A survey looking at "depression and suicidal thoughts" among airline pilots found 12.6 percent met the criteria for "likely depression."
Of the 1848 pilots who completed the survey across the globe, 233 met the depression threshold. In addition, 75 participants – 4.1 percent – reported having thoughts pertaining to suicide or self-harm in the two week period prior to taking the survey.
"Elevated depression symptoms" were recorded in 13.8 percent of respondents who had worked as an airline pilot in the 7 days before taking the survey.
The study, conducted by researchers from the Harvard T. H. Chan School of Public Health, began shortly after a Germanwings flight was deliberately crashed into the French Alps in March 2015. It emerged that the co-pilot responsible for the crash, 27 year-old Andreas Lubitz, had experience of suffering from depression.
The researchers surveyed anonymous pilots between April and December 2015.
The survey speculated that the underreporting of mental health problems among airline pilots was "due to the public stigma of mental illness and a fear among pilots of being 'grounded' or 'not fit for duty.'" Mental disorders are only noted in pilot health records through self-disclosure – and aeromedical examiners do not diagnose mental health conditions – the survey said.
The study claimed that it was the first to focus on airline pilot mental health "with a focus on depression and suicidal thoughts," independent of civil aviation authorities and airline companies.
Madeleine McGivern, head of workplace wellbeing programs at U.K.-based mental health charity Mind, said that while the study "highlights the need for airlines to regularly assess all pilots' mental health," "assumptions about risk shouldn't be made across the board for people with depression or any other illness, mental or physical."
The survey said that 350 million people across the globe suffer from depression, a commonplace mental health disorder. Meanwhile, there are an estimated 140,000 airline pilots internationally with about 70,000 in the U.S.
McGivern emphasized that, "there will be pilots with experience of mental health problems who have flown safely for decades."
Follow CNBC International on Twitter and Facebook.