But I stand firm on using flaps as airbrakes after engine failure.
I prefer to keep drag to a minimum following an engine failure. I will extend flaps for a landing as appropriate, and to increase drag appropriately on final approach. In the case of a forced approach, this would be very late in final, and not to be fiddled with after that. I'll be too focused on making a safe landing.
When the donk quits, you're flying a glider - and glider pilots routinely land using airbrakes for flight path control.
No, if an engine fails, you're flying a power plane without power, nearly none are equipped with airbrakes. A glider is a different type of aircraft, equipped differently, and to be flown differently.
Airbrakes are airbrakes, and flaps are flaps. Airbrakes are not designed to produce lift when they are applied. Airbrakes are intended to be modulated during a normal approach to create drag as desired without a lift change, flaps are very certainly not - they create both lift and drag in varying amounts per extension.
It is very poor practice to attempt to modulate lift with flaps. I agree that with a manual flap plane it is possible, but on final approach, silly, and, if not rather unsafe, at least needlessly distracting. For electric flaps, hopeless - they just don't move quickly enough.
If you feel that you need to reduce the flap extension on final, you should be abandoning that approach - you got it wrong.
The most important thing on the latter stage of the approach is to fully stabilise the approach in that the speed should be on target, the aircraft should be on the correct glide path, on the centreline and correctly configured with landing flap(and trimmed). The stabilisation height should be a target but most GA pilots have never even heard of stabilisation height so its hardly surprising they dont make an attempt to stabilise the aircraft by the target height. We/I use 200 feet on our training aircraft and that also coincides with the obstructed runway solo go around decision height.
This is much more simple than that. Stabilized, in the context of a GA aircraft approach has no numbers which make it right or wrong. It is simply, at every point in the approach, are you
continuing what you are doing to make a smooth transition from flight to rolling down the runway. If you are continuing to descend, maintain a speed with reductions as needed, and configure the aircraft for landing, you have a stable approach. It could be steep or shallow, turning or straight - but it is
not doing then undoing - it's continuing to do. You planned a "good" approach to demonstrate good airmanship, you're going to continue to do that, not start to undo it partway along! If you need to undo it, undo it properly and go around.
If you are flying a manual flap Cessna, with 40 extended, and you think to retract to 20, and miss, and get to zero, you'd better get full power in right away, 'cause you're dropping. That is anything but a stabilized approach.
There is no power plane flight manual which is going to include the modulation of flaps for "control" of the aircraft. Why would pilots think that this is a good idea - are they test pilots?
Lifting flap at 400-500 feet is not much different to selecting flaps full in terms of stabilisation, both are de stabilising but thats not really the point, the point is whatever you have done to destabilise the aircraft on the approach should have it affects negated by the stabilisation height.
I disagree. leaving the flap as is, or extending more as required, will
continue the stable trend toward slowing and increasing lift as will be desirable as you enter the flare. Raising flaps reduces lift and drag, and not necessarily in proportion. As lift and drag, compared to "normal" flight, are desirable at the flare, reducing them during approach is destabilizing.