FAA Aviation Mechanic Airframe (AMA)Fuel, Cabin and Ice Control SystemsHard
An aircraft is cruising at 35,000 feet where ambient atmospheric pressure is 3.46 psi. The cabin pressurization system maintains a cabin altitude of 8,000 feet, where atmospheric pressure is 10.92 psi. What is the cabin pressure differential?
- A7.46 psi
- B10.92 psi
- C14.38 psi
- D3.46 psi
Show answer & explanationAnswer & explanation
Correct answer: A. 7.46 psi
Cabin differential pressure equals cabin pressure minus outside ambient pressure: 10.92 psi − 3.46 psi = 7.46 psi. This differential must remain within the structural limits certified for the fuselage.
Why the other options are wrong
- B. 10.92 psi is the cabin pressure alone, not the differential.
- C. 14.38 psi is the sum, not the difference, of the two pressures.
- D. 3.46 psi is simply the outside ambient pressure at altitude, not the differential.
Cabin Pressure Differential
The difference between the pressure inside a pressurized cabin and the ambient pressure outside the aircraft at altitude; it is a critical structural design limit.
- Differential = cabin pressure − outside ambient pressure
- Exceeding max differential can cause structural damage
- Typical transport aircraft max differential is around 8–9 psi
Memory trick: Differential is what's left after subtracting outside from inside.