QF1 SYD-LHR -- SIN procedures and time

[p--and--t]

That is not universally true. I've flown lots of flights that are direct with one or more stops where you have to remain onboard.

Correct!

Example

UIO (GYE) GPS. Passengers originating in UIO remain on board with seat-belts unfastened while refuelling occurs and new passengers join before taking off again.

I have remained on-board a couple of times in other transit scenarios as well but cant recall where it happened - old age.

 

[p--and--t]

It depends on the port the transfer is happening at and which direction.
eg, CX888 HKG-YVR-JFK, pax continuing to JFK have to get off with everything and go into a secure room for US style rescreening and bag searches.
for CX889 (JFK-YVR-HKG), I hear that pax continuing to HKG don't even have to get off.

My observation is the US don't really give a damn if you are leaving North America, but paranoid if you are entering or transiting.