Fuses and Breakers
Fiddle with them in Flight? Part II

At 08:53 PM 10/13/97 +0000, you wrote: >--> RV-List message posted by: "Tim Lewis"

The "accessible breaker vs inaccessible fuse" debate is interesting to watch, and Bob Nuckoll's articles have had an impact on how I designed my electrical system (RV-6AQ, panel mostly done). I don't agree with everything Bob advocates, but he provides a lot of good food for thought.

It seems to me there are three main arguments in favor of inaccessible fuses:

1. A fuse panel is cheaper than a bunch of breakers.

But just as important for most popular airplanes, they don't have to take up panel space and they install in a fraction of the time with a lot less parts, hence more reliable . . .

2. A blown fuse/tripped breaker usually means something is very wrong, and you won't be able to fix it in flight (so design the panel so nothing on it is flight critical)

3. You can kill yourself fiddling with breakers in flight when you should be flying the airplane.

My opinions on the arguments:

1. True. But the difference is so small that in the overall cost of an RV it really doesn't matter. For example my RV has 13 breakers. Most of them came from Chief at a unit cost of $12.50. That's a total cost of $162.50. Peanuts.

What's the panel space worth in $/square inch? Is there nothing you'd rather put there? Is there nothing you'd rather spend fabrication time on that building and assembling a breaker panel. I'll suggest the differences are much more than dollars. . .
2. I agree with the philosophy of providing a backup system for truly flight critical systems where ever possible.

Which ones are NOT possible?

. . . . . . Having done that, I still consider it worthwhile to provide myself with the option of attempting to restore the primary system if the breaker pops.

Again, which "primary" system do you plan to carry aboard your airplane that creates more than a ho-hum situation if it craps?

. . . It is usually true that one won't be able to restore a tripped circuit in flight, but it's not always true. Circuits with intermittent problems . . .

Generally nuisance tripping due to inadequate overhead in the design. Easily fixed in an amateur-built airplane, almost never fixed in a certified airplane.

. . . . . . may be restorable in flight, and I submit that it's worthwhile to provide the pilot with the opportunity to see if that's possible. For example:

2a. My old Grumman developed an intermittent short in the panel lights one night while I was IFR. I used a flashlight to get to VFR on top, swapped the fuse, and had the panel lights for the rest of the flight. It was very nice to have the whole panel illuminated, even though I had a backup system (the flashlight).

Wouldn't it have been better to have a single lamp, gooseneck mounted map light (optional on the Grummans as I recall) that runs from a separate source . . . mostly used for map lighting in lap but rotatable for panel flood during problems with primary lighting failure -OR- during alternator out operations where minimizing loads on battery are desirable?

. . . . . I was glad that I had the OPTION to replace the fuse.

But suppose it wasn't an intermittent short, suppose the replacement fuse popped too? Think about all the ways the system could have failed. Open wires, shorted fixtures, screws loose, open dimmer, shorted etc. etc. . . . there are many, many ways that almost any system can fail that does not open a breaker/fuse or if it does, re-setting the breaker/fuse doesn't help. Given that you have poor odds in regaining system usage for MOST failure modes, what value is there in not planning for those modes? Especially if you fail to provide adequate backup that is comfortable to use? On the other hand, if comfortable backup is available for all critical systems, why mess with the fuse/breaker at all when there are risks associated with doing so?

. . . . . My RV design includes a small eyeball light as a backup to the panel lights, but in my opinion it is still worthwhile to have the panel light breaker within reach so I can try recycling it if needed.

If there is a "need" to recycle a breaker, then may we assume there is no adequate backup . . . no Plan B?

. . . Cost is minimal, potential convenience is high.

And risk has been raised because of a built in willingness on the part of the pilot to be a mechanic in flight. I would hope your "backup" light is powered from your essential bus and totally independent of other lighting circuit protection and/or controls.

2b. My RV panel has a single KX-155 with glideslope. I have a semi-permanently installed ICOM handheld (Comm and VOR) in the plane as well. If there's an intermittent short that takes out the KX-155 I loose my ILS capability, but I still have Comm and VOR capability from the ICOM. . . .

An excellent move. Given the capabilities of a lot of hand-held equipment, backup for most navigation and communications functions are low cost and remarkable in performance. How about a GPS receiver too for $88?

. . . . . I believe it's worth the effort to wire the system so I have the OPTION to try to bring the radio back on line in flight to restore my ILS capability. One can argue that this isn't likely to happen. That's true, but it's worth $12.50 to me to provide me the OPTION to attempt a reset. (One can argue that I should have a second ILS, but I'm not that rich.)

