Kirby. Good call. No availability of other suitable aircraft to satisfy the route demand as UA attempted to draw down the PS fleet. They're old planes but DL runs 75s like they're band new. The sCO 75s have been a workhorse for years. Until Boeing or Airbus manufacture more RB211s, it's always going to be a catch-up play. Even the 321Neos are on the Pratt geared platform, I understand.

737-900ERs are great aircraft -- but there is no replacing the PS fleet & 75s. John Wayne or Glasgow, it's the only aircraft that you can point to a specific route and it just handles it.