Define TAS and IAS and explain why they differ.

Define TAS and IAS and explain why they differ.

• A. TAS is the actual speed relative to air; IAS is what the airspeed indicator reads; they differ due to altitude, temperature, air density
• B. TAS equals IAS
• C. IAS accounts for wind
• D. TAS measures ground speed

Answer: (A)

TAS is the actual speed of the aircraft relative to the air around it, while IAS is the speed indicated by the airspeed indicator, which reflects the dynamic pressure of the air hitting the pitot system and is calibrated for standard air density at sea level. They differ because air density changes with altitude and temperature. As you climb and the air gets thinner, the same true airspeed produces less dynamic pressure, so the indicated airspeed reads lower than the true airspeed. In other words, for the same TAS, IAS drops with altitude; conversely, to maintain a given IAS at higher altitude, the aircraft must be moving faster through the air. Winds affect ground speed, not IAS or TAS directly. TAS is not ground speed, and IAS does not account for wind.

TAS is the actual speed of the aircraft relative to the air around it, while IAS is the speed indicated by the airspeed indicator, which reflects the dynamic pressure of the air hitting the pitot system and is calibrated for standard air density at sea level. They differ because air density changes with altitude and temperature. As you climb and the air gets thinner, the same true airspeed produces less dynamic pressure, so the indicated airspeed reads lower than the true airspeed. In other words, for the same TAS, IAS drops with altitude; conversely, to maintain a given IAS at higher altitude, the aircraft must be moving faster through the air. Winds affect ground speed, not IAS or TAS directly. TAS is not ground speed, and IAS does not account for wind.