That's exactly what AA
are trying to get antitrust immunity for.
Currently, the oneworld alliance does not have antitrust immunity for code-sharing, mile accrual and mile redemption on trans-atlantic flights to and from London (although I think it is possible for transatlantc flights to other UK destinations like MAN
, etc. -- someone will have to confirm). In other words, the EU and US governments will not allow them to coordinate their flight schedules and mileage programs on these flights. You can, however, earn miles on subsequent legs of these journeys, like in your case. The same would be true if you were flying, say, DFW
. You could not earn AAdvantage miles on the DFW
leg, but could on the LHR
This is not true with SkyTeam and Star Alliance, which is one of the main reasons AA
are pushing for antitrust immunity. The governments previously did not grant this immunity because they viewed AA
as having a stranglehold on LHR
slots. Now that these have been loosened, most observers expect immunity to be granted.
My guess is that you'll be able to earn and use both AA
miles on transatlantic flights by next year.