Avionics power off mid-flight

[swsmith]

So I had a fun experience the other day. I was on a local flight shooting some instrument approaches and during an RNAV approach all my avionics suddenly switched off.

Our next step was calling up ATC on the phone and declare. This was a fun experience since they couldn’t hear us at first but when they did finally hear “N231ER Declaring an emergency, complete avionics failure, IFR” you could hear the ATC controller hurriedly calling her boss. 
 

I lost com 1&2, GPS, Transponder, JPI engine monitor, intercom, and nav radios. Luckily we still had power to the lights, gear and flaps since it was at night. I’ve got a pretty well equipped panel and didn’t have a backup radio so cell phone was the only option. 
 

We got on the ground safely at the nearest airport and started to troubleshoot. We (well really the mechanic) diagnosed the issue was with the Avionics relay, it was no longer creating a circuit. We got the part number (MB4413) and have been trying to track it down. Any leads would be appreciated. I’ve called BAS, Mid-Continental and Lasar. 

Our best option seems to be the avionics relay upgrade kit which is currently $1800 from Lasar. Ouch

Heres a pic of the panel:

we lost everything to the right of the JPI. 

Edited December 21, 2022 by swsmith
Spelling mistakes

[Ragsf15e]

4 hours ago, swsmith said:

So I had a fun experience the other day. I was on a local flight shooting some instrument approaches and during an RNAV approach all my avionics suddenly switched off.

Our next step was calling up ATC on the phone and declare. This was a fun experience since they couldn’t hear us at first but when they did finally hear “N231ER Declaring an emergency, complete avionics failure, IFR” you could hear the ATC controller hurriedly calling her boss. 
 

I lost com 1&2, GPS, Transponder, JPI engine monitor, intercom, and nav radios. Luckily we still had power to the lights, gear and flaps since it was at night. I’ve got a pretty well equipped panel and didn’t have a backup radio so cell phone was the only option. 
 

We got on the ground safely at the nearest airport and started to troubleshoot. We (well really the mechanic) diagnosed the issue was with the Avionics relay, it was no longer creating a circuit. We got the part number (MB4413) and have been trying to track it down. Any leads would be appreciated. I’ve called BAS, Mid-Continental and Lasar. 

Our best option seems to be the avionics relay upgrade kit which is currently $1800 from Lasar. Ouch

Heres a pic of the panel:

we lost everything to the right of the JPI. 

Wowza, that probably wasn’t fun! Nice job thinking of the phone. How did you have their number?

[Boilermonkey]

I had a similar issue when the avionics switch failed on approach in IMC.  That was in my prior M20C.  I was hand flying the approach anyway, so I already had pitch and heading dialed in.  I held everything constant and broke out around 800ft AGL, prior to the missed approach, and landed.  I did have Foreflight with a Stratus 2 with AHARS.  I had that running at the time and it was an invaluable backup in that emergency.  I continue to use a Stratus 2 separate from my panel just in case I have an electric failure. 

I taxied off and got light gun signals!!   That was an interesting day.  We fixed the switch and I continued the day with three more legs and 3 more approaches going to and from Indiana to New York.

[affricate]

Good job 

[Pinecone]

I had a total electrical failure in a T-34.  I was coming back from Springfield Mass, where we did an airshow with my friend's T-34.  I was bringing to MD for a show the next weekend.

It was solid IMC from about 300 feet.  I was being vectored and descended for the GPS circling approach at the home drome.  I broke out before the approach and about 30 seconds later, POOF, everything electric was gone.  And so that meant everything was gone.  ALL the instruments and avionics and flaps and gear.

I cranked down the gear and landed.

Lucky it did not happen in the previous hour, or I would not by writing this.

The master relay failed.  It was mounted up on the firewall, but right under an access panel, I think for brake fluid.  The drain line clogged up, so the space under the access filled up with water and leaking on the master relay.

