Avionics power off mid-flight

[swsmith]

11 hours ago, Will.iam said:

I had mine fail in my 252 the first year i owned her. First time was after taxiing on Oshkosh grass to the runway and i just figured it was a loose connection but still unnerving to loose everything especially ads-b when flying out with everyone visually. At annual i had Brian come over and he said this is a common problem for that 40+ year old relay it was there for incase you start the engine with the avionics on it would turn them off while the engine started to avoid electrical spikes to the radios. The original one is no longer available as it’s replaced with a more robust one problem was the new robust one was bigger in size than the original, and would not fit in the cramped space behind the avionics rack. He recommended putting in a circuit breaker switch on the panel, which I elected to have him do and that way whenever that finally fails much easier to replace in the future without taking the panel apart. 

Thanks this is helpful. What does the circuit breaker switch look like? Did you remove the original avionics switch?

[Will.iam]

11 minutes ago, swsmith said:

Thanks this is helpful. What does the circuit breaker switch look like? Did you remove the original avionics switch?

Ill take a picture next time I’m in the plane yes old relay was removed. Also realize if you forget and left the avionics switch on and start your engine you are subjecting them to voltage spikes as you don’t have the safety of the relay anymore but it’s obvious to me if the switch is on by all the radios going and garmin screen lit up and i just make sure to turn it off before i crank the engine. 

[jlunseth]

So, when this happened you had all your analogs and vacuum operated AI to bring you safely home. Another incident that says the race to all electronics is misguided. Don’t get me wrong, I have all those nifty electronics, but I am keeping the analogs, a vacuum AI, airspeed, VSI, altitude, the only one you can really afford to lose is the analog TC, replace it with a good backup AI.

[Yetti]

Did we find the model of this plane.

The Avionics relay is Normally Closed.   So when the master is turned on the Relay engages and goes to Open (no power to the electronics)   This way if the relay fails the electronics should stay powered.   To venture a guess your mechanic has misdiagnosed the problem unless he knew of the NO relay position.

The Comm switch applies power to the relay and make it go to open state (no power to the electronics)

There is also a wire that comes from the starter relay.   When you apply power to the starter the power is also applied to the Comm Relay and it will turn your avionics off.  There is an inline diode that keeps power from flowing back to the starter relay and engaging it.

The relay is normally on the passenger right sidewall above the intake duct.   There is a rib that has threaded screw holes in it.  If you don't have com panes it will be a bith to get to.   Read.  Take out passenger seat and lay upside down on the floor and work blindly.

 

Possible failures. Bad contacts on the relay.   Remember the relay is On in the resting state.

The switch or a short sent power to the relay and it opened.  Take your phone and take pictures behind the pane of the switch and make sure no screws have dropped down on things.

In a pinch a regular automotive Bosch type 5 pin relay has a NC circuit in it and will work just find on 12v systems.

 

So use Pin 30 and 87a for the avionics circuit.   https://www.stockwiseauto.com/bosch-0332209158-changeover-mini-relays-5-pins-12-v-20-30-a?gclid=CjwKCAiAqaWdBhAvEiwAGAQltsVuRoRccwPB4DT_Qprzg8wOdAOY1oD6_z2cNIki1E1TOEGUT4ev8hoCp2IQAvD_BwE&

 

 

 

 

[Fly Boomer]

12 minutes ago, Yetti said:

The relay is normally on the passenger right sidewall above the intake duct.   There is a rib that has threaded screw holes in it.  If you don't have com panes it will be a bith to get to.   Read.  Take out passenger seat and lay upside down on the floor and work blindly.

This is good info and I want to understand how to fix it if/when my radio master relay goes TU, but I got lost at the sentence "If you don't have com panes it will be a bith to get to."  I'm not a fan of lying on my back trying to get behind the panel so, if there is a better way ...

[Sue Bon]

1 hour ago, jlunseth said:

So, when this happened you had all your analogs and vacuum operated AI to bring you safely home. Another incident that says the race to all electronics is misguided. Don’t get me wrong, I have all those nifty electronics, but I am keeping the analogs, a vacuum AI, airspeed, VSI, altitude, the only one you can really afford to lose is the analog TC, replace it with a good backup AI.

What about the four-hour battery in the G5? Shouldn't that be enough backup? I just removed my only vacuum AI so please say yes.

[PT20J]

17 minutes ago, Sue Bon said:

What about the four-hour battery in the G5? Shouldn't that be enough backup? I just removed my only vacuum AI so please say yes.

That’s what I’ve done. Just need to check the battery before flight and replace when it starts to lose capacity.

