Aircraft Pressurized Cabin

Guides · 5 min read · Dec 02, 2021
Pressurized cabin

The term “pressurized cabin” refers to aircraft with compressed air in the passenger cabins, cockpit, and cargo compartment in the aviation industry. At higher altitudes, most commercial airplanes have pressurized cabins that allow passengers and crew to breathe normally.

Why cabin pressure is maintained?

The amount of pressure acting on the occupants of an aircraft is known as cabin pressure. Cabin pressure altitude refers to the phenomenon in which an aircraft is flying at a higher altitude, but the occupants are exposed to pressures of 8000 feet or less, also known as cabin altitude.

This procedure is used to keep people and cargo safe and allow them to breathe normally to avoid hypoxia or death. Because the air is too thin at higher altitudes and living beings struggle to breathe normally due to a lack of oxygen, commercial aircraft are designed to supply compressed air into passenger cabins and flight decks. When the blood supply to the brain is reduced, brain function begins to deteriorate, resulting in hypoxia or death if exposed to depressurization for an extended period.

Typically, pilots use a cabin pressure regulator to adjust cabin pressure based on flight requirements; however, high-end aircraft can achieve lower pressurization levels for a more relaxing flight. The greater the average differential pressure, the closer the cabin altitude can be kept to sea level. According to FAA regulations, flight crew requires oxygen if they fly above 12,500 feet for more than 30 minutes without cabin pressure, and passengers must use it consistently above 15,000. The pilot’s useful performance time is reduced by one-third to one-fourth of its regular time when the partial pressure of oxygen in the blood decreases.

A pressurized aircraft cabin with passengers sitting in seats equipped with screens.

How air pressure is maintained in the cabin?

Air pressurization systems maintain the aircraft’s cabin pressure. The entire system is made up of several parts that work together to keep cabin pressure at a safe level. To absorb high pressure, the aircraft’s fuselage is sealed, and pressure bulkheads are installed. Engine air compressors provide bleed air for cabin intake, then cleaned and filtered using air filters.

The aircraft’s pilot operates an outflow valve that adjusts differential pressure using a cabin pressure regulator. The temperature of heated air supplied from the turbine is lowered to the aircraft cabin via two separate cooling systems, followed by an expansion turbine that absorbs the heat of hot air. Finally, the cooled air is mixed with the air already within the cabin by a mixer or manifold.

According to Boyle’s law, the pressure and volume of a gas are inversely proportional, which means that whenever there is a condition of differential pressure of air, such as in a climbing airplane, gases inside the body expand. Whenever an aircraft ascends or descends, atmospheric pressure makes our bodies attempt to align with the outer environment by equalizing internal pressure. Although an aircrew helps to equalize the process by keeping the cabin pressurization system, several individuals still feel the impact of pressure differential via ear pain.

Only when differential pressure between inside and outside the cabin equals the maximum differential pressure for which the fuselage structure is designed, increasing the aircraft altitude significantly increases cabin altitude. When the appropriate altitude is attained, a continual pressure differential is maintained with ambient pressure in reference to the outside pressure.

Components of aircraft pressurization

Several components make up the whole system of an aircraft’s pressurization system. However, the entire process is dependent on the air intake and exhaust. If these functions fail mid-flight, the plane will ultimately lose pressure. Electric air compressors are used to squeeze external air into the cabin in former piston-powered commercial plane. Regrettably, this resulted in the aircraft gaining a significant amount of weight. Piston-powered aircraft are no more in service for commercial operations. Modern jetliners compress incoming air from the compressor stages of a turbine engine.

Cabin pressure control, pressure relief, vacuum relief, and the ability to pick the preferred aircraft pressurization in the isobaric and differential range are provided by the cabin pressure control system. Furthermore, pressurization disposal is a feature of the pressure control system. Compressed air safety pressure relief valve for appropriate adjustment and backup high and low-pressure relief features and functions, a pressure regulator, an outflow valve, and pace for fuel-efficiency.

  • Bleed air

Bleed air is drawn from the compressor stages of a turbine engine in sufficient quantities to keep both the engine and the pressurization system operating normally. Bleed air is used for various purposes in airplanes, including cabin pressurization, engine starter motors, wing, and engine ice protection, and air-driven hydraulic pumps.

  • Outflow valve

This valve is used to maintain cabin pressure. The aircraft’s fuselage is constantly exposed to pressure cycles with very high outside air pressure and very low pressure inside the cabin. This pressure acts on the aircraft fuselage’s walls, causing fatigue or bursting of the fuselage in the case of Aloha Airlines Flight 243. The outflow valve regulates pressure; it continuously opens and closes to release excess pressure at a rate determined by pressure sensors.

A pressurized aircraft cabin with demo oxygen masks hanging from the panel above passenger seats.
Image source: https://fantasticfacts.net/5627/

What happens when aircraft is depressurized in mid-flight?

Humans in very high altitudes flights require pressurization to breathe normally in ambient air. If the pressurization system fails during the flight, a sudden pressure difference can result in injury and bloating. At higher altitudes, useful consciousness time is very short, and a lack of oxygen in the blood may cause hypoxia in the brain.

Long-term consequences could lead to death. Each seat on commercial airplanes is equipped with an emergency oxygen supply. This system provides oxygen for 10 minutes, and the captain uses this time to adjust the flight’s altitude to safe levels. Lower cabin altitudes mitigate this adverse effect, but they are only accessible on aircraft designed to resist the pressures, such as the Airbus A350 having composite material in the fuselage. Although there are no long-term risks to staying inside a pressurized aircraft cabin, commuters may experience some strange adverse reactions on board. Because the compressed air has limited moisture levels, occupants will quickly get to be dehydrated. As a result, they’ll want to keep hydrated by drinking lots of water. If consuming alcohol, dehydration can worsen.

FAQs

How does a pressurized cabin work?

A pressure regulator controls the flow of compressed fresh air inside the cabin in a pressurized cabin. The bleed air is drawn from the engine compressor, cleaned, and filtered before entering the cabin. The pilot chooses the required cabin altitude, and the outflow valve controls any excess air.

What happens when the cabin is pressurized?

When the cabin is pressurized, the passengers, flight crew, and sensitive cargo are safe to fly at higher altitudes. Cabin pressure is maintained to keep the natural respiratory system sustainable at higher altitudes. Passengers and flight crew can roam freely around the aircraft without using a mask due to cabin pressurization. Usually, a commercial airliner is maintained at a cabin altitude of 8,000 feet in a cruise flight above 30,000 feet.

Why are cabins pressurised?

Cabins are pressurized to ensure the safety of occupants flying at higher altitudes. When the aircraft cabin is pressurized, passengers and crew feel comfortable and less stressed during flight. Jetliners usually cruise above 30,000 feet to ensure less drag and enhance entire flight performance. Air pressure is very high at such altitudes, which makes it difficult for human beings to breathe normally.

Can a pilot depressurize the cabin?

Yes, the pilot of an aircraft has full control over the aircraft pressurization systems. This could be a suicidal attempt; as the cabin pressure falls, oxygen masks are deployed immediately, the oxygen supply for passengers is only for 10 minutes. Pilots use these 10 minutes to decent aircraft at the minimum altitude of 10,000 feet where natural aspiration is supported.

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Aeroclass Team
A team of professionals with a deep passion for the aviation industry bringing you the newest and the most striking industry-related news and content.

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