Antarctic weather can change in an instant, with a perfectly sunny day transmogrifying into a blizzard that lasts three to five days and packs winds of up to 90 mph. Visibility can be severely impaired even on clear days. With sunlight reflecting and refracting off snow, ice, and water, whiteout can occur. You suddenly lose all sense of size and shape, and your depth perception disappears. What you think is a building in the distance might be a small box at your feet. With no shadows or other non-white features to guide you, you might stumble as you walk because you can't distinguish between horizontal and vertical.
Whiteout is particularly hazardous to pilots, who can become disoriented without landmarks, shadows, or a horizon to guide them. In 1955, a helicopter on a scientific mission in Antarctica crashed full speed into an ice sheet and tumbled for over 70 yards before coming to a halt. A second helicopter rescued the downed pilot and started to fly back to a waiting ship. Realizing he was in a whiteout and keeping his eyes on what he thought was the horizon, the second pilot suddenly felt a jolt: the helicopter had slammed into the ice shelf. Fortunately, it bounced off on its pontoons, and the helicopter returned safely, though the first pilot died of his injuries a few hours later.