I think the question basically boils down to wanting to know what it is about spins which were causing people to die, and spins to be taken off the PPL syllabus???
A correctly maintained aircraft, approved for spinning, within the w+b limits for which spins are approved, when flown in accordance with the POH, will recover within the height specified in the POH.
In the case of common training aircraft, the aircraft will generally recover easily even if an incorrect technique is used. (This makes things quite difficult for the instructor. For example, I have done spinning exercises in a C152 where the student has not used full rudder in the recovery, but the aircraft has recovered with no apparent difference to when full rudder was used. Now try explaining to the student why it is is important to use full rudder.....) This is certainly not true of every aircraft I've ever spun, though, and there are plenty of aircraft out there which will only recover from spins if exactly the right technique is used.
When we are talking about "unrecoverable" spins I think there are a number of possible reasons for the unrecoverability:
1) The aircraft is not approved for spinning, or has not been maintained properly. Let's work on the assumption that this does not apply to flying schools using the aircraft for PPL training.
2) The aircraft is outside its W+B limits for spinning. It is a fact that instructors do not do a W+B before every single flight, and although we know what kind of loads our aircraft can carry and still be within the W+B, I would guess that some instructional flights are carried out with the aircraft outside its limits simply because of the practical constraints placed on instructors. Whilst we can get away with this for many flights (although the insurance company might disagree if an incident were to occur), there's a good chance we won't get away with it for spinning, especially with the CofG outside limits.
3) An unintentional spin at low level, such as when turning base-final. This is probably the area where most accidents, and therefore fatalities, occur. I don't think this situation is relevant to the discussion, though, because the discussion is related to planned spinning.
4) Incorrect technique used due to the pilot not having studied the POH in detail. Again, not relevant to the discussion, because the recovery for most training aircraft is as close to "standard" as it's possible for a spin recovery to be, and they will generally recover even if an incorrect technique is used. But might be very relevant to more advanced types.
5) Not enough height to recover. It is my guess that this is what it boils down to. Instructor knows that he has recovered from a spin in a certain height. So he adds an extra few thousand feet onto that, and uses that as his starting height for spins. But then, once he has a bit more experience, he comes across a student whose progress is being held up by the weather not being suitable for spinning. He knows that the cloudbase is just very slightly lower than he'd normally use, but he decides to do the exercise anyway. It goes without a hitch, and the instructor has just lowered his minimum height. Maybe he lowers it a bit further next time..... and maybe next time the student messes up the recovery........
What my fifth point boils down to is that the requirement to do a spinning exercise might encourage instructors to take students spinning in weather which is not suitable. I would guess that, when people say talk about the removal of the spinning exercise from the syllabus and say "more people get killed practicing it than get killed in an avoidable inadvertant spin after their PPL", this is the scenario they are most likely talking about.
But this post is entirely speculation. I don't have any facts, figures or incidents to back this up, only my own perception. Maybe some of the grizzly old instructors who were around when spinning was mandatory might like to comment???
FFF
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