Originally Posted by BostonPlanesAndTrains

DL staffs based on minimal staffing at least on the narrowbodies. A319/A220/717 will have 3 FAs, A320/A321/737/757-200 will have 4 FAs. I have seen the 767 get sent on on domestic hops with 5 crew but usually there is a 6th. 757-300s will have 5, these are interesting because the 5th can function like an 'addon' (4 ATL/XXX based flight attendants + 1 SEA/LAX/BOS/etc. based).

As mentioned above this is not necessarily true on longer hauls with more labor-intensive services and longer duty periods.