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AeroElectric-List:Wiring integrity!!!

 
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fstringham



Joined: 10 Jan 2006
Posts: 87

PostPosted: Tue May 08, 2007 4:00 pm    Post subject: AeroElectric-List:Wiring integrity!!! Reply with quote

A Cessna 210 on a flight from San Antonio to Seattle when his distress call
said smoke in the cabin. The sad out come was the pilot lost control and
crashed near Springville, Utah.

Now i know that there are other causes of smoke but it raised my concern of
eletrical fires.

I am wiring my plane according Z-13/8. Now the question: What are the usual
failure points that cause electrical fires? in aircraft wiring systems?

I know this is pretty open ended and I must also admit that I haven't done
a search yet so if you want to with hold until I have done my home work
that is fine but if you have some pearls of wisdom .......please
help!!!!!!!!!!!!!!

Frank (at) SGU RV7A "NDY" Panel / electrical.....

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nuckollsr(at)cox.net
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PostPosted: Tue May 08, 2007 9:50 pm    Post subject: AeroElectric-List:Wiring integrity!!! Reply with quote

At 05:57 PM 5/8/2007 -0600, you wrote:

Quote:

<fstringham(at)hotmail.com>

A Cessna 210 on a flight from San Antonio to Seattle when his distress
call said smoke in the cabin. The sad out come was the pilot lost control
and crashed near Springville, Utah.

Now i know that there are other causes of smoke but it raised my concern
of eletrical fires.

I am wiring my plane according Z-13/8. Now the question: What are the
usual failure points that cause electrical fires? in aircraft wiring systems?

This is one of the really BIG problems with 99% of the
stories cited with tid-bits of anecdotal info. I've worked
accidents with smoke in cabin from blower motors, gas-fired
heaters, smoking components within a radio, and a fire
in a junction box precipitated by out-of-sequence switching
of batteries in a 24-48v cranking system on an MU-2. In
every case, pilots got the airplane on the ground but in
the MU-2 a post-landing fire trashed the interior (although
a technician who worked for me years later in the video
business worked on the restoration of the same airplane!).

In the few cases where I've been privy to the initial
failure of a major system component where the pilots lost
control and died, none of them involved smoke in the
cabin and all scenarios stretched a pilot beyond his
ability to cope with the situation. One was a dual
alternator failure on a big piston twin where both
alternators had been overhauled by the same shop who
rewound stators and failed to powder coat the stacks
or install slot liners. The two alternators were overhauled
several hundred hours apart from each other but failed
within minutes of each other on the same flight . . . in
icing IMC.

When queried as to how many accidents had been investigated
at Beech/RAC/Hawker-Beech wherein an electrical system failure
was an initiating or participating event, not one of the
gray beards in the department could cite a case. In
one case, a soft-fault came close to causing an accident.

A C-90 on short final to Clovis NM about 1990 was
suddenly stricken with complete disconnect of control in pitch.
Elevator forces in wheel went to zero. The pilots did a go around
and managed to land safely with power and pitch trim.
A teardown revealed a mis-positioned wire bundle under the
floorboards where a 40A protected wire for co-pilot's windshield
heat had had been rubbing against the elevator cable for some
period of time.

No smoke, no fire, no flickers in the electrical system, no
trips of the 40A breaker. Over the pre-failure interval,
megajoules of energy were released in the erosion of steel
wires (the copper wire was in pretty good shape . . . this
demonstrates why layers of copper are included in the design
of safes . . . nearly impossible to penetrate with a cutting
torch).
Quote:
I know this is pretty open ended and I must also admit that I haven't
done a search yet so if you want to with hold until I have done my home
work that is fine but if you have some pearls of wisdom .......please
help!!!!!!!!!!!!!!

