Question Avionics Circuit Breaker Switch Fail

[Neal]

I ordered spare push pull breakers from CubCrafters. Price was reasonable. The 50A breaker is $315!!! So that's a no for me for the spares kit.

 

[Neal]

I realize I probably missed the ignition breakers on the front of the seat which I believe are 40A's? Doubt I'll get anymore, have what I have for now.

 

[Neal]

I was wrong, the ignition breakers forward of the seat are 5A.

Opened my package from CubCrafters and the packaging for breaks is all aircraft spruce so just buy direct from them.

 

[belchfire]

Many years ago a friend of mine blasted off out of KBFI in a rented Mooney 201 into the overcast. After getting radar contact with departure and a getting on course the entire radio stack died…in actual IFR conditions-the master CB Switch had tripped.

After extracting a bunch of seat cushion from his nether regions and a few unsuccessful reset attempts all of the radios were turned off and the avionics master successfully reset with no load. In a trial and error method radios were turned back on and it was determined that one nav/com with no GS receiver would not trip the master-anything more and Still, no xpnder, no DME, no ADF (it was a while back!), no second nav/com and no precision approach capability!

After re-establishing contact with SEA and declaring my friend got vectored around and pointed back to BFI which fortunately wasn’t that bad-about a thousand and 2 or so and he got back in okay on a localizer approach.

In an effort to learn from the experience of others, when I set up an IFR panel back in the day I had two Master Avionics switches installed in parallel. In order to ensure continued redundancy I would use one on odd numbered days and the other on even number days.

There is little enough redundancy in a single engined airplane and to expose yourself to a single point failure of that kind is an easy fix with almost no cost in weight.

 

[Cactus Charlie]

I understand that most Garmin LRUs can accept multiple power sources, and I further understand that the IBBS can be connected to more than one device.

While some Garmin LRU have 2 independent power inputs I doubt it is true that "most" Garmin LRU have two independent power inputs. GPS 175 (and family) do not, GTX 345R does not, GAD 29 does not, GMC 305 does not, GSA 28 servos do not, G5 does not (but does have independent battery backup option).

In the CC Exec Glass aircraft IBBS powers GDU 465, GSU 25C (feeds GMU 22), and GEA 24. A good IBBS battery will power these for 2 hours or more. Adding loads would reduce that but, if load does not have independent power inputs, additional power switching would be required.

The standard Exec Glass Avionics switch breaker is 10 A and I suspect it is barely adequate. Very surprised that CC did not increase the rating for the IFR fit.

Does the Avionics switch need to be a breaker type? Each avionics LRU has its own CB.

If you are concerned about loss of everything on the Avionics bus then consider two independent Avionics switches. How would you decide which LRU to put on Avionics-1 and which on Avionics-2. You have likely have only one audio panel, one transponder, and one IFR GPS.

I don't have the audio panel in my IFR capable FX-3. I could rig an alternate power source for the GTR 200 but it's not high on the list of priorities.

 

[Cactus Charlie]

The standard Exec Glass Avionics switch breaker is 10 A and I suspect it is barely adequate. Very surprised that CC did not increase the rating for the IFR fit.

CC G3X Schematic shows the Avionics switch breaker as 10 A.

CC schematic -103 CC11-160 POWER DISTRIBUTION AND START CIRCUIT shows a 20 A Avionics switch breaker. This schematic is listed as applicable to the FX-3.

The equivalent schematic in the maintenance manual template is of too low a resolution for the CB rating to be read clearly but I think it is 20 A.