2.12.1 Total Power Loss
A total loss of power to the rotor, due either to engine or transmission failure, will result in a very rapid decay of rotor RPM. The rate of decay will depend on the amount of power being used at the time of failure and will be greatest in high power and low speed conditions. As a general guide, the rotor RPM will decay to the transient poweroff minimum in approximately 2 seconds.
Following a single engine failure it is particularly important to be prepared for the failure of the second engine. Engine failures can have common causes, e.g. icing, fuel contamination or possible damage to the operative engine following a serious first engine failure. When carrying out air tests or training with one engine retarded, the live engine is often working at high power and a failure of this will cause rapid rotor decay. Pilots should familiarise themselves with the indications of a second engine failure (usually this will only be the low rotor RPM warning as RPM decays) and maintain a hand on the collective as much as possible to reduce the delay before the collective is lowered should the second engine fail.
In the event of total power loss in anything other than hovering flight, the prime consideration must be to contain RRPM [Rotor RPM] within safe limits by lowering the collective lever fully and immediately.
Air Accident Report: 3/2015 G-SPAO EW/C2013/11/04
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Appendix G cont
The single most important aspect of a successful autorotation is the maintenance of sufficient RRPM. Do not allow your attention to be diverted away from this function for any more time than is absolutely necessary. Loss of RRPM will be fatal. High RRPM during the flare should be seen as a positive result of good RRPM management during the descent and will contribute to a successful outcome.
