In addition, most programs are based on an honor system, relying on pilots to volunteer information about problems they might have. And to do that, several psychiatrists said, they must overcome the stigma that still clings to mental illness, one that remains strong in commercial aviation, a profession with deep roots in the military that values a cool head and steady hand under pressure.

The screening process for pilots “really falls short for people who are involved in the public’s safety,” said J. Reid Meloy, a forensic psychologist who consults on threat assessments for corporations and universities.

The practice of screening only once a year is a particular problem, he said, because any number of life events — the breakup of a relationship, the death of a loved one or other setbacks — can affect mental functioning. Rather than coming out of nowhere, suicide often represents a convergence of troubled strands. Investigators who delve into a suicide victim’s background — interviewing relatives, co-workers and friends in what is called a psychological autopsy — almost always find a troubled history and often uncover hints about suicidal intentions that were overlooked or ignored by others.