Calibrated airspeed (CAS) refers to the indicated airspeed of an aircraft that is corrected for position and instrument error.
Calibrated Airspeed & Errors
Calibrated airspeed errors include but aren’t limited to ground proximity, flap configuration, angle of attack, and wind direction. It is when an aircraft is traveling at a low airspeed, or with flaps deployed, when these errors are greatest – sometimes totaling several knots.
An airspeed calibration chart can be used to determine the difference between IAS and CAS and account for errors.
What Are the Primary Applications of Calibrated Airspeed?
Calibrated airspeed is primarily used for:
- Navigation: CAS is required as one of the steps to calculate true airspeed (TAS) from indicated airspeed – though this is not used as much due to the widespread presence of GPS and INS (inertial navigation system)
- Aircraft control: CAS describes the dynamic pressure acting on aircraft surfaces, so it is one of the main reference points for aircraft control. This is regardless of existing wind, pressure altitude, or temperature conditions.
CAS vs. TAS vs. IAS vs. GS
Under International Standard Atmosphere (ISA) conditions, calibrated airspeed is equal to true airspeed (TAS).
Indicated airspeed (IAS) and CAS are approximately the same in the cruising and higher airspeed ranges.
If there is no wind, CAS is the same as ground speed (GS).