Skiers board the helicopter and are carried to a landing zone on the mountain. Skis, snowboards and poles are generally carried in an exterior basket loaded and unloaded by a guide. Snow conditions on the mountains vary considerably over the course of the winter as the snow is subjected to sun, wind, temperature variation, and new snowfalls. Snow conditions change almost every day. Risks include those of back country skiing, such as avalanches and tree wells, plus those of helicopter flight. Risks are mitigated by using experienced pilots and certified guides, avalanche transceivers, avalanche air-bags, and radios.