Definition
True airspeed is the actual speed of the airplane through the surrounding air mass, corrected for the effects of altitude and non-standard temperature on the air density. It is calibrated airspeed adjusted for the fact that the air at altitude is thinner than the air at sea level, where the airspeed indicator is calibrated to read accurately.
Plain English
It's how fast the airplane is really moving through the air around it. The airspeed gauge in the cockpit reads low at altitude because the air is thinner up there, so true airspeed is the corrected, real number.
Context Anchor
Seen in cruise performance, jet engine efficiency, and flight planning discussions, especially when comparing speed, fuel use, and range.
Derivation
The word 'true' here means 'actual' or 'real,' as opposed to the indicated value shown on the cockpit gauge. The indicated reading is correct only at sea level on a standard day; the 'true' value is what the airplane is actually doing through the air.
Why Pilots Care
Accurate TAS determines true groundspeed, fuel use, and range, especially important in jet operations at altitude.
Grounding Statement
At higher altitude, the air is thinner, so the airplane may be moving through the air faster than the airspeed indicator alone suggests.
Intuition Check
“True” does not mean perfect or ideal here. It means the aircraft’s actual speed through the air after correcting for air density.
Example Sentence 1
At 10,000 feet the airspeed indicator showed 140 knots, but the true airspeed worked out to about 165 knots once the pilot corrected for altitude and temperature.
Example Sentence 2
Pilots apply TAS to compute accurate flight times and fuel burns during high-altitude cruise.