Definition
An operating mode of an aircraft pressurization system in which the cabin is held at a single, constant pressure altitude regardless of changes in the aircraft's actual altitude, as long as the aircraft remains within the system's design limits.
Plain English
A setting on the pressurization system that keeps the cabin feeling like it is at one chosen altitude, even while the aircraft climbs, cruises, or descends.
Context Anchor
Seen in aircraft pressurization system descriptions, especially when explaining how cabin pressure is controlled during climb, cruise, and descent.
Derivation
From Greek 'isos' meaning equal and 'baros' meaning weight or pressure. 'Isobaric' literally means 'equal pressure,' which fits the mode's job of holding cabin pressure constant.
Why Pilots Care
Maintains consistent cabin altitude for passenger comfort and to avoid physiological effects of pressure changes.
Analogy
It is like holding a room at one steady temperature, except the system is holding cabin pressure steady instead of temperature.
Grounding Statement
Picture the aircraft climbing while the cabin stays at the same comfortable pressure instead of climbing with the airplane.
Intuition Check
Do not read “isobaric” as meaning the airplane stays at the same altitude. It means the cabin pressure is being held at a constant value.
Example Sentence 1
Once level at cruise, the pressurization controller switched to isobaric mode and held the cabin at 6,500 feet.
Example Sentence 2
In isobaric mode, the outflow valve adjusts automatically to maintain the selected cabin altitude.