How does an aircraft's indicated airspeed compare to its true airspeed at high altitudes?

Indicated airspeed and true airspeed are two important metrics in aviation that reflect different aspects of an aircraft's performance. Indicated airspeed is what the pilot sees on the airspeed indicator, which is based on the measurement of dynamic pressure from the air flowing around the aircraft. True airspeed, on the other hand, is the actual speed of the aircraft relative to the surrounding air.

At high altitudes, the air is less dense than at lower altitudes. This reduced air density affects the measurement of indicated airspeed. As an aircraft climbs to higher altitudes, its indicated airspeed will read lower than its true airspeed. This phenomenon occurs because the calibration of the airspeed indicator does not account for variations in air density. Therefore, when the aircraft is operating at high altitudes, the true airspeed increases, while the indicated airspeed appears lower than it actually is in relation to the surrounding air.

Understanding this relationship is crucial for pilots, as it influences flight performance and navigation. It allows pilots to maintain the correct airspeeds necessary for safe flight operations, especially in different phases of flight.