Originally Posted by
mec72
I had both AA segments on BA bookings and BA segments on AA bookings recently and could select seats for all flights. You need to get the other PNR though (BA now helpfully also shows the AA PNR, in the past you had to call), and just select seats for the respective segments on the operating carrier's website.
Yes, the problem that sometimes happens is that actually there are two (or more) SABRE references for the flight, depends a bit on complexity. BA.com may show just one, and that may not be the right one for the flight concerned. Also there is the usual ticketing issue, particularly if the booking was changed at some point - unissued tickets can block seat assignments.
But BA codeshares on AA metal on a BA ticket normally allows seat reservation, broadly speaking if you can find the AA (SABRE) locator, AA.com and their App almost always allows you to select seats. The usual way to find this is on the Seat Selection menu, where both should be shown.
While in the AA booking, check the other details, including passport data and your BAEC number, to ensure all is correct.