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Fuse block, in flight accessible?

B

Brian Vickers

Well Known Member
I have started the panel in my RV4 and was planning to use an Aero Electric recommended fuse block. My airplane and panel is ultra simple. I have seen various references to making the fuse block accessible in flight. This makes perfect sense but I don?t have a good place to do that because the connecting wires fan out on both sides. For aesthetics I was hoping not to look at a fuse block while piloting. I am using so few fuses that I?m rethinking this and considering going with panel mounted fuse holders (screw type). My panel is so bare that I could actually mount it right there if desired (kidding). What have other fuse block users done? Suggestions or comments, about anything fuse block related? Go with panel mount screw in fuse holders?

Sincerely,
Brian Vickers, RV4 project now past a decade but still creeping along
 
If your fuses are properly sized, the only thing that should cause a fuse to blow is a short in the wires. If this has happened, do you really want to be replacing the fuse and feeding current to the short again in flight? This is an activity better attempted on the ground.

Some people argue for fuses that you can replace in flight because the fuse feeds some vital system. Well, if you have a system that is so important, you really need to have a second backup system, as systems can fail for many, many reasons that don't involve a fuse blowing.

Do you have any electrically powered systems that would prevent a safe landing if the system failed, or the fuse blew?

My recommendation is to do the research to figure what what size the fuses need to be so they don't blow unless there is a wiring problem. Then make sure the wiring is hefty enough to handle the fuse's rated current. Put the fuse block out of reach of the cockpit, as troubleshooting an electrical failure is an activity that really should be done on the ground, not in flight.
 
I went with the fuse block because my panel is very simple also. The block is totally inaccessible in flight (and barely accessible on the ground!) My only breaker is for the alternator and it is mounted on the panel. I followed 'lectric bob's logic that so long as there are no "safety of flight" related components being affected, there is no reason to have access to the fuses in flight. And, if a fuse does blow, it probably means there is more of a problem than simply changing it out and a proper diagnosis would be done on the ground.

After 100hrs there have been no issues with my fuses, or anything else for that matter.
 
That will change!

In time, your panel will probably fill up, and you may need more fuses. While I'm not all that familiar with the 4 panel, I put my fuse block (-9A) under the center of the six-pack, hinged so that it folds up out of sight. Hit a lever and it drops down between my knees. No panel space taken, very accessible in flight and not obvious. I have the fuse location chart as a page on my Dynon checklist, so if a fuse blows (as it just did last week) I can drop the fuse block, bring up the list and change the fuse. Of course it didn't fix the problems last week, but it did work as planned. Finding the short in the panel lights fixed the problem.

Bob Kelly
 
Kevin Horton said:
If your fuses are properly sized, the only thing that should cause a fuse to blow is a short in the wires. If this has happened, do you really want to be replacing the fuse and feeding current to the short again in flight? This is an activity better attempted on the ground.

<snip>
Click to expand...

100% right on the money. Given the seemingly chronic fuse blowing/breaker popping that happens in experimentals, I have to think that most people undersize their wiring. When is the last time you or someone you know blew a fuse in your car for absolutely no reason at all. Honestly, I can't even remember the last time I blew a fuse at all.
 
videobobk said:
In time, your panel will probably fill up, and you may need more fuses. While I'm not all that familiar with the 4 panel, I put my fuse block (-9A) under the center of the six-pack, hinged so that it folds up out of sight. Hit a lever and it drops down between my knees. No panel space taken, very accessible in flight and not obvious. I have the fuse location chart as a page on my Dynon checklist, so if a fuse blows (as it just did last week) I can drop the fuse block, bring up the list and change the fuse. Of course it didn't fix the problems last week, but it did work as planned. Finding the short in the panel lights fixed the problem.

Bob Kelly
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When in heavy turbulence, sometimes my legs get bounced around. If my fuse block was hinged up above my knees, there's a very good chance I might have "taken out" my whole electrical system on occasion.

Just playing devil's advocate about the "above your knees" location.
 
I bolted my fuse block to the left side skin up near the firewall. The bolts are hidden by the cowl cheeks. I've got no electricals that are mission critical so I don't need to access them in flight. I also agree that trying to troubleshoot such a failure in flight seems like a bad idea.
 
