AHRS / Heading Indicator Gremlin

[Chris B]

This may be a long shot, but one thing that I noticed recently in the G1000 System Maintenance Manual is that cell phones can create interference "even in a monitoring state." See the attached snips from the DA40 G1000 SMM, which specifically cites AHRS problems. What is bizarre is that there is no equivalent reference in either the Pilot's Guide or the Cockpit Guide...

However, apparently this is not just CYA by Garmin. Shortly after the G1000 introduction some service centers came to the conclusion that cell phones were creating problems. For my part, I've made a mental note to turn off my cell phone prior to flying in IFR conditions!

Chris

[h20wrks]

Today the dealer made arrangements for me to take the plane to Glenn at South Tech Aviation next week, I am hoping for the best.

[Rick]

Jim, you're in excellent hands. Glenn is the best - I have no doubt he'll figure it out for you.

[agmolnar]

Hi Jim, did the avionics shop ever getting to the bottom of this issue? I am also having intermittent HDG failure, mostly in northbound direction (although not always) and in the air (it's generally ok on the ground). The HDG indicator seems to come back up upon a turn of some sort. I have re-calibrated the magnetometer per the instructions but this didn't solve the issue (although I will likely try again).

Best,
Arpad

[h20wrks]

I have had no luck resolving my heading issue, even with another trip down to Premier in Ft Lauderdale. I did talk to George Koulsch at Garmin and he said for $1400 he would replace both my mag and AHRS. I am just not convinced that spending the money will resolve my problem. My problem is intermittent and extremely difficult to diagnose. It mainly fails when I start to add takeoff power on the runway, returning back to service rather quickly. My current work around is to preset my heading indicator to the runway heading during startup so that I can fly runway heading when it returns. I am always open for suggestions.

Jimmy

[Antoine]

Jimmy I have had a lot of these issues, only on the ground, until it happened: a complete loss of HDG after take-off into low OVC clouds. Very unpleasant...

I have talked to many people and tried different things.
Here is what I have learnt that may be of use to you since acceleration seems to play a role in your problem:

There are 4 connectors on the line from the magnetometer to the G1000 rack located behind the rear seats. you need them checked and serviced.
One is under the co-pilot seat (easy enough)
One on the magnetometer (dito)
One on the G1000 side (dito)
and the nasty one is at the wing to wingroot junction. (this requires removing the wing...)
Try to clean the 3 accessible connectors and reseat them first
Remove the PFD and MFD and also clean/reseat connectors there.

For cleaning I used Stabilant 22 which you can buy from a recording studio in NY (!)
http://www.posthorn.com/Stab_2.html

Touch wood, for now, no more worries - wishing you success.

[h20wrks]

As soon as work and weather allow me some time I will try these.

Thanks,
Jimmy

[rwtucker]

Given the dialog above, one thought is that the problem is not the magnetometer.

I'm wondering about electrical connections or a failing component in the associated LRU. I don't have my block G-1000 wiring diagram handy but I would consult that diagram that and work backwards from the magnetometer all the way to the PFD.

First, the next time you start up wait until your engine is warm enough to run up to 1,400 RPM before you initialize the G-1000. See if the problem goes away. Then disconnect and reconnect, and unplug and plug everything you can access in that path. Try the easy stuff first. If that fails, the news may be a worse. The weak connection could be in an inaccessible area or you may have a failing electronic component.

Here is why I'm thinking along these lines. Briefly interrupting an electrical circuit (as in pulling a breaker) that should be essentially zero resistance but has become oxidized or lacks adequate physical contact can bring the resistance within functional levels. Also, you seem to be experiencing the problem when the engine is idling, the alternator is close to zero charge, and the battery voltage is at its lowest. It is not unusual for marginal connections to fail at one voltage and succeed at another. (It gets a little complicated but oxidized junctions can act like a zener diode, although not if they are gold plated.) Unfortunately, the low voltage issue can also be the trigger for failing electronic components or junctions internal to the G-1000 circuit boards. For all of its cool features, the mechanics of the G-1000 are not particularly robust. You can see this easily if you compare a G-1000 circuit board with boards on military aircraft. Electronic components are not of the highest quality and board technology is only a tad above mid-grade.

Where possible, you might try Stabilant, per Antoine's recommendation.

Antoine: Do you know what kind of connector is at the wing root junction? Sounds like poor planning on Diamond's part. Why not connect a few fee in either direction?

[csalewski]

Hello,

When I got my '05 DA40-180 a few years ago I was very concerned about the intermittent heading x-outs on the ground. It always came back on time and I think I got used to it.
At my home base at LZU I start up between metal hangars and as long as I am stationary heading indicator is always ok.
Setting flight plan before moving and memorizing initial heading is crucial because at the hold line to the taxi way the heading is usually x-ed out. That's where I call ground which expects direction of departure not destination for VFR. Looking for the magenta arrow tip and finding an X during the radio call does not help there.

Heading indicator comes back after 10 to 20 seconds straight taxi on 'W' with no further issue. Never had it in the air. I'd say magnetic interference with metal structures and maybe local field disturbance is the most likely cause in my case. Would you agree? Never had it recalibrated and will only do so if it gets worse.

Carsten
N159PS

[agmolnar]

Very illuminating discussion. Robert or Antoine, any thoughts on diagnosis if the problem is happening in the air, at full power? Rather than electrical, could it be a metallic or disturbance of some sort? I have called the avionics folks but I suspect that they will have the same questions and queries and replacing an AHRS may not solve the issue. Although I wonder if lubricating the connections might be a good first step.

Best,
Arpad