What is the purpose of the outflow valve in the aircraft environmental control system?

• A. To maintain cabin altitude
• B. To regulate cabin temperature
• C. To vent avionics bay
• D. To increase cabin pressure

Answer: (A)

The outflow valve serves as the exhaust path for cabin air, and its job is to regulate cabin pressure by varying how much air escapes from the cabin to the outside. The cabin pressurization system uses bleed air to condition and supply the cabin, and the cabin pressure controller adjusts the valve opening to hold the cabin at the intended pressure, which corresponds to a specific cabin altitude. When climbing, the valve can vent more air to prevent the cabin from pressurizing too high; when descending or trying to maintain pressure as outside pressure changes, it vents less to keep the cabin pressure from dropping. A safety relief valve provides overpressure protection, but the outflow valve is the normal control path for maintaining the target cabin pressure.

This function is not about controlling cabin temperature (that’s handled by the air conditioning packs and mixing), and venting avionics bay air is handled by separate vents, not the primary outflow valve.