If you are referring to a Compass flow, it was a grandfathered carryover from Northwest that Delta did indeed cut off as soon as they could. The Compass flow was contractual with NWA and tied to the amount of seats in their airplanes, a way to have more 76 seat planes outsourced from NWA. The Mesaba planes had already been exempted from the days of the Avros. and thus the Mesaba flow had no contractual protections, which is why most of us got the unlubed shaft on that one.