Originally Posted by Islander2
FWIW, this is what is said about turn indicator (not coordinator) errors in my (CAA-flavour) CPL course notes, as produced by the sadly now defunct Professional Pilot Study Centre:
Ok, I consider that a data point. I'd still prefer to have something technically oriented, rather than pilot training oriented. (The FAA stuff has historically been of dubious accuracy.)
I'm wondering if the issue could be that the steeper the bank, the more the turn rate is produced by pitching, rather than yawing? For instance, a 90 degree banked turn would mathematically be entirely pitch, rather than yaw, and might possibly indicate no turn rate in the turn coordinator.