How Does Aircraft Pressurization Work?

We often take flying for granted and never pay a second thought as to how we're able to function so high up in the air. This article will delve into how an aircraft's cabin pressurization system makes it possible to breathe oxygen comfortably while flying and why testing equipment is a necessary part of your ground support equipment fleet.
Keeping passengers safe and comfortable at over 30,000 feet is an accomplishment airplane manufacturers have spent decades trying to master. As humans, we function best at sea level. But airplanes are at their best when at great heights with thin and smooth air. 

As you can see, this creates quite the quandary. So, airplane manufacturers created a cabin pressurization system to keep passengers and employees safe and comfortable while in the air. But how aircraft cabin pressure works can be a little confusing. So, we're answering a few of the most common questions that arise when discussing the ins and outs of aircraft pressurization.

Where Does Pressurized Air Come From?

The answer to this first question is a little complex as it can vary across aircraft manufacturers, so let's dive in. 

Older piston-powered airliners used to use electric air compressors to pump outside air into the cabin of the airplane. However, this tended to add a lot of extra weight to the aircraft. Jetliners then began to use bleed air from the engines to spin the turbo compressors, which then pumped outside air into the cabin. Today, most modern airplanes use bleed air from the engines' compressors to properly pressurize the cabin.

But How Does Aircraft Cabin Pressure Work? 

So, we've answered where pressurized air comes from, but how does it actually work? Buckle up.

The engine's compressor contains a series of spinning blades that draw in fresh air from outside the plane. The air becomes extremely hot as it's compressed. It then enters the engine's combustion chamber where it combines with fuel and is burned. Then, the expanded gasses flow through the engine's turbine blades (powering the compressor blades) and exit the engine, creating thrust. 

The bleed air, which is clean, hot air, is taken from the compressor prior to mixing with any fuel or exhaust gasses. Bleed air can help with the following:

• - Cabin pressurization
• - Wing and engine ice protection
• - Air-driven hydraulic pumps
• - Engine starter motors

While some of the already-hot bleed air is used for things like wing deicing, cabin-bound bleed air must be cooled first. The cooling is conducted within an intercooler, which is a device similar to that of a car radiator. The intercooler works by shedding the heat to ambient air. The air then travels to the belly of the plane where it is cooled even further through the use of air packs, which use an air cycle machine (a refrigeration unit). This surprisingly simple air conditioner utilizes air packs to compress incoming air to heat it before sending it to an additional intercooler to dump the heat outside of the plane. This air then expands through the expansion turbine, resulting in cool air.

At this point, the cooled air is ready to mix with the recirculated cabin air through the use of fans. Automatic systems work throughout the flight to regulate the mixture of the engine's heat and the cold from the air packs. To keep the aircraft cabin pressure at a safe level, any incoming air is held within the cabin through the use of an automatic outflow valve. This valve opens and closes on a regular basis to release the incoming air at the rate regulated by pressure sensors. The outflow valve also acts as an exit hatch for old, smelly air to vacate the plane.

How Do Pilots Control Pressurization?

This is a semi-trick question. During preflight checks, the pilot should turn on a display that will show the altitude of the landing airport. But after this, pilots won't typically do anything related to cabin pressurization for the remainder of the flight. All planes, as we've already mentioned, have an automatic mode that controls the outflow valve. 

Keep in mind that pilots can override the automatic modes in the case of a malfunction. The manual mode will allow the pilot to then adjust the position of the outflow valve.

Are There Any Side Effects?

While there are no long-term risks to being inside a pressurized aircraft cabin, there are some odd side effects you may notice while on the plane. As the pressurized air has low humidity, you will become dehydrated very quickly. So, you'll want to stay hydrated by drinking plenty of water. 

Dehydration can increase when drinking alcohol. So, if passengers decide to drink on a fight, they should be sure to drink water and have something to eat as well.

Aircraft pressurization also reduces your sense of taste and smell. A Lufthansa commissioned study found it can decrease these senses by as much as 30%. This is why extra spices or flavorings are often added to food on airplanes.

Why Can't The Plane Simply Fly Lower?

You may ask yourself, why can't the plane simply fly lower to avoid the hassle of creating perfect aircraft cabin pressure ? While airplanes can certainly fly below 10,000 feet where the atmospheric pressure is ideal, there are some operational drawbacks to doing this for an entire flight. For one, there are many mountain ranges that are higher than 10,000 feet. In addition to this, most bad weather can be found at lower altitudes, so pilots typically want to avoid this. And in terms of efficiency, turbofan engines are extremely inefficient when used at lower altitudes and ground speeds. 

How Can Aircraft Pressurization Be Tested?

To ensure an airplane is safely pressurized prior to a flight, you'll need to test the pressure. To do this, make sure to use the proper airplane cabin pressure testing equipment. These pieces of equipment are vital players in your GSE fleet and help to maintain the safety standards for any airplane coming to or leaving your airport. The following are just a few of the cabin pressure testing equipment options available from Tronair. 

• - A leak fluid dispenser can detect if air is escaping when the cabin is pressurized. 
• - A cabin pressure test unit (also available as a portable unit), in addition to checking for leaks, can test the pressurization components of the airplane, such as the outflow valves, gauges and door seals. 

Let Tronair Help Find the Aircraft Cabin Pressure Testing Equipment for Your Needs

At Tronair, we work tirelessly to offer our customers a diverse and unparalleled selection of GSE products. We understand how important safety is when it comes to aircraft pressurization and air travel overall — it's why we create testing equipment you can count on. Shop our high-quality selection of cabin pressure testing equipment, leak fluid dispensers and more. Have a question or need a quote? Our customer service department and sales team are here to help with any questions you may have regarding our extensive range of products. Contact us today.

Related Articles

GUIDE TO RECALIBRATING AIRCRAFT SERVICING GAUGES From small regional airports to massive airline hubs, service cart gauge calibration regulations are often necessary, especially when servicing nitrogen and oxygen carts. We're explaining why recalibrating aircraft servicing gauges is so important and how to establish servicing unit calibration standards for employees.

GUIDE TO INSPECTING AND PREVENTING TYPES OF AIRCRAFT CORROSION Aircraft corrosion is an ongoing challenge for aircraft owners. It can deteriorate the structure of the aricraft and parts, often leading to dangerous hazards and expensive repairs. What's more, there's no real way to reverse corrosion once it sets in. And if left untreated, it can make an aircraft virtually inoperable in just a matter of years.

HOW AN AIRPORT GROUND CREW CAN PREPARE FOR SERIOUS STORMS The aviation industry is heavily reliant on the weather. While aircraft can function in most environments and situations, some weather conditions pose a real threat to the safety of passengers, airport ground crew and aircraft ground support equipment (GSE). Thunderstorms, in particular, are some of the most dangerous situations in aviation. From powerful wind gusts to lightning accidents, serious storms can have a severe weather impact on air transport operations. Here's what to watch out for and how to prepare when hazardous storms roll in.