flight instrumentsFAA-published sample question (ATM, Aug 2021)
As an airplane climbs to higher altitudes, what happens to the calibrated airspeed in relation to true airspeed?
A
It remains equal.
B
It decreases.✓ Correct Answer
C
It increases.
Explanation
As air density decreases with altitude, the airspeed indicator (calibrated airspeed) reads progressively less than the true airspeed, roughly 2 percent per 1,000 feet, so CAS decreases relative to TAS. They are equal only at sea level in standard conditions.
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