 |
Matronics Email Lists
Web Forum Interface to the Matronics Email Lists
|
| View previous topic :: View next topic |
| Author |
Message |
rhdudley1(at)bellsouth.ne
Guest
|
 Posted: Thu Jan 29, 2009 8:30 am Post subject: NASCAR 2007 Crash- Reset Circuit Breaker |
 |
|
Bob,
The FAA's conclusion of the causes of the NASCAR crash in 2007 was published in the Orlando Sentinel today:
http://www.orlandosentinel.com/news/local/seminole/orl-planecrash2909jan29,0,4517645.story
It is a great example that supports of your rationale for fuses vs circuit breakers.
Regards,
Richard Dudley
-6A (with fuses) sold
[quote][b]
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
 |
nuckolls.bob(at)aeroelect
Guest
|
| Posted: Thu Jan 29, 2009 1:06 pm Post subject: NASCAR 2007 Crash- Reset Circuit Breaker |
|
|
At 10:03 AM 1/29/2009, you wrote:
Hmmmmm . . . it's not clear from this story that
the outcome would have been any different had
the airplane been fitted with fuses.
Both fuses and breakers are crafted with the
hard-fault in mind. I.e. a pretty solid short
or overload that causes a current several times
greater than the protection rating.
We've had some discussions on the List concerning
what I call soft faults. I've had several occasions
to study the difference and have delivered a number
of explanatory presentations to folks in my industry.
The "hard" fault is generally over in tens of
milliseconds but 10 seconds max. And while the current
flow is high, the total ENERGY dissipated in highly
stressed components is relatively low compared
with . . .
Soft faults are those events that DO NOT stress the
over current protection very hard. Examples of this
condition made big news in SwissAir 111 accident
a few years back were it was decided that prolonged
arcing at or below the breaker trip calibration set
un-qualified insulation on fire.
Here are some excerpts from a presentation I gave
on the topic where some folks were agonizing over
the existence of a 10AWG feeder downstream of an
8AWG feeder protected by a 50A breaker.
http://www.aeroelectric.com/articles/Hard_vs_Soft_Faults.pdf
This airplane was built in 1977.
http://www.ntsb.gov/ntsb/GenPDF.asp?id=NYC07MA162&rpt=p
I'm sure the Cessna west-side guys were using the same
wire as us east-side guys . . . Mil-W-16867 type
BN (nylon over pvc). . . Tefzel didn't get a good
grip in local aircraft fabrication for several more
years.
What's more, this insulation was 30+ years old
at the time of the accident. It seems the pilot
might have thought a previous day's smoke event
was limited to the radar or associated wiring when
the first problem abated after a breaker was pulled.
The airplane was so totally destroyed by fire that
we can only guess as to root cause and successive
events. But it's not a far reaching hypothesis to
suggest that the first event may have damaged other
wires in a bundle placing them at risk for continued
failures beyond those associated with the radar
system.
When we see an accident where an electrically
induced fire is suspected, it's almost a 100% bet
that the failure was a soft fault that dumped a lot
of energy without exceeding the ratings of the
fuses or breakers.
Given the nature of modern insulations I'll suggest
likelihood of this type event repeating in your
OBAM aircraft is exceedingly small. Tefzel is about
as close to an ideal insulating material as we've
ever seen. From eye witness descriptions if this
incident we can assume that the problem was less
electrical and more a function of flammable materials
continuing to burn.
The accident stories noted that their last
transmission was interrupted mid sentence. I can
only guess that they were already in a lot of
trouble with an electrical system that was still
energized.
When you smell smoke, the best advice is to shut
down the electrical system in its entirety and
continue with hand-helds as needed to a no-sweat
landing.
If you really NEED stuff on the e-bus, wait until
you know the smoke event is over before bringing
the e-bus back on through the alternate feed. Turn
of any un-needed, e-bus powered accessories before
powering it back up. Be ready to kill it if smoke
resumes.
Bob . . . [quote][b]
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
| Back to top |
|
|
|
|
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum
|
Powered by phpBB © 2001, 2005 phpBB Group
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
