Air Conditioning and Pressurization Systems in Modern Aircraft


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Airplanes flying at/about FL300 (30,000ft). Photo Credit: Bedhan Ball

For any modern aircraft to fly at high altitudes, it must be equipped with an air conditioning and pressurization system, which provides a convenient environment for its passengers. The human body is unable to withstand the effects of a low-pressure atmosphere, which makes the A/C and pressurization system a vital component of modern flight.

JAR-OPS 1.770 and 1.775 by the JAA, along with other regulatory authorities,  have established a minimum pressurization requirement for all modern aircraft which must be satisfied before an aircraft can fly.

Air Conditioning System on the Airbus A 320

Aircraft A/C systems are more or less similar on all modern airplanes. However, the following explanation of the system is specific to the A 320 Airbus. The system is fundamentally comprised of air conditioning packs, a pack flow control valve, a by-pass valve, pack controllers, and a mixing unit.

These components provide conditioned air via the following step by step process:

  • First, outside air enters the airplane engine.
  • Next, compressors within the engine compress this low-density air.
  • Hot compressed air from the compressor (bleed air) is then transported via ducts to the A/C packs.
  • Prior to entering the air conditioner units, the bleed air passes through the pack flow control valve, which regulates the flow of air entering the conditioning packs.
  • Within the A/C unit, two air-to-air heat exchangers are installed that supply outside air via a pack inlet scoop and the air exits through an outlet duct.
  • As the cold air exits from the conditioning pack, it is mixed with warm air.
  • The desired air temperature is achieved by regulating the amount of hot air mixed with the cold conditioned air exiting from the packs through a by-pass valve.
  • The regulated air is then fed to a mixing unit which transports the air further on into the cabin and the cockpit.
  • The by-pass valve, pack flow control valve, inlet scoop and outlet duct are all operated by, and connected to, a pack controller.
In the video below – that’s not smoke, it’s condensation due to the AC system.

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