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Cabin differential pressure calculation

Aviation Mechanic Airframe (AMA) practice question 1 of 15 on Environmental Systems. ACS element AM.II.G.K1 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONAn aircraft is flown where the ambient air pressure is 4.37 psi while the cabin pressure is held at 10.92 psi. What is the cabin differential pressure?

  1. A15.29 psid
  2. B10.92 psid
  3. C6.55 psid
Show the answer and explanation

Correct answer: C. 6.55 psid

  • A — incorrect This is the sum of the two pressures; differential pressure is a difference, not a total.
  • B — incorrect This is the cabin pressure by itself, which is the value the differential is calculated from, not the differential.
  • C — correct Cabin differential pressure is cabin pressure minus ambient pressure: 10.92 psi - 4.37 psi = 6.55 psid.

BACKGROUND

Cabin differential pressure is defined as the difference between the air pressure inside the cabin and the air pressure outside the cabin, expressed as cabin pressure (psi) minus ambient pressure (psi). The handbook abbreviates it psid, or delta psi. It is one of three pressurization terms a technician must know, along with cabin altitude (the altitude on a standard day having the same pressure as the cabin) and cabin rate of climb (the rate of cabin pressure change in feet per minute of cabin altitude). Differential pressure matters because the airframe pressure vessel is designed for a maximum differential, and structural limits are expressed in these terms. A cabin held at 10.92 psi corresponds to a cabin altitude of 8,000 feet.

STUDY TIP

Practice converting between cabin altitude and pressure using the standard atmosphere values, and always subtract ambient from cabin pressure in that order. Getting the sign and the order right is most of the work on differential pressure questions.

KEY POINTS

  • Cabin differential pressure = cabin psi minus ambient psi.
  • 10.92 psi cabin pressure corresponds to an 8,000-foot cabin altitude.
  • Cabin altitude, cabin differential pressure and cabin rate of climb are the three basic pressurization terms.

SOURCES

  • sources/ama-airframe/ch16.txt "Pressurization Terms"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.