Definition
True airspeed (TAS) is the actual speed of an aircraft moving through the surrounding air mass. It is calibrated airspeed corrected for the effects of altitude and non-standard temperature, both of which change air density and therefore the relationship between indicated airspeed and real speed through the air.
Plain English
How fast the aircraft is really moving through the air around it, after correcting the airspeed indicator's reading for thinner air at higher altitudes and for temperature.
Context Anchor
Seen in flight planning, aircraft performance charts, navigation calculations, and discussions of flying at higher altitudes.
Derivation
True' here means 'actual' rather than 'indicated' or 'apparent.' The airspeed indicator shows a reading based on air pressure, which understates real speed as the aircraft climbs into thinner air. 'True' airspeed is the corrected, actual figure.
Why Pilots Care
It determines actual aircraft performance, range, endurance, and groundspeed when wind is factored in.
Grounding Statement
At a higher altitude, the same cockpit airspeed indication usually represents a higher true air speed because the airplane is moving through thinner air.
Intuition Check
“True” does not mean morally true or simply “the number on the airspeed indicator.” Here it means the aircraft’s real speed through the air after allowing for the air’s density.
Example Sentence 1
At 8,000 feet on a warm day, the indicated airspeed read 120 knots, but the true airspeed worked out to about 138 knots.
Example Sentence 2
We used true airspeed to calculate how far we could fly on the remaining fuel.