True airspeed

True airspeed is the aircraft's actual speed through the surrounding air mass. It is commonly abbreviated KTAS when expressed in knots. True airspeed differs from indicated airspeed because the airspeed indicator is calibrated to standard sea-level air density.

How it works

For a given dynamic pressure, an aircraft must move faster through thin air than through dense air. As altitude increases, true airspeed generally becomes higher than the indicated value when the aircraft maintains the same indicated airspeed. Temperature also changes air density, so a complete conversion uses pressure altitude or pressure, temperature, and indicated airspeed.

True airspeed is different from groundspeed. Wind changes the aircraft's movement over the ground, but it does not change the aircraft's speed through the air. A headwind lowers groundspeed for a given true airspeed. A tailwind raises it.

Example

An aircraft maintaining 100 KIAS at a higher altitude may have a true airspeed greater than 100 knots. If the wind is from ahead, groundspeed will be lower than true airspeed. If the wind is from behind, groundspeed will be higher. The navigation result depends on both the airspeed and the wind vector.

Why it matters

True airspeed is used in flight planning, time and fuel estimates, and navigation calculations. It helps pilots relate an aircraft's performance to the air mass around it. The airspeed indicator remains the primary cockpit reference for many aircraft limitations, so a true airspeed value should not be substituted for a published indicated speed limit.

True airspeed calculations depend on the accuracy of the input values and the conversion method. For operational planning, compare the result with the aircraft's approved instruments, flight computer, or POH guidance.

Related terms and tools

• Indicated airspeed
• Density altitude
• FAA Pilot's Handbook of Aeronautical Knowledge