Cabin altitude is best defined as what?

• A. The cabin temperature inside the aircraft.
• B. The cabin pressure expressed as an equivalent altitude above sea level.
• C. The altitude of the aircraft's external surface.
• D. The rate of climb of the cabin altitude.

Answer: (B)

Cabin altitude is the cabin pressure expressed as an equivalent altitude above sea level. The air inside the pressurized cabin is maintained at a pressure that corresponds to a certain altitude, typically about 6,000 to 8,000 feet, even when the airplane is much higher. This keeps oxygen levels and breathing comfortable for occupants. The outside altitude differs because the aircraft is pressurized to a lower pressure than the ambient air as it climbs. The term “equivalent altitude” is what ties the internal pressure to a recognizable altitude. The rate of climb of the cabin altitude or the aircraft’s external altitude are not definitions of cabin altitude.