[Fly Boomer]

1 minute ago, PT20J said:

That’s what I’ve done. Just need to check the battery before flight and replace when it starts to lose capacity.

How often do they need to be replaced?  Have you had to replace yours?

[PT20J]

3 minutes ago, Fly Boomer said:

How often do they need to be replaced?  Have you had to replace yours?

Mine is only 14 months old and it’s still good. Li-ion batteries don’t like heat, so airplanes that live in hot climates may have shorter battery life than those in cooler locations.

[Yetti]

1 hour ago, Fly Boomer said:

This is good info and I want to understand how to fix it if/when my radio master relay goes TU, but I got lost at the sentence "If you don't have com panes it will be a bith to get to."  I'm not a fan of lying on my back trying to get behind the panel so, if there is a better way ...

Before the J model came along the windscreen was more abrupt angle.  so prior F and C models had comm access panels below the windscreen from the out side of the plane that were screwed on with a jilion screws.    This allowed access to the back of the panel without pulling the panel.    Some planes with the new windscreen had smaller comm access panels lower on the side.   If you have one of these the relay is right below it.

And I designed the new panel over on the Starboard side easier to pull.  

Edited December 26, 2022 by Yetti

[Yetti]

With all the older radios, they pulled a lot of amps.   I think I added it up once and the radio master relay was maxed out on amps.   Usually 40 year old relays that are run at max will fail.

[Fly Boomer]

2 minutes ago, Yetti said:

This allowed access to the back of the panel without pulling the panel. 

Got it.  I had forgotten about those somewhat ingenious access panels.  I heard that they often leaked.  Back to "on my back trying to hold my head up and get my bifocals aimed in the right direction".  Thanks.

[Yetti]

1 hour ago, Fly Boomer said:

Got it.  I had forgotten about those somewhat ingenious access panels.  I heard that they often leaked.  Back to "on my back trying to hold my head up and get my bifocals aimed in the right direction".  Thanks.

To be sure there are two relays on that 1" bar.   On my plane the back one is for the landing light relay and the front was the COmm relay.   Your mileage may vary.

Edited December 26, 2022 by Yetti

[Ragsf15e]

1 hour ago, Fly Boomer said:

How often do they need to be replaced?  Have you had to replace yours?

My g5 batteries are ~4 years old and are still fine on both ADI and HSI.  I have tried them both off ships power for over 3 hours and they still had ~20% remaining.

[jlunseth]

3 hours ago, Sue Bon said:

What about the four-hour battery in the G5? Shouldn't that be enough backup? I just removed my only vacuum AI so please say yes.

One of the issues you discover when you have installed some of these all-electronic systems is that there are peripherals and information sources that are required, or required to enable features you thought you were going to have. They are also connected to other electronic devices to form the system. You have to be an electronics engineer to understand what risks you are taking by installing a particular device and what could happen if one of the peripherals or information sources goes down. It is way to easy, if you do not have the electronic engineering background, to focus on marketing about individual features and think they are going to solve your problem. Yes, a four hour backup would be nifty even if the actual life after five or ten years in the aircraft is down to half. But what else is there that could bring the instrument down. There is, after all, a red “X” page in the manual for the G5. Why is that? If it is connected to another device and that device fails or the network connection fails, is there the potential for unexpectedly bringing down the whole system? Was it a design error or maybe an installation error? Do you really care since you are the PIC in the air dealing with the problem and it is your life on the line, not the designer’s or the installers. I have installed, over the years, a 430AW to drive the AP, then a 750 GTN Xi to drive it instead, then a backup AI 275, then dual reversionary 275’s. Each time there have been gotchas and/or pilots on our site have experienced unexpected system failures that were not anticipated, sometimes in IMC.

There is nothing like a good, old, second something that is not part of the nifty system and is a completely different technology.

Don’t get me wrong. My installer has been magnificent. The issue is that when you install a bunch of components on your panel they become a system, and nobody other than you has really taken responsibility for insuring the safety and redundancy of the system.

