Calculate True Airspeed Given Indicated Altitude, Altimeter Setting, Temperature, and Indicated/Calibrated Airspeed The primary goal of the pilot in this phase is to maintain the required rate of climb and the required IAS. Since pressure decreases with an increase in altitude, so does density. This model shows how to compute the indicated airspeed from true airspeed using the Ideal Airspeed Correction block. True airspeed, unlike indicated airspeed and calibrated airspeed (IAS/CAS) accounts for altitude and non-standard temperatures. \$\begingroup\$ Related, also by @User, possibly duplicate: How do you calculate indicated airspeed on a flight plan?. In fact, for every thousand feet above sea level, true airspeed is about 2% higher than indicated airspeed. Enter the values for Indicated airspeed, Mean Sea level altitude and Outside Air Temperature to get TAS. It uses the difference between total pressure and static pressure, provided by the system, to either mechanically or electronically measure dynamic pressure.The dynamic pressure includes terms for both density and airspeed. It is computed using indicated airspeed, pressure altitude, and temperature. I don’t think I ever have. As you climb, true airspeed is higher than your indicated airspeed. The Relation between Indicated Airspeed and True Airspeed. \$\endgroup\$ – User Mar 4 '16 at 4:46 Remember that indicated airspeed drops off as we climb, due to lower air density at (higher) altitudes not having the same impact on the pitot tube. Indicated airspeed (IAS) is the airspeed read directly from the airspeed indicator (ASI) on an aircraft, driven by the pitot-static system. True airspeed is the airspeed that we would read ideally (and the airspeed value easily calculated within a simulation). Figure 4: Garmin G1000 Primary Flight Display showing Indicted and True Airspeed. That’s where true airspeed comes in. Pressure decreases with higher altitudes, so for any given true airspeed, as you climb, fewer and fewer air molecules will enter the pitot tube. \$\endgroup\$ – J Walters Mar 4 '16 at 3:38 \$\begingroup\$ @Pondlife Well I wanted to go from TAS to CAS to IAS, for planning my cross country. Because of that, indicated airspeed will be less than true airspeed. True airspeed is a calculated number depicting how fast the aircraft is moving through a still air mass. True Airspeed Calculator is designed to give a correct value of true air speed based on the speed estimation flying at the planned true airspeed. A digital airspeed indicator will still output the primary airspeed reading as an indicated airspeed but may also show the true airspeed using a mathematical model to determine the ambient air density; a function of temperature and altitude, both available in the cockpit. Consider an aircraft in flight, climbing from about 1000ft above mean sea level (AMSL) to 15,000ft, maintaining an indicated airspeed of 100 kt. When’s the last time you flew at sea level, 29.92 and 15 deg C? Which, let’s face it, is everytime your fly! The Aerospace Blockset™ blocks are indicated in red.