Appendix 3.005d HEMS section:
A/c not in compliance with CAT A ops may operate into/out of a "public interest site" with the following:
1. An exemption from the CAA to do so....
2. certain flight profile recommends..
3. Fitted with HUMS !!!
I believe this is to be done by 2004, HOWEVER, the CAA are trying to exempt <2720kg class (soon to be 3000kg class) from this.
Sorry, can't help you with regard to GA..
but I suspect there will be a requirement for similar somewhere down the line!!!
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Thermal runaway.