FAA Commercial Pilot Airplane (CAX)Aircraft SystemsHard
An airplane's pressurization system maintains a cabin altitude equivalent to an ambient pressure of 22.22 inHg while cruising at a flight altitude where the ambient pressure is 11.10 inHg. Using a conversion factor of approximately 0.491 psi per inHg, and given that the airplane's maximum allowable cabin differential pressure is 5.5 psi, what is the actual cabin differential pressure, and is it within limits?
- A4.46 psi, within the structural limit
- B5.46 psi, within the structural limit
- C11.12 psi, exceeding the structural limit
- D5.46 psi, exceeding the structural limit
Show answer & explanationAnswer & explanation
Correct answer: B. 5.46 psi, within the structural limit
Differential pressure equals cabin pressure minus ambient (flight) pressure: 22.22 − 11.10 = 11.12 inHg. Converting to psi: 11.12 × 0.491 ≈ 5.46 psi. Since 5.46 psi is less than the 5.5 psi structural limit, the differential pressure is within limits.
Why the other options are wrong
- A. This value results from an incorrect conversion factor or arithmetic error.
- C. 11.12 is the inHg difference, not converted to psi, and is misapplied here.
- D. The value is correctly calculated but incorrectly judged as exceeding the limit.
Cabin Differential Pressure
The difference between cabin pressure and outside ambient pressure at altitude, limited structurally to protect the fuselage; calculated in psi from inHg using ~0.491 psi/inHg.
- Diff pressure = cabin pressure − ambient pressure
- Convert inHg to psi using ~0.491 psi per inHg
- Exceeding max differential risks structural damage
Memory trick: Subtract, then convert: inHg difference times 0.491 gives your psi.