The best thing I can offer is do a good job installing
your equipment. Be ready to shut EVERYTHING but the engine
off should you experience a smoke event. But know too that
likelihood of an electrical system generated smoke event
causing a bad day in the cockpit is exceedingly remote. If you
do get a smoke event, keeping your cool is more important
than self recriminations for not having anticipated the
event or loosing sleep over trying to anticipate it now.

I wouldn't worry about it.

Bob . . .


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john_rv10(at)yahoo.com
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PostPosted: Wed May 09, 2007 1:03 am    Post subject: AeroElectric-List:Wiring integrity!!! Reply with quote

Hi Frank,

For what it is worth, we recently had a hangar fire at our airport. The fire
started in a trike, which was wasted, and several other aircraft have been
written off or seriously damaged.

At this stage they believe the fire was started by the battery cable which
was positioned across and sitting on an aluminum angle with no stand off and
no added protection.

Regards,
John

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PostPosted: Wed May 09, 2007 5:43 am    Post subject: AeroElectric-List:Wiring integrity!!! Reply with quote

At 07:01 PM 5/9/2007 +1000, you wrote:

Quote:


Hi Frank,

For what it is worth, we recently had a hangar fire at our airport. The fire
started in a trike, which was wasted, and several other aircraft have been
written off or seriously damaged.

At this stage they believe the fire was started by the battery cable which
was positioned across and sitting on an aluminum angle with no stand off and
no added protection.

Regards,
John

Have you seen any of the forensics on this? When
we conducted some tests on battery feeders against
aluminum some years ago, it was difficult to get
the odd insulation failure event to precipitate
much of an energy release. The high currents
available from a battery would burn the fault open
quickly. High currents flowed for short periods
of time but cleared without much fanfare.

I'm presuming that this airplane was parked and
we're considering a piece of cable that runs between
battery(+) and the contactor. If you have a chance to
learn more about the details and any analysis that
grew out of the facts, I'd be interested in
knowing about them. Thanks for sharing this with
the List.

Bob . . .


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PostPosted: Wed May 09, 2007 12:45 pm    Post subject: AeroElectric-List:Wiring integrity!!! Reply with quote

Bob,

The trike was parked. It had been on a long trip on a trailer the day
before, which may, or may not be relevant.

Investigation at the factory has shown that there is variability in the way
the wiring runs are done, with only some ships wired the way this one was.

If I can learn anymore on the forensics I will let the group know.

John

--


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PostPosted: Sat May 12, 2007 10:56 am    Post subject: AeroElectric-List:Wiring integrity!!! Reply with quote

Bob,

I have now spoken directly to the chap who brought the offending trike home
and parked it on the evening before the fire. He lost a lot of equipment in
the fire and has been personally involved in the investigation.

Following is my interpretation of his comments:-

1. The fuel tank is plastic with a cavity formed in it to hold the battery.
2. The wiring runs in a 1 inch bundle including the main positive and
negative leads. The loom passes across and sits on a plastic saddle in the
fuel tank, level with the top of the battery, and about 2/3rds the way down
from the top of the fuel tank. The loom is wrapped in black spiral wrap
3. The main wires from the battery are reported to be 8mm red pvc coated 80
amp leads.
4. There are 2 parallel fusible link wires swaged to the battery connector
and to the main positive lead designed to withstand 1 minute of engine
cranking. The cranking amps was unknown by this guy.
5. The distance from the battery to the starter solenoid was approx 2 feet
6. On one other factory trike inspected, the wire bundle was plastic cable
tied to an elbow on the water pump. The trike was 18 months old and had done
about 250 hours
7. The distance from the battery to the elbow is about 12 inches
8. There was about 12 inches of the loom recognizable after a fire intense
enough to turn Al tubing to white powder.
9. There were the 2 stubs from the fusible link at one end, and a glob of
fused copper at the other end.
10. The battery was a 12v 18AH Gel Cel. It was recognizable, but had the
top, terminals and start of leads burnt away and was badly distorted

The earlier story about the wires passing over an Al angle was a case of
Chinese whispers.

I trust this is of some use,
John

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