Originally Posted by
jordyn
Because the US requires that you enter and leave on your US passport if you have one. (Although...metaphysical question: what does it mean "to leave the US" since there's no exit immigration controls? But I always check in for ex-US flights with my US passport based on this requirement.)
I think it should work fine to check in on your US passport and then hand over your Dutch passport to the immigration authorities when you land. Having said that, AlwaysAisle is correct that AA may not let you check in this way on your US passport. In theory AA should be able to take note of your Dutch passport to allow you to check in while still keeping your US passport on record, but about 80% of the time in this scenario the AAgent doesn't know how and just replaces the US passport data with the other.
My son with US citizenship resided in Brazil for five years under their form of "green card" program. When he traveled to Sao Paulo from New York, he used his US passport with Brazilian residency card. He marked on his reservation that he was a resident of Brazil so both were required. Upon his arrival in Brazil he showed both at their immigration. You might consider showing both of your passports upon arrival in Amsterdam (?) just to be safe.