Originally Posted by
Viajero
If the runway is what accounts for the difference how come Nort/South fligths, like NRT-SYD do not experience this difference and have the same schedules year round?
NRT-SYD is 9h20m and SYD-NRT is 10h35m. So there is a substantial difference. But it is exactly the opposite of what the OP experienced so it can't be the runway and I would guess this is just the wind.
sdorling, are you sure you have your times right (Tokyo is 3.5 hours ahead of Delhi)? Because I just looked flights up and this is what I got for early April:
NRT-DEL 9h15m DEL-NRT 8h00m
This looks pretty normal to me considering the wind direction on this planet.