So do you consider the ILS to be an absolutely essential piece of equipment for the way you plan to fly the airplane? Do you intend to have a "Plan B" in waiting in the wings when it goes belly up (and belive me, it will) . . . there's the word "intermittent" again . . . very low on the list of probabilities. If you absolutely depend on any single piece of equipment for comfortable termination of any given flight, there needs to be a separately powered backup for that system. Suppose the fault is not intermittent? What's "plan B"? Lacking a "plan B," one is resigned to accept the consequences of any and ALL failure modes whether or not breakers/fuses are involved.
2c. Bob has recommended using an off-the-panel 70 amp fuse in the alternator circuit rather than a circuit breaker on the panel. I almost went that route, until Bob wrote me the following email a month ago:

I've had a couple of readers report blowing of the 70-amp fuse when their 60-amp alternator comes on line and works hard to recharge a dead battery. Most alternators will put out better than rated current when they are cold. I'm going to up size my fuse kits to 80 amps. The fuses are on order. Your dimmer is built and ready to ship.
Bob had done the best design work he could, he proposed a design that a lot of people adopted (me included), and it turned out to have an unexpected problem.

Gee Tim, I don't think I've ever claimed infallability nor possession of a crystal ball. You're an EE . . . have you never encountered un-anticipated problems with a design? Once you decide on a system architecture, there is never a reason for changing it? Hmmmmm . . . you don't work for the FAA do you? [grin]

. . . . . . . . . Unexpected things can happen in aircraft systems, and I believe in providing myself with the MOST options possible (breaker resets included), not the FEWEST possible (fuses out of reach, so live with the problem until you land).I've changed my design to include a breaker for the alternator output. It's a whole lot easier to reset the alternator breaker rather than having to replace a 70 (or 80) amp fuse that's been intentionally removed from the pilot's reach.

I'm very sorry to hear that. Keep in mind that we fly airplanes of our own design and manufacture. We're privileged if not obligated to make changes to designs as operational factors reveal themselves. What size breaker are you putting on the panel for your alternator b-lead? Recall that one of several reasons for the b-lead fuse was to eliminate nuisance tripping of the 60 amp b-lead breaker found on most certified single engine airplanes. The other reason was to reduce the potential for magnetic and metallic conducted noise to the bus by keeping the b-lead feeder out of the cockpit. Be sure the breaker is at least 70 if not 80 amps, a frisky 60-amp alternator may open smaller ones on a cold day.

I've posted a notice on our website for everyone to read that a couple of 60-amp alternators were capable of opening a 70-amp fuse. Hmmmm . . . . if this were a certified ship, and 70-amp fuses were on the type certificate, the issue would probably be swept under the rug just like the 60-amp breakers on the the Cessnas. Since we're NOT certified and because we're able to react, we've reacted in a manner that evolves the system in a beneficial manner.

Again, there are dozens of reasons for an alternator to go off line, not the least of which is a nuisance trip of the aforementioned 70-amp fuse. If your alternator goes off line for any of the OTHER reasons, are you in any better shape for having moved the breaker to the panel? Are you saying that you'd be uncomfortable with the fact that your alternator shut down in flight? Is your design so intolerant of failure that you would have been uncomfortable with being the pilot who told me that the 70-amp fuse was too small? If discovery and evolution of minor design changes presents some philosophical difficulties to you as a designer/pilot, how do you rationalize what you're going to face when the Big Nasty hits your alternator, ILS receiver, or whatever.? The real issue is much more than whether or not breakers/fuses should be within reach. The issue is a builder's willingness and ability to configure a flight system such that no single falure creates a hazard to flight in any mode he wishes to fly.

In my opinion, this is the biggest problem with regulation and certification. Making any change to those airplanes dribbling off the assembly line is so difficult that only major (read AD driven) changes are made with any dispatch and most are NEVER made. The reason your airplane is going to be better is because it can evolve. Why is it that your computer is virtually obsolete in two years? It's because the producers are tightly coupled to their suppliers and their customers. Airplane factories are coupled only to the FAA. Their marketing types would have us believe they have customer interests in mind but ONLY as it pleases the FAA and the FAA doesn't like changes.

