At what Mach speed does the airspeed indicator information become active?

The airspeed indicator information becomes active at 0.40 Mach. This specific Mach number is important because it marks a transition point where aerodynamic effects and control responses begin to be more pronounced, influencing the aircraft's performance and handling characteristics.

At speeds below this threshold, the aircraft may not be able to gather accurate data, as the airflow and aerodynamic behavior are not fully representative of higher-speed flight. Understanding when the airspeed indicator activates ensures that pilots can operate the aircraft safely and effectively, particularly when approaching the regime where transonic effects and potential compressibility issues become relevant. This knowledge is crucial in the context of training and operations to maintain situational awareness and ensure safe maneuvering across different phases of flight.