Lyman
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.
Too many variables, too many questions to understand what you are getting at.
Thrust provided by drag? Conventionally we talk about thrust as provided by engines.
I was briefly visiting gliding because it got a brief mention in the thread, although the OP was talking about deceleration in level flight.
how is thrust not acceleration due gravity, when descending?
BZZZTTT! Dimensions clash!!!!
How is dissipation of momentum not due to the thrust provided by drag?
BZZZTTT! In level flight unbalanced drag will dissipate momentum, yes, but drag does not 'provide' thrust.
Notice I said
gliders equivalent to thrust is a component of its weight
It's equivalent in being (1) a force that is (2) equal and (3) opposite to the drag, thereby (4) keeping the aircraft at a constant speed. But is not actually thrust in terms of being a powerplant squirting air around.
(Personally, as an aside, I find gliding a lot easier to explain by forgetting about drag as a stand alone force. It's only a method for conveniently resolving the total aerodynamic reaction for times when we want to show 4 forces. For a steady glide it's actually a lot easier to say total reaction is equal and opposite weight. Therefore no unbalanced force therefore steady glide.
Energy burnt of as force x distance, power as force x TAS, therefore KE dissipated as drag x TAS. Easy, no vectors because Energy is a scalar.)
pb