Which statement best defines Equivalent Airspeed?

Which statement best defines Equivalent Airspeed?

• A. The calibrated airspeed corrected for adiabatic compressible flow for the altitude, equal to CAS at sea level in standard atmosphere
• B. The indicated airspeed corrected for instrument error
• C. The true airspeed corrected for wind
• D. The airspeed measured by the pitot tube alone

Answer: (A)

Equivalent airspeed is the speed at sea level in standard atmosphere that would produce the same dynamic pressure as the airplane is experiencing in its actual conditions, taking compressibility into account. In other words, it’s calibrated airspeed adjusted for the effects of adiabatic compressible flow so you’re comparing performance at a common reference atmosphere. This makes EAS a useful way to relate speeds across different altitudes, especially for issues like stall speed, which depend on dynamic pressure rather than true speed. Since density decreases with altitude, TAS can be higher than what your dynamic pressure (and thus EAS) would suggest, but the same dynamic pressure would correspond to a sea-level CAS when corrected for compressibility. That’s why this description best captures what Equivalent Airspeed represents.

Equivalent airspeed is the speed at sea level in standard atmosphere that would produce the same dynamic pressure as the airplane is experiencing in its actual conditions, taking compressibility into account. In other words, it’s calibrated airspeed adjusted for the effects of adiabatic compressible flow so you’re comparing performance at a common reference atmosphere. This makes EAS a useful way to relate speeds across different altitudes, especially for issues like stall speed, which depend on dynamic pressure rather than true speed. Since density decreases with altitude, TAS can be higher than what your dynamic pressure (and thus EAS) would suggest, but the same dynamic pressure would correspond to a sea-level CAS when corrected for compressibility. That’s why this description best captures what Equivalent Airspeed represents.