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CABIN ALT NORMAL

System study · Air Conditioning, Pressurization & Ventilation

From Pack Air to Cabin Comfort

Pack air gets mixed, trimmed to temperature per zone, and used to keep the cabin pressurized — almost entirely automatically. Click through the diagram, then quiz yourself on how the CPCs and outflow valve actually work.

Distribution & pressurization click a component

Simplified — not for operational use. Click the mixer unit, a trim valve, a CPC, or the outflow valve.
FROM PACK 1 & PACK 2 RECIRC FANS CABIN AIR REUSE MIXER UNIT BLENDS FRESH + RECIRC TRIM VALVE · CKPT TRIM VALVE · FWD CABIN TRIM VALVE · AFT CABIN AVIONICS VENTILATION CPC 1 / CPC 2 CABIN PRESS CONTROL OUTFLOW VALVE MOTOR-DRIVEN SAFETY VALVES +/- PRESSURE RELIEF
Click any component above to see what it does →

Pressurization — normally hands-off

FULLY AUTOMATIC
NO CABIN ALT SELECTOR

Unlike older aircraft with a manual cabin altitude selector, the A320's two Cabin Pressure Controllers work out the optimum cabin altitude automatically — using cruise altitude and landing field elevation — then drive the single outflow valve to control how much air escapes versus how much pack air comes in. If both CPCs fail, the crew can select manual mode and directly control the outflow valve; if that's also lost, mechanical positive and negative pressure relief valves still protect the fuselage structure.

Quick reference

PRESSURIZATION

  • Two CPCs normally compute cabin altitude automatically
  • Single motor-driven outflow valve does the actual controlling
  • Manual mode available if both CPCs fail

AIR MIXING

  • Mixer unit blends pack air with recirculated cabin air
  • Recirculation improves efficiency and reduces bleed demand
  • Avionics ventilation is a related, separate cooling circuit

TEMPERATURE CONTROL

  • Separate trim air valves for cockpit, forward cabin, and aft cabin
  • Each adds hot bleed air to reach that zone's selected temperature
  • Lets each zone run at a different comfortable temperature

Check yourself

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