Can't think of a title

As I read through Bob's "AC Book" I really identified with his focus on low cost "less is more" philosophy. The EBuss provides essentials in a power problem. Steam gauges cover me in the event of a serious failure, the Dynon and GPS have their own internal batteries. Breakers cost much more in time and money to implement. If I encounter an open fuse, I'll wait till I'm on the ground to shoot it.


Chris...
http://www.n212s.com
RV-7, IO-360, Garmin Stack, 496 GPS, LightSpeed IGN
(Finishing, FWF,Wiring)
 
My electrical system is also pretty simple and is intended for VFR flying. I put the 8 circuit fuse block to my RV-4 vertically on the right bulkhead just below the panel and right next to my knee. I also have a small Radio Shack LED next to each fuse that will light if the fuse blows. It was all very cheap and will give me some additional information should something go wrong plus I can easily cut a circuit should I need to work on something. I can replace the fuses in flight. However, I agree that messing with the electrical system while flying is probably a poor idea and most likely I will not replace a fuse in flight unless absolutely necessary.

Alan
RV-4
 
Philosophically speaking

I hesitate to say anything but the "philosophy", is based on you don't reset any fuse in flight.

In other words: YOU DON'T RE-SET FUSES IN FLIGHT, BECAUSE if it blew the fuse you should (consider) not re-setting it, per this "philosophy". It should not be critical item. You should be able to finish the flight safely and live (fly) with out it.

If it's an item that is critical and you can't live (fly) without it, consider a resettable CB or at least a switch to provide a secondary power supply (the so called E-buss or emergency buss).

One cool idea I saw on one of Van's prototypes was having the fuses exposed in the panel, using the standard car ATC style blade mini fuse holder/boxes. It was not one of the monster 20 circuit ones but a smaller compact 6 or 8 circuit size I estimate.

At least you have the access and the practical option to reset the fuse if you have spares, but don't forget a plastic fuse puller / tweezers (probably steal one from your car). Those little buggers are hard to get out with finger-nails only.

So think about every independent fused circuit and if you can live with out it. If you can't, than have a way to reset the fuse/CB or power it alternatively.
 
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In Canada CB's or fuses must be accessable to the pilot.
I am using a fuse block for ATO type fuses on my current project. I have mounted it on the back of the instrument panel and have the face flush with the front of the panel. The placard over it will identify each fuse.
 
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Kevin I can't remember where I read that rule it was a few years back. It also stated in the same that there must be adequate spare fuses on board of sufficient size for replacements. I will try and find the reference for you.
It would be great if it not required, would make life easier building these panels.
 
CAR 605.16 (1)

Kevin Horton said:
I cannot find this requirement in the Canadian Aviation Regulations , or in Airworthiness Manual 549 - Amateur-Built Aircraft , nor in any of the Airworthiness Manual Advisories that deal with amateur-built aircraft. The official checklist that the MD-RA uses simply asks "Are fuses or circuit breakers employed?"
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Kevin,

Found this:

http://www.tc.gc.ca/CivilAviation/Regserv/Affairs/cars/PART6/605.htm

Pertinent section quoted below. Would seem this applies to night VFR.



Power-driven Aircraft - Night VFR​

605.16 (1) No person shall conduct a take-off in a power-driven aircraft for the purpose of night VFR flight, unless it is equipped with

(a) the equipment referred to in paragraphs 605.14(c) to (n);

(b) a sensitive altimeter adjustable for barometric pressure;

(c) subject to subsection (2), a turn and slip indicator or turn coordinator;

(d) an adequate source of electrical energy for all of the electrical and radio equipment;

(e) in respect of every set of fuses of a particular rating that is installed on the aircraft and accessible to the pilot-in-command during flight, a number of spare fuses that is equal to at least 50 per cent of the total number of installed fuses of that rating;
 
Lycosaurus said:
Found this:

http://www.tc.gc.ca/CivilAviation/Regserv/Affairs/cars/PART6/605.htm

Pertinent section quoted below. Would seem this applies to night VFR.



