Plain English Meaning

Equipment that pushes outside air into a sealed cabin and lets it out slowly, so the air inside stays thicker and easier to breathe than the thin air outside at high altitudes.

Full Definition

Aircraft systems that pump and regulate air inside a sealed cabin to maintain a higher internal air pressure than the outside atmosphere at high altitudes. Engine-supplied compressed air (typically bleed air from turbine engines or output from a turbocharger or dedicated compressor on piston aircraft) is fed into the cabin, while an outflow valve controls how quickly that air is allowed to escape. By balancing inflow against outflow, the system holds the cabin at a chosen '' that is much lower than the aircraft's actual , keeping the air dense enough for breathing without .