Definition
A valve in a pressurized aircraft that controls the rate at which conditioned cabin air is released from the fuselage to the outside atmosphere, thereby regulating cabin pressure. It works in concert with the air conditioning and pressurization system: air is forced in at a steady rate, and the outflow valve modulates how quickly that air leaves, holding the cabin at the scheduled pressure altitude.
Plain English
A controllable opening in the side of a pressurized aircraft that lets cabin air escape at just the right rate to keep the inside of the cabin at a comfortable, breathable pressure.
Context Anchor
Seen in aircraft pressurization system descriptions, maintenance checks, and abnormal cabin pressure discussions.
Derivation
Plainly named for its function: it is the valve through which air flows out of the cabin. The interesting part is that cabin pressure is set not by how much air comes in, but by how much is allowed to leave through this valve.
Why Pilots Care
Correct operation prevents rapid or uncontrolled depressurization and keeps cabin altitude within safe limits throughout the flight.
Analogy
Think of slightly opening or closing a window in a room with a fan blowing air in. The fan supplies air, and the opening controls how much air can leave.
Grounding Statement
Think of the cabin as a balloon with air constantly being pumped in; the outflow valve is the adjustable opening that lets just enough air leak out to keep the balloon firm but not over-inflated.
Intuition Check
Do not think of the outflow valve as the part that pumps air into the cabin. Its main job is to control how much cabin air is allowed to leave.
Example Sentence 1
As the aircraft climbed through 18,000 feet, the cabin pressure controller commanded the outflow valve to close slightly, holding the cabin at 6,000 feet.
Example Sentence 2
The technician tested the outflow valve seal after the pressurization check showed a slow leak.