and maintain safety standards, convinced Congress to pass the Air Commerce Act. This act established the Aeronautics Branch of the Department of Commerce, and charged the Secretary of Commerce with fostering air commerce, issuing and enforcing air traffic rules, licensing pilots, certificating aircraft, establishing airways, and operating and maintaining aids to air navigation (Federal Aviation Administration [FAA], 2002). Lighted airways became more common, and aeronautical radio communications were improved through the use of radio beacons. Hours-of-service limitations were not established by the FAA until 1964 (Patton et al., 2001).

The duty schedules for pilots, air traffic controllers, engineers, flight attendants, airline mechanics, and various other types of crew members are regulated by the FAA under statute 11 C.F.R. 121 (P-S). Rules on duty hours for pilots vary by the size of the flight crew (e.g., one pilot versus a crew consisting of two or more pilots). Pilots working during both scheduled and unscheduled operations (e.g., corporate/executive operations), cannot work more than 8 hours in a 24-hour period if there is only one pilot. When larger flight crews are used, pilots are allowed to work an additional 2 hours (Patton et al., 2001; U.S. Congress Office of Technology Assessment, 1991d). Domestic air carriers are not permitted to issue, and pilots are not permitted to accept, an assignment for a flight if the crew member’s total flight time will exceed 100 hours in a calendar month, 30 hours in 7 consecutive days, or 8 hours between required rest periods (U.S. Congress Office of Technology Assessment, 1991a). Rest periods are also mandated and vary according to the length of the scheduled flight time. If the scheduled flight is less than 8 hours in duration, 9 consecutive hours of rest are mandated between flights; if the scheduled flight is 8–9 hours in duration, 10 consecutive hours of rest are mandated; and if the scheduled flight is 9 hours or more in duration, 11 consecutive hours of rest are mandated (U.S. Congress Office of Technology Assessment, 1991a). Longer rest periods are also mandated if pilots exceed the daily flight time limitations because of circumstances beyond their control (e.g., adverse weather conditions). If flight time limitations are exceeded by less than 30 minutes, a pilot cannot be assigned or accept an assignment that does not allow for 11 consecutive hours of rest. If the flight time limitations are exceeded by more than 30 minutes, but less than 60 minutes, 12 consecutive hours of rest are mandated. And when flight time limitations are exceeded by 60 minutes or more, 16 consecutive hours of rest are mandated before the next flight (Patton et al., 2001).

Although commercial airline pilots typically work only 13–15 days a month (Meenan, 1999), there is ample evidence that fatigue remains a significant problem. Surveys, observational data, and anecdotal reports have documented that flight crews frequently experience unintentional sleep episodes while flying (Co et al., 1999; Gander et al., 1991a; Rosekind et al.,



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