What is the effect on Mach and True Airspeed (TAS) when climbing at a constant Calibrated Airspeed (CAS)?

When climbing at a constant Calibrated Airspeed (CAS), the effect on Mach and True Airspeed (TAS) can be understood through the changes in air density and the dynamics of the atmosphere.

As the aircraft climbs, it encounters thinner air, which results in a decrease in air density. Given that True Airspeed is the speed of the aircraft relative to the air mass in which it is flying, and it increases with altitude due to the decrease in air density, it becomes evident that TAS will increase when CAS remains constant.

Mach number is defined as the ratio of True Airspeed to the speed of sound in the surrounding environment. As an aircraft climbs, the speed of sound varies with altitude and temperature, but since True Airspeed is increasing (because of the reduced air density affecting CAS), the Mach number will also increase.

In summary, climbing at a constant CAS results in an increase in both Mach number and True Airspeed. The nature of the ascent and the relationship between IAS, CAS, and TAS play crucial roles in determining these changes, leading to the conclusion that both Mach and TAS increase under these circumstances.