Mach Number (MN) = (Total Pressure - Static
Pressure)/ Static Pressure
or MN
= (Pt - Ps)/Ps
MN = Dynamic Pressure/Static Pressure = CAS/Ps
In this formula you do not need to take account of temperature and only
need to take account of changes in altitude, ie. the
Ps component.
If the Mach number remains constant and the aircraft is at a constant
altitude then CAS must also remain constant.
If the aircraft is climbing then the Ps component decreases and
therefore CAS also decreases.
Conversely if the aircraft is descending then the Ps component increases
and CAS also increases.
This formula also works for an aircraft flying at a constant CAS and
determining the affect on MN.
Furthermore if an aircraft is flying at a constant TAS use the following
formula:
MN = TAS/LSS In this case you only have to take account of temperature
changes and the affect on the LSS to solve the questions.