It Couldn't Happen---But It Did

[Pinecone]

53 minutes ago, N231BN said:

Mooney could have designed their electrical system like a mulit-engine turboprop or jet and have dual independent buses but it would have added a lot of unnecessary cost and weight.

One item that should be added to all of these airplanes is an emergency avionics master. It is just a simple 30a CB switch that bypasses the avionics relay. I understand that the relays are designed to be fail-safe but there are multiple possible failure modes.

Another option: I installed new avionics in one of the DC-3s I'm involved in, one of the requirements for installing Garmin GTNs in a large aircraft is that they be powered by independent buses. While adding the second bus I added a selector switch to allow it to be powered by the hot battery bus.

One of the failure modes with a hydromatic feathering propeller is the feathering pump relay can weld closed. The only solution if that happens in-flight is to shut off all the power to the airplane. If that would happen in this airplane, I can bring back the audio panel, number two GTN, and transponder. The co-pilot's gyros are vacuum powered so you have a complete functioning panel with both generators and the battery disconnected.

If you did split the avionics bus in a Mooney it wouldn't be too difficult to add a properly sized and fused wire back to the battery to give it an "emergency power" option.

Also, when these airplanes were designed/built, the primary flight instruments were vac, not electric.  And ATC had Primary radar.  So with separate comm, you were good to make it safely to the ground.

But I wrote my piece before I read yours.  I like the idea of a split avionics bus that one side can be fed directly from the battery bus.

[Hank]

This whole thread is a great explanation of the difference between theory and practice. "According to theory, there is no difference between theory and practice."

Theory:  the multiple Garmin glass panel products, with multiple AHRS and separate batteries, cannot all fail together.

Practice:  the multiple Garmin glass panel products, with multiple AHRS and separate batteries, all failed together leaving the panel inoperative.

Be prepared! Have a Plan B and a Plan C. Plan B in this case would be to use the other instruments and battery back ups; what is Plan C for when the electronics all fail?

[whiskytango]

Don,

Really sorry to hear about this.  I hope the fix is relatively simple.

You mentioned that your G5s were off (by choice) at the time of the incident.   Do you know if the G5s will transition from bus power to internal battery power after a bus power loss so that the data is "seamless" i.e., there are no brief lags or freezing etc. on the display?  I am thinking in terms of a failure that occurs on takeoff, in IMC at low altitude. A loss of data integrity during G5 transition from bus power to battery power at that point, even for a short time, could result in a loss of control.

 

[Pinecone]

When I turn off power on the aircraft, the G5 asks if it should keep running on battery or shutdown.

[PT20J]

Don, I've heard that Garmin avionics do not take well to being powered down during a database update. I have a Garmin Nuvi in the car and it bricked after I accidentally powered it down during a database update. I finally got it working again but I had to do a hard reset and delete and reinstall the desktop update app and basically start from scratch. 

So, when you get your power issue resolved, let us know if there is an issue completing the update.

Good luck,

Skip

[PT20J]

On 11/6/2022 at 5:12 AM, toto said:

Don has been an advocate of the Aera 760 as a portable backup, and one of the key features of the Aera 760 is a built-in AHRS with an attitude display. 

From the Garmin website Aera 760 FAQ https://support.garmin.com/en-US/?faq=VFLTVe7r9X7NFh5lttExZA#:~:text=The Aera 760 will only,then press "More Options.":

"The Aera 760 will only be able to use its own internal AHRS if it is panel mounted. If the device is mounted on the yoke, the internal AHRS will not work as expected. "

[toto]

1 minute ago, PT20J said:

From the Garmin website Aera 760 FAQ https://support.garmin.com/en-US/?faq=VFLTVe7r9X7NFh5lttExZA#:~:text=The Aera 760 will only,then press "More Options.":

"The Aera 760 will only be able to use its own internal AHRS if it is panel mounted. If the device is mounted on the yoke, the internal AHRS will not work as expected. "

Yep. My understanding is that the same is true of every AHRS device. 

(Not panel-mounted per se, but an AHRS has to be in a fixed position and can’t be moving around relative to the aircraft.)

[N201MKTurbo]

47 minutes ago, toto said:

Yep. My understanding is that the same is true of every AHRS device. 

(Not panel-mounted per se, but an AHRS has to be in a fixed position and can’t be moving around relative to the aircraft.)

They have erecting sensors that will get them working again eventually. If you put them on the yoke, they are constantly moving, so they won’t know where they are. If you lay it on the seat or the floor it will be fine. Mounted on the panel would be best.

