Originally Posted by
serfty
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.
Two years ago SYD-JNB took us almost 15 hours. Last year JNB-SYD took right on 11 hours, almost 100 kts faster average ground speed.