Airplanes have pressurized cabins to ensure the safety of the people onboard.

As oxygen levels are extremely low at high altitudes, people can’t properly breathe without pressurization, so a pressurized cabin maintains oxygen levels in the plane, ensuring no one suffers from oxygen deprivation.

Planes maintain cabin pressure by using a system that pumps air into the plane and alter cabin pressure by leaking excess air through an outflow valve.

People experience discomfort in their eyes and ears along with breathing difficulties if cabin pressure decreases.

The resulting oxygen loss causes passengers to faint unless they put on oxygen masks. 

Planes Are Pressurized For 2 Reasons

Airplanes are pressurized for these two reasons:

1. For Comfort

The earth’s atmosphere creates an air pressure of around 14.7 pounds per square inch at mean sea level.

But airplanes fly at extremely high altitudes, upwards of 35,000 feet, at which point the oxygen levels become extremely low.

This is why fighter pilots wear oxygen masks.

A pressurized cabin ensures there’s enough oxygen for passengers to easily breathe and stay comfortable, and is also why passenger planes deploy oxygen masks if the cabin depressurizes. 

2. To Prevent Loss of Consciousness 

Airlines pressurize their cabins to safely transport passengers.

Without pressurization at high altitudes, the passengers wouldn’t have enough oxygen to remain conscious for longer than a minute.

Planes have to fly at higher altitudes to reach their destinations more quickly and avoid collision with tall landmasses, like mountains or towers. 

How Are Plane Cabins Pressurized?

Airplane cabins are pressurized by pumping air into them as follows:

  • The excess air from what the plane’s engines suck is diverted to the cabin.
  • The air is cooled, and moisture is added to it.
  • The air is then circulated in the cabin. 
  • Planes can control their cabin’s pressure level with an outflow valve.
  • The outflow valve will open to let out excess air if the cabin pressure is too high.
  • The outflow valve closes once the cabin achieves the appropriate pressure. 
  • The outflow valve system is the most common way to maintain cabin airflow, but some planes use a different system. 

What Pressures Are Airplanes Pressurized To?

An airplane cabin is pressurized to between 11 and 12 pounds per square inch (PSI).

This is the pressure you’d feel while standing on a 6,000 to 8,000-foot-tall mountain. 

Most planes initiate their cabin pressure control system above an altitude of 10,000 to 14,000 feet. 

Not All Planes Are Pressurized

All commercial planes are pressurized, as they fly at higher altitudes, but many smaller planes that don’t fly at high altitudes remain unpressurized.

The exact system for pressurizing varies from plane to plane. 

If a Plane Loses Cabin Pressure, It Spells Bad News

The oxygen levels in a plane would plummet once the cabin loses pressure.

The loss of oxygen would cause breathing difficulties for passengers and lead to fainting. At low pressures, people would also experience discomfort in their eyes and ears.

Simultaneously, they’d experienced breathing difficulties and are required to put on their oxygen masks. A passenger who doesn’t put on their oxygen mask could faint in 15 seconds of exposure to low air pressure. 

Flight crews are trained to handle emergencies in which the cabin loses pressure by deploying oxygen masks and assisting passengers.

A gradual loss of pressure is generally more dangerous than a sudden one, since it’s harder to detect, and continued low-pressure conditions may cause the flight crew to become lightheaded.

The plane will often make an emergency landing in such conditions. 

Planes Were First Pressurized in the 1930s

American entrepreneur Cliff Garret developed the world’s first cabin pressurization system in the late 1930s.

This system was originally intended for military aircraft, but it was later adopted by commercial planes. 

Boeing’s 307 Stratoliner was the first plane to use a commercial cabin pressurization system in 1947.

In 1977, the world’s first digital electronic cabin pressure control system was introduced.

Later in 1979, a fully automatic digital cabin pressure control system was developed. 

In conclusion:

  • Airplanes are pressurized because they wouldn’t be safe to fly in at high altitudes without pressurization.
  • Pressurizing the cabin ensures that passengers have access to the oxygen they need.
  • Without pressurization, passengers would experience a loss of consciousness due to oxygen shortage.
  • The aircraft crew is fully trained to handle low-pressure emergencies by providing passengers with oxygen masks.
  • Virtually all planes use pressurization systems.
  • The world’s first pressurization system was developed in the 1930s.
  • The first fully automatic digital cabin pressure control system was introduced in 1979. 

Helen Krasner holds a PPL(A), with 15 years experience flying fixed-wing aircraft; a PPL(H), with 13 years experience flying helicopters; and a CPL(H), Helicopter Instructor Rating, with 12 years working as a helicopter instructor.

Helen is an accomplished aviation writer with 12 years of experience, having authored several books and published numerous articles while also serving as the Editor of the BWPA (British Women Pilots Association) newsletter, with her excellent work having been recognized with her nomination of the “Aviation Journalist of the Year” award.

Helen has won the “Dawn to Dusk” International Flying Competition, along with the best all-female competitors, three times with her copilot.