Airspeed - Calibrated Airspeed

Calibrated Airspeed

Calibrated airspeed (CAS) is indicated airspeed corrected for instrument errors, position error (due to incorrect pressure at the static port) and installation errors.

Calibrated airspeed values less than the speed of sound at standard sea level (661.4788 knots) are calculated as follows:

minus position and installation error correction.

Where

is the calibrated airspeed,

is the impact pressure (inches Hg) sensed by the pitot tube,

is 29.92126 inches Hg; static air pressure at standard sea level,

is 661.4788 knots;, speed of sound at standard sea level.

Units other than knots and inches of mercury can be used, if used consistently.

This expression is based on the form of Bernoulli's equation applicable to a perfect, compressible gas. The values for and are consistent with the ISA i.e. the conditions under which airspeed indicators are calibrated.