[MikeOH]

As an EE I don't entirely trust moving electrons!  I happen to like having moving air molecules (vacuum pump) as a second source. JMHO

[hais]

12 hours ago, N231BN said:

Mooney could have designed their electrical system like a mulit-engine turboprop or jet and have dual independent buses but it would have added a lot of unnecessary cost and weight.

One item that should be added to all of these airplanes is an emergency avionics master. It is just a simple 30a CB switch that bypasses the avionics relay. I understand that the relays are designed to be fail-safe but there are multiple possible failure modes.

Another option: I installed new avionics in one of the DC-3s I'm involved in, one of the requirements for installing Garmin GTNs in a large aircraft is that they be powered by independent buses. While adding the second bus I added a selector switch to allow it to be powered by the hot battery bus.

One of the failure modes with a hydromatic feathering propeller is the feathering pump relay can weld closed. The only solution if that happens in-flight is to shut off all the power to the airplane. If that would happen in this airplane, I can bring back the audio panel, number two GTN, and transponder. The co-pilot's gyros are vacuum powered so you have a complete functioning panel with both generators and the battery disconnected.

If you did split the avionics bus in a Mooney it wouldn't be too difficult to add a properly sized and fused wire back to the battery to give it an "emergency power" option.

Surely independent buses can’t be weight prohibitive. We are talking having NAV2/COM2 on a separate bus. It shouldn’t cost more than leaving in the vacuum system.

Perhaps someone might find it worthwhile to develop an STC for that. 

[Ragsf15e]

8 hours ago, whiskytango said:

Don,

Really sorry to hear about this.  I hope the fix is relatively simple.

You mentioned that your G5s were off (by choice) at the time of the incident.   Do you know if the G5s will transition from bus power to internal battery power after a bus power loss so that the data is "seamless" i.e., there are no brief lags or freezing etc. on the display?  I am thinking in terms of a failure that occurs on takeoff, in IMC at low altitude. A loss of data integrity during G5 transition from bus power to battery power at that point, even for a short time, could result in a loss of control.

 

They should have a seamless transition… I have pulled the circuit breakers on both my g5s in flight and just left them running that way for several hours.  They were fine for 2 hours +.  And there is zero lag when power is abruptly pulled.
 

If you have some kind of surge or other weird electrical gremlin, who knows how seamless the transition to battery will be?

[toto]

15 minutes ago, bluehighwayflyer said:

I have flown a hundred or so hours now with both an Aera 660 hardwired to a GDL50 for AHRS and a D3 Pocket Panel, all of which are panel mounted, and as much as I love the Aera for it’s many other functionalities I would never trust it as an attitude reference.  The thing rolls over all the time.   The D3, on the other hand, has always been 100% rock solid.   I highly recommend them both, but I only trust the AHRS in the D3.  

Out of curiosity, do you think the sketchy AHRS is the GDL50, or the Aera? One of the selling points of the 760 is the built-in AHRS, but I wouldn’t think that an external Garmin AHRS source would be any less reliable. 

[PT20J]

One of the selling points of the GTX 345 is that it has a AHRS that can be Bluetooth linked to an iPad running Garmin Pilot or ForeFlight. I tried it with both apps and all it was good for was directing me into an unusual attitude. I had the GTX 345 replaced on warranty and the second one was better but would pitch a few degrees when turning and would drift after a while. I would not want to trust my life to it. Interestingly, when a G3X is installed with a GTX, the software disables the GTX AHRS. So, I think some AHRS, even from Garmin, are just toys.

Skip

[Ragsf15e]

1 minute ago, PT20J said:

One of the selling points of the GTX 345 is that it has a AHRS that can be Bluetooth linked to an iPad running Garmin Pilot or ForeFlight. I tried it with both apps and all it was good for was directing me into an unusual attitude. I had the GTX 345 replaced on warranty and the second one was better but would pitch a few degrees when turning and would drift after a while. I would not want to trust my life to it. Interestingly, when a G3X is installed with a GTX, the software disables the GTX AHRS. So, I think some AHRS, even from Garmin, are just toys.

Skip

My gtx345 ahrs has been ok for ff, but I agree it’s not perfect.  I actually think my stratus 2 was better (which I sold when I got the -345).

The other obvious problem with the -345 ahrs is tgat any electrical gremlin that takes out your primary attitude system will likely take out the -345 as well.

I think it comes down to personal comfort level and how much you fly IFR. 2 g5s/275s should be redundant and have battery backup.  If you want more, A D3 or similar “pocket panel” can be charged and have zero connection to the airplane electronics.  Finally, a vacuum attitude source can be a backup without any electrical need whatsoever.  You could also use a different electric ADI with battery like @PT20J did, but it is connected to the electrical system.

