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The following information is for an aircraft in the cruise at 11:50 UTC.

Cruise level: FL410
OAT: ISA +10°C
Mach No: 0.86
Wind component: -25 kt

What will be the Groundspeed?

  • A
    504 kt
  • B
    479 kt
  • C
    529 kt
  • D
    467 kt

TAS = Mach No × 38.95 √ OAT (Kelvin)

ISA temp. FL410, 15 - 2 x 41 = - 67 ºC. As the ISA temperature goes only to - 56.5º C, we will consider - 56.5º + 10º = - 46.5º

Finally convert to Kelvin, 273º - 46.5º = 226.5º K

TAS = 0.86 x 38.95 √ 226.5 = 504 kts

A negative wind component means that component is slowing the flight path of the aircraft over the ground, G/S = 504 - 25 = 479 kts.

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