I don't know how strict they are in European airports, but Riley has traveled with me more times than I can count in US airports and I have always carried her in my arms through every airport I have been in. Not one person has ever told me to put her in her carrying case. At the check-in desk, they are more concerned with the weight of the case plus the weight of the dog, so they will weigh them together, but I don't have to put Riley in it. Not one person has asked if she is able to stand inside the case. But if Dashy can walk into it, he can stand in it, so I wouldn't worry. If you have a long layover, you might be able to find an area outside that has grass so that he can pee and walk around. You'd have to go through security again, but it might be worth it before the transatlantic flight. Good luck. Riley is a dream of a flier. I hope Dashy turns out to be. I think the hum of the engines puts her to sleep.