Thanks zalt for the reading advice and to Nick for the comments re the rather dubious and inherently failure prone White metal high speed input bearing.
To my knowledge all S61 machines are now fitted with the emergency lubrication system. (stay on the ground if not) Inherently this type of bearing requires a constant oil film to retain its integrity and even when initially engaging the rotor after engine start it was imperative that the ELS was used as a pre lube to the bearings.
The failure of the said bearing could occur within seconds of the lube being lost from the bearing. Seizure of the high speed input and shearing of the GB input HSS and the whole assembly exiting from the gear box, and that was during initial engagement after engine start. Extremely exiting and a relief I expect that it failed when it did.
As I expect Nick will confirm the engineers have a cunning way of monitoring the gear box condition. A sample of the MGB oil was sent to a Lab, I think it was every 50 hrs. They carried out SOAP analyses. This gave the PPM analyses of the metal partials in the oil. So an increase in Tin and Copper would indicate a white metal bearing under stress and if deemed excessive generate an inspection. I seem to recall increase in Magnesium indicated a possible bearing location problem in the casing and steel? Gear tooth meshing problems. Any way I am sure some expert engineer would be able to clarify but you see the basic idea.
Add to that the computer analysis of the harmonics of the rotating components available with the modern HUMS system and in theory you can, identify developing problems, start maintenance actions to investigate developing trends, and catch the nasty event before it develops into a in flight emergency.
So, the engineer’s tool box now contains new tools that if used to the best advantage and had been in use years ago may have prevented the historical “Catastrophic Events”
So going back to the thread subject, with the new tools available to the engineer and the finding from another similar failure, is the system working and if not why not.
To all still flying the old and faithful lady, she is a comfort,predictable and a delight, however as a lady will sometimes come back and show her independence. Most from the early days are now enjoying retirement and the experience gained is lost to the new blood. (Except I suspect from old PPrune viewers)
Good luck and enjoy, I know I did then.
Outhouse.