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An aircraft's indicated airspeed in knots is typically abbreviated KIAS for "Knots-Indicated Air Speed" (vs. KCAS for calibrated airspeed and KTAS for true airspeed). The IAS is an important value for the pilot because it is the indicated speeds which are specified in the aircraft flight manual for such important performance values as the stall ...
Since indicated, as opposed to true, airspeed is a better indicator of margin above the stall, true airspeed is not used for controlling the aircraft; for these purposes the indicated airspeed – IAS or KIAS (knots indicated airspeed) – is used. However, since indicated airspeed only shows true speed through the air at standard sea level ...
for navigation, CAS is traditionally calculated as one of the steps between indicated airspeed and true airspeed; for aircraft control, CAS (and EAS) are the primary reference points, since they describe the dynamic pressure acting on aircraft surfaces regardless of density, altitude, wind, and other conditions.
The indicated airspeed is close to the true airspeed only at sea level in standard conditions and at low speeds. At 11 000 m (36 000 ft), an indicated airspeed of 300 kn may correspond to a true airspeed of 500 kn in standard conditions.
In aviation, equivalent airspeed (EAS) is calibrated airspeed (CAS) corrected for the compressibility of air at a non-trivial Mach number. It is also the airspeed at sea level in the International Standard Atmosphere at which the dynamic pressure is the same as the dynamic pressure at the true airspeed (TAS) and altitude at which the aircraft ...
Airspeed is commonly given in knots (kn). Since 2010, the International Civil Aviation Organization (ICAO) recommends using kilometers per hour (km/h) for airspeed (and meters per second for wind speed on runways), but allows using the de facto standard of knots, and has no set date on when to stop.
In practice the ram rise is negligible for aircraft flying at (true) airspeeds under Mach 0.2. For airspeeds (TAS) over Mach 0.2, as airspeed increases the temperature exceeds that of still air. This is caused by a combination of kinetic (friction) heating and adiabatic compression. Kinetic heating. As the airspeed increases, more and more ...
An airspeed indicator for an aeroplane. Indicated airspeed is displayed on the black background (in this case both in knots (kn) and miles per hour (mph)). The pilot sets the pressure altitude and air temperature in the top window using the knob. Based on that, the white background scale in the lower left window moves to give true airspeed.