On which airlines, does same flight number mean same plane?
 

On which airlines, does same flight number mean same plane?

Yes: WN, AS

No: UA

Others?

Yes - NZ, QF, BA, SQ, LH
No - AA, LA

No - DL

No: CO, US

No: NW

Only partially true.

UA has flights which run ORD-HKG-SIN and SFO-NRT-SIN (and many others) which continue onward with the same flight number AND the same aircraft.

NW also has a PDX-NRT-SIN flight which retains its flight number and aircraft for the whole trip. Probably several other flights as well.

However, on domestic legs of these international flights, the aircraft gets switched (I believe the UA ORD-HKG-SIN flight originates in PHL, but the PHL-ORD leg is operated with a different aircraft).

But on international flights which continue onward using 5th freedom rights, it's usually almost always the same aircraft if the flight number does not change.

SFO-NRT-SIN??

I think it is IAD-NRT-SIN

Not on NW. Their "local" Asia and long hauls meet in NRT hub for a grand switcheroo party. The good news is all the gates are next to each other(usually) except they may make you run 1/4 mile to security and back first. :D The no extra charge DVT Prevention Run. :D Some NW connect at KIX, with fewer planes perhaps it is more likely to be the same metal.

NW 11 is DTW-NRT-PEK. The DW-NRT leg is a 747-400. NRT-PEK is a A330-200. Sometimes the 747 continues to an Asia final destination, but the 747 is used for the long haul (back to MSP or DTW or LAX) and the A330 (with Y IFE ^) is used for the 2 to 6 hour Asia commuter legs (Thanks be all the Break Down of the Day DC-10 clunkers are retired from NRT-SIN.:D)

So is it fair to say the following?

Non-US carriers: Yes
US carriers: No

Exception: LA

Not excusing the U.S. airlines but they tend to operate domestic flights going through hubs, while most non-U.S. airlines don't do that (only Russia and Canada, and maybe Australia being big enough to do that?). Of course, that doesn't excuse the change of gauge for flights that go from an international city to a U.S. hub, before going to another U.S. destination (or v-v).

Yes: CX - 888 HKG-YVR-JFK & 889 JFK-YVR-HKG

Have you seen the current Southwest ad? The one where they brag about never sticking you on a RJ and Promise that Every flight will be on a full size jet at least as big as a Boeing 737? :D

I don't think so. QF, NZ, LH, LX, BA, LA, etc all have tag leg flights.

I interpreted the question as "On which airlines, does same flight number always mean same plane?" To me this made more sense than listing out for each airline which flights currently are same flight number same a/c and which ones are same flight number different a/c, which can be further complicated by changes over time.

but they are all through a 3rd country, not a home country hub.

FWIW, when QF was operating SYD-HNL-YVR/YYZ for a while back in 2000/01, some a/c would operate YYZ/YVR-HNL and back, and another would operate SYD-HNL-SYD. All nominally the same a/c (767-300ER) but....