DA62 road landing in Dallas, Texas

[SkymanIL]

I got a response today from Diamond support in Austria saying that they are waiting for the NTSB report in order to learn more about this incident. I tried to extract additional information but without success. The only comment that the support person made is that he is also curious to learn how this specific airplane, with two independently working engines, ended up losing both.

[Davestation]

http://support.diamond-air.at/fileadmin ... Wiring.pdf

[photoSteveZ]

http://support.diamond-air.at/fileadmin ... Wiring.pdf

That didn’t take long!

[Boatguy]

http://support.diamond-air.at/fileadmin ... Wiring.pdf

1) This is confirmed as a maintenance induced failure?

2) If so, was it a DSC?

3) Why would this be limited to the DA62 and not potentially be a problem for any Austro engine?

4) This seems like an absurdly simple condition to detect during the self test. I would hope there is an ECU firmware update coming that will address this condition.

This is a great opportunity for Diamond to put all Austro engine owners at ease with a transparent explanation which can certainly be done without naming names.

[Soareyes]

So the test to see if they are hooked up correctly involves removing the instrument panel cover and checking voltages with a multimeter. Not hard to do but that implies there is no way for the pilot to check it during preflight, say on the first flight after annual inspection.

Looking at the pictures; all black wires bundled together, not color coded, not (at first) even labeled with a + or - before going to the positive and negative terminals on the batteries?!

There was reportedly a Diamond twin a few years ago that had battery wires hooked up in reverse during maintenance. Not sure which battery but it fried the entire electrical system, requiring all new electronics. Reverse polarity detection - hard to do?

Questions remain about the accident DA62. Do we know if it had the polarities reversed or was it some other error? Regardless of the error with the back up batteries, why was the main battery down to 70% capacity? Both alternators not charging?

[Davestation]

If you know anything about electrical at all it’s pretty intuitive and the way the wires are zip tied and their lengths etc. lends to correct installation. Also there’s a diagram in the AMM.

[chili4way]

Since the ECU batteries are replaced annually, the incident plane was a 2020 model, and the SB is "check for correct wiring," it's hard to see how this is anything but a maintenance-induced failure (MIF) related to the ECU backup battery installation.

It seems likely that the two 12V batteries were mistakenly misconfigured (single 12V cell or maybe opposing polarity) instead of in series. The diagnostic in the SB appears to focus on the proper voltage more than the polarity. [Completely reversing polarity would probably create a dramatic consequence much sooner.]

Such miswiring possibly affecting other models is technically possible, but the ECU backup battery physical configuration differences between the DA40 and DA62 suggest this is improbable.

DA62

DA40NG

[Davestation]

P.S. the 42NG and the 42-TDI batteries are identical to the 62.

[Chris]

It seems likely that the two 12V batteries were mistakenly configured in parallel instead of in series. The diagnostic in the SB appears to focus on the proper voltage more than the polarity. [Completely reversing polarity would probably create a dramatic consequence much sooner.]

I don't think it's possible to wire the batteries up in parallel with the harness provided. You'd need an extra jumper wire and connection points in order to connect both '-' and both '+' together along with the external leads.

I sketched out six possible configs, only one of which is correct, and two of which would involve shorting + and - of a single battery together, which I would expect to be noticed immediately. Reverse polarity in series is one other option, as you mentioned, and without looking at the rest of the schematic to see how these are connected up to other systems, you are probably right that it would get noticed quickly. Unless, however, it simply blew the fuse and rendered the batteries effectively disconnected from everything else.

The other two configs involve connecting the single jumper to either both positive or both negative terminals and then the ground and fused leads to the remaining two leads (either both negative or both positive). Maybe call this is a "half-parallel" configuration. I think it would try to produce 0V across the external circuit and sink current from there, but I'd have to think about it more. If the misconnected backup batteries actually took down the entire electrical system, then I'd guess it was from one of those two.

Detecting this during self-test may or may not be possible. I'm guessing there's not a way to isolate and measure that circuit with the way it is connected to the bus. Perhaps it would show up as abnormal current draw from the battery prior to starting the engines?

[Boatguy]

Detecting this during self-test may or may not be possible. I'm guessing there's not a way to isolate and measure that circuit with the way it is connected to the bus. Perhaps it would show up as abnormal current draw from the battery prior to starting the engines?

This airplane has lots of isolation and redundancy to avoid the simultaneous loss of both engines. A single point of failure that takes both engines out of service is a very serious design flaw.

If this can't be addressed with a firmware update to the ECU self test, then I suggest there needs to be an MSB to add the circuitry needed to do so, or make it impossible for an A&P to make this mistake.