Second ADAHRS or One + G5

[Freemasm]

Seems topical considering the previous couple of posts.

Background:
Electrically Dependent Aircraft
Dual/Redundant Electrical Architecture (4 wattage sources)
Very Limited Panel Space (tandem seat aircraft)
Two G3X powered from separate busses (current plan)

Saving $ is always nice but not a driver here. Only talking ~1 AMU price difference. Per the above, does a G5 really add significant safety margin over a second (independently powered) ADAHRS as some people have opined?

Side/related issue. I can shoehorn a G5 onto the panel but the audio panel would become remote mount/less bluetooth. Certainly a live-able option but opinions welcomed here as well.

 

[Carl Froehlich]

If the options are:
- Dual EFIS, a G5 and a single ADAHRS
- Dual EFIS, dual ADAHRS and no G5
I would go with the dual ADAHRS option. Easy decision.

Carl

 

[bmellis11]

Keep in mind that the G5 is a completely separate architecture from the G3X system. There could be a software issue or something else that brings down both G3Xs due to their common architecture and then you would be without instruments unless you had some other backup instrument.

You could always add a second ADAHRS if you are concerned about the first one going out.

 

[Bavafa]

Keep in mind that the G5 is a completely separate architecture from the G3X system. There could be a software issue or something else that brings down both G3Xs due to their common architecture and then you would be without instruments unless you had some other backup instrument.

You could always add a second ADAHRS if you are concerned about the first one going out.

Plus one. Other than electrical issue, there are other possibilities that could result the failure of the system. I had a faulty GAD27 that affected the CAN bus completely. A G5 will provide a second ADHAR as well as a completely independent system just to get you down safely.

 

[gfb]

Let me be overly dramatic in my answer :-D

If I sat in your plane for an IFR flight and noticed you didn't have a fully independent AI/AHRS backup I would decline to go on the flight.

A fully independent source of attitude for IFR flight is crucial. The G5 fits that bill by being completely independent.

Also keep in mind that having 2 attitude sources is great, but what happens when they don't match? Which one do you chose? 50/50 chance of going upside-down in the clouds. This is why big airplanes have an odd number of attitude sources, so they can "vote" and decide which one is correct. Of course, for our kind of flying, 2 hopefully covers the majority of possible failure scenarios.

 

[Draker]

I was struggling through most of Phase 1 with my GSU 25 giving erroneous attitude indications, and so I was glad to have a G5 backup to "sanity check" the GSU. I briefly flew with two ADAHRS plus the G5, but once the vibration issue was solved, I opted to go back to just one ADAHRS. I can easily install a second one onto the back of the display if I feel it's needed in the future.

 

[JDA_BTR]

Attitudes change with time. I flew IFR in my Arrow for years. One six-pack, two nav radios, two com radios, one DME, one approach indicator, one vacuum pump. No GPS. VOR, ILS and ADF approaches. There was no suggestion we would have a second six-pack, fully redundant systems, etc etc.

On the other hand, the G5 is so much for the money that it just makes sense to have it and not a second ADAHRS. If your glass screen fails the second ADAHRS isn’t worth **** but that G5 will do what you want including run with the autopilot.

 

[g3xpert]

ADAHRS Sources

Seems topical considering the previous couple of posts.

Background:
Electrically Dependent Aircraft
Dual/Redundant Electrical Architecture (4 wattage sources)
Very Limited Panel Space (tandem seat aircraft)
Two G3X powered from separate busses (current plan)

Saving $ is always nice but not a driver here. Only talking ~1 AMU price difference. Per the above, does a G5 really add significant safety margin over a second (independently powered) ADAHRS as some people have opined?

Side/related issue. I can shoehorn a G5 onto the panel but the audio panel would become remote mount/less bluetooth. Certainly a live-able option but opinions welcomed here as well.

Good Morning,

There are many advantages to including a G5 in a G3X Touch system.

The GSU 25 and G5 vary slightly in their methods for determining attitude. As a result of this, it is less likely that a problem in one will affect the other, which is an advantage from a system architecture standpoint, providing a slightly improved margin of safety against an issue with either ADAHRS unit in the aircraft.

The G5 ADAHRS hardware is built directly into the display, it therefore does not rely on any aircraft databus wiring to provide its attitude and airdata indications. This eliminates certain types of wiring failures as a source of attitude failure.

The G5 can also be installed with a backup battery attached directly to the unit, protecting the unit against many types of electrical system failures.

In the rare event that there is an issue with the G3X Touch display, the G5 can act as the flight director for the GFC 500X Autopilot, as long as the GMC 507 autopilot controller and GSA 28 servos are online and operating normally. This is a very helpful failover state in the event that a primary display has an issue.

If there is an issue with the GSU 25 ADAHRS, the attitude and air data information generated by the G5 is shared via CAN bus, and will be displayed on the G3X Touch PFD.

When you stack it all up, the G5 is a very nice complement to a G3X Touch, and provides multiple layers of redundancy to the system. You can of course always include an additional GSU 25, but if you are going to go with a total of 2 ADAHRS sources, 1 GSU 25 and 1 G5 is not a bad choice, from a system architecture perspective.

Thanks,

Justin

 

[bmellis11]

Attitudes change with time. I flew IFR in my Arrow for years. One six-pack, two nav radios, two com radios, one DME, one approach indicator, one vacuum pump. No GPS. VOR, ILS and ADF approaches. There was no suggestion we would have a second six-pack, fully redundant systems, etc etc.

You didn't need a second six pack because one six pack has built in redundancy--if you lose your AI, you can keep level with your airspeed, altitude, and turn coordinator, etc. If you lost your vacuum you would still have electrical. You also had multiple types of NAV devices--lose one, no problem, just use the others.

