PA-28 + dual G5s heading issue

[Flying_Nun]

My club plane has dual G5s installed with the magnetometer mounted in the wing and a single feed to both of them. One of the units consistently shows a 1 degree difference from the other. We switched them around and the error remained with the one unit. This same unit will also throw an out of tolerance error and flag the heading in yellow.

Per Garmin's instructions, the magnetometer has been calibrated and firmware updated. Installation of the magnetometer has been verified within spec.

Has anyone experienced this and found a solution? It's making instrument training difficult when you are suspicious of your heading indications.

 

[bnt83]

Is the G5 system throwing a fail flag any more? If not then I'd say who cares. If its still flagging then keep on garmin to get it figured out.

Did you know that a legal compass is +/- 10 degrees on any heading?

Dose of reality - look at your compass correction card, when was the last time it was updated? If it looks like its 25 years old then I'd bet your compass hasn't been checked for that long. IOW your compass hasn't been calibrated since then and its probably been messed up since the radio job completed after the last compass check.

I've installed two G5s myself from start to finish, GMU11 is in the wingtip (as far away from the nav light as practical, no strobes in them) calibrated it on a compass rose used by the local corporate jet MX facility, and have had great luck with them.

If its still flagging then some thing I'd look at, do you have an overlay or something that rubs on the G5 inducing some sort of vibration that that is throwing it off? I would take the airplane back to the compass rose and rerun the interference test and post the numbers. Or perhaps get another new G5 and swap the ne your having trouble with and see if it goes away. Then only other thing I can think of is panel thickness, does the metal instrument panel meet the thickness minimum is the STC Installation Manual? My hole panel meets the rule but I ended up making doubler & filler plates that ultimately made the panel about .120" thick at the G5s.

 

[CC268]

1 degree difference? Who cares

 

[Flying_Nun]

1 degree difference? Who cares

This is not helpful. Regardless, it is not the amplitude of the difference but the fact that there is a difference when both instruments are being fed the same data.

Is the G5 system throwing a fail flag any more? If not then I'd say who cares. If its still flagging then keep on garmin to get it figured out.

The internal tolerance failure is ongoing although intermittent. They were installed before I joined so I'm unsure about panel thickness. I'll run these suggestions by our maintenance folk. Will vibrations really cause issues?

 

[mondtster]

This is not helpful. Regardless, it is not the amplitude of the difference but the fact that there is a difference when both instruments are being fed the same data.

I don’t know the system well, but are you absolutely sure they’re being “fed the same data”? Is that data an analog or a digital signal? What gets calibrated? The unit providing the data or the individual G5’s?

See where this is going? Despite having two identical looking units mounted right next to each other, it is likely that they still function largely independent of each other.

There are advantages to having analog dials on instruments. One degree would never be seen...

 

[Flying_Nun]

I don’t know the system well, but are you absolutely sure they’re being “fed the same data”? Is that data an analog or a digital signal? What gets calibrated? The unit providing the data or the individual G5’s?

See where this is going? Despite having two identical looking units mounted right next to each other, it is likely that they still function largely independent of each other.

There are advantages to having analog dials on instruments. One degree would never be seen...

Yes. There is one magnetometer in the right wing which feeds both instruments. Per the maintenance folk, they are "wired together." Perhaps there is some signal interference in that arrangement. The magnetometer gets calibrated not the G5.

 

[bnt83]

The internal tolerance failure is ongoing although intermittent. They were installed before I joined so I'm unsure about panel thickness. I'll run these suggestions by our maintenance folk. Will vibrations really cause issues?

Like it or not, youhave two independent gyros in front of you, they are both seeing the same GMU11 but are seeing two separate independent accelerators inside the instrument. If you held the G5 in you hand and the GMU11 stationary the compass card will move all over the place. You can move the GMU11 all over and the G5 stationary and get very little change.

In fact, there is just enough bow in my panel that the vertical pitch offset numbers aren't exactly the same between the two to get the horizons looking the same.

Also, what GPS positioning is provided to the G5s? RS232 from a panel mounted GPS or are they installed with their own antenna?

 

[mondtster]

Yes. There is one magnetometer in the right wing which feeds both instruments. Per the maintenance folk, they are "wired together." Perhaps there is some signal interference in that arrangement. The magnetometer gets calibrated not the G5.

You didn’t mention if the magnetometer was feeding the G5’s an analog or digital signal. If it is analog, there would be little you could do to have the precision you seek. My bet is that the output is digital however, in which case Bnt’s comments about the accelerometers would be more influential.

