With a BAEC Silver number in an AA reservation, you should get free checked baggage, MCE seats at time of booking, and Boarding Group 3 -- as long as AA recognizes your oneworld Sapphire status.
With an AAdvantage Platinum, Platinum Pro, or EXP number in a BA reservation, you should get free seat selection at time of booking -- as long as BA recognizes your oneworld Sapphire or Emerald status.
And welcome to FlyerTalk!
Edited to add: What class of service do you typically fly on AA? On BA? When you fly BA, is it just to LON, or do you connect there to a point beyond?
Last edited by guv1976; Dec 4, 2023 at 9:54 pm