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 bedtime (2200 to 2300 Seoul local time) and a time at which his body would have been primed for sleep.

CVR evidence indicated that the captain was tired. At the beginning of the approach, the captain made unsolicited comments related to fatigue, stating "eh...really...sleepy." In its investigation of the 1993 American International Airways accident at Guantanamo Bay, Cuba, the Safety Board noted that individuals often tend to underestimate their own level of fatigue. Thus, the captain's comment could have reflected a significant performance degradation. Neither the first officer nor the flight engineer made similar comments.

According to his family, the captain slept his normal sleep routine in the days before the accident and had an opportunity to receive adequate rest. He also took a nap from 1100 to 1340 (Seoul local time) on August 5 and would therefore have been awake for 11 hours at the time of the accident. The Safety Board has found this time since awakening to be associated with greater errors.

For example, in its investigation of the 1993 accident in Pine Bluff, Arkansas, the Board determined that the captain and first officer had both been awake for 11 hours.

Further, the sleep history provided by the captain's family does not address the quality of sleep he received. For example, the time of the captain's reported nap corresponds to a typical physiological period of wakefulness when napping is difficult204 and of limited efficiency at reducing sleep debt. If the captain actually napped at this time, it suggests that he may have had unusual sleep needs that were not indicated by the number of hours in his reported sleep history.