If you just have one glass screen and you lose it then you're SOL if you can't see outside. True redundancy in a glass cockpit can only be achieved through additional devices. The beauty of a G3X screen + ADAHRS with the G5 is that you get two independent instrument displays and two independent sources of air data, so total failure is extremely unlikely.

 

[iamtheari]

Seems topical considering the previous couple of posts.

Background:
Electrically Dependent Aircraft
Dual/Redundant Electrical Architecture (4 wattage sources)
Very Limited Panel Space (tandem seat aircraft)
Two G3X powered from separate busses (current plan)

Saving $ is always nice but not a driver here. Only talking ~1 AMU price difference. Per the above, does a G5 really add significant safety margin over a second (independently powered) ADAHRS as some people have opined?

Side/related issue. I can shoehorn a G5 onto the panel but the audio panel would become remote mount/less bluetooth. Certainly a live-able option but opinions welcomed here as well.

Since you have two G3X Touch displays planned in, I would strongly prefer the remote audio panel (GMA 245R with Bluetooth) so it takes up zero panel space and can be fully controlled from either seat. If you're going to have a Comm #2, I would also go with a remote unit that you can control from either seat (GTR 20). Same with the transponder. Your G3X Touch panel can control a lot of stuff from one place and you should take full advantage of that in your limited panel space.

A G5 is a great backup and crosscheck in a G3X panel because it covers numerous failure scenarios in one device. I like having the second GSU 25 but if I had to give things up I would let the second GSU 25 go before the G5. Especially in a tandem plane where the guy in front has no chance of maintaining control by reference to the display behind him if the front display fails or loses power.

 

[Carl Froehlich]

Keep in mind that the G5 is a completely separate architecture from the G3X system. There could be a software issue or something else that brings down both G3Xs due to their common architecture and then you would be without instruments unless you had some other backup instrument.

Really? This is a risk with Garmin?

Has this ever happened or is this just another internet story? At any rate, I would not even consider this an issue for a dual Dynon EFIS install.

Carl

 

[Ed_Wischmeyer]

Really? This is a risk with Garmin?

Has this ever happened or is this just another internet story? At any rate, I would not even consider this an issue for a dual Dynon EFIS install.

Carl

It's a theoretical possibility, not an internet story. And who knows, Garmin might be more reliable than Dynon -- but who's going to have any non-anecdotal, non-opinionated data to say one way or the other? There's lots more emotion than fact in aviation, especially homebuilts...

Not that this Dynio service bulletin posted today is definitive, but:
TECHNICAL SERVICE BULLETIN: 104808-000
Early SV-AP-PANEL Failure, Rev A

 

[bmellis11]

Really? This is a risk with Garmin?

Has this ever happened or is this just another internet story? At any rate, I would not even consider this an issue for a dual Dynon EFIS install.

Carl

I have only heard anecdotes of screens freezing or losing data, but haven't researched it. Bavafa mentioned an experience that may be relevant to that earlier in the thread.

Garmin is a very professional company and test their products, so it would be rare that such a bug could make it into people's airplanes. But logically if an EFIS and ADAHRS combo has some bug that makes the system go offline when a certain condition is met then that same condition should make an identical EFIS and ADAHRS combo go offline as well.

Garmin must think it's an issue because they went out of their way to design the G5 with a dissimilar architecture (per a former Garmin engineer, they even used different engineers and programmers to design it so there wouldn't be unintentional similarities) and they mention the benefits of the dissimilar architectures often.

 

[Carl Froehlich]

SNIP

Garmin must think it's an issue because they went out of their way to design the G5 with a dissimilar architecture (per a former Garmin engineer, they even used different engineers and programmers to design it so there wouldn't be unintentional similarities) and they mention the benefits of the dissimilar architectures often.

Anyone from Garmin wanting to put some credibly in this statement?

Carl

 

[PilotjohnS]

Wonkey

Well, there i was at 14500 feet flying over the desert and my mfd (right screen) on my g3x failed to respond to my touches. I dont know if it was hot due to seeing direct sun at 14500’ or what, but I pulled the breaker and rebooted it. I didnt have a inkling to troubleshoot while flying. Never had an issue since. But things can go wrong unexpectedly. It only takes one muon particle in the right memory location……

 

[BobTurner]

Anyone from Garmin wanting to put some credibly in this statement?

Carl

My mind is a bit fuzzy on the details, perhaps Garmin will chime in and fix up anything I say that is incorrect. However, I seem to recall that a decade or more ago, a new revision to operating software came out, and a bug slipped by the beta testers. Everything was fine if you told the EFIS you were going to KSFO or KLVK, but when someone typed in 'C83' the error propagated to everything interconnected and systems crashed. It seems the new software couldn't handle alpha-numeric airport IDs. It was discovered very quickly and fixes sent out. No one was caught in the clouds, etc. But it was enough that I put in a back up mimi-EFIS (Dynon D6) that was not interconnected to anything. Yes, to this day, every altimeter change, I need to change two boxes. Zero interconnects.

 

[rleffler]

To answer the OP’s original question. If you plan to fly in IMC, I would recommend two adahrs and the G5. That’s what I did in my most recent panel upgrade.

I’ve had two adahrs for about ten years, along with a Trutrak Gemini PFD as a backup. What I quickly learned that the Gemini PFD didn’t add much value as a backup device.

I replaced it last year with a G5. AFS can incorporate the G5 as adahrs. Since it’s the third adahrs, I now have an independent tie breaker if one stops working properly.

 

[DavidHarris]

I put dual AHARS and a g5 in my rv7 build. Each serves a valuable function. The cost of doing both during a fresh install is modest compared to the cost of doing anything in a certified airplane or the hassle of adding anything to a completed build. The dynon AHARS are stacked behind the baggage bulkhead with convenient access to the static lines.