DA40 TDI Backup ECU unsafe !

[LeeP-PA28]

Hi all

Was flying the DA40 today for the first time on a demo flight. First sector to a local airport went fine, all pre and post landing checks completed without any drama.

However, when doing the power checks on the return, one of the stages is to fail the ECU during which it performs various tests, feathering the prop and the like. The last stage is when the 'ECU Backup Unsafe' light extinguishes.

After the test, 5 secs later the ECU Backup unsafe lights starts blinking and won't stop - we recycled the engine master and the avionics master but problem persists. Anyway, opted to leave the aircraft there and not risk a flight back.

Is this the problem that I've read about where the ECU fails / loses battery / FADEC fails and it all ends up badly?

I left the aircraft with Diamond to sort out, just wondering if anyone here has experienced it - was it something or nothing?

Cheers

Lee

[FlyingStone]

The ECU backup battery is only installed in IFR-approved DA40 aircraft, since you can't turn off all electrical equipment if in IMC. In VMC in case of alternator failure, you should turn on the essential bus switch and turn off all electrical equipment that isn't required and the ECU will then be powered by the aircraft's main battery.

If you do have the ECU backup battery installed, its warning light should turn itself off (stop blinking) after a successful FADEC test, but will remain continuously lit in case that the ECU backup battery charge level is less than 70%. DA40's KOEL only requires the backup battery and the warning light for IFR flights, so you can fly VFR if you deem it safe - nevertheless, I would have the system checked ASAP.

Just nitpicking, but DA40 doesn't have feathering propeller, it just goes to full coarse (high) pitch during FADEC test.

[LeeP-PA28]

Thanks for that, useful information.

So the blinking light indicates a problem and a solid light is charge not above 70%. Is it possible that under normal running, i.e. in flight with 70% engine load, it would indeed be charging and the solid light extinguish?

Aircraft hadn't run for some time, so was intrigued into the background behind the failure/problem.

And thanks for the feathering prop pickup too :ok:

[soay]

Coincidentally, I also had this problem yesterday, fortunately before taking off from my home airfield. That was its first flight after bringing it back from its annual, when both ECUs were sent off to Thielert for inspection. Looks like Diamond will be busy today.

[A and C]

I think Flyingstone is talking about 70% of battery power (or less) remaining, this has nothing to do with the engine power setting.

Later I will get into the books and have a look at the peramiters for this light coming on, as with all of these things the devil is in the detail and most of the stuff never gets put in the flight manual.

Soay..........it is one ECU box with two channels, another detail that fails to make the flight manual no doubt !

[BackPacker]

Anyway, opted to leave the aircraft there and not risk a flight back.

Good call.

I've had a DA40 TDI fail on me in Duxford. Engine would deliver full power and everything, but the FADEC B light would not extinguish. Took us 24 hours to find an engineer with the right laptop to reset the FADEC.

The eventual diagnosis was a failing common rail outflow valve or something liek that - the one that keeps the common rail at constant pressure. Apparently FADEC B was the one that picked up on the fluctuating pressure and threw a "computer says no".

[100LL]

LeeP, Flyingstone is right,

When you press and hold the ECU Test button Both ECU A and B captions will illuminate. After a couple of seconds ECU swaps to channel B, raises the Engine speed from 900 to 1100 Rpm and cycles the prop once, Engine speed will then drop back down to idle, ECU will swap to channel A and repeat the process.

During the test, a battery tester, installed in the instrument panel, measures several parameters of the ECU Backup Battery. This will be indicated with a red flashing LED installed on the left hand side of the instrument panel.

If the capacity of the ECU Backup Battery is found to be less than 70% of its rated capacity then the 'ECU BACKUP UNSAFE'- light will be illuminated. It’s sometimes easy to confuse the flashing with a problem.

ECU backup battery will trickle charge from the ECU bus. the AFM is a little vague regarding departing with the light on, it only mentions IFR Flight, but the VFR Aircraft do not have these battery's fitted.

From previous experience ECU battery tester sometimes gets a little paranoid especially if it’s cold, ECU test button is released before the test has finished or the ECU test has been performed several times before takeoff.

Soay, ECU Internal battery is separate to the ECU backup battery. ECU backup battery is located under the rear seat Starboard side. ECU internal battery’s are soldered onto each channel in the ECU.

AFM is freely available on Diamond's Website, Checklist can be found here Diamond Aircraft :: Checklisten (http://www.diamond-air.at/checklist.html)

[LeeP-PA28]

Thank you very much,

Battery replaced and all OK now. It would found to be very low on charge, and after a night of testing, not charging!

Thanks all :)

Lee