Originally Posted by
ShyTorque
I thought this had already been discussed at some length earlier on.
A tail rotor drive failure, believe it or not, is relatively straightforward to deal with, albeit needing altitude and time once the engines are shut down.
A tail rotor control failure is most definitely not the same kettle of fish and is likely to be far more difficult to deal with, unless the tail rotor blade pitch remains at a setting close to neutral. A control runaway to maximum positive pitch may require maximum collective pitch to slow the yaw (and then what, how do you get the aircraft down under control?).
A tail rotor which runs away to minimum pitch will very likely have enough authority to yaw the aircraft at a high rate even after the engines are shut down. If you think about this, a helicopter in full auto rotation needs enough tail rotor authority to enable full yaw control in both directions, so there is more negative pitch designed in than some might realise. For example, one aircraft I used to instruct (RAF Puma) had something like 35 degrees of positive pitch and 17 degrees of negative pitch. We regularly used a full motion simulator to practice tail rotor malfunctions of all types and it showed that runaways to negative pitch were usually impossible to deal with, especially if the failure occurred at high engine power settings, as in the Leicester accident being discussed here. The tail rotor control system failed and drove the tail rotor blades to full negative pitch. As recently stated by others here, shutting the engines down immediately the failure occurred would nothave stopped the yawing.
A helicopter yawing out of control in this instance is unlikely to remain stable in the roll and pitch attitudes and may go completely out of control despite the best crew in the world sitting in the cockpit.
Thank you for the explanation.