Neil,

Why not?


Because you won't make a recovery from a fully developed spin in less
than 920 feet with a plane of the approximate weight and size of the
Cirrus, say a Bo. Remember, you have done one complete turn in a fully
developed spin. Then you start counting when you apply rudder in the
opposite direction and push the yoke (or whatever conventional recovery
is to you). From that point to a positive climb rate, there's no way
you'll lose less than 920 feet of altitude. And certification doesn't
even require you to.

--
Thomas Borchert (EDDH)

I did a little adding machine calculation,
and you appear to be correct. :-(

Obviously a situation to be avoided.

Peter