Power-driven Aircraft - Night VFR​

605.16 (1) No person shall conduct a take-off in a power-driven aircraft for the purpose of night VFR flight, unless it is equipped with

...
snip
...
(e) in respect of every set of fuses of a particular rating that is installed on the aircraft and accessible to the pilot-in-command during flight, a number of spare fuses that is equal to at least 50 per cent of the total number of installed fuses of that rating;
Click to expand...
That just says that if your fuses are accessible in flight, and you fly night VFR (or IFR at day or night, in a later section), you must carry spare fuses. It doesn't say that your fuses have to be accessible in flight.

This is hot issue for me, as my fuse blocks are not accessible in flight. I know of no regulatory or logical reason that my design would not be acceptable in Canada.
 
Oh yea!

Fights ON! :rolleyes:

I personally think its a good idea and why have those expensive Klixon reset/pull-able CB's. They look COOL lined up on the panel. :rolleyes: (I am kidding I have them because I got them surplus cheap and had them on hand.)

Of course if you read Bob's Aeroelectric, he has a whole chapter why hidden fuses are a great idea (to him) and there is no need to reset them, and if you do anything different the terrorist will win. :D

FAR: 91.205
(b)(6) One spare set of fuses, or three spare fuses of each kind required, that are accessible to the pilot in flight.


Its pretty clear, "accessible", but like our brothers up north it says "THAT ARE ACCESSIBLE". It does not say you can't make them all un-accessible.

Being experimental we don't need to follow it any way even IF (and it does not) say you must be able to reset them.

Still its moot for RV's under the experimental banner, but I don't think the FAA condones the hidden fuse design. You may get an inspector to balk if he asks where are the fuses/CB's and you say, under this panel, behind this door and 4 screws, 3 feet from the pilot's seat and upside down. Than you have to explain why its safe and the FAR's to them. Do you still need to carry the spare fuses? Nope
 
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Kevin Horton said:
That just says that if your fuses are accessible in flight, and you fly night VFR (or IFR at day or night, in a later section), you must carry spare fuses. It doesn't say that your fuses have to be accessible in flight.

This is hot issue for me, as my fuse blocks are not accessible in flight. I know of no regulatory or logical reason that my design would not be acceptable in Canada.
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Good point Kevin. I also wonder why they quote 50% of fuses are required to be carried as spares. How many times will you be changing out the fuses before you give up and acknowledge you have a short .... or a fire on-board?

I am going with a combination of fuses and breakers. Fuses will be changed on terra firma. I will carry spares as specified. Breakers are for items I absolutely need, such as fuel pump etc.

Found the requirements for the fuses. Seems they need to be accessible if the circuit is essential for safety in flight. What does that mean? Heated Pitot a safety item? Strobes?

Following is info from:

http://www.tc.gc.ca/civilaviation/RegServ/Affairs/cars/Part5/Standards/523vla.htm
[523-VLA.1357 Circuit Protective Devices]​

[Aeroplanes limited to VFR day operation shall meet the requirements of JAR-VLA 1357, for aeroplanes intended for VFR night or IFR operation the following requirements shall be met:

(a) protective devices, such as fuses or circuit breakers, shall be installed in all electrical circuits other than:

(1) main circuits of starter motors used during starting only, and

(2) circuits in which no hazard is presented by their omission;

(b) a protective device for a circuit essential to flight safety shall not be used to protect any other circuit;

(c) each resettable circuit protective device ("trip free" device in which the tripping mechanism cannot be overridden by the operating control) shall be designed so that:

(1) a manual operation is required to restore service after tripping, and

(2) if an overload or circuit fault exists, the device will open the circuit regardless of the position of the operating control; and

(d) If the ability to reset a circuit breaker or replace a fuse is essential to safety in flight, that circuit breaker or fuse shall be so located and identified that it can be readily reset or replaced in flight;

(e) for fuses identified as replaceable in flight:

(1) there shall be one spare of each rating or 50 percent spare fuses of each rating, whichever is greater, and

(2) the spare fuse(s) shall be readily accessible to any required pilot.]
 
