Definition
Knots calibrated airspeed (KCAS) is indicated airspeed corrected for instrument and position errors, expressed in knots. Position error arises because the static port cannot sense perfectly undisturbed air at every angle of attack and flap configuration, so the raw indicated value needs a small correction. The resulting calibrated value more accurately reflects the airplane's true airspeed through the surrounding air mass at sea level on a standard day.
Plain English
It is the airspeed shown on the cockpit gauge after small built-in errors have been corrected, given in knots. Think of it as the cleaned-up version of the speed the pilot sees on the dial.
Context Anchor
You will see KCAS in airplane handbooks, performance charts, and discussions of airspeed limits or stall speeds.
Derivation
Knot comes from the old practice of measuring a ship's speed by counting knots tied at intervals along a line trailed in the water; one knot is one nautical mile per hour. Calibrate comes from Latin and French roots meaning to set a measuring instrument to a correct standard. Together, KCAS means a knots reading that has been adjusted to remove the gauge's own small errors.
Why Pilots Care
Accurate KCAS values ensure performance calculations such as takeoff distance and climb rate remain reliable.
Intuition Check
Do not assume KCAS is simply whatever the airspeed indicator shows. KCAS is the corrected airspeed value, expressed in knots.
Example Sentence 1
The POH lists the flap extension limit as 95 KCAS, so the pilot checked the airspeed correction table to see what that reads on the indicator.
Example Sentence 2
At sea level on a standard day, KCAS equals KTAS.