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RV-12 engine compartment fire

JRo

Well Known Member
Guys,

I was running my engine today prior to flight, waiting for the oil temperature as always. SkyView warned "Shutting down in 30 seconds" and "Aircraft Power Lost". I shut down immediately, smelled smoke, then saw smoke at my feet. Exited the cockpit, peeked through the oil service hatch, saw yellow flames about 3-4" tall burning gently at rear of engine, straight below GPS antennae about 7". Extinguished immediately. Removed top cowl. Disconnected ship's battery. Fire appears electrical, but cause unknown. Pitot tube melted away for about 6" section (that appears to be mostly the combustion). Wire bundle severely compromised. Both throttle cables and both choke cables badly burned where they're bundled together and tie-wrapped to motor mount about 6" forward of firewall.

The hits just keep on comin'!

Jim
N448JR
 
Wow, Jim, if it had to happen, I'm glad it happened on the ground where you had options. Let us know what you find.
 
Guys,

Both throttle cables and both choke cables badly burned where they're bundled together and tie-wrapped to motor mount about 6" forward of firewall.

The hits just keep on comin'!

Jim
N448JR

Very sorry to hear about the fire, I know that is discouraging.

Since the throttle and choke cables are fried the first thing that comes to mind is that something is wrong with the engine to airframe ground strap. If that ground is compromised, the electrons may decide the control cables are the easiest path to ground.
 
Very sorry to hear this. These are our babies. It's terrible to hear something like this. Please let us all know when you find the cause.

Rich
 
Jim,

Very sorry for your loss.
That withstanding, it was good that nobody got hurt and you had not departed yet.
It's just metal, rubber and plastic . . . and it can all be replaced.

When it is all sorted out, please let us know what happened.
What you find out may help another operator avoid a similar situation.
We are all here to help each other out.
 
Guys,

I was running my engine today prior to flight, waiting for the oil temperature as always. SkyView warned "Shutting down in 30 seconds" and "Aircraft Power Lost". I shut down immediately, smelled smoke, then saw smoke at my feet. Exited the cockpit, peeked through the oil service hatch, saw yellow flames about 3-4" tall burning gently at rear of engine, straight below GPS antennae about 7". Extinguished immediately. Removed top cowl. Disconnected ship's battery. Fire appears electrical, but cause unknown. Pitot tube melted away for about 6" section (that appears to be mostly the combustion). Wire bundle severely compromised. Both throttle cables and both choke cables badly burned where they're bundled together and tie-wrapped to motor mount about 6" forward of firewall.

The hits just keep on comin'!

Jim
N448JR

Any info on the source of the fire yet?

Will you have to make an NTSB report?

Between this and another reported brake fire on another Van's airplane, I am glad I picked up that small fire extinguisher from ACS.

Glad the only damage is wiring and pitot tube, those can both be replaced!
 
I think Sam B's thought re: throttle cable/choke cable acting as a primary GROUND may be on-target. That or possibly a shorted power wire chafed through at the firewall?
 
I think Sam B's thought re: throttle cable/choke cable acting as a primary GROUND may be on-target. That or possibly a shorted power wire chafed through at the firewall?

I would think a shorted wire would have popped a breaker or fuse somewhere.

I would think the OP would have found the cause by now.
 
It looks as though the wire from the starter relay to the cockpit switch panel became compromised. It is NOT fused. It is "hot" whenever the master switch is on. The insulation melted off this wire like a snakeskin from the starter relay to the point where it crosses beneath the choke cable, and heat became excessive, but very local. Damage was to the firewall forward wire harness, choke cable, throttle cable, pitot tube forward of the firewall, and GPS antennae cable (which is permanently attached to the GPS antennae). Damage was all contained in a very small area, and would likely not have spread, especially once the master is switched off.

Fire extinguisher should always be handy. But remember, an extinguisher which operates through suffocation of the fire will also suffocate the occupant(s) of a small enclosed area, like the RV-12 cockpit.