[Sue Bon]

1 hour ago, jlunseth said:

One of the issues you discover when you have installed some of these all-electronic systems is that there are peripherals and information sources that are required, or required to enable features you thought you were going to have. They are also connected to other electronic devices to form the system. You have to be an electronics engineer to understand what risks you are taking by installing a particular device and what could happen if one of the peripherals or information sources goes down. It is way to easy, if you do not have the electronic engineering background, to focus on marketing about individual features and think they are going to solve your problem. Yes, a four hour backup would be nifty even if the actual life after five or ten years in the aircraft is down to half. But what else is there that could bring the instrument down. There is, after all, a red “X” page in the manual for the G5. Why is that? If it is connected to another device and that device fails or the network connection fails, is there the potential for unexpectedly bringing down the whole system? Was it a design error or maybe an installation error? Do you really care since you are the PIC in the air dealing with the problem and it is your life on the line, not the designer’s or the installers. I have installed, over the years, a 430AW to drive the AP, then a 750 GTN Xi to drive it instead, then a backup AI 275, then dual reversionary 275’s. Each time there have been gotchas and/or pilots on our site have experienced unexpected system failures that were not anticipated, sometimes in IMC.

There is nothing like a good, old, second something that is not part of the nifty system and is a completely different technology.

Don’t get me wrong. My installer has been magnificent. The issue is that when you install a bunch of components on your panel they become a system, and nobody other than you has really taken responsibility for insuring the safety and redundancy of the system.

Hmmm. I get what you're saying, but it's too late. My vacuum pump was removed two weeks ago. I can't go back now.

I guess if I have a complete electronic failure that wipes out my panel, plus failure of the backup g5 battery, all in full IMC with no quick escape, I will accept that it is just my time and I will go in my cockpit, which is my happy place.

[jlunseth]

One possibility is to leave some of the electronics unconnected from rest of the system. That’s what I did with my 430AW. I left it in the panel but it is connected to its own CDI and not connected to anything else. If the GTN/275’s/AP go down together I have the 430AW and the CDI for navigation. I could have connected it to the system so if the GTN went down I would be able to drive the AP with the 430, but I would sacrifice safety. I also have the vacuum AI. So what if I have to hand fly, I will be perfectly safe with functioning instruments. Even if all electrical goes out I will have the vacuum AI. I put in a new pump this summer. After lots of actual IMC and reading about others’ system failure, you start to think about these things and ignore some of the marketing.

[PT20J]

55 minutes ago, Sue Bon said:

Hmmm. I get what you're saying, but it's too late. My vacuum pump was removed two weeks ago. I can't go back now.

I guess if I have a complete electronic failure that wipes out my panel, plus failure of the backup g5 battery, all in full IMC with no quick escape, I will accept that it is just my time and I will go in my cockpit, which is my happy place.

You can drive yourself nuts overthinking this stuff. First of all, the electronic instruments are inherently more reliable than mechanical gyros and vacuum pumps. It's the same technology as laptop computers which I have been using exclusively at work and home for over 20 years, probably ten hours a day, and I have had exactly one failure (a memory card) in all that time. 

It doesn't make sense to me to design past single failures because the joint probability of uncorrelated multiple failures is infinitesimally small given how seldom modern avionics fail in the first place.  So,  a system with a G3X, G5, GTN and GFC 500 is pretty robust. I also carry an iPad. I figure with all this capability I'm much safer than all those years I flew with only one AI and a vacuum pump. Those that wear suspenders with their belt buy a portable AHRS device to pair with the iPad.

A total electrical failure is a pretty rare single point failure. I'll bet it happens less frequently than engine failures. Let's see, how many engines do we have?

Skip

 

[Will.iam]

3 hours ago, Sue Bon said:

Hmmm. I get what you're saying, but it's too late. My vacuum pump was removed two weeks ago. I can't go back now.

I guess if I have a complete electronic failure that wipes out my panel, plus failure of the backup g5 battery, all in full IMC with no quick escape, I will accept that it is just my time and I will go in my cockpit, which is my happy place.

Sue just add one of these it’s cheap life insurance when you are in the soup and need to keep the greasy side down and everything else went electrically dark. 
https://dynonavionics.com/pocket-panel.php

 

[201Mooniac]

I think one important thing is to go out and fail things and see what happens.  There are certainly installation and configuration issues that can cause bad outcomes but you can test this by failing each and every device one at a time or in combination to see what the results are.  In my case, I have turned off the avionics master to see what happens along with pulling each circuit breaker in turn.  I know what the failure modes are and I completely agree with Skip that this has a better MTBF than the vacuum pump and iron gyros I used to fly with.  I happen to be an electrical engineer and I design consumer electronics so I have an understanding of the risks and the benefits and decided to remove my vacuum pump.  While I know my failure modes, I do fly with an AERA 660 and an iPad with an internal GPS to augment my GI 275.  I'm likely going to add a GDL 50 in the near future as well.

