Question

A general aviation airplane is flying at an altitude of 5000 m. The indicated airspeed is 250 km/h. Assume that there are no instrument errors and position errors. Neglecting compressibility effects, which one of the following options is FALSE?

• A. The true airspeed is greater than 250 km/h.
• B. The calibrated airspeed is 250 km/h.
• C. The true airspeed is 250 km/h.
• D. The equivalent airspeed is 250 km/h

Hint:

Indicated airspeed increases with altitude due to the decreasing air density. True airspeed must be calculated from IAS to account for changes in atmospheric conditions at higher altitudes.

Answer 1

The Correct Option is C

At an altitude of 5000 m, the indicated airspeed (IAS) does not equal the true airspeed (TAS). Here's why:

• Indicated Airspeed (IAS) is what is read directly from the airspeed indicator and does not account for changes in air density with altitude.
• True Airspeed (TAS) is the actual speed of the aircraft through the air. Because air density decreases with altitude, TAS is greater than IAS at higher altitudes.
• Calibrated Airspeed (CAS) is IAS corrected for instrument and position errors. In many cases, CAS is assumed to be approximately equal to IAS unless otherwise specified.
• Equivalent Airspeed (EAS) is CAS corrected for compressibility effects and air density, and it can also differ from IAS at altitude.

Therefore, the false statement is (C): "The true airspeed is 250 km/h," because at 5000 m altitude, TAS is higher than the IAS shown.