Installation of an Avionics Master Switch - Major or Minor?

kontiki

kontiki

Cleared for Takeoff
Joined
May 30, 2011
Messages
1,181
Display Name
Display name:
Kontiki
I'm soliciting opinions.

I'm looking at the undocumented installation of an Avionics Master switch. It's a simple 35A current protected SPST switch in series with smaller breakers that power to all the Com, Nav, GPS, and XPDR gear on the airplane.

It does happen to be a 35A switch/breaker installed at the load end of a 12 AWG wire from the power bus. It is too big a breaker to protect that wire. At the load end, it protects only about the last 2"-3" of wire between the switch breaker and the other breakers. The 2ft of wire between the switch breaker and the power bus are completely unprotected.

I'm getting ready to pull it out, but I thought I'd see what consensus is. It's my own airplane, I'm still getting acclimated to the wild west world of GA coming from an airline perspective. I do appreciate the ability to share the experienced insights others.
 
It probably could be viewed as a minor alteration, however, if it fails and something bad happens, "they" will say it was a major that wasn't approved.
 
"(xii) Changes to the basic design of the fuel, oil, cooling, heating, cabin pressurization, electrical, hydraulic, de-icing, or exhaust systems."
As in ATA 24, verses ATA 31 and 34?
 
To be honest, I don't really know where the partition between basic and non-basic is.
 
kontiki said:
To be honest, I don't really know where the partition between basic and non-basic is.
Click to expand...

Wonderful little handout from Western Region FAA about thirty years ago with this absolutely sage advice: "It is the opinion of the installing mechanic if there is question about whether a modification is major or minor." If a mechanic is an electronic whiz, a complete radio stack with antennas and such may be minor, but the same task falling to an engine expert may well turn out to be major. That little piece of plastic signed by the Administrator with A&P on it confers a pretty hefty dose of leeway AND responsibility with it. More so the IA.

If you fully understand the ramifications of installing an avionics master switch, then YOUR OPINION may well consider it minor. If Ohm is spelled in Greek for you, then you had best either find a sparky mechanic to advise you OR rip it out by the guts, your call.

Jim
 
No one has asked yet: Why bother?

Reference the numerous threads that discuss the need to isolate the avionics during start-up / shut-down. They seem to indicate it is just as unnecessary as isolating the alternator field.

That said, if I did want to put one in a certificated aircraft, it would be done by an A&P or under the supervision of one.
 
It's simple.

If the technician that installed the switch submitted a 377, it's major. If they didn't, it's minor.
 
kontiki said:
To be honest, I don't really know where the partition between basic and non-basic is.
Click to expand...

Obviously somewhat open to interpretation and why you asked what you asked to begin with.

IMHO the basic design is what came from the factory - wire A goes to Bus B, bus B feeds items x,y,z. If there was a switch installed between bus B and items x,y,z then that is a change to the basic design.

As you said though it was an undocumented change.

In all reality there is no one from the FAA going around asking to look under your dashboard to see if your wiring is factory design or not.

I would go with what Jim said personally and just document it something like "repaired existing wiring connection..."
 
rolivi said:
No one has asked yet: Why bother?

Reference the numerous threads that discuss the need to isolate the avionics during start-up / shut-down. They seem to indicate it is just as unnecessary as isolating the alternator field.

That said, if I did want to put one in a certificated aircraft, it would be done by an A&P or under the supervision of one.
Click to expand...

I'm not willing to subject tens of thousands of $ in avionics to the buss during starter operation. My airplane does not have an alternator switch from the factory though, nor am I going to put one in.
 
kontiki said:
To be honest, I don't really know where the partition between basic and non-basic is.
Click to expand...
The basic design is the Electrical blueprint from the factory.
Would changing the design to include a AV-master, change that basic design?
 
That is the major/minor rat hole that any authority can use against you. If all small things where nit picked and elevated to major there would be a whole lot of airplanes on the ground waiting for approvals.
Tom-D said:
The basic design is the Electrical blueprint from the factory.
Would changing the design to include a AV-master, change that basic design?
Click to expand...

IMHO no. The basic design aspects would be alternator rated for X amps, the system is 12 volts with a negative ground. My airplane was full of capped and stowed wires from the factory for options that were never installed. I threw that crap in the recycle bin because I'm not ever going to install the ground power recepticale, under-wing courtesy light etc etc.
 
Many here do not understand the purpose of the 337. One of the many purposes of the 337 is to aid the trouble shooting and maintenance of the system later.
 
Even if you do consider it major, 43.13 seems appropriate to use as approved data for a 337.
 
bnt83 said:
That is the major/minor rat hole that any authority can use against you. If all small things where nit picked and elevated to major there would be a whole lot of airplanes on the ground waiting for approvals.
Click to expand...
And this is why we are asking for the re-write of part 23. easier approvals of changes to the aircraft.
 
I do believe the addition of a AV-master would be a minor alteration, but should be documented for later reference. I see no need for the FAA to run the whole gambit of a field approval. the IA should be allowed to make this decision as to airworthiness of the minor change.
in cases like this. JMHO
 
bnt83 said:
Even if you do consider it major, 43.13 seems appropriate to use as approved data for a 337.
Click to expand...
There are much advanced methods better than that reference, which btw was written many many years ago.
 
Tom-D said:
Many here do not understand the purpose of the 337. One of the many purposes of the 337 is to aid the trouble shooting and maintenance of the system later.
Click to expand...

True. But even better than a 337 is a diagram of what and how was changed in the maintenance records of the airplane. Whether that is a verbose detailed description in the logbook entry of a minor modification or a reference to a diagram dated and kept as part of the airplane records (just like we keep the original equipment list and w/b signed by Claude Cessna as it walked out the Wichita door) and referenced in the logbook entry, the fundamental question is whether a simple switch between the master bus and the avionics bus, properly protected with a current interrupter (fuse/breaker) is a major or minor alteration. I vote for minor if done properly. Just my 8% of two bits.
 