[Ragsf15e]

4 hours ago, jlunseth said:

One possibility is to leave some of the electronics unconnected from rest of the system. That’s what I did with my 430AW. I left it in the panel but it is connected to its own CDI and not connected to anything else. If the GTN/275’s/AP go down together I have the 430AW and the CDI for navigation. I could have connected it to the system so if the GTN went down I would be able to drive the AP with the 430, but I would sacrifice safety. I also have the vacuum AI. So what if I have to hand fly, I will be perfectly safe with functioning instruments. Even if all electrical goes out I will have the vacuum AI. I put in a new pump this summer. After lots of actual IMC and reading about others’ system failure, you start to think about these things and ignore some of the marketing.

My opinion, so take it for that… navigation is the least of your worries if you have a major failure.  The key is being sure you’ll have an ADI.  If you have an ADI, then follow the comm out rules for lateral and vertical with your phone, ipad, etc and you’ll be fine.  I can navigate very close to 430w capability with my phone.  Obviously no glide slope, but I have FF on 2 phones and an iPad.  That’s 3 x gps.  
 

The one thing I would like in addition to an ADI is a radio.  With a radio you get nav (no gryo vectors), terrain and traffic avoidance and other help from atc.  Maybe even an ASR approach.  I have a portable, but your 430 would be nice for comm.  The extra navigation it provides? Meh.  Not necessary.

[EricJ]

15 minutes ago, Ragsf15e said:

My opinion, so take it for that… navigation is the least of your worries if you have a major failure.  The key is being sure you’ll have an ADI.  If you have an ADI, then follow the comm out rules for lateral and vertical with your phone, ipad, etc and you’ll be fine.  I can navigate very close to 430w capability with my phone.  Obviously no glide slope, but I have FF on 2 phones and an iPad.  That’s 3 x gps.  
 

The one thing I would like in addition to an ADI is a radio. I have a portable, but your 430 would be nice for that.  The extra navigation it provides? Meh.  Not necessary.

+1 on all that. 

I did a practice approach just using my tablet, which has geo-synched approach plates in Avare, and my air instruments and a G5 for ADI.   It was a lot easier than I had expected, and got me pretty close to where I would have been with vertical and lateral guidance from the GPS.    Even with a total electrical failure I have the G5s for quite a while on their batteries, the compass will always work, and the air instruments will always work, and my tablet(s) will work for a long time, too.   I have a stratux that has its own battery that is plugged into ship's power, so if power dies it'll run for hours on that battery.   It has a GPS and AHRS in it, too.

Fingers crossed I'll never, ever need it, but power failures aren't something I worry about too much any more.    I think I'm way better off than depending on a vacuum pump that can randomly die any time after around 500 hours or so.

With two G5s they can replicate each other, so even with a power failure you can turn one of them off and run the other until the batt dies, and if you're not on the ground by then, turn the other one on.   Even with crappy batteries that should give you two to four hours, which one would hope would be more than enough to get on the ground somewhere useful.

I think practicing an approach on a geo-synched approach plate on a tablet can be practiced on a lot of simulators, too.

 

[PT20J]

1 hour ago, EricJ said:

I think practicing an approach on a geo-synched approach plate on a tablet can be practiced on a lot of simulators, too.

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[T. Peterson]

3 hours ago, Will.iam said:

Sue just add one of these it’s cheap life insurance when you are in the soup and need to keep the greasy side down and everything else went electrically dark. 
https://dynonavionics.com/pocket-panel.php

 

That’s cool!! I didn’t know such an animal existed. Thanks for posting. You’re an ok fella no matter what everyone else says!

I bet Sue feels a lot better also.

[carusoam]

Congrats SWS!

For a job well done…. And reporting it so well!

 

Things we know about the avionics ‘fail proof’ circuit…

1) It works really well when a power line fails to supply power to the relay… the relay keeps itself closed, as it is normally closed.

2) When the relay itself fails… this is where the problem is… if it decides to fail partially open, it stops flowing the required electrons…

3) the European version of the FAA… requires a second power line to feed the avionics bus in the event of a rare relay deciding not to work properly…  this comes as a surprise when importing fine aircraft to Europe!

 

Around here… we see a few various relays croak every year…. Most often a starter relay…

 

If you fly in IMC…

Make sure you have a second source of attitude and communications….

Verify they are on different sources of power than the rest of the ship.  Either vacuum or battery…

 

There are about a dozen relays in a Long Body… many are the same type… but the avionics master is going to be NC…  fortunately, it won’t be a Mooney specific part, so there will be many supply houses with one in stock…

 

PP thoughts only, not a mechanic… last time I bought a relay it took about eight weeks to get….  Faster than a battery ordered at the same time…

Best regards,

-a-