Definition
Calibrated airspeed (CAS) is indicated airspeed that has been corrected for installation error and instrument error in the airspeed indicating system. It is the speed the airspeed indicator would show if those small built-in errors were removed. KCAS expresses calibrated airspeed in knots. CAS still reflects the dynamic pressure the aircraft is flying through and is not corrected for air density (that further correction produces true airspeed).
Plain English
It is the airspeed reading after the small built-in errors of the gauge and its plumbing have been taken out. It is a more honest version of what the airspeed indicator is showing you.
Context Anchor
Seen in performance charts, high-speed aerodynamics discussions, and places where the handbook needs a more corrected airspeed than the raw airspeed indicator reading.
Derivation
Calibrated' comes from the Latin calibrare, meaning to measure or adjust against a known standard. In aviation it means the indicated reading has been adjusted to remove known measurement errors, giving a truer figure.
Why Pilots Care
Aircraft performance data such as takeoff distances and climb rates are calculated using calibrated airspeed values.
Analogy
It is like adjusting a bathroom scale that reads two pounds high. The first reading is what the scale shows; the calibrated value is the reading after correcting the known error.
Intuition Check
Do not read calibrated as meaning perfect or final. Here it means corrected for specific airspeed-system errors; it does not automatically mean speed over the ground or the airplane’s actual speed through the air mass.
Example Sentence 1
The POH lists the short-field approach speed as 62 KCAS, so the pilot checked the airspeed correction table to find the matching indicated reading.
Example Sentence 2
At low altitude the difference between indicated airspeed and calibrated airspeed was only a few knots.