I have chosen to stick with just the g5s but I don’t fly much ifr.  

[N231BN]

GDL-52 hardwire to Aera 660 is very solid, I don't trust the BT connection for this. I only have a little experience with a D3 but I wanted to throw it out the window. YMMV

[N231BN]

12 hours ago, hais said:

Surely independent buses can’t be weight prohibitive. We are talking having NAV2/COM2 on a separate bus. It shouldn’t cost more than leaving in the vacuum system.

Perhaps someone might find it worthwhile to develop an STC for that. 

I agree, a split avionics bus is simple and lightweight. My first paragraph was referring to the electrical system as a whole. That is much more complex.

[Vance Harral]

21 minutes ago, PT20J said:

I had the GTX 345 replaced on warranty and the second one was better but would pitch a few degrees when turning and would drift after a while.

That's been my experience as well.  I periodically cover other attitude instruments and fly myself or ask my instrument students to fly using just an iPad and a GTX 345 AHRS connection for attitude.  What I've observed is that it will keep you upright in a pinch (haven't had the really bad experience PT20J has), but it is "swimmy" - seems to lag a bit, and seems to show small banks when the aircraft is actually level.

I've had worse experiences with the AHRS in Stratus/Sentry devices, that so many people seem to be counting on as a backup these days.  I continue to find instrument pilots who feel good about having Foreflight and a bluetooth connection to AHRS as a backup solution, but who it turns out have never actually trained with it; so I always cover everything else and ask them to fly that way.  In roughly 25% of these scenarios, there is a major glitch.  One time it was the device falling off its suction cup mount, which is bad, but presumably fixable.  The more disturbing thing is that I've seen a Sentry have a major pitch glitch, even with a good mount.  We were flying along, and the indicated pitch began to oscillate between zero and about 15 degrees up, for no explicable reason.  I no longer trust these devices as a backup.

[Ragsf15e]

One big benefit to using the ahrs pfds as primary instead of vacuum is in error reporting.  This cannot be overstated.  If your primary vacuum adi gives up, most of them slowly roll over and die.  By the time you figure it out, you can already have an unusual attitude.  The ahrs pfds have some built in fault detection, can red x themselves, and can auto switch to the backup.  I’m not saying that’s perfect, but it’s much better than nothing.  Since it’s very unlikely both electric and vacuum would fail at them same time, a vac backup would be nice there.  I would think that a completely separate ahrs system would also be fine if it is actually separate.

[PT20J]

37 minutes ago, Ragsf15e said:

One big benefit to using the ahrs pfds as primary instead of vacuum is in error reporting.  This cannot be overstated.  If your primary vacuum adi gives up, most of them slowly roll over and die.  By the time you figure it out, you can already have an unusual attitude.  The ahrs pfds have some built in fault detection, can red x themselves, and can auto switch to the backup.  I’m not saying that’s perfect, but it’s much better than nothing.  Since it’s very unlikely both electric and vacuum would fail at them same time, a vac backup would be nice there.  I would think that a completely separate ahrs system would also be fine if it is actually separate.

I had a KI 256 attitude gyro on a KFC 200 fail once in VFR. It slowly pitched down with the autopilot dutifully following. It was pretty subtle.

I gave a lot of thought to failure modes when designing the new panel. I have a G3X with its ADAHRS powered by ship's power. I have a G5 backup with separate ADAHRS which will run on the G5 battery if ship's power fails. During normal operation, if the G3X ADAHRS fails, it just uses the G5 ADAHRS. The software compares the two ADAHRS, and if there is a soft failure, a MISCOMPARE is annunciated. I have an AV-20-S as a tie breaker if that ever happens. The GFC 500 also has a AHRS internal to the GMC 507 and it will disconnect the autopilot if if senses something amiss with the primary ADAHRS (I know this works because it happened once. It was a false alarm, but better to be too sensitive than not enough so long as it doesn't cry wolf too often).

The ship's battery is 16 Ah. My panel with everything running draws about 10 A. So, I should have over an hour of power if the alternator quits even if I don't shut down non-essential equipment. In the unlikely event that I suffer a catastrophic electrical system failure as Don did, I'd be down to a G5 and an iPad. My iPad is always fully charged because I power it in flight with a dedicated USB power cube.

Lastly, I don't have a turbo or FIKI, so I don't fly all that much IFR which minimizes my exposure.

