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Report on the double ECU FAIL message I had the other day (DA40NG)

This is what I was sent regarding the double ECU FAIL message I got in the climb (and after that at any time I was on a high power setting), and led to an emergency diversion. I suspected a governor problem but it’s even more interesting (and possibly interesting to all pilots / owners of same type of engine)

The engineer found that the ECU FAIL message had been caused by a problem with the governor. When he opened the cowling he found that there was a wire to the governor that had been routed incorrectly and it had been cable tied to a flexible rubber hose. As a result there was too much tension on the wire. On high power settings the vibration in the rubber hose was sufficient to compromise the connection of the wire to the governor. This caused a FAIL message. Both ECU A and ECU B failed because there is only one sensor feeding both ECUs for this particular issue so both ECUs received the same signal. When you are flying the plane and you get a double ECU FAIL it feels as through the problem is much more significant than if only 1 ECU fails but this event shows that this is not necessarily the case but the pilot has no way of knowing! The engineer said that when the governor failed it would stay in a safe pitch for most power settings to protect the propeller. It effectively became a fixed pitch prop. This is why the RPM was going into the YELLOW range at high power settings because the pitch was safe but courser than normal for a very high power setting. The engineer wanted me to let you know this because he knew you had been planning to go over the Channel and he wanted you to know that the engine wouldn’t have failed! The engineer’s finding also explained why the ECU fail was intermittent – because it was only happening when the vibration in the rubber hose caused the wire to disconnect.

I had same error (DA42, CDI-135 engines) on right engine and the cause was failure in waste gate actuator which supplies info to both ECUs.

LDZA LDVA, Croatia

I also had double ECU FAIL when fuel pressure was low. When an engine parameter is out of range, both ECUs report it. A double ECU FAIL is not a double ECU failure, but rather something else failed and both ECUs can see it.

Last Edited by loco at 13 Dec 14:43
LPFR, Poland

Yep. I had pretty much ruled out the double ECU failure since low power settings made the alert go off. Both the warning and the emergency checklist not very helpful in that regard. An indication such as “Engine in safe mode” would be helpful. In my case, I didn’t worry much because I was in a very comfortable situation (almost in glide range of a large airport, in a beautiful day, over flatland), but these sort of indications can be worrying.
If the indications hadn’t gone away (which I think is probably what happened to Emir, but he had a 2nd one), the item on the checklist is “Prepare for engine failure”, which could lead to an accident of it’s own.

Relevant checklist pages:

(What I had was a mix of the part hinting the failsafe mode, but not exactly in that way, as there were a few conditions that didn’t manifest exactly in that way) – My situation had an immediate loss of power (heard, and seen on indicator)

Last Edited by Noe at 13 Dec 14:52

Noe, please note that there is another relevant checklist in the section that treats G1000 warnings… This is an area which is really confusing

LFPT, LFPN

I took the 1st litlte part from that section (I think!)

OK. My memory fails me.

Let me tell you a little story: I got a (partial) dual engine failure (55% on one side and 30% on the other) on a DA42 where BOTH ECU A and ECU B illuminated on both sides within a short time. I just got started on the EMERGENCY L/R ECU A AND B FAIL checklist when I had to divert my attention to dealing with asymmetry and inability to maintain altitude over mountains (in IMC)

Let me just say that I wish the checklist I selected had been this (DURING FLIGHT):

So for what it’s worth, my advice on the Thielerts and Austros is that if you ever get an engine problem, regardless of what the checklist says, your VFA (vital few actions) should be the first four above. You may add “Activate fuel transfer pump” or “Activate crossfeed” to the list. And those should be engrained in you just as much as those on Lycosaurus (mixture, alternate air or carb heat, fuel tanks, mags). Only after having completed these should you turn to the checklist.

In retrospect I also think that this checklist is particularly poorly written. The emergency and abnormal parts should have been regrouped

The end of the story is that I recovered engine power after having descended 2500 feet, and made a normal landing at the nearest airport.

Last Edited by Aviathor at 13 Dec 16:46
LFPT, LFPN

Your double engine issue was nothing to do with ECUs, they were just the first thing that spotted the problem. There can be only two sensible scenarios that could present concurrent engine problems and, bearing in mind you got the engines running properly again, I’m speculating DA42 AFM 3.9.4 refers to the circumstances you were faced with.

Air, fuel and electrics (spark) are vital actions for engine troubleshooting in any piston engine; the DA series aircraft aren’t unique.

Fly safely
Various UK. Operate throughout Europe and Middle East, United Kingdom
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