Originally Posted by
simpleSnow
The problem is though when the EU ETIAS goes into effect, as a dual EU/US you need to be able to purchase a ticket tied to two passports so you can check-in online both ways. Esp with passports sometimes having certain name spelling or ordering differences.
This is not entirely true. As long as the spelling of the name is the same, you might change your travel documents interchangeably by calling reservations up until check in regardless of what nationality you initially put on your PNR. APIS are transmitted by the airline -72h, -24h and upon take off. So you may have your US passport detail on your PNR which will be transmitted -72h and -24h but check in with your EU passport. Whatever document you check in with will be the one going to the final APIS.
In cases where the name of your EU passport is drastically different (married/maiden name, Lithuanian/Polish spellings, etc), it is entirely up to the check-in agent to decide which document to swipe and it needs not be the exact same spelling as the reservation. Logically, one will first present the document that has the same spelling as the reservation and then present the alternate document that would be used for entry.