Aircraft systems and instrumentsQuestion 589 of 934

What does the manifold pressure gauge show when the engine is not running?

  1. Zero
  2. The oil pressure
  3. The ambient air pressure
  4. The pressure in the fuel tank
Show answer

Correct answer: The ambient air pressure

With the engine off, the gauge shows ambient pressure, for example 29.92 inches of mercury at standard sea level.

Source: Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Chapter 7: Aircraft Systems — Propeller — Adjustable-Pitch Propeller, page 166

Practice aircraft systems and instruments

Questions last reviewed: 18 October 2026