When I flew United IAD - ZRH in May they said to me that at some point in the merge both airlines will only be taking dogs as cargo; no longer would they be accepted as accompanied baggage. But when you call to reserve the pet space on the phone they can explain fully. If you want them to go as excess, make sure you find out if space is available for pets on that flight BEFORE you book your ticket.

It's much easier to take them as excess baggage, in my opinion, and it costs less on that route at least.

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