FAA Airline Transport Pilot (ATM)Transport Aerodynamics and High-Altitude OperationsEasy
While climbing through FL280, a flight crew notices the cabin altitude climbing more slowly than expected and the cabin rate of climb indicator shows a controlled rate. Which component is primarily responsible for regulating this cabin climb rate by modulating the amount of air released overboard?
- AThe safety relief valve
- BThe cabin altitude selector
- CThe outflow valve
- DThe bleed air valve
Show answer & explanationAnswer & explanation
Correct answer: C. The outflow valve
The outflow valve controls the rate at which pressurized air is released overboard, thereby regulating cabin altitude and cabin rate of climb/descent. It is automatically modulated by the pressurization controller to maintain the scheduled cabin pressure while the safety relief valve only activates if pressure limits are exceeded.
Why the other options are wrong
- A. The safety relief valve only opens to prevent over- or under-pressurization, not for normal control.
- B. The selector sets the desired cabin altitude schedule but doesn't itself regulate airflow.
- D. The bleed air valve controls air entering the system, not the rate of release.
Cabin Outflow Valve
The outflow valve controls the rate of pressurized air leaving the cabin, thereby regulating cabin altitude and rate of change, under command of the pressurization controller.
- Modulated automatically by the pressurization system
- Closes to increase cabin pressure, opens to decrease it
- Distinct from the safety/positive & negative pressure relief valves
Memory trick: Outflow valve is the cabin's exhaust pipe