As airspeed and pressure altitude increase, equivalent airspeed becomes what relative to calibrated airspeed, and what must be subtracted to obtain the corrected value?

• A. It becomes lower; subtract compressibility corrections
• B. It remains the same; subtract nothing
• C. It becomes higher; subtract compressibility corrections
• D. It becomes higher; subtract temperature corrections

Answer: (C)

When speed increases, especially at higher altitudes, compressibility effects become more pronounced. Equivalent airspeed is the speed at sea level in standard atmosphere that would produce the same dynamic pressure as the air actually flowing past the airplane. Because compressibility makes the measured dynamic pressure (and thus the calibrated airspeed reading) higher than what the incompressible case would predict, the equivalent airspeed ends up higher relative to the calibrated airspeed. To get the corrected value, you subtract the compressibility correction from the calibrated airspeed—the correction grows with Mach number, so it becomes larger as speed and altitude increase.