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Cabin air safety valve setting

Aviation Mechanic Airframe (AMA) practice question 13 of 15 on Environmental Systems. ACS element AM.II.G.K8 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONOn most aircraft, at what cabin differential pressure are the cabin air pressure safety valves set to open?

  1. ABetween 2 and 4 psid
  2. BBetween 18 and 20 psid
  3. CBetween 8 and 10 psid
Show the answer and explanation

Correct answer: C. Between 8 and 10 psid

  • A — incorrect This is far below normal operating differential pressure, so the valve would open during routine flight and prevent pressurization.
  • B — incorrect This is well above the design differential of transport pressure vessels, so the valve would never protect the structure.
  • C — correct The handbook states that on most aircraft safety valves are set to open between 8 and 10 psid.

BACKGROUND

Pressurization systems include features that limit human and structural damage if the system malfunctions. A cabin air safety valve is a pressure relief valve set to open at a predetermined pressure differential, allowing air to flow from the cabin so internal pressure cannot exceed design limitations; on most aircraft it opens between 8 and 10 psid. Wide-body transport category aircraft may carry more than one safety valve, and some outflow valves incorporate the safety valve function through a pilot valve that opens at a preset differential. Cabin altitude limiters close the outflow valves when cabin pressure drops well below the normal range. A negative pressure relief valve opens inward to admit ambient air when outside pressure would otherwise exceed cabin pressure.

STUDY TIP

Sort the protective devices by the direction of the problem: safety valves and dump valves handle too much cabin pressure, negative pressure relief handles too little. Knowing which way each valve opens answers most questions about them.

KEY POINTS

  • Safety valves on most aircraft open between 8 and 10 psid.
  • Negative pressure relief valves open inward to protect against outside pressure exceeding cabin pressure.
  • Cabin altitude limiters close the outflow valves to stop cabin altitude from rising further.

SOURCES

  • sources/ama-airframe/ch16.txt "Cabin Air Pressure Safety Valve Operation"
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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.