Airliners are pressurized to a level that is equivalent to outside air at about 8,000 ft of elevation (roughly 75 kPa).
Airplanes travel at elevations between 31,000 and 38,000 ft. The outside air pressure at that height is roughly 25kPa – about a quarter of the pressure at sea level (~101kPa).
This would be very uncomfortable for humans. Passengers of a Jet Airlines plane in 2018 can attest to this because their crew forgot to pressurize the cabin.
So the cabins of planes that fly that high are pressurized to keep everything comfortable. However, you may have noticed that your ears may pop as you ascend and descend, and bags of chips will expand and contract. Even cans of pop behave differently at altitude, becoming more fizzy than they are at ground level.
This tells us that it’s less than the pressure on the surface and less than the outside pressure.
Most aircraft cabins are pressurized to 8,000 feet above sea level, an altitude that lowers the amount of oxygen in the blood by about 4 percentage points, researchers say.
This decrease in oxygen saturation isn’t enough to bring on acute mountain sickness.
Why don’t they set the pressure equal to ground level?
The structure of an airplane is designed to withstand the dynamic effects of acceleration, air resistance, and turbulence, but they also need to handle the forces created by the pressure differential between the interior of the cabin and the outside atmosphere.
Pressurizing the cabin to 1 atm (~101kPa) would mean that there is a greater pressure differential and the airframe would have to withstand greater force. This would mean that stronger, heavier materials would need to be used, and the weight of the airplane would have to increase.
The increased weight would reduce fuel efficiency and diminish the aircraft’s range (and the price of your plane ticket would go up as a result).
How does an airplane cabin get pressurized?
The engines of an aircraft are used to pressurize the air in the cabin.
Pressurization happens via the engines, which compress incoming air, heat it up, and then divert some of that hot compressed air to the cabin. On its way to the cabin, the air temperature is lowered via two different cooling systems and then an expansion turbine…