Last year, an investigation into a deliberate plane crash in the French Alps that killed 150 made the startling revelation that the aircraft’s pilot suffered from depression and unnoticed suicide attempts. The tragedy prompted researchers to reexamine mental health issues among commercial airline pilots, and, sadly, what they found was that the case was not a one-off.

In an anonymous survey given to nearly 3,500 pilots by Harvard researchers, only 1,848 were willing to answer mental health questions. But of those that did, 233 pilots, or 12.6 percent, met the criteria for clinical depression and 75, or four percent, reported having suicidal thoughts, that is “having thoughts of being better off dead or self-harm,” within the past two weeks. Of the 1,430 pilots that filled out mental health questions and flew a plane in the last seven days, 193, or 13.5 percent, met the criteria for depression.