Jim (the guy with the fire)
N448JR
 
Hey Him,

So sorry for your troubles. Sure hope that the damage is limited to the area that you mentioned, and that repairs go well for you.

If you get a chance, a few pics would sure be helpful in providing a better understanding of the problem. There is a lot of talent on this forum, and actually seeing this area just might offer some additional insight.

Tom
 
I have a fuse position marked "START". I thought that protected the starter relay circuit. There was an old thread that recommended going to a 3A fuse versus 2A due to the fuse blowing.
 
It seems that JRo is describing wire P157-12-43 which is the main unfused feeder from the battery that powers the aircraft. From JRo's description, it sounds like that wire shorted out to the choke cable.
 
It seems that JRo is describing wire P157-12-43 which is the main unfused feeder from the battery that powers the aircraft. From JRo's description, it sounds like that wire shorted out to the choke cable.

That is correct Joe. I have photos and will post them at some point, when appropriate, with JRo's permission.
 
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The wire in question is WH-P157, battery power wire (white). And it is always "hot" with the master switch on, not the starter. It is a #12 wire. It apparently shorted out in my case, causing an extreme heat source. In fact, it got so hot that about 6" of wire simply "vaporized"! It is extremely important to note that this cable was not fused or protected in any way. Almost always throughout the industry, cables of this type are protected by a fusible link, which will, by design, fail internally and cut the current in case of an extreme overload, such as a short. Without such protection, the extreme heat will continue until the wire melts away (as it did in my case) or until the current is switched off.

Based on what I know now, I would strongly advise installing a fusible link on the battery power wire in the RV-12, as well as any other big-draw circuits that are not already protected in some way.

Several of you mentioned the issue of an engine-to-fuselage ground. Although it's a realistic concern, it was definitely NOT the case with my plane, as I long ago took the precaution of adding a very solid & substantial ground wire from the top of the right rear cylinder (where there's already a tapped screw hole) to the fuselage nearby.

Thanks,

JRo
N448JR
 
Almost always throughout the industry, cables of this type are protected by a fusible link, which will, by design, fail internally and cut the current in case of an extreme overload, such as a short.

Some industries this may be the case, but not light aircraft.
There are tens of thousands of Cessnas and Pipers (and others) configured the exact same way. I imagine the majority of RV's are also.
I am not arguing that a fuse-able link is not a good idea, just saying that there is nothing standard about it (in general aviation light aircraft anyway).

Sorry to hear about your incident, but glad that it looks to be rather minor.
 
I long ago took the precaution of adding a very solid & substantial ground wire from the top of the right rear cylinder (where there's already a tapped screw hole) to the fuselage nearby.

N448JR

would you put a pic of this connection please ? Any recommendation from VAN's ?

thanks
 
Based on what I know now, I would strongly advise installing a fusible link on the battery power wire in the RV-12, as well as any other big-draw circuits that are not already protected in some way.

Not to pile on your already unfortunate experience, but standard practice is to route/protect the fat wire so it can't chaff against the choke cable (or anything else)?

Fusible links usually aren't used in this location because a momentary spike or defective fuse can take down the entire system.
 
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The design of an aircraft electrical system involves compromises, just as does the airframe. Considerations are cost, weight, and complexity (more failure points). The way that the RV-12 (and many TC aircraft) is wired, with an unprotected main feeder, has been found to be the best way. But it is not the only way. A fuseable link could be used. But that introduces more failure points. Fuseable links are 4 wire sizes smaller than the wire that they protect. So the fuseable link would be 16 awg. Not only would it be an electrically weak link, but also mechanically weak. So the designer has to weigh the danger of an electrical fire against the danger of a power failure caused by more parts that might fail.
Another approach is to take precautions against the feeder shorting out by using more cushion clamps and wire-ties and using double insulation at critical points like at the firewall penetration.
 
