aviation psychologist Diane Damos, whose company specializes in pilot selection and screening, told NBC News last year.
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Airlines can require their own psychological screenings for new hires. Germanwings' parent company, Lufthansa, didn't immediately respond to a request about its protocols following Tuesday's crash of Flight 4U9525 in the French Alps.
Lufthansa's online list of requirements for would-be pilots doesn't specifically mention mental health either. It does note that applicants can't be listed in Germany's registry of traffic offenders for alcohol or drug use and must have a "sense of responsibility, discipline, dependability, and team compatibility as well as convincing CV and high motivation."
According to Lufthansa's Pilot Training Network, pilots must also pass aptitude tests, including a psychological assessment.
The subject of pilots acting bizarrely or even sabotaging their planes is rare, but not unheard of. In 2012, a JetBlue flight was diverted after leaving New York City when the captain began pounding on the cockpit door and yelling threats. In February 2014, a co-pilot of an Ethiopian Airlines flight took control of the plane, locking his co-worker out of the flight deck in order to demand political asylum.
And the March 2014 disappearance of Malaysia Airlines Flight MH370 has led some aviation experts to speculate pilot suicide or some unexplained nefarious plot.
The co-pilot in the Germanwings crash was identified Thursday as 27-year-old Andreas Lubitz, who French investigators say refused to allow his co-pilot into the cockpit right before the fatal plunge. At a news conference, Lufthansa CEO Carsten Spohr said there was "no indication what could have led the co-pilot to commit this terrible act."
John Gadzinski, a Boeing 737 captain and aviation safety consultant, told NBC News that this crash may be just the wake-up call the industry needs for talking about mental health issues.
"It doesn’t matter if it’s a person who has an AR-15 shooting out 4 year olds or a pilot who’s going to kill 150 people on an airplane," Gadzinski said. "The question is how do you prevent a statistically unlikely event from catastrophically occurring?
"We can either shake this off," he added, "or this event can fundamentally transform how we look at mental health and aviation."