From various sources of information, it seems clear neither engine was producing power in the moments leading up to the accident. That's rather unusual. Possible causes?
1) Lack of fuel to the engines.
2) Damage to the engines.
3) Closing down the engines.
Scenarios:
1) Since a significant amount of fuel was drained from the aircraft, (presuming no contamination) we have to assume a fault occurred causing inadequate delivery to the engines. Combined with a separate indication fault which would have disguised the developing deficiency in the supply tanks. Even in such a situation the system is designed in such a way that one engine should stop some minutes before the other. I forget the precise time, but I would anticipate all EC135 pilots would know what it was?
2) Engine damage can be caused by both external, and internal issues. An example of externally initiated damage would be Birdstrike. Internal damage would very likely be due to mechanical causes. To be a complete explanation here, any damage would have to have been caused to both engines, even if one engine's problems caused damage to the other - not unheard of.
3) Closing down the engine(s) might occur in two scenarios: Most obviously when an engine was unreliable/misbehaving/damaged. But also to remove torque during a tail rotor problem. Removing torque by closing down both engines would require an immediate entry into autorotation. Torque itself is of course not a problem when the aircraft is in forward flight, as aerodynamic forces on the fuselage flying 'sideways' balance the power required to fly level. Closing down of both engines is essential only when a tail rotor failure occurs in or very close to the hover.
How does this fit with what very little we (joe public) currently know?
The witness statements referred to by 4listair are very revealing. Everyone interested should read them. They might be taken to suggest that, within seconds of the accident, the aircraft was in forward flight, at very low level, making odd noises, and producing sparks?
Any aviator will be familiar with the phrase; aviate-navigate-communicate. It seems the "communicate" phase was never reached?
Finally, it seems very likely that autorotation was (for some reason) not successfully established?
Which of 1) 2) or 3), or combination thereof might explain such an event?
It is possible the clues are there?
Last edited by Tandemrotor; 17th Jan 2014 at 14:01.