When I do a panel upgrade, I plan on dual avionics busses.  Two paths from battery to split busses with one attitude and com/nav on each one.

[PT20J]

Nice job keeping your cool!

It would be interesting to know what the actual failure mode was. The avionics relay is "fail safe" in that it is off when energized. So, a failure of the coil or wiring or avionics master should turn the radios on assuming that the contacts are good and that the internal parts of the relay can move. 

If this happened to me, I would first try cycling the avionics master switch a couple of times. If that didn't work, I would try pulling the Aux Bus circuit breaker since the avionics relay is powered from the aux bus. The aux bus also powers the row of circuit breaker switches on the panel, so you would lose all those items (mostly lights).

Skip

[swsmith]

12 hours ago, Ragsf15e said:

Wowza, that probably wasn’t fun! Nice job thinking of the phone. How did you have their number?

ForeFlight

[Fly Boomer]

16 hours ago, swsmith said:

I lost com 1&2, GPS, Transponder, JPI engine monitor, intercom, and nav radios. Luckily we still had power to the lights, gear and flaps since it was at night. I’ve got a pretty well equipped panel and didn’t have a backup radio so cell phone was the only option.

I wonder if that massive jolt of adrenaline takes days off your life.  Or maybe an occasional jolt might be beneficial in some way.

Maybe you didn't get the jolt.  Sounds like calm, cool, and collected. 

[Ragsf15e]

46 minutes ago, swsmith said:

ForeFlight

Ok, I’m searching for it.  That’s good info.  Can you tell me where in FF?

[RobertGary1]

I had a secondary installed when I had my panel redone. Its labeled as "ground power" to power a limited set of equipment before start up but serves this dual purpose.

 

-Robert

[N201MKTurbo]

Although they are hard to find, you could find a switch that would carry the avionics load and mount it under the panel or some out of the way place on the panel. You could even use a circuit breaker and put one of those removable rings on it to keep it open. Label it "Emergency Avionics". The switch or breaker would bypass the avionics relay and supply power to the avionics buss.

[swsmith]

10 minutes ago, Ragsf15e said:

Ok, I’m searching for it.  That’s good info.  Can you tell me where in FF?

Depends on the airport. We were shooting the RNAV into KTIW, we found approach’s number but not tower’s number. Approach then contacted the tower for us. 

[hais]

Great job getting down safely!

Do lost comms procedures assume a working transponder? I wonder whether that condition is unsafe for separation. 

[Aerodon]

I have a spare 28V avionics relay from a 1996 M20.

But I am curious as to how yours failed - the relays are supposed to be 'normally closed' (on) and held in the off position by power.  In my Seneca, the voltage could drop during cranking, bringing the avionics momentarily on.

Aerodon

[Ragsf15e]

47 minutes ago, swsmith said:

Depends on the airport. We were shooting the RNAV into KTIW, we found approach’s number but not tower’s number. Approach then contacted the tower for us. 

Thanks. Nice job handling the problem!

As others said, these are typically set to fail to avionics on.  Weird that yours went off.

[PT20J]

57 minutes ago, hais said:

Great job getting down safely!

Do lost comms procedures assume a working transponder? I wonder whether that condition is unsafe for separation. 

No. I asked a controller once how they dealt with lost coms and transponder and was told it happened so infrequently that they didn't assume anyone followed procedures and they just cleared out the airspace everywhere you might reasonably be or go. I imagine the ripple effect near a busy terminal like Seattle would be interesting to unravel.

[A64Pilot]

The contacts inside the relay itself could have corroded over time and be what failed. Relay still clicks but no power gets through, a lot like a starter that will work once you “tap” it.

I think an emergency switch that bypasses the relay is the easiest and safest answer, worst case if it was accidentally turned on the only thing that would happen is that the Avionics couldn’t be turned off without turning off the Master.

Which brings up that it’s another relay that could fail, and if it did, it would take down everything electric. Master that is.

‘But if you pull the Aux Bus with Master off does it energize the Avionics ? Something odd happens if you pull it I remember that.

