UK Air Navigation Order
146 (1)(2)
A person must not act as a member of the crew of an aircraft to which this article applies if they know or suspect that they are suffering from or, having regard to the circumstances of the flight to be undertaken, are likely to suffer from, such fatigue as may endanger the safety of the aircraft or of its occupants.
Many/most have fallen asleep while operational - some planned and deliberate, others accidental. At what stage does this start to endanger the the safety of the aircraft? Surely any crew with sleep inertia or liability to microsleep is less safe than a well rested crew during their normal waking hours. Do airlines have safety mitigations for this (where?) or is it just quietly forgotten until the court case?