Is there any possibility of spinning while coordinated? Of course, any CFI would tell you no, but I wonder if the the following situation could result in a spin while coordinated:
Yes, what you describe is perfectly possible. A stall in banked flight can result in a spin, given you fly the "right" plane.
My first flight in an ASW-20C was late in the afternoon, when most thermals had died down. I got a winch launch to maybe 350 m (the ASW-20 is rather poor in winch launches) and tried to find an updraft. In maybe 270 m I found one, but it was weak and narrow. So I slowed down to tighten the circle. Having flown a Discus all day before, I was not really alerted to watch out for a departure on stall. At some point the lateral stick force faded markedly, and out of the Discus habit I threw the stick into the circle so the inner aileron would deflect downwards to support the stalling wing. Bad choice! This aggravated the incipient stall, the aircraft rolled into the circle and pitched down. While the view from the cockpit before was blue above and green below, it got now all green. I was entering a spin.
The weakening stick force was the result of flow separation over the aileron, and while the Discus airfoil would still provide more lift with more deflection, the ASW-20 airfoil simply went into full stall.
I immediately pushed down and levelled the plane, and went on to land straight away, having lost maybe 100 m. It all took only seconds, and only long after the flight I could piece all details together. My next flight in the ASW-20 was when the thermals were much stronger. I went up to 1000 m and did stall training until I knew how it felt when stall starts and what my options are. I should had done this on the first flight, and do so on all subsequent new types I fly.
Aeroplanes with no wing washout (twist in the wing that gives a lower incidence outboard) can drop a wing more easily while ‘holding off’ bank when flying close to the stall.
When turning, the wing on the outside of the turn is going faster and so develops more lift.
All the powered light aircraft I can think of need some opposite aileron to hold the bank angle steady when turning.
Let’s say we are in a 30 degree banked left turn 10 knots above stall speed in a plane with no washout. We need some right stick/yoke to keep the bank angle steady. Right stick means the right aileron is deflected upwards and the left aileron is deflected downwards.
The downward deflected aileron (left in this case) increases the effective angle of attack on the left outboard wing putting it very close to the stalling angle.
Any slight inattention in flying, a fraction more nose up for example or a gust could result in the left outboard wing stalling and dropping.
One should apply the correct control inputs to recover from an incipient spin at that point, but mere mortals with lack of recent training will more than likely apply more right aileron which will make the situation much worse.
While giving Britten-Norman Islander (BN2) training for a type-rating to a young man this happened to us. The aircraft entered a fully developed spin but recovered with standard actions by the startled instructor.
While pondering the incident later I realised what had probably killed a few of my friends flying in the tropical mountains in Islanders with heavy loads and without the benefit of 5000 feet of height agl.
I am not disparaging the Islander, while I don’t know any pilot who really loved flying them, they are a good bush plane and we were provoking it in the above case. The stall warning was on and the student was just that bit slow in relaxing the back pressure etc.
outside aileron to counter over banking tendency
One of the best things to practice at altitude, especially in a new type of aircraft, is its tolerance to "opposite" aileron to control "overbanking tendency" in slow flight.
This is generally not the best technique because the inside aileron is down, raising the angle of attack. If a stall occurs, it will be on the inside wing first.
There are other ways of "roll control" starting first with the vertical stabilizer and wing dihedral. Rather than using opposite aileron (each aileron is half a speed brake), try slipping a bit and let the vertical stabilizer and wing dihedral help.
By the way, rudder into the turn also helps one roll away from the turn, again, because the vertical stabilizer is asymmetric to the center of gravity. Any yawing force it creates also produces an opposite rolling force.
But if rudder is over done, relative wind is now from the outside, and dihedral will try to roll you into the turn. Aircraft with very long wings and small tails may be more susceptible to this and may benefit more from slipping.
Seek expert advice from someone familiar with the characteristics of the particular aircraft. You may find that few recommend opposite aileron to "hold up" a turn.
