WHEN an aircraft takes off, the air pressure in the cabin is the same as the air pressure outside. As the plane climbs, the cabin pressure falls, making our ears pop.
Once the aircraft reaches 8000 feet, the height at which oxygen levels starts to drop, the plane takes in air from the outside atmosphere and compresses it through the air-conditioning unit to maintain the cabin pressure at the equivalent of 8000 feet above sea level.
Your ears pop again when the plane descend below 8000 feet and cabin pressure begins to increase once again.
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