Regardless of major/minor issue, IS IT SAFE?

Can you compare your installation to that of a similar make/model aircraft that has an Avionics Master ? It would seem that a more recent factory install would be sufficient data to verify the install in your plane (if comparable) regardless of a major/minor classification.
 
I'm backpedaling on this one. It's an alteration to a bus tie. That would be part of the electrical system, not part of the instrument and/or navigation systems even though it controls them. It is an alteration from basic design, uncontrolled to controlled. It is a Major alteration.
 
The difference, Glenn, is that I can sign it off as the IA and you can't. I've been signing stuff like this for nearly 40 years and I have a really good handle on the difference between major and minor. As yet, no nasty visits from the FAA. Well, one, and it was the genesis of the FAA General Counsel's opinion on Owner Produced Parts in which he backed me up WAY beyond my interpretation, but that's just ancient history and the law of the land right now. 21.303(b)(2). You could look it up.

Jim
 
weirdjim said:
I've been signing stuff like this for nearly 40 years and I have a really good handle on the difference between major and minor. As yet, no nasty visits from the FAA. Well, one....
Jim
Click to expand...
Pretty amazing, Jim. As an RII Inspector for almost 30 years I've bought off hundreds of major repairs and alterations. Procuring aircraft from everywhere can really create problems for flight crews, so, we were constantly performing fleet standardization campaigns, which were usually major alterations. I'm talking 727, 757, L-1011, DC10. Zero visits from the FAA.
 
Glenn, you have your authority from your airline, which is one step removed from the FAA. My authority is directly from the FAA. You come on to what is a SMALL AIRPLANE forum and try to tell us how your airline experience is directly applicable to small airplanes. It ain't.

I spend a fair number of years with a VERY major airline and I'd never TRY to pull something like an avionics master installation on a DC-3 (the first airliner I worked on) or a 737-400 (the LAST airliner I worked on). Never. No way.

But I've worked on small airplanes for nearly 60 years, which you obviously have never turned a wrench on. So don't come in here and tell those of us who have spent the majority of our lives keeping these little puddlejumpers in the air how to do it.

And I asked you what your FAA credentials/certificates were and you still haven't answered it. My sense is that you don't have one scrap of paper from the FAA that says that you are a mechanic or a pilot, so don't come on here and tell us how great you are because you work on big aluminum tubes. Most of us have done so and have no respect for those of you who think you are mechanics because your airline says you are. You ain't.

Jim
 
weirdjim said:
True. But even better than a 337 is a diagram of what and how was changed in the maintenance records of the airplane. Whether that is a verbose detailed description in the logbook entry of a minor modification or a reference to a diagram dated and kept as part of the airplane records (just like we keep the original equipment list and w/b signed by Claude Cessna as it walked out the Wichita door) and referenced in the logbook entry, the fundamental question is whether a simple switch between the master bus and the avionics bus, properly protected with a current interrupter (fuse/breaker) is a major or minor alteration. I vote for minor if done properly. Just my 8% of two bits.
Click to expand...
Remember what goes into block #8?... a complete description of the alteration. which can be a drawing. that becomes part of history of the aircraft. and can be gotten from FAA @ OKC.
 
There again, Jim, your senses are afu. My authority also comes from the FAA, (my A&P, which was paper, but now is plastic), and my company, based on experience, training, and recurrency, just like you. Requirements are spelled out in CFR Title 14, just like yours, and my company's General Maintenance Manual. I worked on F-4D and T-38 in the Air Force for 4 years before going to A&P school (Columbus Technical Institute), and I worked on Gulfstream 159 (G-1) aircraft for 4 year, right out of A&P school. Not all big aluminum tubes. Greatest compliment I ever received was from a G-1 pilot that told me I was a goldmine for the little company we worked for. Besides my A&P, I have two letters from the FAA, from when I had considered seeking employment there. They acknowledge I meet the requirements for Aviation Safety Inspector, Maintenance and Avionics. I didn't complete the application process due to pay disparity. I don't need your approval.
 
Last edited:
weirdjim said:
I spend a fair number of years with a VERY major airline
Jim
Click to expand...
Which translates to: So few years...

weirdjim said:
I've worked on small airplanes for nearly 60 years
Jim
Click to expand...
You must be a Charles Taylor Master Mechanic Award Recipient! Congratulations! Why isn't your name on the Honor Roll?
 
Last edited:
Another reason why experimental amateur built is the most practical path for small private aircraft ownership.
 
Tom-D said:
Many here do not understand the purpose of the 337. One of the many purposes of the 337 is to aid the trouble shooting and maintenance of the system later.
Click to expand...

I totally disagree with you. the 337 is a legal form. it is titled major alteration or repair. not major alteration or repair, or minor or description document. it is to meet the requirement of the regulations of a major repair or alteration. the aircraft records should be used to document a minor alteration or repair. the 337 has been abuse for years and is now a scapegoat for many IA's and FAA people to cover their backside. If you deem it a major go ahead and fill out the 337, that's your call and I would not fault you at all, but if a minor then the form is not required and should not be fill out. its not the legal purpose of the form.
 
unsafervguy said:
the 337 has been abuse for years
Click to expand...

That can be said about all of them including but not limited to STCs, 8100-9, 8110-3 and 8100-11, not just 337.

The term "FAA approved" is the most abused in the industry. Sad really but schools around country and even FAA inspectors themselves frequently label OEM manuals as FAA approved, I'd say a good 65% of them aren't.
 
You must log in or register to reply here.
Back
Top