In 1998, a team of eight British soldiers attempted to climb 6194 metres to the summit of Mount McKinley, the highest mountain in North America. For a team of highly trained soldiers it should have been easy. But as the men approached the mountain summit they ran into trouble. Caught off-guard by McKinley's unpredictable weather, some of the men became stranded close to the peak, prompting the most daring helicopter rescue attempt ever carried out.
Helicopters find high altitudes hard work because the air is much thinner. Not only do the engines struggle to work as efficiently, because of a lack of oxygen for the fuel mix, but also the rotors have less air to bite into for generating lift. This means that at high altitudes, helicopter engines have to work much harder to stay aloft.
