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nuckolls.bob(at)cox.net
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 Posted: Mon Jul 14, 2008 11:49 am Post subject: Sleep well tonight, our government is AWAKE! |
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Over the past several years I've referred to my participation
in an investigation into the failure of a couple of switch-breakers
on a Beech Baron. The part is almost exactly the same device you
can buy at Aircraft Spruce and looks like this:
http://aeroelectric.com/Pictures/Breakers/W31_1.jpg
It seems that about 80,000 switch breakers were supplied to
Beech after a production change at Potter Brumfield that
eliminated the functional equivalent of the little piece
of insulation you see upper left inside corner of the
bracket was left out. No big deal . . . sorta.
As long as the bundle of fine wires maintains continuity
between the lower arm of the switch and the frame, everything
is right with the world.
The switch has passed many mechanical and electrical life
cycle tests in the lab over the past 20+ years. Everything
was cool.
Now comes the unexpected event that all those little copper
wires no longer maintain their intended electrical continuity . . .
in switches that are seldom operated in the airplane. Deice.
Hmmmm . . . how can this be? It seems that laboratory tests
for vibration did not reveal the effects of 10-20 years
of service that with effects of corrosion, low level but
persistent vibration, and UNRELIEVED stress risers right
at the points where the braids were spot-welded to their
respective locations on the switch arm and the frame.
For all the fuss-n-bother we went to in crafting
two-crimp terminals for wires where stress risers in
the wire grip are relieved by support at the insulation
grip . . . here we have the internal components of a switch-
breaker that do not enjoy the same level of fuss-n-bother
for equally vulnerable features.
Okay, so the wires break, now what? Since current can
no longer flow between the switch arm and frame on a nice
fat copper conductor, it flows instead through the spring. If
the breaker is lightly loaded . . . like the 5 and 10 amp
applications, no big deal. However, on airplanes fitted
with electric De-Ice heaters, it's another deal altogether.
So, as you can see in the picture, P-B is now installing
an insulator between frame and spring that prevents the
spring from becoming a toaster-element in high current
situations where the braid string is broken.
Beech has been using these breaker-switches from Skippers
to Barons for a very long time. The implications of a
fleet wide AD were, shall we say, $significant$? There was
a great deal of testing and analysis to deduce
justification for a blanket AD . . . or a testing
procedure (my little 4-wire ohmmeters at:
http://aeroelectric.com/articles/grnding.pdf
and
http://www.aeroelectric.com/articles/LowOhmsAdapter_3.pdf
will easily detect a failed or nearly failed
braid jumper).
We spent considerable time justifying an opinion that the
smaller breakers (the vast majority) did not represent
a hazard. Even the large breakers, while they squirted
smoke out the panel from around the toggle handle) the
represented a very low risk of propagating into a fire.
Folks at numerous user groups including the Bonanza Society
agreed.
But today I became aware of this jewel from our ever vigilant
benefactors/protectors in Washington . . .
http://www.aeroelectric.com/Reference_Docs/FAA/2008-13-17.pdf
It's obvious that the folks who were in the position of
deciding whether or not the FAA agreed or disagreed with
lowly commoners do not have a clue as to the physics of
the matter over which they have command and control. The
problem was not an "internal short" but an open that happens
only after a lot of time in service. Other verbiage in the
FAA document suggests that the writers have no knowledge
of the physics and an excellent knowledge of the rules
upon which one bases a you-can't-be-too-safe decision.
I'll call your attention to the compliance costs analysis
on page 5 of the document. The cost to an owner-operator
to replace this $25 breaker is about $185 each on airplanes
that range from the lowly Skipper (no De-Ice installed)
to the Barons with as many as 15 such switches (I think 3 of
the 15 were high-current applications).
This little mini-seminar has important lessons for us
in the OBAM aviation community. Its a demonstration
of risk for improperly connected wires of any size even
if INSIDE a product were you're not able to inspect them.
It's a demonstration of the value of lower parts count,
simpler construction in terms of reliability. The fuse-block/
fuse/switch combination suggested in my writing could not
get much simpler, less expensive to install, or less
expensive to maintain.
Finally, it's a small insight into a growing lack of
expertise on the part of individuals who WE pay to protect
us from ourselves. Once the TC pistons have become too
expensive to own/operate, the ever growing numbers of
protectors with too little to do will be looking for
new venues to ply their skills . . . or lack thereof.
Guess where THAT's going to be?
Bob . . .
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kahuna
Joined: 02 Feb 2007
Posts: 93
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| Posted: Mon Jul 14, 2008 1:09 pm Post subject: Sleep well tonight, our government is AWAKE! |
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|
Even after 10+ years of watching every email on this list, I still get educated for free everyday.
This list is one of lifes great pleasures.
The free classroom, the discussions, and yes even the banter is entertaining.
Thanks Bob yet again for spending the time to tell your story. Great read.
Best,
Mike
do not archive.
