I saw the Everest IMAX awhile back and I remember them mentioning that the base camps were put more or less where the Russian helicopters could ascend to. 30k feet in a helicopter is amazing. They must have had to fit the helicopter with an Oxygen supply and retrofit it for that bitter cold.
I bet it must be burning fuel like crazy to keep the rotor speed up and at max prop pitch at the peak due to the thinning air!
