Originally Posted by
wrench1
You'll find in newer models they use more electro-mechanical controls which require specific conditions to check various systems. In some cases its the opposite where electrical power must be on prior to manually moving a control input. I believe this is one and is not a general rule but have seen similar warnings with other specific mx tests. If it were a general limitation it would be in the RFM so pilots wont break stuff.
Bell have come back to me already and agree the warning should be more widely used (specifically in the towing and tie down sections). Nice to see some manufacturers get back to you quickly.
From that response I am assuming I was correct in that it is nothing special about the FCC check that makes damage possible, but simply turning the rotor backwards - I think one suggestion (thank you whoever that was) was inadvertently getting all the crap back off the filter into the pump. That seems possible with the hydraulic diagram from the Systems Description.
Extract from Bell 429 hydraulics diagram