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AerodynamicsQuestion 409 of 934

Compare moist air with dry air at the same temperature and pressure. Which statement is correct?

  1. Moist air is heavier, so density altitude increases
  2. Moist air is lighter, so density altitude decreases
  3. Moist air has the same density, so performance is unchanged
  4. Moist air is lighter, so density altitude increases
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Correct answer: Moist air is lighter, so density altitude increases

Water vapor is lighter than air. More water in the air makes it less dense and raises density altitude.

Source: Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Chapter 4: Principles of Flight — Effect of Humidity (Moisture) on Density, page 92

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Questions last reviewed: 18 October 2026