Originally Posted by
tusphotog
Not terribly uncommon if there's a delay and they do an aircraft swap. If you look at Flightaware, PVD-BWI is operating as WN859 and BWI-FLL is operating as WN9018. It's not apparent to the passengers, but to ATC it's a different flight.
I imagine there's only a handful of connections that can be accommodated on a later flight.
Exactly correct. The 9000-series are for what are call "stubbed" flights. In all likelihood, the crew for the PVD-BWI leg was due to go off-duty and be replaced by a new crew, so that new crew was assigned a new aircraft, and the BWI-FLL went out on time under the 9000 series flight number. There are pros and cons to this practice, as usual. Any FLL pax from PVD would have to be protected on other flights. On the positive side, the new crew at BWI wouldn't have wasted x-hours of limited duty time awaiting the flight from PVD to get there. Additionally, should the aircraft's eventual travels beyond FLL put it into a place that had a noise curfew (like, say, SNA), it would have been on time and thus not subject to cancellation.