What does an increase in density altitude typically indicate for aircraft performance?

An increase in density altitude generally signifies that the air is less dense than it would be at sea level, which has several implications for aircraft performance. When density altitude rises, the amount of oxygen available for both engine combustion and for generating lift decreases. This ultimately leads to decreased engine efficiency, as the engine may not be able to perform optimally due to insufficient oxygen.

Additionally, the reduction in air density affects the lift generated by the wings of the aircraft. As density altitude increases, the lift produced at a given speed is lower, which can hinder climb rates and overall maneuverability. Similarly, fuel performance may also be impacted negatively since the engine may not burn fuel as efficiently without adequate oxygen. Thus, an increase in density altitude primarily indicates decreased engine efficiency, making it the correct choice in this context.