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An aircraft is flying at FL370 with Mach 0.915.

OAT = ISA -4°C.
The compressibility factor is 0.942.

Calculate the TAS.

  • A
    520 kt
  • B
    495 kt
  • C
    490 kt
  • D
    530 kt
TAS = Mach No × 38.95 √ OAT (Kelvin)
ISA temp. FL370, 15 - 2 x 37 = - 59 ºC. As the ISA temperature goes only to - 56.5º C, we will consider - 56.5º - 4º = - 60.5º.
Finally convert to Kelvin, 273º - 60.5º = 212.5º K

TAS = 0.915 x 38.95 √ 212.5 = 520 kts

NOTE: The compressibility factor is only used to convert IAS/CAS to TAS.

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