Why do some Crew pairings have long halts?
Crew pairings within the published roster are a function of the commercial schedule, and is constructed based on operational stability and availability of crew at a base while maintaining an acceptable level of duty productivity. There is also an element of quality of life that is considered for the operating crew.
Mostly, long halts are found on single day trips and/or on the last day of a multiple day trip. This is done so as to bring the crew back to base and terminate the trip. There are also instances of long halts to cater for swapping of aircraft as per the planned rotation, and in some cases to retain the same crew on the aircraft rotation.