Which maximum range factor decreases as weight decreases?

The maximum range factor that decreases as weight decreases is airspeed. As the weight of an aircraft decreases, it generally requires a lower airspeed to maintain level flight. This is because, with less weight, the lift requirement is reduced, allowing the aircraft to operate efficiently at a lower speed without a significant loss of lift.

In the context of range, flying at the optimal airspeed is critical since it affects fuel efficiency and overall performance. As weight diminishes, the aircraft can achieve its best lift-to-drag ratio at a slower speed, which allows for longer flight durations without expending excessive fuel. This is particularly important in maximizing the aircraft's range capabilities.

While altitude and angle of attack also relate to range factors, they do not specifically decrease as weight decreases in the way airspeed does. The lift-to-drag ratio improves with optimal configurations, but it doesn’t inherently decrease with weight reduction. Therefore, airspeed is the correct factor that illustrates a direct relationship with decreasing weight in the context of maximum range.