Capt bull...

If frame of reference can be exchanged, how is thrust not acceleration due gravity, when descending? How is dissipation of momentum not due to the thrust provided by drag? If the calculus is interchangeable due the acceptance of any increase in acceleration as due to thrust, positive or negative, then any loss of velocity can be expressed in terms of only two forces, gravity and drag, both of which accelerate the airframe.

Owain. If the heavy a/c is at AoA producing maximum lift, is it not About to Stall? There can be only an instant of maximum lift without power?

How can one equation serve to express two variable results, when it cannot contain a non common variable?

Sorry, it's late.