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Aircraft systems and instrumentsQuestion 506 of 934

The pilot uses the alternate static source. How does the altimeter read?

  1. Slightly lower than the actual altitude
  2. The same as the actual altitude
  3. Slightly higher than actual altitude
  4. Much lower than the actual altitude
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Correct answer: Slightly higher than actual altitude

The pressure in the flight deck is lower than the outside pressure. The ASI also reads higher than actual, and the VSI shows a momentary climb.

Source: Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Chapter 8: Flight Instruments — Pitot-Static Flight Instruments — Static Pressure Chamber and Lines, page 205

Practice aircraft systems and instruments

Questions last reviewed: 18 October 2026