Originally Posted by
Jhieminga
There was a second reason for the stop at Shannon: passengers were processed through US customs during this stopover so that when arriving at JFK, they could proceed as if getting off a regional flight.
They were on the earlier of the two flights each day but not the later flight which served dinner on the ground as described and ended with the usual unfriendly reception from JFKs customs officers. I assume the reasoning behind the Shannon pre clearance was to allow passengers to get into Manhattan earlier for business meetings; the later flight arrived in the early evening in time for a dinner meeting or drinks so time spent in JFK was less of an issue.