(IAS) is the airspeed read directly from the aircraft Airspeed
Calibrated Airspeed: (CAS) is Indicated Airspeed corrected for instrument installation
error. Airspeed indicator correction information is generally displayed
on an airspeed calibration card placed in the aircraft cockpit.
Calibrated airspeed data should be used in place of Indicated
airspeed where possible.
(TAS) is calibrated airspeed corrected for air density (altitude and
temperature) and is the speed of the aircraft through the air mass.
(GS) is the actual speed of the aircraft relative to the ground and is
found by correcting TAS for head/tail wind.
True Airspeed (TAS) is the speed of the aircraft through the air mass and is not affected
by wind speed or direction. The airspeed indicator in the cockpit gives IAS information
which must be corrected for instrument error and density to determine TAS. (Figure 4.4-4)
Figure 4.4-4 True Airspeed