FAA Aviation Mechanic Airframe (AMA)Fuel, Cabin and Ice Control SystemsHard
A technician is inspecting the pressurization system of an aircraft and finds a spring-loaded valve designed to open if the outside atmospheric pressure becomes greater than the cabin pressure, such as during a rapid descent. This valve prevents structural damage from an inward-acting pressure differential. This valve is the:
- APositive pressure relief valve
- BCabin altitude selector
- CNegative pressure relief valve
- DOutflow valve
Show answer & explanationAnswer & explanation
Correct answer: C. Negative pressure relief valve
The negative pressure relief valve opens when outside pressure exceeds cabin pressure (a negative differential), such as during a rapid descent, allowing outside air into the cabin to prevent the fuselage from being crushed inward by reversed pressure loading.
Why the other options are wrong
- A. The positive pressure relief valve protects against excessive cabin pressure being higher than outside, the opposite scenario.
- B. A cabin altitude selector is a cockpit control input device, not a pressure relief valve.
- D. The outflow valve regulates normal cabin pressure but does not specifically protect against negative differential.
Negative Pressure Relief Valve
A spring-loaded valve that opens to admit outside air into the cabin when outside pressure exceeds cabin pressure, preventing structural damage from inward pressure loads.
- Opens during rapid descent scenarios
- Prevents fuselage crush from negative differential
- Works opposite to positive pressure relief valve
Memory trick: Negative valve = guards against the cabin getting 'sucked in'