And there are plenty of airports regionals operate in where a mainline plane would never be able to go. It’s not always a matter of consolidating 5 daily flight to 1 weekly flight, or maintaining slot/gate space, or whatever frequency is required at small airports for EAS agreements. Sometimes it comes down to size and performance. You’ll never see mainline at State College, Flagstaff, Aspen, Ithaca, or any number of small airports.

you’d be surprised where 727’s landed in 1981

Very few airfields actually limited by runway length

Yup, they did milk runs, multiple small towns in loop from the hub.

Most small town muni airports got runways long enough for jets back in the 50's and 60's. Concrete was cheap back then.

I think you can count on both (or maybe one) hands the US airports which currently have commercial service and are severely limited by performance for NB's.

The real issue is frequency. Given travel habits, one or two round-robin services was plenty back in the golden age. But today people are busy, and travel casually, so they like frequency options. More than anything else that's the RJ sweet spot.

yes. In the day they had frequency with half full 727’s at $$$

only viable option now is full(ish) RJ’s at $

a 717 could do ITH or SCE with minimal changes to the ramp. The A220 has the performance for ASE but wings are too long and it’s too heavy for local ordinances. Don’t forget the 737-700/A319 have comparable/ better short field performance to a CRJ200

I thought everything had better short-field performance than a 200. Except a 900.

Nothing is stopping mainline from operating their own 175's.

Far far from it. It's a code share agreement, which is a huge difference. As far as I know, it only applies to certain parts of the route structure.

Only flights to/from NY and BOS, excluding JB’s future London flights (maybe some others).

yes, but that subject has been argued to death for years. We would all love to be absorbed by a major. They’ll never do it though.