gfc500 won't stay in heading mode

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Wagondriver

Line Up and Wait
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375Taylor
I haven't had time to call the avionics shop yet.
I was flying to MSO a few weeks ago in pretty rough air, using heading mode to stay in the valley and not have to climb over terrain. It kept kicking out of heading mode and into roll mode. It was pretty rough, I was on my way to get a pitot static check done, the guy there suggested that a wing tip mounted magnetometer was likely the culprit in rough air.
Today I was flying in pretty nice smooth air and again the autopilot kicked out of heading mode and into roll mode. When I got to where I could use nav mode, it was fine. On the return trip, same smooth air or maybe less, it never kicked out of heading mode.
When I first intstalled it last summer, it would hold heading perfectly, anyone with similar issues?
 
Groundpounder said:
Did you have any fault messages?
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I was thinking the same thing, but don't know enough about the '500 to know how it works with the G5/GI275 when a fault is registered.

I presume that you (the OP) have either G5's or GI275's installed along with the autopilot. I have GI275's working with a Century IIB autopilot, and the '275 installation required that a relay be put in the power lead to the IIB autopilot. In the event of a fault in the '275, the relay contactor is opened and the autopilot is turned off.

In my case the faults were instantaneous and power was restored to the autopilot before I recognized that it has ever been turned off. The autopilot, however, did not turn itself back on when its power was restored.

If the '500 handles a G5/'275 fault by reverting to roll mode, that could be your situation.

BTW, the only way that I could prove the instantaneous fault was by video recording the '275s and the autopilot controls in flight (in the same frame with 1 camera). I could see when the autopilot turned off, and at that point I could see the fault message flash on the upper '275 for only 3 frames (0.1 second). The fault turned out to be due to vibration, even though the installation had passed the installation vibration tests. In your case I guess the shocks of the turbulence could have triggered a fault...and maybe caused something to shift so that it triggers with weaker bumps.
 
bkspero said:
I was thinking the same thing, but don't know enough about the '500 to know how it works with the G5/GI275 when a fault is registered.

I presume that you (the OP) have either G5's or GI275's installed along with the autopilot. I have GI275's working with a Century IIB autopilot, and the '275 installation required that a relay be put in the power lead to the IIB autopilot. In the event of a fault in the '275, the relay contactor is opened and the autopilot is turned off.

In my case the faults were instantaneous and power was restored to the autopilot before I recognized that it has ever been turned off. The autopilot, however, did not turn itself back on when its power was restored.

If the '500 handles a G5/'275 fault by reverting to roll mode, that could be your situation.

BTW, the only way that I could prove the instantaneous fault was by video recording the '275s and the autopilot controls in flight (in the same frame with 1 camera). I could see when the autopilot turned off, and at that point I could see the fault message flash on the upper '275 for only 3 frames (0.1 second). The fault turned out to be due to vibration, even though the installation had passed the installation vibration tests. In your case I guess the shocks of the turbulence could have triggered a fault...and maybe caused something to shift so that it triggers with weaker bumps.
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Great information.
I will look at all wiring connections. and the magnetometer mount. The magnetometer was mounted 3 years ago, auto pilot is new as of june.
Its driven by g5's.
 
As I understand it, the g5/gi275 is the brains. The a/p can't even do straight and level without the g5.

I had trouble with mine doing something similar initially. Iirc the g5 wasn't getting the dgps from the gtn. The g5 apparently uses GPS to augment the magnetometer. I often got "yellow" headings and the g5s would display headings that were several degrees apart from each other and like 30 off the wet compass at times. I think they were each calculating their own heading using their internal GPS (with no antennas, so a very poor signal). If that sounds like what yours is doing, I could ask my shop what they did to fix it.

Iirc, because I was using the g5 as the altitude encoder as well, they ran out of ports. Because of that they didn't have the usual place to hook up the dgps in. They eventually figured out how to run an additional wire to make it work.
 
Download the GFC500 Instructions for Continued Airworthiness and read it, may give you an idea what to look for.
 
Jim K said:
As I understand it, the g5/gi275 is the brains. The a/p can't even do straight and level without the g5.
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While that is true there may be a hidden AHRS inside the GMC507 Controller

1701349495015.png
 
bnt83 said:
Download the GFC500 Instructions for Continued Airworthiness and read it, may give you an idea what to look for.
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I downloaded it, and read it. Is there something specific you think I should note?
 
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