PRESSURIZATION refers to which of the following?

• A. The air in the cargo hold
• B. The system that supplies cabin air at a pressure equivalent to sea level
• C. The air that is compressed by the engines and fed into the cabin to maintain a lower cabin altitude than the aircraft is actually flying
• D. The system that humidifies cabin air

Answer: (C)

Pressurization is the system that keeps the cabin at a lower altitude pressure than the aircraft’s actual altitude, creating a comfortable and safe environment for passengers and crew. At cruising height, outside air is thin and very cold, so air is brought in, compressed, and conditioned before it’s distributed into the cabin. Bleed air from the engines (and sometimes the APU) is used, then cooled and mixed with cabin recirculated air, with an outflow valve regulating how much air leaves the cabin to maintain a steady cabin pressure. This maintains a cabin altitude around 6,000–8,000 feet, even though the plane may be cruising at 30,000 feet or higher.

This isn’t about the air in the cargo hold, nor about keeping the cabin at sea-level pressure, and it isn’t the function of humidifying cabin air. Humidity control is a separate part of the environmental system.