So when exactly is someone too mentally unstable to be trusted with the flight controls of an aircraft?

In the wake of the Germanwings co-pilot mass murder/suicide this spring, we can expect the usual hysteria and overreaction from politicians and regulators and additional pages of compliance trailing behind. But it all really comes down to personal responsibility.

A pilot instinctively knows when he or she is mentally or physically fit to fly. You're tired, irritable, have a slight fever, etc.? Time to call in and go home.

That's where the question really begins and ends. The recent trend to loosen medical fitness requirements for recovering addicts or medicated depressives are moves in the right direction inasmuch as they no longer encourage pilots to lie to their flight physicians or deprive the sky of otherwise talented individuals who are responsibly treating their illnesses in a way that does not impair their ability to command an aircraft.

Mental illness, like many other varieties, is not a one-cure-fits-all proposition. To this day it is generally stigmatized and badly misunderstood by the general public. Pilots who are responsibly treating their mental illnesses are far less of a threat to the flying public than the sedentary pilot who throws a blood clot in midflight. But no one is talking about maximum body weights and mass indices and 40-yard dash times for pilots in command — yet.

Granted, mandatory psychological testing prior to flight training might not be a bad thing. But if someone wants something bad enough, there are always workarounds.

Psychopaths in the cockpit get a lot of news play because it is such a rare event. Pilots need to work in close proximity with others on a daily basis, and a mentally unfit pilot — or one with 80-proof cologne — gets noticed in a hurry.

Aviation is a remarkably self-cleansing profession, and I don't mean that mortally speaking. Because the majority of pilots are so professional and so dedicated to their craft, the bad apples stand out and quickly.

No battery of new-fangled tests can keep every sociopath from taking the controls in the cockpit. That requires the vigilance of all of us, every day.

It is incomprehensible to fathom that some flight attendant or some captain Germanwings co-pilot Andreas Lubitz flew with never noticed he was just a little off. Crews that self-police do more for safety than any body of regulation ever will.