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Given the following information, calculate the TAS.

CAS: 250 kt
FL250
OAT at FL250: -40ºC
Compressibility factor: 0.975

  • A
    360 kt
  • B
    380 kt
  • C
    415 kt
  • D

    365 kt

Important Note: We have received some conflicting feedback on the correct answer for this question. It appears the UK CAA considers 363 kt the correct answer, while the Swedish Authority maintains that 360 kt is correct. Please note as below if using a CRP5 do not use the compressibility factor given. Instead, use the compressibility correction window. We eagerly await additional feedback for this question. Thank you!


Refer to figure.
Using your flight computer:

(1): Align OAT -40˚C with 25 000 feet pressure altitude.

(2): Find CAS 250 kt (inner scale, outer ring) and find the corresponding value of TAS approx. 370 kt (outer scale).

(3): Apply the compressibility factor provided of 0.975:

  • 370 kt x 0.975 = 360 kt

Note. - Using the Pooleys CRP-5 Computer:

  • Do not use the compressibility factor provided in the question text when using the CRP-5, instead use the “COMP. CORR.” Window provided.

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