Do Part 121 routes ever switch from regional to mainline? I don't know how the contracts work between the carriers on how easy that is. Putting more capacity on a route via adding an additional flight per day is probably easier than moving from regional jets to bigger jets. But what does that look like? We have a route to DFW twice daily that is always booked solid and with my former employer now moving it's HQ to Dallas, the demand on that route is even higher than ever. Just wondered if AA would ever move it over to bigger jets. Not sure how many A319s they have but that would be the next logical step to me from the E175.