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Lycosaurus said:
Following is info from:

http://www.tc.gc.ca/civilaviation/RegServ/Affairs/cars/Part5/Standards/523vla.htm
[523-VLA.1357 Circuit Protective Devices]​

[Aeroplanes limited to VFR day operation shall meet the requirements of JAR-VLA 1357, for aeroplanes intended for VFR night or IFR operation the following requirements shall be met:

(a) protective devices, such as fuses or circuit breakers, shall be installed in all electrical circuits other than:

(1) main circuits of starter motors used during starting only, and

(2) circuits in which no hazard is presented by their omission;

(b) a protective device for a circuit essential to flight safety shall not be used to protect any other circuit;

(c) each resettable circuit protective device ("trip free" device in which the tripping mechanism cannot be overridden by the operating control) shall be designed so that:

(1) a manual operation is required to restore service after tripping, and

(2) if an overload or circuit fault exists, the device will open the circuit regardless of the position of the operating control; and

(d) If the ability to reset a circuit breaker or replace a fuse is essential to safety in flight, that circuit breaker or fuse shall be so located and identified that it can be readily reset or replaced in flight;
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You have quoted from the design requirements for JAR-VLA, which are essentially a watered-down version of FAR 23, used for type-certificated aircraft like the Diamond Katana. We are not required to comply with JAR-VLA.

Essential to safety in flight has historically been interpreted to refer to an item that must be functional in order to make it to an airport (e.g. power supply for electronic ignition on an aircraft with only one ignition system). If you have any such items, you also need to consider the failure case where that item simply fails (i.e. the fuse didn't blow). This would almost certainly drive you to installing a backup system (e.g. a second ignition system), in which case the primary system is no longer essential to safety.

This would not apply to strobes or pitot heat, as the aircraft will fly quite nicely without either of those.
 
Kevin Horton said:
You have quoted from the design requirements for JAR-VLA, which are essentially a watered-down version of FAR 23, used for type-certificated aircraft like the Diamond Katana. We are not required to comply with JAR-VLA.

Essential to safety in flight has historically been interpreted to refer to an item that must be functional in order to make it to an airport (e.g. power supply for electronic ignition on an aircraft with only one ignition system). If you have any such items, you also need to consider the failure case where that item simply fails (i.e. the fuse didn't blow). This would almost certainly drive you to installing a backup system (e.g. a second ignition system), in which case the primary system is no longer essential to safety.

This would not apply to strobes or pitot heat, as the aircraft will fly quite nicely without either of those.
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Kevin is correct. He knows what he is talking about.

As a DAR that does initial airworthiness inspections on Amateur Built aircraft in the US, I cannot deny the airworthiness certificate to an experimental aircraft that does not comply with FAR 23.

I recently spent 8 hours doing an inspection on an airplane that I wanted to deny the airworthiness certificate to and could not find any justification to deny it. It had circuit breakers that were resetable in flight. There were other things that I did not like, not the best way of doing things, but nothing that would make it unsafe for flight.

My RV-6 will be 10-years since first flight in September of this year. It has 2,004 hobbs hours on it when I put it away after the last flight. The electrical circuits are protected by fuses that are located on a swing down piece under the panel. You CANNOT get to the fuses in fight. They are too high up under the panel to be able to hit with your knee in [font=&quot]turbulence[/font].
 
Kevin Horton said:
Essential to safety in flight has historically been interpreted to refer to an item that must be functional in order to make it to an airport (e.g. power supply for electronic ignition on an aircraft with only one ignition system).
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Good. Thanks for clarifying that. That would have thrown a monkey wrench into my fuse (mainly) panel design as well.

I did not find any other references for Canadian requirements for fuses to be replace-able in-flight. I guess we're good to go now.
 
Part 91 DOES apply to Experimental aircraft

gmcjetpilot said:
FAR: 91.205 (b)(6) One spare set of fuses, or three spare fuses of each kind required, that are accessible to the pilot in flight.

Being experimental we don't need to follow it any way even IF (and it does not) say you must be able to reset them.
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The regulation you have sited is from Part 91 General Operating and Flight Rules. Part 91 applies to the operation of Experimental aircraft in the same way that it applies to Certified aircraft.

The rules that we do not have to comply with are those pertaining to Certification of aircraft.
 
One cigar for Dave

Paragraph 1 of your operating limitations state "...this aircraft shall be operated in accordance with applicable air traffic and general operating rules of part 91 and all additional........"
Paragraph 7 states "...for night and/or instrument flight the aircraft must be in compliance with part 91.205......"
 
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