indicatedairspeed

Indicated airspeed (IAS) is the airspeed shown by the airspeed indicator in an aircraft’s cockpit. It is derived from the dynamic pressure measured by the pitot tube relative to the static pressure from the aircraft’s static port, and it is presented on the instrument without corrections for instrument or position errors or nonstandard atmospheric conditions. IAS is the raw reading of the instrument and can vary with installation, sensor position, and ambient conditions.

The airspeed indicator is part of the pitot–static system, which senses stagnation pressure from the pitot tube and static pressure from a separate port. The instrument converts the difference between these pressures into a speed indication, calibrated to reflect speeds at sea level in standard atmosphere. As a result, IAS is influenced by air density and temperature only to the extent that those conditions affect the measured dynamic pressure. At higher speeds, compressibility effects introduce errors that IAS does not compensate for, which is why calibrated airspeed (CAS) and true airspeed (TAS) are used for more accurate speed measurements in performance calculations.

IAS is related to but distinct from other airspeed concepts. Calibrated airspeed (CAS) corrects IAS for instrument and position errors. True airspeed (TAS) further corrects CAS for air density (pressure and temperature) to reflect the aircraft’s actual speed through the air. Equivalent airspeed (EAS) provides a density-adjusted measure tied to dynamic pressure. In practice, IAS is commonly used for flight maneuvering, stall limits, and approach speeds, while CAS and TAS are used for performance planning and navigation.

Ground speed and other velocity concepts are independent of IAS, representing the aircraft’s speed relative to the ground rather than through the air.