We shouldn't get too exciting about the news.
Its most likely that AA takes over the second (almost) daily flight LHR-SEA from BA. Three oneworld flights SEA-LHR would have been an overkill.
So no increase in real seat capacity! However, pax will have a joice of a better J hard product and better lounges at LHR (T3 lounges are way better and less crowded than their T5 counterparts).
AA has a JVA with BA -> hence, even the slot may even come from BA.
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Last edited by JY1024; Feb 13, 2020 at 5:46 pm
Reason: redacted off-topic discussion