Definition
True airspeeds are the actual speeds of an airplane through the surrounding air mass, corrected for the effects of altitude and non-standard temperature on the indicated airspeed. As altitude increases, air becomes less dense, so the airspeed indicator under-reads — meaning true airspeed is higher than indicated airspeed at altitude.
Plain English
These are how fast the airplane is really moving through the air, not just what the airspeed gauge shows. At higher altitudes the air is thinner, so the gauge reads lower than the airplane's real speed through the air.
Context Anchor
Seen in aircraft performance discussions, especially when comparing how a turbocharged airplane performs at higher altitudes.
Derivation
‘True’ here means ‘actual’ or ‘real’ — the airspeed corrected to reflect what the airplane is genuinely doing through the air, rather than the raw reading on the instrument.
Why Pilots Care
True airspeed determines actual aircraft performance, fuel flow, and navigation accuracy; it increases with altitude even when the airspeed indicator reading stays the same.
Grounding Statement
In thinner air, the airplane may have to move faster through the air to create the same cockpit airspeed reading.
Intuition Check
“True” does not mean the only correct speed and all other airspeeds are false. Here it means the airplane’s actual speed through the surrounding air, adjusted for altitude and temperature effects.
Example Sentence 1
At 18,000 feet the airspeed indicator showed 140 knots, but the pilot's true airspeed was closer to 185 knots.
Example Sentence 2
Turbocharging lets the engine maintain power so the airplane can hold higher true airspeeds at altitude than a normally aspirated engine could achieve.