Originally Posted by
plunet
This depends on the regulations of that country, and from a very practical point, if new domestic passengers can board the flight at the intermediate stopping point before flying onto the final domestic destination. If passengers can board, you now have a mixture of domestic and international passengers on the same flight, .....
It's probably more common in these situations for all passengers at intermediate stop points before flying onto another domestic airport to have to disembark and clear immigration, so they fly onwards as a domestic passenger. Luggage may be a different issue and it could be that luggage is cleared customs at the final destination.
In Australia it is fairly simple process. The flight SYD-CBR is treated as an international flight, and goes between international terminals. Customs/Quarantine and Immigration clearance is done at final destination (and immigration outbound at initial port). As pointed out by other posters, passengers are required disembark and pass through security again, although as Australia is generally an end of line destination (except for NZ/SWP connections), the security for intl-intl transfers tends to be very quick.
Foreign airlines do not have rights to sell domestic tag sectors (not sure if they can even sell stopovers on the same service, ie. DOH-SYD, SYD-CBR, CBR-DOH). However Australian airlines do have the ability to sell purely domestic journeys on tag flights, so you do get mixing of domestic and international passengers.
Jetstar do so now and Qantas have done in the past, and will do again soon when they commence MEL-PER-LHR services. Passengers booking domestically are rewarded with a "D" sticker on their boarding pass and do need to present that and appropriate photo ID at immigration in both directions, and also can potentially have their bags x-rayed for customs & quarantine purposes. (nb: it is not uncommon for Qantas Platinums to have a "day out" by purchasing a cheap jetstar fare, then accessing QF first lounge for a few hours, taking flight before returning home on normal domestic flight
although these sort of tags are becoming much rarer now).