Double Bogey
Effective epicyclic gear diagnostics has not been developed and proofed in an operational role. The last report I saw from the CAA was that HUMS missed or false detected 70% of epicyclic faults. This would result in three falses for every true. With this rate coupled with cockpit alarms the SAR guys would stay busy.
As HC a lot of research is ongoing to improve this, but their is a long way to go. A recent test where an epicyclic fault was introduced in a bench test clearly showed the fault. However, when put on an aircraft the rotor vibration hid the signature. It is amusing that this data was shared with a major HUMS supplier along with data from a good transmission. The vendor was not told which was which. In their final report they showed conclusively that their advanced diagnostics could reliably detect the fault. The only problem is they identified the good transmission as having the fault.
The Sultan