Due to the work nature of airline pilots, who often cross several timezones and regions of sunlight and darkness in one day, and spend many hours awake both day and night, they are often unable to maintain sleep patterns that correspond to the natural human circadian rhythm; this situation can easily lead to fatigue. The NTSB cites this as contributing to many accidents[unreliable medical source?]  and has conducted several research studies in order to find methods of combating fatigue in pilots. COUNT 5
QSN1 Whose work habits and environment prevents them from maintaining a regular sleep pattern? ANS1 airline pilots QSN2 What can the lack of regular sleep patterns cause? ANS2 fatigue QSN3 What organizations cites this disruption of sleep patterns as a cause of accidents? ANS3 NTSB QSN4 What has the NTSB conducted to find the cause of pilot fatigue? ANS4 research studies QSN5 Of what does the NTSB want to find a means of doing? ANS5 combating fatigue