In cruising and higher airspeed ranges, which two airspeed measures are approximately the same?

• A. Indicated airspeed and calibrated airspeed
• B. Indicated airspeed and true airspeed
• C. Calibrated airspeed and true airspeed
• D. Indicated airspeed and maximum allowable airspeed

Answer: (A)

In cruising and higher airspeed ranges, the readings you rely on are the indicated airspeed (what the instrument shows) and calibrated airspeed (IAS corrected for instrument and installation errors). The corrections for those errors are small at these speeds and conditions, so IAS and CAS end up nearly the same. True airspeed, which is the actual speed through the air, differs because it accounts for air density changes with altitude and temperature, so TAS is not the same as IAS or CAS in cruise. The term about maximum allowable airspeed isn’t a measurement in the same sense, but a limit, so it doesn’t apply to this comparison.