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During the climb phase in the standard atmosphere, after passing the cross-over altitude, the TAS will decrease through the troposphere and...
  • A
    thereafter decrease at a higher rate through the tropopause.
  • B
    the tropopause at the same rate.
  • C
    thereafter increase through the tropopause.
  • D
    thereafter remain constant through the tropopause.

Refer to figure.
Variation of TAS with Altitude at a Constant Mach Number

Mach no. = TAS ÷ LSS

then, TAS = Mach no. x LSS

  • As altitude increases the temperature drop, local speed of sound decreases and TAS decreases up to the tropopause and then remain constant.
  • As altitude decreases the temperature will rise, local speed of sound will increase and TAS will increase.
Above the tropopause the temperature will remain constant, with no further reduce of the local speed of sound. Climbing or descending above the tropopause at a constant Mach no. the TAS will remain constant.

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