What is the difference between true airspeed and indicated airspeed?

True airspeed and indicated airspeed are important concepts in aviation that reflect different measurements of speed. True airspeed (TAS) is defined as the actual speed of the aircraft relative to the surrounding air. This measurement accounts for variations in air density, which can change due to altitude and temperature. As an aircraft climbs to higher altitudes, the air becomes less dense, and TAS provides a meaningful representation of the aircraft's performance in those conditions.

Indicated airspeed (IAS), on the other hand, is the speed read directly from the airspeed indicator in the cockpit. This measurement does not account for changes in air density; it is the speed that the aircraft seems to be flying based solely on the dynamic pressure of the air flowing into the pitot tube. For pilots, IAS is particularly important for understanding the aircraft's performance in terms of lift and stall speeds, but it does not give a complete picture of the aircraft's actual speed through the air.

Understanding the relationship between these two speeds is essential for aircraft operation, especially at high altitudes where differences can be significant. High true airspeeds can often mean that the aircraft is flying more efficiently, but the pilot needs to first comprehend both measures to make informed operational decisions.