Definition
True Airspeed (TAS) is the actual speed of an aircraft moving through the surrounding air mass, corrected for the effects of altitude and non-standard temperature on indicated airspeed. As altitude increases and air becomes less dense, TAS becomes progressively greater than the airspeed shown on the airspeed indicator.
Plain English
How fast the airplane is actually moving through the air around it, after accounting for the fact that thinner, warmer air makes the airspeed indicator read low.
Context Anchor
Seen on avionics displays that show nearby traffic, especially in discussions of modern cockpit technology and traffic awareness equipment.
Derivation
True' here means 'real' or 'actual' — the airspeed corrected to reflect what the aircraft is genuinely doing through the air, as opposed to the uncorrected reading on the gauge.
Why Pilots Care
Accurate TAS is essential for determining actual ground speed, fuel consumption rates, and aircraft performance at varying altitudes.
Intuition Check
Do not confuse TAS here with true airspeed. In this Figure 8-17 context, TAS means Traffic Advisory System, a traffic-awareness system in the aircraft.
Example Sentence 1
At 8,000 feet on a warm day, the indicated airspeed read 110 knots but the TAS was closer to 125 knots.
Example Sentence 2
The pilot used TAS to calculate the estimated time en route for the cross-country flight.