What is indicated by the airspeed at point D in aircraft performance figures?

The airspeed at point D in aircraft performance figures typically represents the never-exceed speed, commonly referred to as Vne. This is the maximum speed that an aircraft should not exceed under any circumstances, as exceeding Vne can result in structural failure or uncontrolled flight characteristics. It is crucial for pilots to adhere to this limit to maintain safety and ensure the integrity of the aircraft's structure throughout its flight envelope.

Understanding Vne is critical for flight instructors to communicate to students the importance of speed management, particularly in turbulent conditions or when maneuvering close to the aircraft's performance limits. Knowing and respecting Vne helps prevent dangerous scenarios that could compromise both the aircraft's safety and the safety of its occupants.

Other speeds, such as Vno (the maximum cruising speed), maneuvering speed (Va), and stall speed (Vs), each play important roles in flight operations but are defined differently in terms of their purpose and when they apply. Therefore, the indication of airspeed at point D aligns with the definition and significance of the never-exceed speed in maintaining safe operational practices.