A decrease in air density will result in a decrease in which of the following?

A decrease in air density directly affects both lift and thrust because both are dependent on the mass of air that interacts with the aircraft's wings and propellers.

Lift is generated when air flows over the wings of an aircraft, and it is primarily impacted by air density, velocity, and wing area; a lower air density means there are fewer air molecules available to create lift. As a result, the aircraft would require a higher speed or a larger wing area to achieve the same lift that it would at a higher air density.

Thrust is also affected by air density because propellers or rotor blades work by pushing against a certain volume of air. With decreased air density, there is less air for the propellers to push against, which can result in a decrease in thrust produced, making it harder for the aircraft to climb or maintain speed.

The other options do not accurately reflect the effects of decreased air density. For instance, while speed may be impacted indirectly, it is not a direct consequence of air density alone. Understanding these interactions is crucial for piloting unmanned aircraft effectively, especially under varying environmental conditions.