How does cabin pressurization achieve a controlled cabin altitude?

• A. By regulating bleed air flow and exhaust through outflow valves and packs in the ECS.
• B. By adjusting the cabin temperature with the air conditioning packs.
• C. By closing all outflow valves to trap air.
• D. By varying cockpit window pressure with safety valves.

Answer: (A)

Pressurizing the cabin is about balancing the air entering the cabin with the air leaving it to hold a chosen cabin altitude. Bleed air from the engines is cooled and conditioned in the air conditioning packs and then supplied to the cabin. The cabin pressure controller monitors cabin and outside pressure and continuously adjusts the overboard vent, the outflow valve, to regulate how much air escapes. Bymetering this exhaust, the system maintains the cabin at the selected altitude even as the aircraft climbs or descends. Temperature control is handled by the packs, not the pressure system, while closing outflow valves to trap air would create dangerous overpressure, and cockpit windows aren’t used to regulate cabin pressure.