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Given the following information, calculate the Mach number:

TAS: 485 kt OAT: ISA +10ºC FL410.

  • A
    0.89
  • B
    0.60
  • C
    0.85
  • D
    0.72

TAS = Mach No × 38.95 √ OAT (Kelvin)

ISA temp. FL410, 15 - 2 x 41 = - 65 ºC.

As the ISA temperature goes only to - 56.5º C, we will consider - 56.5º + 10º = - 46.5º.

Finally we will convert it to Kelvin, 273º - 46,5º = 226.5º K

Mach No = 485 / (38.95 √ 226.5º K ) = 0.83 (Closest answer is 0.85)

Note: According to the feedback we are offered the closest option 0.85 Mach. If you come across this question please give us feedback.

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  • Austro Control