CAS
EAS
TAS /MN
Altitude
At constant CAS
As altitude decreases
Speed TAS
& MN decrease
Or:
CAS is a measure of dynamic pressure = ˝ρV2
Where ρ = air density (increasing in descent) and V = TAS (decreasing to keep CAS constant)
LSS is constant in isothermal conditions (temperature constant)
MN = TAS/LSS = Decreasing/Constant = Decreasing