What is mean by Cabin Pressurisation in aircraft?
A Brief History of Cabin Pressurization:
Ever since the Wright Brother’s first powered flight, humans have strived to fly higher. Beyond the thrill of looking out your cockpit and seeing the world pass by like a distant fairy tale, flying high provides many benefits.
- Flying above the turbulent lower atmosphere means a more comfortable flight, while also providing an economic advantage due to the reduced air density.
- It allows military pilots to escape pursuit from less capable aircraft and avoid anti-aircraft fire from the ground
As we climb higher, air molecules are spread farther apart. When we breathe, our lungs take in less air, and less oxygen. At 18,000 feet, the atmospheric pressure is down to 7.3 psi, about half the sea-level pressure. There just isn’t enough oxygen in a breath of air to adequately supply the brain. At this pressure, a healthy adult has only 20-30 minutes of useful consciousness. Altitude sickness, hypoxia and decompression sickness create a triple threat that can ultimately kill the occupants of a high flying aircraft. Early pilots wore flight suits and oxygen masks to counter-act these effects. To survive high altitudes, occupants of an aircraft need help breathing. The solution is to pump air into the airplane so the interior pressure is high enough to keep the humans happy. But full cabin pressurization offered superior comfort, which was essential for commercial aircraft.
Why bother with pressurization? Why not fly down low?
Airplanes can certainly fly below 10,000 feet where the atmospheric pressure is a comfy 10 psi or higher, but it has some drawbacks:
- It’s tough to cross a 14,000-foot mountain range at 10,000 ft.
- Most bad weather is at lower altitudes.
- Turbofan engines are very inefficient down low.
- Aircraft ground speeds are slower at lower altitudes.
If you want a fast, smooth ride in a fuel-efficient airplane that can fly over a mountain range, we need to pressurize
How to achieve cabin pressurization:
Consider the airplane body, fuselage as a long tube which is capable of withstanding a fair amount of air pressure. It is hard to perfectly seal it. Even if it is sealed, the passengers could use all the available oxygen. To solve this problem, the pressurization systems constantly pump in the fresh outside air into the fuselage. To control the interior pressure and allow old stinky air to exit. There is a motorized door called as outflow valve located near the tail of the aircraft .it’s about the size of a briefcase and located on the side or bottom of the fuselage. Larger aircraft often have two outflow valves. The valves are automatically controlled by the aircraft’s pressurization system. If higher pressure is needed inside the cabin, the door closes. To reduce cabin pressure, the door slowly opens, allowing more air to escape. It’s one of the simplest systems on an aircraft cabin pressurisation.
Benefits of cabin pressurization:
- The constant flow of clean, fresh air moving through the aircraft.
- The environment becomes more comfortable for the passengers and making the transport fuel efficient.
Where does pressurized air come from?
- Electric Compressors
- Engine Bleed Air
How do pilots control the pressurization?
It is very easy During preflight checks, pilots turn one knob to display the altitude of the landing airport.