Flying Along

Ok, time for a new puzzle. I found this one a few months ago over at Tanya Khovanova's math blog:

You are sitting at the equator and you have three planes. You would like to fly around the equator. Each plane is full of gas and each has enough gas to take you half way around. Planes can transfer gas between themselves mid-air. You have friends, so that you can fly more than one plane at once. How do you fly around the equator?

Its sort of like an old puzzle involving camels going into the desert and you only have a finite amount of food for them, but a bit of a twist on this one. Anyway, thats it for now.