Originally Posted by alect
I think they won't let you check in on a one-way ticket unless you are a US Citizen or Perm Resident - USCIS restriction I would guess.
Weird. I checked in for one way LHR-IAD last September with no problems. I did have a K-1 fiancee visa in my British passport but it was never checked and I didn't intend to enter on it. My return was on the same airline on a separate itinerary, maybe they could tell that...