Which statement about indicated airspeed (IAS) and true airspeed (TAS) with altitude is true in standard atmosphere?

Which statement about indicated airspeed (IAS) and true airspeed (TAS) with altitude is true in standard atmosphere?

• A. IAS is affected by dynamic pressure; TAS increases with altitude.
• B. IAS increases with altitude; TAS decreases with altitude.
• C. IAS is affected by dynamic pressure; TAS increases with altitude.
• D. IAS and TAS both decrease with altitude.

Answer: (C)

In standard atmosphere, indicated airspeed is a direct measure of dynamic pressure (q = 1/2 ρ V^2) read by the pitot system and calibrated to sea‑level density. As you climb, air density ρ decreases. For a given true airspeed, the dynamic pressure drops, so IAS would read lower. Conversely, if you hold IAS constant and climb to higher altitude where the air is thinner, the true airspeed must increase to maintain the same dynamic pressure because V = sqrt(2q/ρ). This means TAS increases with altitude when IAS is held fixed. So the statement that IAS is affected by dynamic pressure and that TAS increases with altitude is the correct reflection of how these speeds behave with changing density in standard atmosphere.

In standard atmosphere, indicated airspeed is a direct measure of dynamic pressure (q = 1/2 ρ V^2) read by the pitot system and calibrated to sea‑level density. As you climb, air density ρ decreases. For a given true airspeed, the dynamic pressure drops, so IAS would read lower. Conversely, if you hold IAS constant and climb to higher altitude where the air is thinner, the true airspeed must increase to maintain the same dynamic pressure because V = sqrt(2q/ρ). This means TAS increases with altitude when IAS is held fixed. So the statement that IAS is affected by dynamic pressure and that TAS increases with altitude is the correct reflection of how these speeds behave with changing density in standard atmosphere.