What is the difference between calibrated airspeed (CAS) and indicated airspeed (IAS)?

Calibrated airspeed (CAS) is the value derived from indicated airspeed (IAS) after making corrections for instrument errors and any errors resulting from the instrument's specific installation on the aircraft. IAS is the raw speed read directly from the airspeed indicator, which can be affected by various factors such as pressure and temperature deviations, as well as installation-induced errors, meaning it does not always reflect the true airspeed that the aircraft is experiencing relative to the surrounding air.

When these errors are taken into account, the resulting CAS provides a more accurate portrayal of the aircraft's true performance characteristics in the atmosphere. This distinction is crucial for pilots as it can affect calculations related to performance metrics such as lift, drag, and other aerodynamic properties crucial for safe flight operations. Understanding this difference between CAS and IAS helps pilots make informed decisions regarding the aircraft’s behavior in flight, ensuring safer and more effective navigation and control.