Originally Posted by
Wally Bird
Going by the hint, I'd guess Air Wisconsin BAe146 MKE-MCI before they joined United Express.
The question is set in 1981 and the first Air Wisconsin 146 was delivered in June 1983, so not that. In my August 1980 ABC* it's one Braniff and three United, so must have changed after that.
* : Now some of you know these are nowadays stored up in the far reaches of our attic, slightly beyond the Gulfstream 1 production list (and for a month or two more, the infamous lawnmower as well). Fortunately it's the weekend and some more household items needed to go up and down.
Mrs W

(distantly) : "Been a long time up there, dear, not looking at the aeroplane books are you ?"
Self : "Now would I do something like that ?"
Mrs W (closer) : "When there's a long silence like that - yes .....".