The Air Line Pilots Association has published a white paper decrying any effort to permit single-pilot airline operations. “Those promoting single-pilot operations argue that reducing crew size will lead to cost savings,” it wrote. “However, the current body of evidence and experience, including more than a decade of study by NASA and the FAA, shows that the safety risks and challenges associated with single-pilot operations far outweigh its potential benefits.”

Pilot incapacitation is the key issue. The association refers to published FAA data revealing that there were 262 occurrences of pilot incapacitation in single-pilot Part 91 operations from January 1980 through July 1989, resulting in 180 fatalities. During the same period, there were 32 occurrences of pilot incapacitation in single-pilot Part 135 operations, resulting in 32 fatalities. In Part 121 operations over the same period, there were 51 pilot incapacitation occurrences that resulted in normal aircraft recovery by the other pilot.

Although this data is 30 to 40 years old, the association also cited more recent data. According to the Australian Transport Safety Bureau, from 2010 to 2015 there were 23 pilot incapacitation occurrences per year on average, 75 percent of them happening in high-capacity air transport operations. With multi-pilot crews, incapacitation had “minimal effect on the flight.” But for single-pilot general aviation operations, incapacitation often meant returning to the departure airport or crashing.