The speed range between high and low speed buffet:

The correct answer highlights a key aspect of aircraft aerodynamics related to the behavior of the stall margin and buffet onset during changes in altitude and airspeed. As an aircraft descends at a constant indicated airspeed (IAS), the airflow over the wings and the general aerodynamic characteristics of the aircraft can change significantly due to variations in air density.

In a standard scenario, as the aircraft descends, the true airspeed (TAS) increases for a given IAS because the air density increases as altitude decreases. This increase in TAS can lead to greater airflow around the wing, which can raise the point at which low-speed buffet occurs (the onset of aerodynamic stall) as well as the high-speed buffet occurrence (associated with compressibility effects).

Thus, the overall speed range between high-speed buffet and low-speed buffet expands during a descent at constant IAS. This occurs because the aircraft can handle greater speeds before experiencing buffet because of the increased dynamic pressure and airflow management.

This concept is fundamental in understanding the operational limits of an aircraft, especially during maneuvers involving altitude changes. It is essential for pilots to be aware of these dynamics for effective aircraft performance management and safety.