[img]cid:1__=0ABBFE15DFE08E368f9e8a93df938(at)us.ibm.com[/img]"Robert L. Nuckolls, III" ---07/14/2008 04:32:04 PM-----> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)cox.net>
[img]cid:3__=0ABBFE15DFE08E368f9e8a93df938(at)us.ibm.com[/img]
To
[img]cid:3__=0ABBFE15DFE08E368f9e8a93df938(at)us.ibm.com[/img]
aeroelectric-list(at)matronics.com [img]cid:3__=0ABBFE15DFE08E368f9e8a93df938(at)us.ibm.com[/img]
cc
[img]cid:3__=0ABBFE15DFE08E368f9e8a93df938(at)us.ibm.com[/img]
[img]cid:3__=0ABBFE15DFE08E368f9e8a93df938(at)us.ibm.com[/img]
Subject
[img]cid:3__=0ABBFE15DFE08E368f9e8a93df938(at)us.ibm.com[/img]
Sleep well tonight, our government is AWAKE! [img]cid:3__=0ABBFE15DFE08E368f9e8a93df938(at)us.ibm.com[/img][img]cid:3__=0ABBFE15DFE08E368f9e8a93df938(at)us.ibm.com[/img]
--> AeroElectric-List message posted by: "Robert L. Nuckolls, III" <nuckolls.bob(at)cox.net>
Over the past several years I've referred to my participation
in an investigation into the failure of a couple of switch-breakers
on a Beech Baron. The part is almost exactly the same device you
can buy at Aircraft Spruce and looks like this:
http://aeroelectric.com/Pictures/Breakers/W31_1.jpg
It seems that about 80,000 switch breakers were supplied to
Beech after a production change at Potter Brumfield that
eliminated the functional equivalent of the little piece
of insulation you see upper left inside corner of the
bracket was left out. No big deal . . . sorta.
As long as the bundle of fine wires maintains continuity
between the lower arm of the switch and the frame, everything
is right with the world.
The switch has passed many mechanical and electrical life
cycle tests in the lab over the past 20+ years. Everything
was cool.
Now comes the unexpected event that all those little copper
wires no longer maintain their intended electrical continuity . . .
in switches that are seldom operated in the airplane. Deice.
Hmmmm . . . how can this be? It seems that laboratory tests
for vibration did not reveal the effects of 10-20 years
of service that with effects of corrosion, low level but
persistent vibration, and UNRELIEVED stress risers right
at the points where the braids were spot-welded to their
respective locations on the switch arm and the frame.
For all the fuss-n-bother we went to in crafting
two-crimp terminals for wires where stress risers in
the wire grip are relieved by support at the insulation
grip . . . here we have the internal components of a switch-
breaker that do not enjoy the same level of fuss-n-bother
for equally vulnerable features.
Okay, so the wires break, now what? Since current can
no longer flow between the switch arm and frame on a nice
fat copper conductor, it flows instead through the spring. If
the breaker is lightly loaded . . . like the 5 and 10 amp
applications, no big deal. However, on airplanes fitted
with electric De-Ice heaters, it's another deal altogether.
So, as you can see in the picture, P-B is now installing
an insulator between frame and spring that prevents the
spring from becoming a toaster-element in high current
situations where the braid string is broken.
Beech has been using these breaker-switches from Skippers
to Barons for a very long time. The implications of a
fleet wide AD were, shall we say, $significant$? There was
a great deal of testing and analysis to deduce
justification for a blanket AD . . . or a testing
procedure (my little 4-wire ohmmeters at:
http://aeroelectric.com/articles/grnding.pdf
and
http://www.aeroelectric.com/articles/LowOhmsAdapter_3.pdf
will easily detect a failed or nearly failed
braid jumper).
We spent considerable time justifying an opinion that the
smaller breakers (the vast majority) did not represent
a hazard. Even the large breakers, while they squirted
smoke out the panel from around the toggle handle) the
represented a very low risk of propagating into a fire.
Folks at numerous user groups including the Bonanza Society
agreed.
But today I became aware of this jewel from our ever vigilant
benefactors/protectors in Washington . . .
http://www.aeroelectric.com/Reference_Docs/FAA/2008-13-17.pdf
It's obvious that the folks who were in the position of
deciding whether or not the FAA agreed or disagreed with
lowly commoners do not have a clue as to the physics of
the matter over which they have command and control. The
problem was not an "internal short" but an open that happens
only after a lot of time in service. Other verbiage in the
FAA document suggests that the writers have no knowledge
of the physics and an excellent knowledge of the rules
upon which one bases a you-can't-be-too-safe decision.
I'll call your attention to the compliance costs analysis
on page 5 of the document. The cost to an owner-operator
to replace this $25 breaker is about $185 each on airplanes
that range from the lowly Skipper (no De-Ice installed)
to the Barons with as many as 15 such switches (I think 3 of
the 15 were high-current applications).
This little mini-seminar has important lessons for us
in the OBAM aviation community. Its a demonstration
of risk for improperly connected wires of any size even
if INSIDE a product were you're not able to inspect them.
It's a demonstration of the value of lower parts count,
simpler construction in terms of reliability. The fuse-block/
fuse/switch combination suggested in my writing could not
get much simpler, less expensive to install, or less
expensive to maintain.
Finally, it's a small insight into a growing lack of
expertise on the part of individuals who WE pay to protect
us from ourselves. Once the TC pistons have become too
expensive to own/operate, the ever growing numbers of
protectors with too little to do will be looking for
new venues to ply their skills . . . or lack thereof.
Guess where THAT's going to be?
Bob . . .
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