Left alternator failed

[mfdutra]

During a practice go around, this happened:

...and it stayed there for the entire flight back home. We followed the checklist and disconnected that alternator from the bus, even though it was outputting current at 28V just fine.

After landing, we shutdown everything and restarted the left engine twice. The CAS alert didn't clear, but the 28V was there normally, charging the battery.

A couple days later, the service center picked up the airplane to troubleshoot and everything is normal. No more CAS alerts.

Has anyone seen that?

I'm "glad" the alternator seems to be fine, but WTF? Technically, this grounds the airplane.

[Boatguy]

I think the CAS is a latched warning that has to be cleared with the Austro s/w.

I assume you were still seeing 28v because the R alternator was working fine.

How was this resolved? Was the alternator just reconnected or replaced? Was it the alternator or the current sensor that actually failed?

[mfdutra]

Nothing was fixed. The problem is gone.

I was seeing 28 volts and current flowing with only the left engine on.

[chili4way]

The CAS system (G1000 NXI) primarily assesses alternator functionality through its separate current sensor in parallel with the current sensor used by the alternator regulator. (Below from AMM 24-30-00, page 2.)

It would be helpful to know the electrical readings on the MFD engine page, which shows what the G1000 sees for both bus voltage and current produced by the LH and RH alternators (but not the optional alternator that powers the air conditioner).

If the current output reading were zero, that would be how the CAS system would assess an alternator failure. (It's also how it determines the ALT AMPS warning.). So, if you only had the LH engine running, the bus voltage was ~28V, and you had zero amps showing, that suggests an issue with the G1000 current sensor or its wiring to the GEA71B LRU. (see AMM section 92-00-00 page 45). If both engines were running, as Boatguy mentioned above, the 28V could be from the RH alternator.

There's an excellent write-up about the DA62 LH/RH alternator control systems on page 7-64 of the AFM.

What did the MX folks do to assess and resolve the problem?

[chili4way]

I was seeing 28 volts and current flowing with only the left engine on.

That's very puzzling. I don't understand why you'd have an alternator fail message with 28V and current being produced by the LH alternator with the RH engine not operating. Your service center needs to address this with Diamond Technical Support (and perhaps with Garmin).

[mfdutra]

Unfortunately, I didn't take a picture of the MFD engine page during the event, but I remember well that I could see Amps on both sides, and they were balanced. Later on the ground, with only the left engine running, the bus voltage was 28 volts and I could see amps flowing on the left side, all while the failed CAS message was there.

When I disconnected the left alternator from the bus, the right one picked up all the load.

The service center pulled the left engine logs and sent to Diamond. We didn't hear anything yet.

Given the alert came exactly after applying go-around power, I guess it was a transient variation of voltage or current that triggered the alert.

[Boatguy]

Given the alert came exactly after applying go-around power, I guess it was a transient variation of voltage or current that triggered the alert.

That seems likely.

As far as I can tell the Austro data logs and the G1000 logs only report battery voltage.

I don't see a filter for it, but I would think that the Austro event or engine log would list a CAS and might have more information. You could either download the logs again (assuming you have the dongle), or ask the service center to mail them to you. You can download the Austro AE300 Wizard software here.

https://partners.diamondaircraft.com/s/files

[mfdutra]

The MFD logs have volt1 and volt2, not any current. I analyzed them and nothing really interesting happened during the go-around.

Absolute pulled the left engine log, but I don't know what those logs have. I've never seen them.

I have the dongle, but I've never used it. Laziness. I need to learn all that.

[Boatguy]

I have the dongle, but I've never used it. Laziness. I need to learn all that.

Besides allowing analysis of engine operating data, the Austro Wizard can clear latched errors. If upon restart, the latched error immediately returns, then it's probably a real problem rather than a transient error. That said, the real problem could still have been a sensor or voltage regulator, not the alternator itself.

It's a nuisance, but on any overnight trip away from home, I now carry my laptop. Virtually all of us fly with an iPad. If you're listening Diamond/Austro, it would be so much more convenient if you created an iPad version of the Wizard. It would also be much more efficient for DSCs, Diamond support and Austro support if owners could capture diagnostic data, and implement simple diagnostic procedures like clearing latched errors, in the field. Much less expensive than having a Diamond field or DSC rep travel to the AOG airplane.

[CFIDave]

I had a single alternator failure (for real) during an IFR flight in our Austro DA42-VI some years ago. Besides the alternator fail annunciation, the volts/amps went to zero on that engine (this was a legacy G1000, not NXi). The good news is that I didn't have to do anything to continue the flight normally, because the other engine's alternator automatically took over the full electrical system load.

I had the failed alternator replaced under warranty by a Diamond service center that conveniently was located at my destination airport (KMYF).