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a109s Grand

Standard for an overspeeding engine is to put it into manual, and back off the power to a useful level. Shouldnt have caused a crash unless the overspeed protection failed for some reason, and the engine oversped so much it had a catastrophic event.

NPCP: That was my thought also, something like a rotor burst but .. it would seem unlikely!

Note - there is a fair degree of supposition in the following, but it may be worth considering.
If the engine oversped to the point of the power turbine wheel bursting (but not the compressor turbine), with this engine there would be no indication of an engine failure, and hence no access to the contingency power ratings.

This has happened before - the power turbine wheel disintegrated, and the compressor ran up to maximum fuel flow in an attempt to get the N2 signal back to 100%. Needless to say, since the compressor was working just fine, there was no engine failure declared by the computers, and the 2 minute and 30 second power ratings would not automatically be avaiable.
In the earlier incident, the pilot had time to look inside and figure out something was wrong and selected the correct engine to shut down. This allowed the contingency power ratings to be used and he landed safely. But the cockpit indications would be very confusing -on 'bad' engine- N1 and TOT maximum, zero torque, zero N2. 'Good' engine would have N1 and TOT appropriate to torque and good N2 signal. Probably have both low rotor warning and overtorque warning on at the same time. (Could you figure this out if it happened to you??)
Like I said, quite a bit of supposition here, but it may help someone who is trying to sort this out.

Was that on a PT6?

Would there not be visible damage to the engine cowlings?

Do we talk about FCU failure on that flight?

Shawn, that is an adept supposition, but it would be a rare thing, and SM is correct in that there would indeed be visible damage in the vicinity of the engines.

As you alluded; 'managing' (presumably shutting down) the correct engine would be crucial - there are enough examples where this procedure has been fouled-up even when the cockpit displays were blindingly obvious (or not .. as in the cases referred to!).

I would be keen if there was someone who could provide a brief overview of the mechanical (and other) factors which influence the onset of engine overspeed.

What ever happened to GET the Collective DOWN on any low Rotor rpm?
Studied the history on the S-58. The single 1820 had a better survival rate than the PT 6 twinpac, Get back to basics & quit studing to death the engines & keep the rotors turnin. Rotor RPM is life.

There is a (interim) report pubblished, yet?

That comes across as very arrogant and belittling, especially as we don't know the details of the failure. How do you know the failure involved low rotor RPM? If it was a runaway up, rather than a rundown, the opposite might have been true. There are other scenarios which could possibly result in the aircraft ending up looking like it did. The rotor rpm might have been used up in the last few feet, cushioning the touchdown over what looks to be a very restricted area.

Having flown this sole type for the past five years I have to say that that the engine display (strip gauges) are not the clearest ones I know.

If the N2 wheel disintegrated, it's not a given that parts would fly out of the side of the engine, so there may not be any damage to the cowlings.

Look at the damage as seen-No mistery-Even If you pulled pitch at the top of the trees the rotors show no rotational/inertial damage=Low or no Rotor rpm. It fell like a stone.Vertical crushing impact .Arrorgant? Belittling? Just looking at a wrecked Agusta with no post impact fire ,Vertical crushing , a rotor system with little if no leading edge damage. In any helicopter RPM is life-This example had None.

Especially with the containment rules we are required to comply with. Bits may come out of the exhaust though.

So, bearing in mind there were survivors, how far do you think the aircraft fell with no Nr? The 109S has very good OEI performance and it looks for all the world that this was no straightforward engine failure.

Look at whats left.

Just over a year on from this, anyone know the final verdict? Has an official report been published? Blender?