In the unpressurized operating range, which statement about cabin altitude is correct?

• A. Cabin altitude is always lower than aircraft altitude
• B. Cabin altitude equals aircraft altitude
• C. Cabin altitude can be higher than aircraft altitude
• D. Cabin altitude is controlled by the isobaric range

Answer: (B)

In unpressurized operation there is no system actively maintaining cabin pressure lower than outside air. The cabin pressure simply follows the ambient air pressure, so the cabin altitude—the altitude corresponding to the cabin pressure—matches the aircraft’s altitude. If you’re flying at 12,000 ft, the cabin altitude is 12,000 ft; at 20,000 ft it’s 20,000 ft. That’s why the correct statement is that cabin altitude equals aircraft altitude in the unpressurized range.

The other ideas don’t fit because there’s no mechanism to keep the cabin at a lower or higher pressure than the outside when not pressurized, and there’s no isobaric-range control in an unpressurized state.