Types of Airspeed
Calibrated Airspeed (CAS)
Calibrated airspeed (CAS) is indicated airspeed corrected for instrument and position error. When flying at sea level under International Standard Atmosphere conditions (15 °C, 1013 hPa, 0% humidity) calibrated airspeed is the same as equivalent airspeed (EAS) and true airspeed (TAS).
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en.wikipedia.org
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Groundspeed (GS)
An airspeed indicator indicates the aircraft's speed relative to the air mass. The air mass may be moving over the ground due to wind, and therefore some additional means to provide position over the ground is required.
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en.wikipedia.org
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trafficschoolonline.com
True Airspeed
The true airspeed (TAS; also KTAS, for knots true airspeed) of an aircraft is the speed of the aircraft relative to the airmass in which it is flying. The true airspeed is important information for accurate navigation of an aircraft.
source:
en.wikipedia.org
image:
en.wikipedia.org