High Quality Content by WIKIPEDIA articles! Cabin pressurization is used to create a safe and comfortable environment for passengers and crew in a high altitude aircraft by pumping air into in to the cabin faster than the air flows out of the cabin. The air used to condition and pressurize the cabin is usually bled off from the engines prior to the combustion stage. The air is then cooled and moisturized in air conditioning packs before being mixed with recirculated air and distributed into the cabin. The exact pressure is controlled with an outflow valve, which regulates the rate at which air leaves the cabin. It is often managed by a environmental control system.