Albatross,
Do not know if the planetary problem was isolated to the two examples and not seen again. I know it caused some significant concern on the Army's part as the scenario is pretty ugly:
1. A major drive component developing a crack and generating a lot of material.
2. No chip indications.
3. No oil filter bypass indication.
4. First indication was problems with oil pressure being noted by the flight crew.
A lot of bench testing was conducted with damaged planetaries to develop methods for HUMS to detect the fault. The last stuff I saw was that there was no reliable method to detect the fault in operational service using vibration analysis.
Nick,
The only slurs I have seen on this thread are from you (the "airmanship" post is making the rounds). I am ambivalent to the S-92 as it is just another helicopter. However, it is fact that the CAA in the early 2000's set the bar so high for drive system reliability that it was almost impossible to prove by analysis alone. One method of relief was to add a HUMS and at a CAA meeting it was stated that the S-92 and 235 took this approach. Now North Sea operators are mandated to comply with CAP 693/753 and have comprehensive HUMS. These have to have all sorts of gearbox analyses to be compliant. It will be interesting to see the final report and whether or not HUMS should have detected the fault before it resulted in a ship in the dirt, and how this will impact HUMS mandates.
212Man:
Liked your HUMS response. My experience with HUMS is it can be damn good detecting the second occurance of a problem. On the first undetected occurance the excuses generally are the "analysis was not tuned properly", the accelerometer was in the wrong place, the operator did not buy the proper support package, etc.... Once an incident does occur, all of the data can be reviewed and a proper analysis done to detect the next exact same event. Note: While I question the usefulness of HUMS gearbox diagnostics in the real world (chip detectors work very well), it is damn good at shafts, grease packed bearings and tail rotors all of which in the pre-HUMS days had faults go undetected for hours/days/weeks before they finally failed and caused loss of the aircraft.
The Sultan