What is the relationship between density altitude, pressure altitude, and temperature on TAS and fuel burn?

• A. Pressure altitude sets the baseline; density altitude (affected by temperature) determines air density, which affects engine power and prop efficiency; higher density altitude increases TAS needed for same power and tends to raise fuel burn.
• B. Density altitude sets the baseline; temperature has no effect on TAS.
• C. Temperature has no effect on TAS.
• D. Density altitude is unrelated to air density.

Answer: (A)

Density altitude is what you get when you translate the actual air density into an equivalent altitude in the standard atmosphere. Pressure altitude sets the reference level, but what really matters for performance is how thick or thin the air is, which is driven by density altitude (influenced by temperature and elevation).

When density altitude is high, the air is thinner. That thinning lowers engine power output and propeller efficiency, and it also reduces lift for a given speed. Because the aircraft is operating as if it were in a higher, thinner atmosphere, you must fly faster (increase true airspeed) to achieve the same thrust and lift you had at lower density altitude. In other words, for the same power setting, you end up needing a higher TAS to maintain the same flight condition.

Fuel burn tends to rise with higher density altitude because the engine has to work harder to produce the reduced thrust and maintain speed, so more fuel is consumed to try to sustain performance.

The other statements ignore how temperature (and thus density) affects air density, engine and propeller efficiency, and lift, and they falsely claim temperature or density altitude has no effect on TAS or air density.