Trust the FADEC... but monitor it

Sorry Thielert boys, but as any system, your contains some flaws. I will not put apart my "Plastic Evangelist" cap, or deny all what I wrote before, but will just report here a problem I had.

This happend after taking of from a 3500ft AMSL mountain airport. During climb, we (I say we because I was on the right seat, a friend of mine in the left seat, so I had a perfect observer position) reduced power to 95%, because the day was quite hot.

Passing 5'000ft AMSL climbing, we got a "low volt" warning, that went off immediately. Probably one of these problems that would not have been noticed on a classical not FADEC monitored engine.

Approximately 30 seconds later, the FADEC decided that 95% power was not a good setting, and it reduced to 65%. My fellow pilot did lower the nose to maintain speed, and we started troubleshooting the problem. However after 15 seconds, not even the time to switch to FADEC B to see if its perception was better, the engine was again running under 95%. To say everything, I must add that the air was quite turbulent, so the hypothesis of an unwanted throttle movement was not irrealistic.

We reported that to the maintenance, so the data has been inspected by a Thielert approved mechanic. This is where the FADEC played its black -box role perfectly. The mechanic could confirm:

1) the low volt transient alarm
2) the power loss
3) the fact that the throttle was not moved !

The problem had been reported to Thielert, and it was unknown at this time. I will report on this if I get an update.

This event was of no consequence as it did not happend in a critical phase of flight. However, should it happend immediately after take-off on a short runway, with 4 on board, this could be more critical.

To be a bit more analytical, this kind of problem can happen on any plane, with any type of engine. What makes it feel slightly different with a FADEC engine is that it alerts you about all trouble, but you're left with so few things to do (switch to FADEC B), that you can feel power-less.

Something more about switching to FADEC B. If the FADEC A fails, it will switch automatically to FADEC B. This is the only case when it will happen. If this automatic switch does not take place, a switch allow to force FADEC B.

Most of the alerts however do come from sensor problems, and if FADECs are doubled, most of the sensors are unique, feeding both FADECs.

If you think now that these bloddy plastic engines are risky and full of single points of failure, please re-open the AFM of your airplane / engine. You could be surprised by the number of single points of failure...

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