A109 automatic engine shutdown ?
 

Hi

am I understand it right ? the ECU will automatically shutdown engines when TRQ is above 110% ? the other helicopters have similiar/same ?

Regards

Not shut down. It restricts fuel flow to prevent torque going higher. Wording is poorly translated from Italian to English.

Yes. The only time engines get shut down by their automatic control systems is for power turbine overspeed.

many thanks

so theoretically when you do negative G and simultaneously reduce collective you may have turbine overspeed and that may cause eng. shutdown .

I also heard that during descent is better to avoid TRQ less than 7% that's because FADEC may switch the eng off - I'm not sure this is only when GOV in MAN mode or during normal operations as well

CHR,

At the 110% ME Tq limit the fuel flow will be "restricted" not cut off, it basically causes the TQ to sit at 110% on the affected engines, and prevents any further TQ being delivered, with a resulting RPM Droop.

The Overspeed "Cutoff" is a bit of a blunt instrument, it doesn't stop the engines, it cuts the fuel using a solenoid in the FMM (from memory), that causes the N2 to fall, once it falls below a threshold value it is free to try and Overspeed again, if the load on the engine has not changed.

Never heard of an issue with 7% Tq being mentioned, I can only assume that is someone's rule of thumb to prevent NR overspeed due to keeping N2 and NR "matched" by always having some Torque applied.

It's fairly easy to overspeed (within transient limits) NR on the S and SP, with brusque manoeuvring when you first start to fly them, the Rotor head is more aerodynamic than the E model and it can come as a bit of a surprise, NR goes up quick, but it also comes down fairly quickly, even with my meagre skills.

FADEC's don't switch engines off. Pilots switch engines off by moving the ECL to off.

but they do sometimes have the authority to shutdown an engine, or reduce it to IDLE, particularly on types with no manual throttle controls.

None that I am aware of, except for overspeed protection and hot start protection.

In certain EECU failure conditions on the AW169 it will automatically bring the engine back to IDLE where it can remain online as a generator, provided the EECU can still control the stepper motor. There is no manual throttle. The only automatically commanded ‘shutdown’ is the hot start protection.

Much prefer the single-channel DECU with a manual reversion to a full FADEC.

Doesn't a dual-channel DECU always have a manual reversion?

On the S92 a FADEC dual channel failure results in the engine shutting down, with no manual reversion/control. (Well, it did unless recent updates have changed that). I was never clear why that decision could not be left to the pilot, because a frozen engine will/should not cause serious problems unless you make a significant change to the 'power demanded/required' vs the 'power available' (or, 'power being provided')

Oh, that comes as a surprise, dual channel failure logic to shut down the engine. In the S76C++ dual channel DECU failure reverts to manual control. Or you can revert to manual control any time you want by flicking a switch. We could even do both engines in manual control in the simulator which was a little bit silly as that was so unlikely to ever happen. But it was a good airmanship exercise for those who could do all the other stuff.

I think it was a question of the cost of installing a back up control system vs the probability of a dual channel failure - could be wrong and maybe JD will comment? Either way, I still don't understand why it could not have just frozen the metering valve. EC155B just froze, then B1 incorporated a back up mode

The clue is in the title - FADEC is Full Authority and implies no manual control. A dual channel DECU would be a different beast and could include a manual reversion.

Anyone know of an aircraft with dual channel and manual reversion?

The Wessex fuel computer could freeze leaving you with fixed power whereas the Sea King (same engine and computer) also allowed manual control.

139 has manual reversion as does the AS 365 N3

S76C++ has dual channel DECU with manual reversion.