Equivalent Airspeed (EAS)

Equivalent airspeed (EAS) is calibrated airspeed (CAS) corrected for the compressibility of air at higher speeds and altitudes. At low altitudes and airspeeds typical of general aviation, EAS and CAS are virtually identical. At high altitudes and transonic speeds, compressibility becomes significant and EAS diverges from CAS.

When EAS Matters

EAS is primarily relevant for structural load calculations and high-altitude, high-speed aircraft. Aircraft structural limits (manoeuvering speed, never-exceed speed) are defined in terms of EAS, ensuring the same structural load regardless of altitude. For most general aviation pilots at normal operating altitudes, the distinction between CAS and EAS is negligible.

Related Terms

See also: CAS, True Airspeed, IAS.