Originally Posted by
bocastephen
Well there are no exit controls in the US as you know, so the passport used to exit is basically the passport the airport agent types into the reservation.
Having said that, the rule is a US citizen should exit and (always) enter the US with their US passport...but it's not like anything will happen to her if she doesn't.
The complication will arise if she can't get the passport renewed abroad in time, but expired or not, she is still a US citizen with a right of re-entry - it's just unnecessary complication and stress.
Why not use one of the expedited services to get it renewed this week before departure?
CBP can and does random departure checks, to include rolling out the computers and swiping documents. It is a small number of flights each day relative to the number that leave the US but it happens.
I have flown eight int'l US orig flights in the last two months (not counting GUM) and three had CP in the jetway, including a recent IAH-NRT flight. Two of the three were just the open the passport money/work questions, one they were actually swiping passports of some at the remote computer kiosk they roll out.
Point is, while somewhat rare, outbound CBP checks happen everyday around the US.