Which factor primarily affects aircraft performance in relation to density altitude?

The primary factor affecting aircraft performance in relation to density altitude is temperature and pressure. Density altitude is a theoretical altitude that reflects an aircraft's performance based on the air density at a given location. This density is influenced by variations in both temperature and atmospheric pressure.

When temperatures rise or pressure decreases, the air becomes less dense. This means that the aircraft will have a lower performance level, requiring longer takeoff distances, reduced climb rates, and potentially affecting fuel efficiency. At higher temperatures, for instance, the air expands, resulting in fewer air molecules in a given volume, which can lead to a decrease in engine performance and lift generated by the wings.

While weather conditions can influence temperature and pressure, they are not the direct factors affecting density altitude. Similarly, while the weight of the aircraft does impact performance, it is secondary to the effects of temperature and pressure on air density. Lastly, humidity levels can have some impact on aircraft performance due to their effect on air density, but the primary contributors remain temperature and pressure. Therefore, understanding these two elements is crucial for aircraft operations, especially in varying environmental conditions.