A pilot flying a pressurized airplane notices the cabin altitude climbing above the selected value even though the outflow valve appears to be closing normally. What system component, if malfunctioning, would most directly explain an inability to maintain cabin pressurization despite outflow valve operation?
- AThe static system alternate air source, which has no connection to cabin pressurization
- BA cracked cabin door seal or fuselage leak allowing pressurized air to escape faster than it is being supplied
- CThe landing gear squat switch, which inhibits pressurization systems only while airborne
- DThe cabin rate-of-climb selector, which only affects how quickly cabin altitude changes, not the final pressure achieved
Show answer & explanationAnswer & explanation
Correct answer: B. A cracked cabin door seal or fuselage leak allowing pressurized air to escape faster than it is being supplied
If the outflow valve is functioning correctly (closing to retain pressurized air) yet cabin altitude still climbs, the most direct explanation is a pressure leak elsewhere in the fuselage, such as a faulty door seal, cracked window, or structural leak, allowing bleed air to escape faster than the pressurization source can supply it, overwhelming the system's ability to maintain the selected cabin altitude.
Why the other options are wrong
- A. The static system is unrelated to cabin pressurization air supply.
- C. Squat switches typically prevent pressurization on the ground, not affect pressure once airborne.
- D. The rate selector controls climb/descent rate of cabin pressure, not whether the target pressure can be maintained.
Cabin Pressurization Leak Diagnosis
If cabin altitude rises despite a properly functioning outflow valve, a structural or seal leak is allowing pressurized air to escape faster than bleed air supply can compensate.
- Outflow valve regulates cabin pressure by controlling air exhaust rate
- Leaks (door seals, windows, fuselage cracks) bypass the outflow valve's control
- Rate controller only affects cabin climb/descent rate, not achievable maximum pressure
Memory trick: Valve's fine, but air's leaking out the side