I believe the UA and AA scope limits are tied to the number of aircraft in the mainline fleet. AA grew their mainline fleet, so they could add a few more 76-seaters, but they are close to being scoped out. With their current orders and projected retirements, I think they have room for about 30 more 76-seat RJ, but they won't be able to go into service until mainline gets theirs delivered (or delays a proportional number of retirements).