Indicated Airspeed (IAS) – Canadian Flight Trainers

Indicated airspeed (IAS) is the uncorrected reading from the airspeed indicator — the direct output of the pitot-static system before any corrections for instrument error, position error, or air density. All aircraft V-speeds (V_NE, V_A, V_FE, etc.) are expressed in IAS, as are all POH performance figures.

Why IAS Is Used for V-Speeds

V-speeds are expressed in IAS because the dynamic pressure acting on the aircraft structure — the force that creates aerodynamic loads — is directly proportional to the instrument reading, regardless of altitude or density. Flying V_A in IAS at 10,000 ft produces the same structural load as V_A in IAS at sea level.

IAS and True Airspeed

At sea level in standard conditions, IAS = TAS. As altitude increases, air density decreases, and IAS reads lower than TAS. At FL180 in standard conditions, TAS is approximately 30% higher than IAS. For navigation (groundspeed calculation), TAS must be used; for aircraft limitation compliance, IAS is used.

Related Terms

See also: CAS, True Airspeed, Airspeed Indicator.