Skip

 

[jlunseth]

For those relying on the backup batteries in Garmin devices, I just put in the dual 275 setup and was a little concerned when the documentation said that in cold temps, the 1 hr. backup time can fall to 30 mins. In the upper Midwest I have been in temps so cold at altitude that all the windows iced over even with the heater full on. We were really cold in the cabin. Fortunately we were also going like the proverbial bat out of hell because of the tailwinds so it was not that long. One hour is not enough as far as I am concerned, because on occasion I fly places, like over the Rockies, where it would take that long at least to find a place to land and fly an approach, but 30 minutes is not enough even in flatland locations. I opted to keep the vac pump and run a backup vac AI. I am going to stick with that and have abandoned plans to go all electronic. 

I also have had a vac failure in VMC. Mine slowly pitched up as it fell and I gain altitude foolishly trying to follow it since it seemed to be working. Figure it out and got out of the problem.

[Ragsf15e]

1 hour ago, jlunseth said:

For those relying on the backup batteries in Garmin devices, I just put in the dual 275 setup and was a little concerned when the documentation said that in cold temps, the 1 hr. backup time can fall to 30 mins. In the upper Midwest I have been in temps so cold at altitude that all the windows iced over even with the heater full on. We were really cold in the cabin. Fortunately we were also going like the proverbial bat out of hell because of the tailwinds so it was not that long. One hour is not enough as far as I am concerned, because on occasion I fly places, like over the Rockies, where it would take that long at least to find a place to land and fly an approach, but 30 minutes is not enough even in flatland locations. I opted to keep the vac pump and run a backup vac AI. I am going to stick with that and have abandoned plans to go all electronic. 

I also have had a vac failure in VMC. Mine slowly pitched up as it fell and I gain altitude foolishly trying to follow it since it seemed to be working. Figure it out and got out of the problem.

I agree 30 minutes isn’t enough.

I suspect they had to pass some pretty rigorous testing since they’re certified for business jets as well, so maybe “very” cold.  You should pull the CBs on a long flight and see what you get.  I have done it several times on my G5s and they indicate 4 hours remaining.  I have personally let them run off battery for 3 and they still had 20+ minutes remaining.  I was probably not at too cold a temp though…

[Scottknoll]

5.12.5 of the ICA specifies the rundown time of the battery for airworthiness. I know part 91 need not comply. But for an additional data point, it requires 60 min rundown time for aircraft operated above FL250 and 30 min for aircraft operated at or below FL250. It does not specify a temperature to conduct the test at. So you could be in compliance with just a 30 min rundown at normal temps... FL250 @ 1000FPM gives you 5 min to spare to sea level. Scary stuff.

I also imagine the unit generates some sort of heat that may keep the battery above cockpit temperature, but that’s just a wild guess.

[jlunseth]

Yes, the temp at the unit would be an unknown variable. In my aircraft the temps forward of the heat vents are generally quite a bit colder than aft. That would affect temps behind the panel. Probably there would be some amount of heat generated by the devices behind the panel but how much. So the questions is, how cold is it and how long will that battery last? If its cold, the duration is between 30 min and 1 hr., I don't think there is clear information out there about exactly what that duration would be given "x" conditions or how one would measure the conditions. 

[Ragsf15e]

42 minutes ago, jlunseth said:

Yes, the temp at the unit would be an unknown variable. In my aircraft the temps forward of the heat vents are generally quite a bit colder than aft. That would affect temps behind the panel. Probably there would be some amount of heat generated by the devices behind the panel but how much. So the questions is, how cold is it and how long will that battery last? If its cold, the duration is between 30 min and 1 hr., I don't think there is clear information out there about exactly what that duration would be given "x" conditions or how one would measure the conditions. 

I fly a corporate pa-46t that uses an Aspen to backup a g1000.  It’s also tagged as 30 minutes.  I pull the CB once in a while to check, and it’s probably only about 45 minutes worth of battery.  I agree that’s a little scary from the flight levels.

You should try the gi-275 on battery and see what it actually does?

[jlunseth]

39 minutes ago, Ragsf15e said:

You should try the gi-275 on battery and see what it actually does?

I just had them installed. The first thing I need to do is figure out how everything works.

The problem with checking them though, is that batteries are never as good after say 5 years, as the day they were born. There is a requirement in the AFMS to test every 392 days and the procedure is described for the test, that probably helps. I just decided I am not ready to risk my life on the backup batteries in the 275s. I am keeping my vac AI backup just because I then don’t have a single point of failure. I ditched the old King Flight Director/AI and bought an inexpensive vac AI without the director. When the 275s first came out we had a poster on this site who had both 275s go to “red x” mode, something about the system that the two form that failed. Never heard what they figured out with that. Garmin became involved I believe. Could have been an install error, but then who here with more than a few hours has not had an install error cause some kind of problem. That’s why we have redundant systems.