AHRS / Heading Indicator Gremlin

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h20wrks
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AHRS / Heading Indicator Gremlin

Post by h20wrks »

I recently purchased a refurbished DA40FP and I could use some advise as to troubleshooting my AHRS. After startup I usually have to cycle to breaker once or twice to not get a heading failure. It seems to not fail if the plane is moving after cycling the breaker. The dealer has replaced the AHRS unit and magnetometer trying to solve my problem. It has not failed in flight and it seems to fail whether I fire up near the hanger or out in the tie down area, so I have ruled out proximity to metal mass. It only impacts my heading meter and I guide use a little guidance.
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Rick
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Re: AHRS / Heading Indicator Gremlin

Post by Rick »

Welcome to the forum, Jim!

Did they try the magnetometer calibration procedure before replacing it? And did they calibrate the new one after replacing it? There is a (pretty simple) procedure from Garmin to follow to calibrate the magnetometer, which has solved the X'ed out HDG indication for several of us here in the forum. Our symptoms were very similar to yours - it always happened on the ground after startup, and (usually) never in the air. In my case, it always went away on its own by the time I had taxied to the runway, but did happen once in the air for a few minutes. After calibrating, it never happened again.
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Antoine
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Re: AHRS / Heading Indicator Gremlin

Post by Antoine »

h20wrks wrote: It has not failed in flight and it seems to fail whether I fire up near the hanger or out in the tie down area, so I have ruled out proximity to metal mass.
I recommend investigating this possibility further. Try and move to another airport for the test. The impact of a metal element on the local magnetic field is site-specific, so try and rule this out before spending more effort on the part itself.

Mine will also randomly fail when starting up near hangar, fuel station and the like.
I never cycle the breaker. Just taxi away and wait. It has never let me down beyond run-up area so far.

This said I have had a failed magnetometer once, but this was not intermittent - it just died once and for all. I know the shop did the calibration on the new part.
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h20wrks
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Re: AHRS / Heading Indicator Gremlin

Post by h20wrks »

Forgive my ignorance, they have taken the plane out mid field numerous times, swinging circles if that is the calibration process that you are referring to. Yesterday the heading indicator was ok during startup, but it failed on the taxiway right before I turned on the active. Resetting the breaker had resolved my problem by the time I had lined up on the runway.
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Re: AHRS / Heading Indicator Gremlin

Post by Rick »

h20wrks wrote:...they have taken the plane out mid field numerous times, swinging circles if that is the calibration process that you are referring to...
Yes, that sounds like it. Glad to hear they tried this first!
h20wrks wrote:Yesterday the heading indicator was ok during startup, but it failed on the taxiway right before I turned on the active. Resetting the breaker had resolved my problem by the time I had lined up on the runway.
If you DON'T cycle the breaker, does the HDG come back after some time, or dose it remain failed until you cycle power? Does it ever come back by itself, or do you always need to cycle power to get it back? Also, does anything else on the PFD ever X out (like the OAT or the wind vectors), or is it always just the HDG?

One last question - when your HDG is failed, have you looked at the last AUX screen on the MFD that shows the status of all the LRU's? If you scroll down, are there any red X's on that page when it's failed?
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h20wrks
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Re: AHRS / Heading Indicator Gremlin

Post by h20wrks »

If I don't cycle the breaker, the heading indicator usually comes back in a few minutes if the plane remains stationary. This time interval appears shorter if I turn or taxi the plane. I will make sure to check the aux screen the next time I experience the heading failure.
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Re: AHRS / Heading Indicator Gremlin

Post by Jean »

Antoine wrote:
h20wrks wrote: It has not failed in flight and it seems to fail whether I fire up near the hanger or out in the tie down area, so I have ruled out proximity to metal mass.
I recommend investigating this possibility further. Try and move to another airport for the test. The impact of a metal element on the local magnetic field is site-specific, so try and rule this out before spending more effort on the part itself.
I would check that too. We have the same problem at our home base EBLG. We have that problem only when departing from South Apron. AHRS comes alive when we line up. There is a warning in the Crew Briefing Room for magnetic disturbance on that area.
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h20wrks
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Re: AHRS / Heading Indicator Gremlin

Post by h20wrks »

I do not think that is my issue as my heading indicator has failed at 2 airports in Florida and 3 in North Carolina, practically every airport that I have visited.
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Re: AHRS / Heading Indicator Gremlin

Post by SlowFlight »

When I was having issues with my HDG X-ing out, these were recommended:

1. Unplug charging accessories from the DC port (I had a poor quality charger for the iPad that created interference).
2. Turn off electronics (iPad, iPhone, etc.) or at least the device's radios (cell, wifi) to rule these out.
3. Recalibrate the magnetometer.
4. Ensure that brass screws instead of ferrous metal screws are securing the inspection port on the outboard wing on which the mag is mounted (right wing on my 2007 XL).
-tyson

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ForeFlight / Co-founder & CEO
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Re: AHRS / Heading Indicator Gremlin

Post by Tommy »

Take your plane to your favorite avionics shop.
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