The Turn-Coordinator I believe was never designed for anything but a rate one turn so relying on that for interpretation of spin direction and IMC recovery would be bad news.
As a newcomer to this thread (but also as a spin instructor), I'm quite surprised by the distrust people have in the Turn Co-ordinator. I don't just want to pick on one individual's comment, but may I point out that the Turn Co-ordinator will indicate the direction of spin reliably in an erect spin? And in an inverted spin too in most cases. I'm quite surprised to read the opinion that a pilot might deliberately ignore the TC in a spin - what else will you use?
When easing out of the dive, I'd rather have a TC than a TI - according to my JAR ATPL notes it's less sensitive to looping error. Granted, it can't be calibrated accurately for rate 2+ turns, but how many civil pilots have a requirement for regular & accurate rate 2 turns?
Perhaps that's why light aircraft tend to be fitted with TC's not TI's. When I buy an aircraft approved for inverted spinning, maybe I'll have to go out and find an old TI to use instead...
Thanks for this topic mad_jock - it's very interesting!
O8