When I was a college kid I had an old Corvair that shorted the accessory lead from the positive terminal of the battery. The cable was completely destroyed in seconds. My then girlfriend must have been impressed by my jury rigged repair that got us off the highway because she married me. 😀
 
A mechanic acquaintance (non-VAF member) read this thread and asked me to offer these thoughts:

"Have been a mechanic all my life so can speak without seeing the problem.... An electrical short will show damage from the source of power to the short but not beyond. He found his problem as it shorted to the throttle and the other cable but not beyond."
 
When I was a college kid I had an old Corvair that shorted the accessory lead from the positive terminal of the battery. The cable was completely destroyed in seconds. My then girlfriend must have been impressed by my jury rigged repair that got us off the highway because she married me. 😀

Maybe she married you because of that hot rod you were driving?
 
Quote:
Originally Posted by RFSchaller View Post
When I was a college kid I had an old Corvair that shorted the accessory lead from the positive terminal of the battery. The cable was completely destroyed in seconds. My then girlfriend must have been impressed by my jury rigged repair that got us off the highway because she married me. 😀
Maybe she married you because of that hot rod you were driving?

Or maybe the savings in fuel costs would translate into shoes and purses!?!

Pat
 
The worst breakdown was when the Corvair fan belt broke and I had to use her panty hose to make one good enough to get us 20 miles to a gas station! 😱

God, I miss the 70's! 😀
 
The worst breakdown was when the Corvair fan belt broke and I had to use her panty hose to make one good enough to get us 20 miles to a gas station! ��
��

Worst breakdown?? I'd rate that one as excellent!!
 
Photos

Hello Jim,

I am in the midst of my annual and would appreciate any photo so I might review my installation. Thanks, hope the repairs are going well.
 
On the issue of a fusible link, it is not true that it would create a weak spot electrically. A fusible link will not fail in the event of a spurious spike in current; only in the event of a major, uncontrolled power draw....a short circuit. It is true that it is 4 wire sizes smaller ( or 4 numbers larger); 16 awg in the case of the RV-12 battery power wire. Regarding the philosophy of aircraft design, to wit; the issue of a system failure versus a fire aloft is hardly worth discussion. Seriously? In a VFR, daytime-only RV-12, we'd consider a fire aloft a better deal than a display failure?! I appreciate all the redundant advice to carefully route & shield the battery power wire. Great advice. Took care of it. But that is a separate issue of the wire becoming shorted for whatever unforeseen reason. And there seems to be much naive comment on this blog that if there's a problem, a fuse would blow. It needs to be clearly understood here that if a power wire shorts out in the RV-12, a fantastically dangerous hot spot will result; in essence, an arc welder. That's what I had, and the damage was devastating. Additionally, it needs to be understood that proper engine-to-fuselage grounding will not protect against such a short circuit. My engine is properly grounded, In fact, I long ago took the precaution of an additional ( and very substantial) electrical ground wire. Unprotected +12v current will find ANY path when it "shorts" out. In my case, it virtually welded right through both the throttle & choke cables, as well as destroying the #22 (black) ground wire in the GPS antenna/receiver cable all the way to the connector on the Vans AV-5000A control module in the avionics bay (a $600 piece).
 
If the circuit has a fuse it will blow and prevent the levels of current that generate enough heat to weld and start combustion. That's why they are there. If one doesn't put a fuse in a circuit I think it's like playing russian roulette. My starter switch is fused as is my main power lead. I never really knew why, since it is such a tiny current draw, but now I know. If the main fuse blows I'll deal with it quite happily vs a fire ( especially since my airplane is wood:eek:). I am surprised to read here that some circuits are not protected.
 
The ASTM specs that the RV-12 is certificated under specifically prohibit the use of of a circuit protector that is not resetable by the pilot.

That means the wire highlighted in this discussion can not have a fusible link or any other circuit protection that would actually be capable of preventing a failure in the location that this one was.

