Rest between disruptive schedules CS FTL.1.235(a)(1), (see also ORO.FTL.105(8)): The rule for transition between late finish/night duty and early start says that the rest between the FDPs needs to include a local night. Does this mean that the rule only applies if the late finish/night duty and the early duty are FDP’s?
It depends on the type of the early duty following a late or night duty.
If an early duty is a standby or a duty at the airport that leads to an FDP, then the rest period before that early duty must include a local night.
Otherwise, the rest period between the 2 other duties or between a FDP and other duty (e.g. night training in a simulator) does not need to include 1 local night.
Nevertheless, Subpart FTL provides a system of measures which jointly act to reduce the risk of increased fatigue and reduced alertness and performance levels of crew members, and to mitigate the acute disruption of the sleep pattern in the case of disruptive schedules.
For example, the operator must avoid practices that cause a serious disruption of an established sleep/work pattern, such as alternating day/night duties (ORO.FTL.110).