Definition
An instrument in a pressurized aircraft that displays the effective pressure altitude inside the cabin, allowing the crew to monitor the cabin pressurization environment that the occupants are actually breathing.
Plain English
A gauge that shows how high the inside of the cabin 'feels' in terms of air pressure, even when the aircraft is flying much higher than that.
Context Anchor
Seen on the pressurization panel or pressurization display in aircraft that maintain cabin pressure during flight.
Derivation
From 'cabin' (the enclosed occupant space) and 'altimeter' (an instrument that measures altitude by sensing air pressure). The name reflects what it does: it measures altitude, but for the cabin instead of the aircraft.
Why Pilots Care
Enables continuous monitoring to keep cabin pressure within safe limits and avoid hypoxia for passengers and crew.
Grounding Statement
In a pressurized airplane at cruise, the aircraft may be very high while the cabin altimeter shows a much lower cabin altitude because the cabin is being held at a higher pressure.
Intuition Check
Do not read cabin altimeter as the airplane’s altimeter. It shows the pressure condition inside the cabin, expressed as an altitude, not the aircraft’s height above the ground or sea level.
Example Sentence 1
Cruising at 35,000 feet, the crew checked the cabin altimeter and confirmed the cabin was holding steady at 7,000 feet.
Example Sentence 2
As the aircraft climbed through 20,000 feet, the cabin altimeter stabilized at 8,000 feet thanks to the pressurization system.