Because of that, special care must be taken with this wire, and that was done on the RV-12 design, with some strategically placed adel clamps that would make sure that the wire harness bundle could not come in contact with anything that would cause a short circuit.

If the plans are followed, and the clamps are properly installed as specified, I think the likelihood of a failure like this is quite remote.
 
rvbuilder2002,

Can you provide the ASTM spec that you are citing. I would be very interested in reading that.


Thanks,

-Jeff
 
rvbuilder2002,

Can you provide the ASTM spec that you are citing. I would be very interested in reading that.


Thanks,

-Jeff

ASTM F2245, the primary criteria for design and performance spec's.

Unfortunately ASTM's are copyrighted and are only available by subscription/purchase.
 
Ok, I found what I think is the correct ASTM standards document:

ASTM F2245 - 14. Standard Specification for Design and Performance of a Light Sport Airplane.

Does anyone have a copy of this I could read?

rvbuilder2002 - If that is the wrong standard or you are aware of another one, please let us know.

Thx,

-Jeff
 
Ok, I found what I think is the correct ASTM standards document:

ASTM F2245 - 14. Standard Specification for Design and Performance of a Light Sport Airplane.

Does anyone have a copy of this I could read?

rvbuilder2002 - If that is the wrong standard or you are aware of another one, please let us know.

Thx,

-Jeff

That is the next revision that will be Accepted/adopted by the FAA Not sure what date it will become effective.
The one currently in use (and regulatory) is F2245-13B
 
I posted on the AeroElectric list about this fire incident, questioning the practice of not protecting main bus feeders. Bob Nuckolls, the electrical guru who wrote the book on aircraft wiring responded. Below is an excerpt from his response:
The fusible link is mechanically attractive.
Installs with splices, ties right into a wire
bundle with the rest of the wires. If it's in
a bundle, it would be a good thing to add a layer
of silicon impregnated fiberglass sleeving like
that described in my articles and offered in
B&C's fusible link kit.
In any case, protecting light feeders (that are)
directly attached to a battery is a good idea.
Bob
 
The ASTM specs that the RV-12 is certificated under specifically prohibit the use of of a circuit protector that is not resetable by the pilot.

rvbuilder2002

I was able to review the pertinent sections of ASTM 2245-14 and I don't find any language that supports that claim. I'm wondering if perhaps that language was in a previous version of the spec and has since been removed.

Can you reference the actual text that lead to the above statement?


-Jeff
 
The ASTM standards seem ambiguous and open to interpretation and are even contradictory.
A2.9.2 Circuit Protection Requirements?Circuit overload
protection (fuses or circuit breakers) must:
A2.9.2.3 Be accessible to and in clear view of the pilot
(It is not clear if that includes fusible links.)
A2.9.2 Circuit Protection Requirements?Circuit overload
protection (fuses or circuit breakers) must:
A2.9.2.1 Be installed on each circuit containing wiring,
equipment, or other components rated for less than the maximum
output of the battery
So one rule says that protection is not allowed out of reach of the pilot, and another rule says it must be installed in circuits that are not capable of handling maximum battery current, which could be several hundred amps. Which rule should be followed? Which makes the most sense?
 
rvbuilder2002

I was able to review the pertinent sections of ASTM 2245-14 and I don't find any language that supports that claim. I'm wondering if perhaps that language was in a previous version of the spec and has since been removed.

Can you reference the actual text that lead to the above statement?


-Jeff

The ASTM standards seem ambiguous and open to interpretation and are even contradictory.

(It is not clear if that includes fusible links.)

So one rule says that protection is not allowed out of reach of the pilot, and another rule says it must be installed in circuits that are not capable of handling maximum battery current, which could be several hundred amps. Which rule should be followed? Which makes the most sense?

Guys, I am not going to get sucked into a debate on this subject.
The person that is responsible for F-2245 at ASTM has been consulted many times regarding topics that seemed ambiguous (that is part of the license fee paid to use the document) . The RV-12 electrical system was designed based on that feedback.
 
