Originally Posted by
EricH
You'll have to get your bags at IAD on your return to go through customs. The only difference is where you get them. If you're connecting, they'll be at the midfield terminal. Otherwise, they'll be at the main terminal.
There is NO DIFFERENCE for passengers arriving at IAD on BA (or any other non-Star Alliance carrier). Whether the passenger is connecting or not, all passengers from those flights go to IAB in the Main Terminal.