Only in rare circumstances which are usually cleared in advance. The flight is cleared to fly between its scheduled ports only. In fact I remember a few years ago at RDU
we had some AC
diversions because ZJX radar was out. Even though the flights were pre-cleared in Canada, pax could not get off because the flights were cleared to Florida airports. We even had to get a form from U.S. CBP
to allow them to proceed. I think it was called a "Permission to Continue" or something like that. It was more of a formality than anything else, since we opened the door on the aircraft.
Then Xmas of 2004 (maybe '03) we had the NYC/DC area shutdown due to snow and we had diversions from Tokyo to London. They did in fact clear customs at RDU
. I think the crews all timed out due to the extensive shutdown and backups.
When I was at IAD
we once had the NRT
777 divert to IAD
. Same thing, crew timed out. Pax cleared customs, got back on the same plane, and a new crew took them to JFK
. Our rampers were very excited about unloading the bags and the reloading them on the same plane... A few pax were terminating in IAD
. They were allowed to stay at IAD
. Note: CBP
wanted us to clear the pax at IAD
, because they were having issues at JFK
with all the late flights...