Context: 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.

Question: Whose work habits and environment prevents them from maintaining a regular sleep pattern?
Answer: airline pilots

Question: What can the lack of regular sleep patterns cause?
Answer: fatigue

Question: What organizations cites this disruption of sleep patterns as a cause of accidents?
Answer: NTSB

Question: What has the NTSB conducted to find the cause of pilot fatigue?
Answer: research studies

Question: Of what does the NTSB want to find a means of doing?
Answer: combating fatigue

Question: Who follows a very natural human circadian rhythem?
Answer: Unanswerable

Question: what does a natural circadian rhythem lead to?
Answer: Unanswerable

Question: Who conducted studies on sewardes fatigue?
Answer: Unanswerable