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If you are flying at FL100 in an air mass that is 10°C warmer than a standard atmosphere, what is the outside temperature likely to be?
  • A
    +5°C
  • B
    +15°C
  • C
    -10°C
  • D
    -15°C

In the standard troposphere, air temperature on average decreases with height at an overall positive lapse rate of about 2ºC/1000 ft, until the tropopause, the boundary between the troposphere and stratosphere, is reached. ISA surface temperature is +15ºC.

- To find ISA standard temperature for a given altitude, here's a rule of thumb: double the altitude, subtract 15 and place a - sign in front of it.

ISA temperature = 15 – [(height/1000) x 2]

  • ISA temperature at 10 000 ft = 15 - [(10 000/1000) x 2] = -5ºC
  • If the an air mass is 10 °C warmer than a standard atmosphere, its temperature is: -5ºC + 10ºC = +5ºC

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