Originally Posted by
Bob'sYourUncle
You can certainly travel TO France (and beyond) on your French passport, but the airline will not let you board back to the US on an expired US passport.
They might, they might not; it is not a forgone conclusion.
Originally Posted by
Often1
+1 - As a USN, you can't be denied entry, but it's a crap-shoot as to whether you are allowed to board the return and then a lengthy go-around w. CBP on arrival.
What makes you think this would cause a lengthy go-around with CBP? Do you think they've never seen an expired document before? I'm sure it would take a little longer than a standard entry, but a "lengthy go-around" sounds more like speculation than reality.
I personally know of two recent instances of travelers using expired travel documents at a US POE with minimal delay. By minimal, I mean that a supervisor was called and said that the expired passport was acceptable, and it was a normal entry after that. Both were US Citizens. Using an expired US passport to enter the US just isn't that big deal, particularly close to the expiration date.