Definition
True Airspeed (TAS) is the actual speed of the aircraft through the surrounding air mass, corrected for the effects of altitude and non-standard temperature on the airspeed indicator. As altitude increases and air becomes less dense, the indicated airspeed reads lower than the aircraft's real speed through the air, so TAS is calculated by correcting Calibrated Airspeed (CAS) for these density effects. TAS does not account for wind, so it is not the speed across the ground.
Plain English
How fast the airplane is actually moving through the air around it. The airspeed indicator under-reads at higher altitudes because the air is thinner, so TAS is the corrected, real-through-the-air speed.
Context Anchor
Pilots see TAS in performance charts, flight planning, navigation calculations, and cruise speed discussions.
Derivation
True' here means 'actual' or 'real' — the genuine speed through the air, as opposed to the indicated reading on the cockpit instrument, which is distorted by air density.
Why Pilots Care
Accurate TAS determines true groundspeed, fuel burn, and range, especially at higher altitudes where air density drops.
Analogy
Think of swimming in a moving river. Your TAS is like your swimming speed through the water; your speed along the riverbank also depends on how the water itself is moving.
Intuition Check
TAS does not mean the speed shown directly on the airspeed indicator. It means the aircraft’s actual speed through the air around it.
Example Sentence 1
At 8,000 feet on a warm day, the indicated airspeed read 120 knots, but the TAS worked out to about 138 knots.
Example Sentence 2
Flight planning software used current temperature and pressure to compute TAS for the en-route segment.