 

[bnt83]

You didn’t mention if the magnetometer was feeding the G5’s an analog or digital signal. If it is analog, there would be little you could do to have the precision you seek. My bet is that the output is digital however, in which case Bnt’s comments about the accelerometers would be more influential.

Each G5, magnetometer and GAD29 (ARINC 429 converter) communicate over a common two-wire CANBUS. It is dirt simple wiring, power, ground, CANBUS, identity strap (AR), and RS232 or coax to antenna (AR).

 

[mondtster]

Each G5, magnetometer and GAD29 (ARINC 429 converter) communicate over a common two-wire CANBUS. It is dirt simple wiring, power, ground, CANBUS, identity strap (AR), and RS232 or coax to antenna (AR

That’s what I assumed but figured I’d ask. Thanks!

 

[Chris Metcalf]

Hello All,

I wanted to follow up and see if there had been any resolution to this issue. I recently installed a dual G5 System with a GNC 355 in my Cherokee and I am seeing the same thing. I also have a couple of buddies that installed them in their aircraft, that are also seeing this issue. Their aircraft are a beech 19 (430W) sport and a Cessna 172 (GTN 650). The 172 has his GMU 11 in the left-wing, the Beech has his installed in the fuselage, and my Cherokee has it installed in the right-wing. I don't know that the type of GPS used has any bearing on this issue, but thought I would include that information. As I said, we all see this same issue and ours is intermittent at well. Thanks!

 

[chemgeek]

I don't think this is necesaarily abnormal. During certain rapid maneuvers, one or the other of my G5s will momentarily flash yellow and disagree by a degree or two. It returns to normal within a few seconds. I suspect that the gyros derive heading information from both the GMU-11 and the internal accelerometers, and may take a moment to re-establish a robust heading solution. I've never seen the yellow caution persist for more than 10 seconds or so, and it's never off by more than a few degrees. I don't think I've ever seen both the AI and HSI off at the same time.

 

[Rex Kwan Do]

I know I’m bumping an old post but I’ve got a PA28-180 with dual G5, GNX375 and GFC500. I notice the yellow box during commercial maneuvers or at low altitude. It occurs randomly on the ADI or HSI. I have the GMU-11 on the right wingtip and have restrung the nav light with a shielded conductor and have the nav light grounded. I have the most current firmware and have recalibrated the GMU-11. Appreciate hearing if anyone found a smoking gun…

Has anyone else talked to Garmin or their installer about this? My installer has never heard of the issue before.

 

[sourdough44]

I have the two G5’s installed, I get the yellow ‘heading caution’ at times also, mostly during mild maneuvering. For the most part I just disregard it, I’m not interested in a shop digging around trying to make it go away.

That may sound careless, or I’m being to easy, I will say, during the process the heading is about 30 times more accurate than the old vacuum heading indicator.

 

[Rex Kwan Do]

I have the two G5’s installed, I get the yellow ‘heading caution’ at times also, mostly during mild maneuvering. For the most part I just disregard it, I’m not interested in a shop digging around trying to make it go away.

That may sound careless, or I’m being to easy, I will say, during the process the heading is about 30 times more accurate than the old vacuum heading indicator.

I’m sort of the same way, it’s always one of the other and never both and the ground track never changes so it’s not like I don’t know where I’m going. when I’ve been in HDG mode on the AP it’s never moved. So I agree just a nuisance. I was just curious because it is annoying and I’m just waiting for it to happen on a check ride and have the DPE start asking lots of questions….

 

[ricardol]

i had this issue too on my dual G5’s. during turns or on takeoff the heading indicator on the G5’s would turn yellow. (Would happen once or twice per flight, and lasted only a few seconds). not the biggest deal but a PITA if you happened to be on HDG mode on the GFC500 at the time.

mentioned it to my installer, they took a look at the GMU11 and they added a grounding wire to the GMU11 connector. (i can’t get more specific than this, since this is how they described it)

Prior to this fix the yellow indicator would happen on almost every flight, flew 2x since and it did not happen yet, (4+ hrs of flight) .. time will tell if this is the problem, but thought i’d mention it.

 

[machkhatib]

I don't think I've ever seen both the AI and HSI off at the same time.

Most of the time it’s one G5 or the other but I have seen it happen simultaneously. See the attached photo. I even have a short video clip of it.

My avionics shop - which is a Garmin dealer - has been troubleshooting this for months. They installed everything and I noticed yellow heading anomalies immediately after the install. The good news is the shop is honoring their work and they’re committed to getting this right for me. The bad news is they’ve recalibrated everything, moved the magnetometer, shielded wires, downloaded data from the G5’s and sent it off to Garmin, and have done everything Garmin suggested but still haven’t fixed the issue. At this point it’s time to start replacing Garmin equipment under warranty.