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Can I bring a bit of simpleton pilot into the discussion?
Four 'forces' act on a powered aircraft. Weight/Mass (not much that we can do about that), lift, thrust and drag. In any stage of flight where the aircraft is not accelerating (ie changing velocity - I'll sidestep the fact that gravity is actually an acceleration in space) these forces are balanced. So, if an aircraft is descending on final, we have lift & drag balanced against mass & thrust (this may not actually be the case as in some scenarios elements of the lift vector may act as thrust). In this scenario, and indeed almost all scenarios, lift does not equal mass and thrust does not equal drag - the forces involved are not at right angles to each other but the overall result is a steady state. (I've got some pretty atpl notes that show lift is not at right angles to relative air flow)
If Biggles changes one of these forces (either in size or direction) the whole system will adjust to re-achieve a balanced state. Whether the pilot induced change is pitch or thrust, the inter-relationship is such that the other will also change unless Biggles doesn't want it to.
What does that mean? If Biggles uses PnP or 'power for flightpath' he will have to use the other control to maintain one element of balance. If he pitches down to increase speed, he will have to add power to maintain flightpath. Conversely, if he uses power to increase speed, he will have to adjust pitch (AoA) to maintain flightpath. The order in which he does this is largely irrelevant and we should actually be teaching that the controls be used in unison.
Of course, I am just a simpleton so I may be completely wrong.
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