Definition
The pressure altitude inside the cabin of a pressurized aircraft, expressed as the altitude at which the same air pressure would naturally exist in the unpressurized atmosphere. It reflects the effective altitude the occupants' bodies are experiencing, not the altitude the aircraft is actually flying at.
Plain English
How high your body thinks it is, based on the air pressure inside the cabin. The aircraft might be cruising at 35,000 feet, but the cabin is held at a much lower effective altitude so passengers can breathe comfortably.
Context Anchor
Seen in pressurized aircraft systems, cabin pressure instruments, warning systems, and emergency procedures for loss of cabin pressure.
Derivation
“Cabin” means an enclosed room or compartment, and “altitude” comes from a word meaning height. Together, the term means the height represented by the air pressure inside the aircraft’s cabin.
Why Pilots Care
Monitoring cabin altitude helps prevent hypoxia and ensures passenger comfort and safety on high-altitude flights.
Grounding Statement
If the aircraft is flying at 25,000 feet but the cabin pressure matches outside air pressure at 8,000 feet, the cabin altitude is 8,000 feet.
Intuition Check
Cabin altitude is not the airplane’s actual altitude. It is the pressure inside the cabin stated as an equivalent height.
Example Sentence 1
At a cruise altitude of 35,000 feet, the cabin altitude was maintained at about 7,000 feet.
Example Sentence 2
A rising cabin altitude prompted the crew to don oxygen masks and begin an emergency descent.