Where are we getting the notion that Ryanair love being in T3? It has no more than 12 B737 sized contact stands and is shared with BA amongst others. The taxi difference between T1 and T3 is negligible, whereas T1 has way more B737 sized stands. The CX in T3 with a fleet of 189 seaters is sub par for all all concerned in infrastructure built for mainly sub-100 seat aircraft. In BAU, how much bussing do Ryanair do? Stand 57-59 are bussed? Or is it the case that post flybe, it's effectively "theirs" in which case the impact on other airlines is neglible? (looking at you BA GOLD and Silver card holders
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I agree on the point about Oneworld connections except there did seem to be quite a few when I used to fly MAN-LHR, that's why the biometrics were extended to T3! Not a connection I ever fancied but it did happen often enough to employ people to police it. They used to sell LHR-MAN-ORD on AA as well as LHR-MAN-HEL on AY.
BTW there's surely quite a growing list of airlines who have been based in all 3 terminals by now, Ryanair being one of them.