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Derive or compute TAS, given IAS, pressure altitude and air temperature in degrees Celsius.

To Find the TAS you will need the following:

  • Pressure Altitude
  • OAT (Outside Air Temperature)
  • CAS or IAS 

(Use CAS if it is available, otherwise use IAS)

Example one.


Given CAS 110 knots, P.alt 18'000 feet, OAT 15ºC what is the TAS


Using airspeed window set temp against OAT

Find CAS on inner scale

Read off TAS opposite on outer scale 


TAS 156 knots

Solve mathematical equations: (a) multiplication (± 2%); 

Solve mathematical equations:  (b) division (± 2%); 

Solve mathematical equations:   (c) proportion (± 2%).

Calculate time, speed, or distance, given two factors.

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