부산대학교 도서관

To the Editor.—The communication by Cobb and Rose (224:489, 1973), concerned with excess illness in air traffic controllers, is clearly a sophisticated epidemiological investigation. I believe that an important definition was omitted, however, and that this may be confusing to some readers and might seriously hamper independent intellectual evaluation of the work. The definition omitted is that of "second class airmen."I have not heard that term before, and, therefore, do not know with certainty what the authors mean by it. One possibility is that they mean men who hold a Federal Aviation Agency medical certificate of the second class. If so, it refers to full-time or parttime professional pilots (who may not take kindly to being called secondclass airmen). Many of your readers may not be aware that airline pilots are required to maintain a medical certificate designated as first-class; other commercial pilots and flight instructors must have a