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A jet aeroplane is climbing at constant Mach number below the tropopause. Which of the following statements is correct? (Assume standard atmospheric conditions)
  • A
    IAS decreases and TAS increases.
  • B
    IAS increases and TAS increases.
  • C
    IAS decreases and TAS decreases.
  • D
    IAS increases and TAS decreases.

Descent at a Constant Mach Number in Standard Conditions

During a descent, LSS will be increasing, as temperature increases. Therefore, if Mach number is being kept constant the TAS must be increasing (Mach number = TAS/LSS). During the descent air density increases TAS is increasing and CAS also increases at a greater rate (Dynamic Pressure = 1⁄2 ρ V2). Similarly, in a climb at constant Mach number the TAS or CAS both reduce.

Maximum operating speed, called VMO when using indicated airspeed. VMO could be exceed while Maintaining a constant Mach no. during descent.

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