Originally Posted by
LarryJ
A layover must be a minimum of ten hours. Without an intervening 10-hour layover, the pilots would remain on duty all night. The flight duty period limit for an evening report (5pm-9:59pm, with two flight segments) is 12 hours and starts one-hour before schedule departure time.
To be legal, you either have to fit the entire trip within that 12-hour flight duty period or you have to have a minimum of a 10-hour layover to break it into two flight duty periods. So, for an 8:00pm departure the night before, you'd have to be scheduled to complete the return no later than 7:00am the following morning. You must be estimated to arrive within those constraints at the beginning of the takeoff roll on each flight which is why you can sometimes taxi out but, after a delay, have to return back to the gate due to crew legalities.
https://www.law.cornell.edu/cfr/text/14/part-117
Table B is the applicable duty time limits.
My father was a CO pilot. Back when he was on the MD-80, he got this trip a few times that he hated. The times are. not exact, but it went something like this
Day 1: EWR 1600 - DTW 1830. 12 hour rest period
Day 2: DTW 0700 - ACY 0930. 12 hour rest period. ACY 2300 - DTW 0130. 5 hour rest period
Day 3: DTW 0700 - ACY 0930. 12 hour rest period. ACY 2300 - DTW 0130. 4 hour rest period
Day 4: DTW 0600 - EWR 0830
IIRC the DTW - ACY flights were either charters or something special. Keep in mind this was either in the late 80s or early 90s, when ACY was worth taking a flight to see.