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An aircraft is flying at FL350 with CAS = 300 kt . OAT = ISA + 4°C. The compressibility factor is 0.939.

Calculate the TAS.

  • A
    540 kt
  • B
    509 kt
  • C
    479 kt
  • D
    535 kt

CAS to TAS with your flight computer

  1. Set pressure altitude in the window opposite the OAT in Celsius.

  2. Without moving the computer’s scales, read TAS on the outer scale opposite to CAS.

If the aircraft is flying in excess of 300 kts, a larger uncorrected compressibility error rises.
Any conversion from CAS to TAS results in TAS higher than 300 kts a a correction has to be made using the compressibility factor or using the compressibility window in your flight computer.

ISA temp. FL350 = 15 - 2 x 35 = -55º C, OAT = -55º + 4º = -51º C

Read TAS 541 kts on the flight computer , and finally apply the compressibility factor, 541 x 0,939 = 508 kts.

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