Two most critical factors in aviation performance are _________ and _________.

• A. Altitude and Humidity
• B. Humidity and Temperature
• C. Density and Viscosity
• D. Temperature and Pressure

Answer: (D)

Air density is what mainly governs aircraft performance because it determines how much lift the wings can produce and how much air the engine can ingest. The density of that air is set primarily by temperature and atmospheric pressure. When the air is warmer, it expands and becomes less dense, which reduces lift and engine power. Conversely, higher ambient pressure makes the air denser, improving both lift and thrust. Humidity can alter density a bit (humid air is lighter than dry air), but its effect is smaller compared with changes in temperature and pressure. That’s why temperature and pressure are the dominant factors controlling performance, and they’re combined conceptually in density altitude to explain how the air actually behaves for takeoff, climb, and engine output.