Refer to figure.
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.
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