Originally Posted by sdorling
... I initially thought it maybe due to crossing restricted airspaces, but that doesn't explain the shorter return leg. Winds could be another reason, but surely not that favourable?
The "jetstream" winds often have quite an effect. It more in relation to East/West travel than North/South.
e.g. Qantas schedule their 743's SYD to PER duration for 4:45 and 4:00 hours on the return. NZ schedule their AKL-PER flights at 7:35 and 6:25, 1:10 less on the return.
NRT is ~63° east of DEL & 7° North, so it's quite the latitudinal route.
Of course, there would be other locality related issues; but not as significant methinks.