(CNN) -- As part of the investigation into the disappearance of Malaysia Airlines flight 370, experts say, authorities will likely review the performance records and the psychological evaluations of the pilots.
No evidence has so far turned up in the background of either pilot to suggest any wrongdoing. But with investigators scrutinizing every possibility, the head of the airline was asked at a news conference on Monday whether the pilot and co-pilot had passed psychological evaluations.
"The psychological test, the psychometric test and all that is standard procedure for pilot recruitment. They must go through that test," said the CEO of Malaysia Airlines, Ahmad Jauhari Yahya. "Going forward, we will obviously look into all this and see whether we can strengthen, tighten, all the various entry requirements."
While Yahya did not describe the exams, current and former pilots tell CNN that such testing depends on the airline, as well as the governing body in the country where the airline is based.
In the United States, all pilots must have physical exams once or twice a year, according to the FAA, and as part of that, a doctor is supposed to include an assessment of the pilot's psychological condition. Pilots are also required to disclose any psychological conditions and any medications they take. Any potential concerns are forwarded to the FAA flight surgeon for further evaluation.
But one former captain said those annual checks focus primarily on physical health, rather than mental health.
"I flew for over 20 years. I don't think I had any further in-depth psychological screening from the FAA," said former pilot Mark Weiss, a CNN aviation analyst who is now with The Spectrum Group. "The most that would happen would be, the FAA examiner would ask me, How is everybody at home? Things going okay?"
Instead, Weiss said, psychological evaluation is done primarily by the individual airlines, and is done when the pilot originally applies for the job. The applicant typically goes through a battery of exams that can last several days, he said, and some of the test questions are designed to evaluate temperament and psychological fitness.
"The standards were pretty strict, because there were so many people trying to get those jobs," he said. "They were coveted jobs, and they really weed out a lot of the people."
Les Abend, who currently flies the Boeing 777 for an airline he did not wish to name, said his psychological exam included questions such as "Do you like your mother? Do you hate your father? Have you ever harmed a small animal?"
"People are vetted incredibly," he said.
But once a pilot has been hired, Abend said, psychological questions are not typically asked during the pilot's annual physicals. Instead, he said, it is up to pilots themselves, along with their coworkers, to report any psychological issues.
The FAA, in its medical examiners guide, says pilots who take certain antidepressants may still receive medical clearance on a case-by-case basis.
But some pilots hide their conditions, according to two pilots who spoke to CNN on condition of anonymity out of concern for their own careers.
One veteran with three decades of experience said he's known just a single pilot who sought treatment for depression. The treatment lasted eight or nine months, and he never told his employer, the pilot said.
Another veteran pilot told CNN, "Pilots are flying around depressed, because if they do (admit depression), they'll be grounded."
The issue of psychological screening for pilots came up two years ago, when a JetBlue pilot had a meltdown during a flight from New York to Las Vegas. According to prosecutors, passengers subdued the pilot after he yelled jumbled comments about Jesus, September 11th, Iraq, Iran, and terrorists.
"It just seemed like something triggered him to go off the wall," said passenger Jason Levin.
But Weiss said that additional psychological testing of pilots in the United States would be unnecessary.
"Pilots are for the most part very mentally stable, very sound people," he said. "Very determined, very professional."
CNN's Marnie Hunter and Thom Patterson contributed to this report.