Hkg-sin-hkg???
 

Is HKG-SIN-HKG a valid routing?

A valid route on what? CX has at least 4 non-stop flights a day on HKG-SIN, so it should be valid.

Depends. You are only allowed one stop per airport, but multiple transfers.

LHR-HKG(stop)-SIN-HKG(transfer)-LAX is ok.
2 stops (more than 24 hours) is not.

Er, what? If this is xONEn type tickets we are talking about then there are no restrictions on the number of times you can stop at one airport above the "2 stopover in continentof origin" rule. I take 3 stopovers in HKG on all of my AONE3s.

Not a problem - as long as you start in another continent. I've done HKG-BKK-HKG as well as the SIN and will be doing HKG-ICN-HKG in a few weeks. Good way to build up miles.

I second christep.
My AONE3 itienary looks like

CAI-xLHR-HKG-NRT-HKG-NRT-HKG-NRT-HKG-YVR-...-CAI
with additional purchase of 2 segments.
I did another route like
CAI-xLHR-NRT-HKG-NRT-HKG-NRT-HKG-...-CAI

Additional 2 segments of Y/C/F = 300/800/1100 USD are
bargain for NRT-HKG roundtrips.

Christep is correct. I've just done two identical HKG-SIN-HKG journeys as part of an AONE3.

It's worth noting that CX don't have a non-stop First Class HKG-SIN - you have to go via Bangkok. Very tedious if you want to earn First Class mileage and tier points - six hours, as opposed to three and a quarter. SIN-HKG has F.

Tedious yes, but doable as a day trip. It is a 747. CX 713 leaves around 9 AM and arrives in SIN around 3 PM. The aircraft returns to HKG as CX 716, elaving SIN around 6 PM and returning to HKG around 9 PM. Roughly a 12 hour trip.

In terms of mileage, it is only approximately 1500 base miles each way, around 300 miles less than an NRT turn-around (which many FTers have done). Another option I recall someone doing is a day trip to Jakarta, which I think gets F service at least a few days per week. That should be around 2000 base miles or 200 more than NRT.

I've just done the day return HKG-SIN-HKG. You're right. HKG-NRT-HKG would have been a better bet - more miles, less time. However, if you have to camp out for a few hours in an airport, SIN is far preferable.

i actually flew hkg-sin-hkg once only to use the swimming pool :D