Originally Posted by steve64

So, we're in agreement then.
Which means that 2 of your posts above need to be corrected to show the routing as LHR-PHX-LHR, not the PHX-LHR-PHX that you indicate.

Listing the routing as you have, has made some of us think you believe the plane that just flew PHX to LHR is going to turn at LHR back to PHX. Which, in the absence of any "tag" legs to/from PHX, means that in PHX the plane can only turn back to LHR and repeat. Thus my comment about "dedicated airframe".

My apologies to Ldnn1 who described typical TATL routings as a "W". In my days at AA Ops, we never used that term, so it went way over my head. In this reply, I realized that my long post above is saying the typical TATL routings are a "W".
To combine your "PHX-LHR-PHX" routing with Ldnn1's "W" and my generic routing gives us .... (ignore the dots below, they were needed to get the slashes and airport codes to align correctly)

USA Maint Base....USA Maint Base
....\............................/....
.....\ ........LHR........../.....
......\....... /.....\ ......../......
.......\..... /........\..... /.......
........PHX........PHX.......

Correcting the verbiage of your routing to "LHR-PHX-LHR" gets all of us in agreement ...
USA Maint Base....USA Maint Base
....\............................/....
.....\ ........PHX........../.....
......\....... /.....\ ......../......
.......\..... /........\..... /.......
........LHR........LHR.......