Flight crew fatigue V: long-haul air transport operations.

We monitored 32 flight crewmembers before, during, and after 4-9 d commercial long-haul trips crossing up to 8 time zones per 24 h. The average duty day lasted 9.8 h, and the average layover 24.8 h. Layover sleep episodes averaged 105 min shorter than pretrip sleep episodes. However, in two-thirds of layovers, crewmembers slept twice so that their total sleep per 24 h on trips averaged 49 min less than pretrip. Greater sleep loss was associated with nighttime flights than with daytime flights. The organization of layover sleep depended on prior flight direction, local time, and the circadian cycle. The circadian temperature rhythm did not synchronize to the erratic environmental time cues. Consequently, the circadian low point in alertness and performance sometimes occurred in flight. On trip days, by comparison with pretrip, crewmembers reported higher fatigue and lower activation; drank more caffeine; ate more snacks and fewer meals; and there were marked increases in reports of headaches, congested nose, and back pain. Scheduling strategies and countermeasures to improve layover sleep, cockpit alertness, and performance, are discussed.