So when should we hand fly the aircraft? At the beginning of the 13 hour duty while we are "fresh" and "alert" making us more fatigued at the end of the day should an emergency occur.Or at the end of the day while we are tied and likely to make mistakes?It's a catch 22 brought about by excessive duty time fatigue on the day,possible accumulated fatigue from previous duty times or potential fatigue that may occur should the day be unexpectedely extended.It's not as obvious as we would like.