FAA Commercial Pilot Airplane (CAX)Aircraft SystemsMedium
An airplane's pressurization system includes a valve that automatically opens to admit outside air into the cabin whenever cabin pressure would otherwise become lower than outside atmospheric pressure, such as during a rapid descent. This valve is the?
- APositive pressure relief (safety) valve
- BCabin rate-of-climb controller
- COutflow valve
- DNegative pressure relief valve
Show answer & explanationAnswer & explanation
Correct answer: D. Negative pressure relief valve
The negative pressure relief valve prevents a structurally dangerous situation where outside pressure exceeds cabin pressure (which can happen during a rapid descent when the cabin can't depressurize fast enough) by letting outside air flow in. The outflow valve controls normal cabin pressure regulation, the positive pressure relief valve prevents excessive cabin pressure buildup, and the rate-of-climb controller manages the speed of cabin pressure changes, not pressure differential direction.
Why the other options are wrong
- A. Positive relief protects against too much cabin pressure, the opposite condition.
- B. The rate controller manages smoothness of pressure change, not this safety function.
- C. The outflow valve regulates normal cabin air outflow, not this failure protection.
Negative Pressure Relief Valve
A safety valve that opens to let outside air into the cabin whenever cabin pressure drops below outside pressure, preventing structural damage.
- Protects against inward-collapsing loads on the fuselage
- Activates typically during rapid descents
- Works opposite to the positive pressure relief valve
Memory trick: Negative valve lets air back in.