It's actually less crazy than you think. At some point a month or so ago I worked out how many frames were needed to cover the schedule, and it came out to something like 19 or 20 out of a 24-strong fleet. For the domestic 757s based out of PHX, it was 9 out of 10.
The departure numbers per frame might be lower with UA's schedule, but UA flies their 752s on much longer routes on average.
I get it, thanks for this. But still, doesn't AA operate the 757 out of PHL on TATL routes and PHX to Hawaii? I feel like it's more on the aggressive side with only 34 frames, but I could be totally wrong.
Of the 10 PHX-based domestic 752s, there are 6 frames required for the Hawai'i flying (1x LIH, 2x HNL, 2x OGG, 1x KOA). There's quite a bit of downtime in between the Hawai'i flights, so a few additional shorter turns can be fitted in (PHX-SAN-PHX, PHX-DFW-PHX). That leaves 4 out of 10 frames. Of those 4, three run longer out-and-back trips (PHX-CLT-PHX, PHX-DCA-PHX, PHX-CUN-PHX) and RON at PHX. That leaves 1 spare, and some pretty decent downtime for the frames that are flying.
The 24 international-configured 752s don't actually fly too many intercontinental routes at this point. There's DFW-KEF, DFW-LIM, MIA-LIM, MIA-VVI, MIA-BSB, PHL-SNN, and PHL-EDI. Those routes essentially tie up one frame each (VVI and BSB are deep South America routes, but they have daylight northbound flights so they don't require 2 frames like most other deep South America flights that are redeyes in both directions). That leaves 17 frames to cover the hub-to-hub, domestic, and short range international flying.
Since the MAX grounding, AA has moved 2x daily MIA-UIO flights from 7M8s to 752s, so they've reduced some of the domestic 752 flying that had previously been loaded to compensate for that.
This is my signature until I think of a better one.