Personally I think keeping Vacuum instruments prudent, but having an electric back-up, I installed a back-up artificial horizon in my Maule and an Air Wolf wet vacuum pump as they are very reliable and will out last the engine. The standby attitude indicator we had at the plant and they are insanely expensive.

A battery back-up AHARS and an Ipad ought to get you down without breaking the bank.

[PT20J]

Phone numbers are also listed in section 4 of the Chart Supplement (What used to be called the Airport/Facility Directory). I'm sure we all have that handy. But you could always load up a few in your contacts. However, I think if you used the clearance delivery number for any airport and declared an emergency they would be able to deal with it and/or give you the phone number for the appropriate facility.

[A64Pilot]

Good thing the phone worked, most often since they went digital they won’t work at anything but low altitude, low as in I guess about 2000 ft.

‘Next time your out flying try it, you most likely can’t make a call, but can usually get a txt out for some reason.

[bradp]

8 hours ago, Aerodon said:

I have a spare 28V avionics relay from a 1996 M20.

But I am curious as to how yours failed - the relays are supposed to be 'normally closed' (on) and held in the off position by power.  In my Seneca, the voltage could drop during cranking, bringing the avionics momentarily on.

Aerodon

Don - I had one fail in the “open” position. The wire to the relay must be 10 or 12 awg.  It is relatively heavy for the quick disconnect 1/4 inch paddles on the relay housing.  The backside or the paddle itself had wiggled loose in its housing not allowing the contacts to physically touch when the magnet was de-energized. 
 

@swsmith I don’t have easy access to the electrical schematics or IPC for your model - but in the link I shared you can clearly see that there are two sets of identical contractors.  The control circuit for the relay are the small gauge wires. In my circumstance, we simply swapped the 12V and avionics bus cables to the other side and called it a day. 

If you can’t find the MB-4413 relay- look at Schneider electric legacy relays.   These are simple electrical parts, so there is language in the regs that you may replace with a certified (ie IEEE) replacement component that meets the OEM specifications - you should be good to go. 
 

https://www.se.com/us/en/brands/local/serelays/

https://photos.app.goo.gl/zdw5TWQoQCShg3pC9

[PT20J]

My 28v J uses a Kissling 28.64.01.  These are available. There are 12v versions also available. https://www.te.com/content/dam/te-com/documents/industrial-and-commercial-transportation/global/kissling-documents-data-sheets/Data_Sheets_Documents_Kissling/contractors/KI-Relay26-100A-ds-a4-K1166685-en-2012.pdf

[Aerodon]

59 minutes ago, bradp said:

I had one fail in the “open” position. The wire to the relay must be 10 or 12 awg.  It is relatively heavy for the quick disconnect 1/4 inch paddles on the relay housing.  The backside or the paddle itself had wiggled loose in its housing not allowing the contacts to physically touch when the magnet was de-energized. 

Yes, the Seneca relay was something like that, looked more like something you would install in a tractor.  I would definitely be replacing a spade connect relay with something better.

The Kissling relay that I have is 100A, with nice studs/lock washers and nuts for good reliable connections.  And it makes sense to have a nice heavy duty 100A  relay to switch maybe 20A/28V on at once.

Aerodon

 

[Will.iam]

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. 

[bradp]

On 12/21/2022 at 10:59 PM, PT20J said:

My 28v J uses a Kissling 28.64.01.  These are available. There are 12v versions also available. https://www.te.com/content/dam/te-com/documents/industrial-and-commercial-transportation/global/kissling-documents-data-sheets/Data_Sheets_Documents_Kissling/contractors/KI-Relay26-100A-ds-a4-K1166685-en-2012.pdf

Those look really nice - all the 12 V versions are unfortunately normally open. 

[PT20J]

4 minutes ago, bradp said:

Those look really nice - all the 12 V versions are unfortunately normally open. 

Oops, I missed that.