US/EU flying to Germany via the U.S. — which passport for check-in?
I am a dual U.S./EU citizen currently in Mexico. I entered Mexico from South America using my EU passport.
I now have a flight from Mexico to Germany, but the itinerary connects through the United States.
I am confused about which passport to use for airline check-in / online check-in.
My concern is:
- I entered Mexico on my EU passport, and Mexico apparently relies on airline data for departures.
- Since the flight goes through the U.S., I assume the airline also needs my U.S. passport, because I am a U.S. citizen and cannot use ESTA.
- My final destination is Germany/EU, where I would normally use my EU passport.
- I also prefer not to give the airline more passport information than necessary or link both passports in their systems if I do not have to.
So what should I do for check-in if the airline asks for one travel document?
Has anyone dealt with this kind of situation before — especially involving Mexico exit records, U.S. transit as a U.S. citizen, and final entry into the EU?
Also, how would this work in the future once ETIAS is implemented? Would this make the situation even more complicated for dual U.S./EU citizens, since a U.S. passport might need ETIAS for Europe, while an EU citizen would normally enter the EU on the EU passport?
I am not trying to avoid any rules. I just want to do it correctly without creating a messy immigration record or sharing more data than necessary.