Definition
The range of flight altitudes through which a pressurization system can maintain a selected, constant cabin altitude regardless of changes in the aircraft's actual altitude. Within this range, the cabin pressure stays fixed even as the airplane climbs or descends.
Plain English
The band of altitudes where the pressurization system can hold the cabin at one steady chosen pressure, no matter how high or low the airplane is flying within that band.
Context Anchor
Seen in discussions of pressurized aircraft, cabin altitude, and how the pressurization system manages pressure during climb and high-altitude flight.
Derivation
From Greek 'isos' meaning 'equal' and 'baros' meaning 'weight' or 'pressure.' 'Isobaric' literally means 'equal pressure.' The term describes the range over which pressure is held equal (constant) inside the cabin.
Why Pilots Care
Keeps the cabin comfortable for passengers and crew without constant pressure adjustments during normal cruise.
Analogy
It is like a thermostat holding a room at one temperature while the weather outside keeps changing. The outside condition changes, but the system works to keep the inside condition steady.
Grounding Statement
As the aircraft climbs, the outside air pressure drops, but during the isobaric range the cabin pressure stays nearly the same.
Intuition Check
“Range” here does not mean how far the airplane can fly. It means the band of aircraft altitudes where the cabin pressure is held steady.
Example Sentence 1
As long as we stay within the isobaric range, the cabin will hold 8,000 feet even as we climb from FL230 to FL310.
Example Sentence 2
Above the isobaric range the system switches to constant differential mode to protect the airframe.