I would hope that most readers of my work or anyone else's don't become discouraged because things CHANGE. GA is dying right now because it could not change (did you know the fleet has been falling by 4000+ airplanes per year since 1988?). The LR-3 regulator design I did for B&C has enjoyed six major updates since it was flown around the world on Voyager. The reason for those changes included the same reason we raised the b-lead fuse from 70 to 80 amps . . . practical experience in the field suggested this was a good thing to do to evolve the product's design forward. There are hundreds of these fuses flying. An occasional nuisance failure is NOT a hazard to flight and for the few folk who experience the event, a permanent remedy is close at hand. For you, the remedy was in place before initial installation.

3. It is true that you can kill yourself by piddling with breakers when you should be flying the airplane. I believe that problem is best solved by training, not by changing the aircraft design so that the pilot can't even reach his circuit protectors.

The FAA agreed with this position a number of years back when airplanes were having troubles with ni-cad battery fires. Seems that under normal situations, the battery could warm up, go into thermal runaway, buckle some insulators, short a cell and catch fire. Then as now, it was well understood that a voltage regulator's absolute, #1 task was to take care of a battery. Rather than mandate installation of voltage regulators with temperature sensors to take care of ni-cads, the rule-makers and industry elected to add a battery temperature gage to the panel along with yellow and red warning lights. Should one of these lights illuminate, the pilot was trained to take the battery off line until it cooled enough to be safely brought back on line. More gadgets on the panel and pilot training to go with it . . . . I'm sorry Tim but it just doesn't wash . . . when simpler, less expensive, work-load reducing techniques are there for the asking . . . .

In conclusion, I believe accessible breakers are a good way to provide circuit protection. They don't cost much more than a hidden fuse block, and they give the pilot the option to troubleshoot if pilot workload permits and the situation warrants it. I believe the decision whether or not to troubleshoot an electrical problem during a particular flight should be the PILOT'S decision, not the DESIGNER'S decision.

Shouldn't it be a task of every pilot/designer to configure the airplane so that it's not necessary to reach 'em? . . . . we're not talking about designers driving pilots but the other way around. I am a pilot and every time I set in the seat of the machines I rent I think, "how crude, how archaic, how ridiculously expensive for value received." Then I go home to work with hundreds of other pilots who are also builders. We are . . .

  • Reducing pilot workload by designing the need for it out of the system . . .
  • Improving system reliability because parts count goes down . . .
  • Designing modern, lower cost products into the system . . .
  • Reducing time to install and maintain . . .
  • Using effort expended on honoring tradition for more productive endeavors . . . .
  • Producing failure tolerant system where failure of any device is simply an event.

    The FAA still believes in their heart-of-hearts that everything associated with airplanes should be failure-proof: an admirable goal. But it's only a "goal". People admire lofty goals so the expenditure of about any amount of money is justified. The bad part is your money and mine is spent in its pursuit. As near as I can tell, amateur built aviation is not rooted in goal chasing - rather incremental improvements to design.

  • Bob, I have your Rev 7 of the Aeroelectric Connection. I agree with most of it's content and it's a handy reference for electrical data. That does not mean that my experience does not count or its wrong to have a different opinion.

    Never said so . . never intended to imply it either. Paul, please understand that MOST of the people out here building airplanes are pretty bewildered by it all . . . I suspect that's a major contribution to the number of airplanes that are started but never finished.

    The real issue is not to dictate ones opinion (or try to support it with ones background) but present your position and let the readers decide what is best for them. . . .


    I have seen both sides of the discussion and think there is room for both. Further I have found most people willing and able to decide for themselves which way they want to go.

    I guess that's the variable that I don't know how to quantify. When it comes to "deciding for one's self" who is the most persuasive? The techno-wienie who speaks in some undecipherable language or the guy who sez, "I've been there and by golly, re-setting that breaker sure saved my buns!" Did you ever see the movie "Never Cry Wolf"? It's a fun piece but there's a scene in there wherein our hero has to "hold 'er steady" while the pilot climbs out the window to bang on a frozen fuel line with a wrench. I can laugh at the scene for its humor but the serious side is scenes like that drive public perception of aviation. Trading wing-and-a-prayer stories over a suds is fun too . . . but we're building airplanes here and lots of people are listening . . . while we're laughing over some guy's pucker-factor, someone else's wife is wondering if she really wants her husband to build his own "death trap."

    That's why I like people to learn data-speak. Just for grins, let us suppose there were an FAA rule tomorrow that sez all breakers shall be out of reach and left it at that. Do you suppose we could learn to live under that rule and design the airplane so it was not necessary to reach 'em. Sure we could. Well . . . if we can do it to accomodate the unwelcomed regulation, why not strive for that kind of reliability on our own?

