If we have normal conditions; temperature decreasing as we climb in the troposphere.

                                              CAS

                                          EAS              TAS

                                                                    MN

                           Altitude

 

                                                                                                At constant CAS

                                                                                                As altitude increases

                                                            Speed                           MN increases  

 

Or:

CAS is a measure of dynamic pressure = ½ρV2

Where ρ = air density (decreasing in climb) and V = TAS (increasing to keep CAS constant)

LSS is decreasing as temperature decreases.

MN = TAS/LSS = Increasing/Decreasing = Increasing