Originally Posted by
shuigao
I can't comment on the CGK route, but the SIN-NRT/HND routes are most definitely excessively padded. For example I flew on SQ12 the other day, it's scheduled for 7hr5min (9.25am - 5.30pm+1hr), but as you can see on
flightaware the actual flight time is consistently below 6hr

I believe we are discussing about SIN-CGK.
For longer flight, there are many other factors, like head/tail winds and as it is longer flying time, if you can speed up a bit, it will decrease the flying time.
Do take a look also on SQ 11, most of the flight are closer to 7hours. Longer flight may be advantage by tail wind and it will save you time. I do remember typically one direction will be benefited by tail wind and the opposite direction will be disadvantaged by head wind.
I remember long time ago my flight from SFO-HKG-SIN has to be delayed for more 1 hour as they said we will experiencing stronger tail wind which mean shorter flying time, but we cannot arrive in HKG too early due to curfew.