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AHARS Failure

Postby gdtrfb58 » Thu Sep 22, 2016 4:26 pm

I have been working on this for months and I am really stumped (as are the GRT team), so I thought I would "put it out to the group".

I have a single screen HXr with GRT Autopilot and the "Original" dual AHARS.

A few months ago (after ~2 years of trouble free AHARS) I was flying in IMC at ~5000 feet, about to enter the approach, on AP, and I entered a diving left turn. This wasn't "uncommanded" because the EFIS showed me suddenly at 12000 ft in a hard right turn. I disconnected the AP and hand flew the approach on my back up EFIS (Dynon D10A) and the 480 HSI. I actually flew the missed (runway made) and stayed in VMC for the ride home. Here I made a mistake. Instead of trying to select 1 AHARS at a time, I left it on "Dual" and used my VPX to power off the AHARS 1 at a time. Ultimately, neither worked for the flight home. When I next flew, I determined that only AHARS 2 was bad.
After OSH (a lot of troubleshooting, but no answers), I sent the box back to GRT for "repair". They sent me an entirely new Dual AHARS. When I connected it up, AHARS "1" came up (on the ground) in a steep right turn (not a steady one). A week later, I powered up to fly to an Avionics shop for some work and both AHARS came up ok. ~20 min into the flight (VMC), I again went into a left turn. This time, I switched between AHARS and they were BOTH doing similar gyrations (not exactly the same pitch or pattern). When the avionics tech powered up the panel (I hadn't told him about this), he called to tell me that both AHARS were acting crazy and showing the plane flying all over the sky. Later, after powering down and up again, only AHARS 1 was bad.

Note" no movement of aircraft when AHARS starting up, until aligned.
At the Avionics shop we have:
    switched cables (no change. still top AHARS in box is bad)
    Checked/cleaned the cables-no change
    put a meter on each power pin (24.7V on each) and checked each ground wire (no V and appropriate resistance to ground block)
    pulled all the power pins from the VPX and run power directly from the (28v) battery (no change)
    confirmed that Pin 10 (OAT) is empty on both cables

It sure seems like AHARS 1 is "bad" in this box, but it seems unlikely that there would be 2 AHARS bad in 2 different boxes. Nothing explains both going at once.
Note: the 2 AHARS share nothing (except the ground plane they connect to). They are each on a separate Bus in the VPX (separate processors and power supplies).

Any ideas out there??
Posts: 58
Joined: Wed Mar 13, 2013 1:17 pm

Re: AHARS Failure

Postby jpfli » Fri Sep 30, 2016 1:42 pm

Please don't take this the wrong way, but is is possible GRT made a shipping error and sent your old AHARS back to you instead of the replacement unit they intended?
Posts: 16
Joined: Mon Jul 29, 2013 3:06 am
Location: KHXF

Re: AHARS Failure

Postby gdtrfb58 » Thu Oct 06, 2016 6:37 pm

No. Different SN. Case is different (there were markings on old case).
Different AHARS "bad" it was the bottom 1 the first time and the top 1 now.
Posts: 58
Joined: Wed Mar 13, 2013 1:17 pm

Re: AHARS Failure

Postby GordonTurner » Thu Oct 06, 2016 9:44 pm

Its probably in the literature somewhere, but is the HXr AHARS the same components and software as the Mini AHARS?

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Joined: Mon Oct 13, 2014 5:31 pm

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