The CAO refers to a Slip and Turn Indicator. It would seem "Slip" and "Balance" are interchangable.
Thanks for all the posts so far.
If I can summarise, the additional requirements for Charter operation is in case of inadvertent IF. The regs specify a S&T rather than AH because either:
> Thats all Kingford-Smith had so it should be good enough for the rest of us or
> Electrically power instruments are more reliable than vacuum indicators (that is why T&B rather than AH)
Is that a fair summary?
By the way I'm not sure what a ROC is. Rate of Change indicator? Is this same as a VSI?