Which type of airspeed is essential for navigation on charted routes?

True airspeed is essential for navigation on charted routes because it represents the actual speed of the aircraft relative to the surrounding air. This measurement accounts for variations in air density, which can change based on altitude and temperature. When flying by charted routes, pilots must understand their true airspeed to accurately determine their groundspeed and estimated times of arrival at waypoints or destinations.

Ground speed, while also relevant to navigation, is based on the aircraft's movement over the ground and is influenced by factors such as wind. While indicated and calibrated airspeeds are important for understanding aircraft performance and behavior, they do not provide the necessary information for long-range navigation. Only true airspeed integrates the necessary variables to ensure pilots can follow their courses effectively.