> How did Boeing decide to kill the 757 and to continually delay the "New Midsize Airplane", and to progressively extend and modify the 737 until it reached 757 size in the 737 MAX 9?
> Southwest Airlines has only operated Boeing 737 jetliner models, except for a period from 1979 to 1987
I expect that sort of things was part of the decision. Even more so as Boeing never really try to unify their offering and provide airbus-style CCQ[0][1] so there is a very strong incentive & pressure to update frames and keep them in the same rating to avoid crew retraining costs.
[0] moving from an A320 to an A380 can take as little as 15 days, other moves are much shorter (down to 2 days CCQ for — I believe — moving between the A330 and the A340)
[1] boeing does have some common type rating courses but only between a few pairs e.g. between the 757 and 767, or from the 777 to the 787
> Southwest Airlines has only operated Boeing 737 jetliner models, except for a period from 1979 to 1987
I expect that sort of things was part of the decision. Even more so as Boeing never really try to unify their offering and provide airbus-style CCQ[0][1] so there is a very strong incentive & pressure to update frames and keep them in the same rating to avoid crew retraining costs.
[0] moving from an A320 to an A380 can take as little as 15 days, other moves are much shorter (down to 2 days CCQ for — I believe — moving between the A330 and the A340)
[1] boeing does have some common type rating courses but only between a few pairs e.g. between the 757 and 767, or from the 777 to the 787