Main Gear Box Seizure
A semi related question, food for thought...
On the S76A/A++/C with mechanically governed engines, the collective is mechanically linked to the FCU and therefore if I understand the system correctly, actually limits the amount of power the engine can put out (in conjunction with the engine lever position).
On the S76C++, there is no longer a mechanical linkage to the FCU. Once the levers are in FLY, the DECU governs the engine to 107% N2 and the collective position transducer sends a signal to the DECU to trim the engines to prevent transient droop or spikes during collective movement. So, the collective on a C++ does not *limit* engine power output the way the mechanical linkages do on the A/A++/C. With me so far?
So can anyone explain to me why the wisdom imparted in FlightSafety checklists, recurrent training, etc is that during a Main Gearbox failure on a C++, with a slowly seizing gearbox, the pilot should "maintain low/moderate torque setting to ensure that the engines continue to drive the MGB." It is implied that the pilot has control of the minimum torque and should not lower the collective fully to 0% torque, which I think is false advice. Lowering the collective even fully could not reduce the torque below that required to overcome the friction generated by the seizing MGB as the DECU attempts to maintain 107% N2.
In other words, if say 57% torque was required to overcome the additional friction in the MGB as it began to seize, then the indicated torque would read 57% at collective flat pitch, and the pilot could not "reduce torque to 0% with the collective", so to speak.
Shouldn't the correct advice be that the pilot "Maintain the engine levers at FLY so that the DECU continues to throw fuel into the engine to govern the N2 at 107%, thereby putting torque into the MGB to overcome the friction"?
I'm reasonably happy that the prevailing wisdom is applicable to the S76A/A+/A++/C but I'm not so sure that it is applicable to the S76B/C+/C++/D or actually any modern heli that uses electronic engine controls.