AGAINST the background briefly outlined together with the development of increasingly sophisticated powerplants as well as the research activities conducted into the operational aspects of rotating wing aircraft, it was realised that major benefits could be expected from fully exploiting health monitoring techniques. Applications would not only be for future helicopters but also for retrospective action for those currently in service. The Civil Aviation Authority (CAA) has conducted extensive investigations into many aspects of these proposals and published a report by a working group in 1985, the membership of which was drawn from industry, the Ministry of Defence (MOD) had the CAA. This report has been prepared to satisfy HARP recommendation No 11.