Guys, I am not going to get sucked into a debate on this subject.

Good call, brings back memories of some of the arguments I would get into with mechanics at the airline "I don't care what Boeing says, that's not right and I'm not doing it" :confused:
 
From the ASTM website:
ASTM membership and staff are prohibited from providing official interpretations of ASTM standards. While an ASTM member may offer a personal opinion, the only action a committee or subcommittee may take is to introduce a revision to the standard to further clarify its intent. Any response is personal opinion and unless otherwise stated does not represent that of the committee of ASTM.
So any advice that Van's Aircraft received from an ASTM member is only a personal opinion and is not legally binding and might not even be good advice, considering the recent engine fire. I think that aircraft manufacturers are free to interpret ambiguous ASTM standards in a way that will result in the safest aircraft.
 
From the ASTM website:

So any advice that Van's Aircraft received from an ASTM member is only a personal opinion and is not legally binding and might not even be good advice, considering the recent engine fire. I think that aircraft manufacturers are free to interpret ambiguous ASTM standards in a way that will result in the safest aircraft.

I guess anyone is entitled to have an opinion that a design aspect that has been duplicated in literally 10's of thousands of certificated aircraft, and probably the majority of the 8900+ RV's that are flying, is totally wrong and unsafe.

Jim has chosen not to publicly provide detailed info regarding the cause of his engine compartment fire at this time. The info I have received privately makes me have faith in leaving the design as it is (the same as 10's of thousands of other aircraft).
 
Jim has chosen not to publicly provide detailed info regarding the cause of his engine compartment fire at this time. The info I have received privately makes me have faith in leaving the design as it is (the same as 10's of thousands of other aircraft).

That's good enough for me!!

Tom
 
Scott, I did not mean to imply that the practice of not protecting the battery feeder is totally wrong and unsafe. And I am not necessarily recommending the installation of a fusible link, although it would not hurt. The point that I was trying to make is that ASTM standards do not specifically prohibit fusible links in the engine compartment. The ASTM standards are not clear on this subject, so I have suggested to ASTM org a wording change.

Existing A2.9.2.3 standard: "Be accessible to and in clear view of the pilot"

Suggested change: "Be accessible to and in clear view of the pilot. (This standard shall not apply to fusible links). This standard shall not prohibit protection of remote circuits nor shall it prohibit complying with A2.9.2.1

We might disagree on some minor issues, but overall I think that we agree that the RV-12 is a great airplane and the fire was not a design fault.
 
Just a crazy thought

Seams this would be a great place for a remote circuit breaker with a solenoid with a ground wire reset
 
I'd be concerned about adding a lot of complexity to a circuit who's rate of failure is pretty low. If you want to improve on the current design, you may want to consider putting the solenoid on top of the battery box, or otherwise, shortening the unprotected wire to it's shortest length possible. That would practically eliminate any possibility of it shorting out against structure.

I'm pretty comfortable with the current design. I checked my wire as part of my condition inspection and I verified that it's not touching anything and no other wires or structure interfere with it's run over to the solenoid.

As a side note, I wired my Cobra in a similar manner as my airplane because I wanted to eliminate the possibility of hot wiring the starter. I used a fusible link on the power wire because of it's proximity to structure. Just another data point.
 
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Randy,

I think the wire in question is down-stream of the master solenoid/relay. In other words, this wire goes from the load side of the master solenoid to the fuse/distribution panel near the instrument panel.

It is not the wire from the battery to the batt side of the master solenoid, therefore moving physically closer to the battery would have no effect.

But I do agree that an exotic remotely-resetable circuit breaker is not the solution. A simple current limiter, like an ANL or similar, would be just fine and would have prevented this fire.


-Jeff
 
Ah, thanks Jeff. I went back and re-read the thread. Should have done that instead of using my memory.
 
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