Which measurement is primarily affected by air density?

True airspeed is primarily affected by air density because it represents the actual speed of an aircraft through the air, adjusted for the effects of altitude and temperature. As altitude increases, air density decreases, which affects how the aircraft interacts with the atmosphere.

Indicated airspeed, on the other hand, is what is shown on the instrument and is based on the dynamic pressure of the air against the pitot tube, while calibrated airspeed is indicated airspeed corrected for instrument errors. Ground speed refers to the speed of the aircraft relative to the ground and is influenced by wind conditions rather than air density directly. Thus, the relationship between true airspeed and air density is fundamental, reflecting how changes in altitude and temperature modify the aircraft’s performance and speed through the air mass.