After the AAIB Special Bulletin was released I stated that in order for the aircraft to meet the CAA's description of a high speed vertical impact with rotors stopped, it was likely that the aircraft suffered a complete loss of power and that, for whatever reason, pitch was maintained on the main rotor. (This being the only probable explanation for such an impact, albeit speculative).
From the examples provided in this thread, and from experience, we know that in single engine flying there is an attentiveness (or at least there is supposed to be) towards the potential for a loss of power. This attentiveness is geared towards rapid response in the event of an engine failure with the certain knowledge that it will be necessary to conserve and manage Nr. The lever is going to have to do down in nearly all cases (apart from a low hover etc.) meaning this action can be taken (along with the necessary cyclic inputs) without delay.
With twins there are additional considerations, principally the second engine, and specifically determining which one has failed. The multi-engine pilot response to a power failure is therefore slightly delayed (in principal) to that of a single engine pilot. This delay is compensated for to some extent by the relatively low risk of double engine failures in twins.
However, on those rare occasions that a double engine failure does happen, it is possible to see how a multi-engine pilot may not instantly take the required action in the same way as a single engine pilot would, and for the right reasons, because the multi-engine pilot must assess the nature of the power failure, even if it is to determine that both engines have failed. In a single, any sort of interruption to powered flight is not only obvious but it is equally obvious that there is no recourse. This is not the "normal" mindset of a multi-engine pilot who will be trained to recover from a power failure with partially powered flight from the remaining engine.
Now that Eurocopter have officially admitted that there is a problem with the EC135 (and related types) fuel indication system and that this problem includes the possibility of over reading, are we seriously looking at the potential of a double engine failure due to a shortage of fuel? A prospect which I had initially discounted as being improbable.
If the ill-fated G-SPAO suffered a double engine failure below 1000ft, at night, I am starting to see how it may have been possible with a low inertia rotor to maintain pitch for some moments after both engines failed - even though a part of me still struggles to accept this.
What I am still unable to envisage is how the rotors stopped so completely prior to impact in order to achieve the unscored and unmarked blades which were apparent at the crash site. We are talking about a few seconds from a loss of power to "blades still"!
