If I want to calculate static air temperature (OAT), but I'm only given an altitude and a true airspeed. Is there such an equation that relates these principles together. I've had a look at wikipedia and to calculate OAT, the total air temperature is required. Problem is, I don't have a Mach number to solve the equation. Is there another way to solve this problem

  • $\begingroup$ And to know the Mach # you need the static air temperature... a circle of doom question I'd say... $\endgroup$
    – John K
    Nov 18, 2019 at 20:24
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    $\begingroup$ You don't have calibrated airspeed? How do you get true airspeed without the calibrated airspeed? $\endgroup$
    – JZYL
    Nov 19, 2019 at 1:58
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    $\begingroup$ OAT and pressure altitude (PA) lets you compute density, from which you can relate calibrated airspeed (CAS) and true airspeed (TAS). So if you know any three of OAT, PA, CAS, and TAS, you can get the forth. Right now you are short a piece of information in order to "close the loop" and get OAT. Note: I am assuming you are at a slow speed and can ignore Mach number. $\endgroup$
    – MikeY
    Nov 19, 2019 at 2:32

1 Answer 1


Provided that your calculations take place for a standard day, below 11 km altitude the Outside Air Temperature is simply a linear function of altitude. From the wikipedia article for Standard Atmosphere:

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So OAT = 15 - 1.98 * Altitude, with OAT in °C and Altitude in 1,000 ft. Airspeed data is superfluous.

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    $\begingroup$ With a big emphasis on standard (average) day, with delta ISA being zero. $\endgroup$
    – JZYL
    Nov 19, 2019 at 14:46

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