Density altitude affects fixed-wing aircraft through which combination?

• A. Increased air density and more oxygen for combustion
• B. Increased air density and less oxygen for combustion
• C. Decreased air density and more oxygen for combustion
• D. Decreased air density and less oxygen for combustion

Answer: (D)

Density altitude describes how air density varies with altitude and weather. As it rises, the air gets thinner—air density decreases. That thinner air means there are fewer air molecules, including oxygen, in a given volume, so there is less oxygen available for combustion even though the oxygen fraction stays about 21%. For fixed-wing aircraft, this combination reduces engine power (less oxygen for burning fuel) and lift (less dense air for the wings to push against). So the correct description is decreased air density and less oxygen for combustion.