    The difference in reliability is insignificant in the real world and builder comfort is more important. I am much more worried about the auto engine conversion with only one battery than if he uses fuses or CB and where they are located.
    Discomfort comes from lack of knowlege and skills. Most of our bretheren out there come from the padded cockpit environment where they were taught everything necessary to fly this here airplane, including the preflight check of breakers. I remember sitting there in the left seat waiting for my flight instructor to continue with some lessons on inflight systems diagnosis after he told me how useful it was to be able to push and pull on those things. But that was it . . perhaps two sentences

    . As the FAR's (23.1357 (d)) do require crew replaceable/resettable fuses/CB for "critical equipment" It seems to me the only one to make the decision as what's critical is the builder/pilot based on his own comfort factor and the type of flying being done.

    When I proposed the idea of remote fuses to my friends here at the FSDO, their eyebrows went up too . . . until I followed up with the statement that the system would be designed such that NO systems were critical to flight. Most of the folk on the lists are not designers . . . they ask questions and appreciate lucid answers. Most lack the skills to deduce criticality and are unable to make considered decisions as to what is or is not "critical." One contributor to this conversation made a statement to the effect that, "everything is critical . . . or it wouldn't have been installed in the airplane!"

    That's your and my responsability. As experienced pilots and knowledgable users of the hardware, we need to put our experience out there in the Plan A/Plan B format suitable for POH publication. That's where striving for system designs favorable to out-of-reach fuses is helpful . . . the instructions get real simple and the pilots get real confident.

    Further what about all the existing factory and experimental acft that were wired with CB? Should we worry these people by suggesting their acft is less reliable?
    Worry them, no . . . I fly lots of those same airplanes. As the #2 item on my systems reliability list, I as a pilot couldn't care less if ANY of those breakers are open or closed at any given time in the way I use the airplane. My fondest wish would be to wave a magic wand and make all pilots as confident of thier ability to cope as I am . . . and yes, compared to what we are building, those spam cans ARE less reliable . . . that's why I refuse to depend on certain aspects of their equipment lists.

    Both fuses and CB's fail and when they do the failure rate is unimportant to the pilot. The ability to replace in flight is a personal one and largely depends of the type of flying being done. What applies IFR over an overcast in mountains is quite different from VFR in the Midwest.

    But Paul, I'm not sure you understand the point. It's not a matter of breakers/fuses or the ability to fiddle with them in flight. If I'm IFR in the crud and a 10-cent resistor cracks, or a coax comes unhooked, or a knob suddenly fails to rotate the mechanism behind the panel, what comfort is there in being able to see that row of circuit protection? All of those goodies that depend on the power making it through the fuses can fail in so many ways.

    The frustrating thing for me is not the argument over hardware styles rather the importance we put on them. I.e. why spend $100 for a mil-spec switch to control a landing light when you KNOW the light bulb is going to fail? Extend that fact into every other system in the airplane and it makes this discussion on hardware look like a playground argument. That's why I fly with the assumption, mind set and backup equipment that ASSUMES that none of that stuff is going to be working when I land, and I DO intend to land on my own terms.

    My flight instructor hadn't the foggiest notion of that concept. It took me a long time to acquire it on my own but then the FAA would have a fit if we proposed this line be added to the approved flight sylabus, "Instruct student on use of aircraft in J-3 mode" How many new Bonanza owners would appreciate that kind of instruction? That's why we call some of those airplanes (doctor, lawyer, etc.) killers. Those folk paid a LOT of money for the things, the idea that they should KNOW how to get along without that panel full of goodies is UNTHINKABLE . . . so the training never happens.

    Can you see why I get wrapped around the axle of the "dark and stormy night" anecdotes? They have no educational value and serve only to make pilots more apprehensive because of what they DON'T know. There are reasons now to believe that John Denver was working a transponder problem with center or approach just before the accident. Wouldn't it be ironic if the man died with his head down, trying to get a band-aided, WW-II derelict working for the convenience of ATC and didn't see a bird coming?

    The answer seems quite clear to me . . . the fewer goodies to fiddle with the better. Deal with situations in a predetermined, simple, Plan A/Plan B procedure. I'd be very pleased to have you join me in helping to achieve this kind of cockpit environment. If we can reduce costs, weight and installation time too, that would be super. Interestingly enough, getting rid of excess baggage by the use of considered design tends to have those by-products. I'd love to look the administrator in the eye at OSH some year and seriously suggest, "certified aviation has fallen behind in some important safety issues and that some tutorials from the vast knowlege base that is (or should be) EAA are available for any interested FAA personnel."

    Fly comfortably . . .

    'lectric Bob . . .