Why does a heavier airplane have increased V_A?

A heavier airplane has increased V_A, or maneuvering speed, primarily because it can sustain greater load factors. As the weight of the aircraft increases, the load factor that the wings can handle before stalling also increases. V_A is defined as the maximum speed at which you can safely make full deflections of the controls without risking a stall. At greater weights, the aircraft will experience a higher stall speed during maneuvers, but it also has the structural capacity to handle higher loads without compromising safety. Thus, maneuvering at speeds above V_A when the aircraft is heavy allows the pilot to execute abrupt maneuvers while maintaining a margin of safety against stalling.

Considering the other options, while heavier aircraft do indeed have higher stall speeds, which is partially related to the increased V_A, it is the capacity to withstand greater load factors that directly impacts the definition of V_A. The notion of requiring more altitude for safe maneuvering does not directly correlate to an increase in V_A. Additionally, decreased wing loading is not associated with heavier aircraft; rather, heavier aircraft typically have increased wing loading, which affects stall speed and, consequently, V_A differently.