If we assume normal conditions; temperature increasing as we descend in the troposphere.
CAS
EAS TAS
MN
Altitude
At constant CAS
As altitude decreases MN decreases
Speed
Or:
CAS is a measure of dynamic pressure = ˝ MN decreases ρ V2
Where ρ = air density (increasing in descent) and V = TAS (decreasing to keep CAS constant)
LSS is increasing as temperature increases.
MN = TAS/LSS = Decreasing/Increasing = Decreasing