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Should a tripped circuit breaker be reset in flight?

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user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Thu Oct 09, 2014 7:07 am Post subject: Should a tripped circuit breaker be reset in flight?

There is an article in the October 2014 issue of Sport Aviation on page 92 titled, "I'll Never Do That Again".  The author experienced an avionics failure while in IFR conditions.  Other pilots in similar emergency situations have crashed.  This pilot was very experienced.  After briefly losing control, he was able to use backup instruments and land.  While safely on the ground, he noticed a popped circuit breaker and reset it.  It immediately tripped again, accompanied by an unusual smell.  The pilot wrote, "I will never reset a breaker in the air.  I did not have a fire, but I clearly was cooking something while I was on the ramp.  Flames on the ground are a problem.  Flames in the air are deadly."

  Take away the resettable feature of circuit breakers and they have no advantage (in most cases) over fuses, other than the cool factor of the appearance of a neat row of breakers.  Fuses cost less, weigh less, and never fail to open when overloaded.

Joe

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Joe Gores

rv8builder

Joined: 02 Jan 2009
Posts: 56

Posted: Thu Oct 09, 2014 9:35 am Post subject: Re: Should a tripped circuit breaker be reset in flight?

In my former life as an airline pilot, the policy on reseting CB's in flight was "If it is absolutely needed for flight (gear, etc), one reset was allowed.  If it was not needed for flight (galley, cabin lights, cabin entertainment, etc) no reset in flight was allowed.



Dale

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Dale

stearman456

Joined: 14 Aug 2010
Posts: 49

Posted: Thu Oct 09, 2014 12:38 pm Post subject: Re: Should a tripped circuit breaker be reset in flight?

 	  rv8builder wrote: 	
		  In my former life as an airline pilot, the policy on reseting CB's in flight was "If it is absolutely needed for flight (gear, etc), one reset was allowed.  If it was not needed for flight (galley, cabin lights, cabin entertainment, etc) no reset in flight was allowed.



Dale 	




That pretty much covers my current airline's philosophy:  "At the discretion of the captain ONE (1) reset is allowed, except for anything involving fuel" (gauge, pump, etc).  For a fuel related item there is no reset - it becomes a problem for the maintenance guys at the next landing.  And if it's something not required for the safe completion of the current flight then we just live with it being u/s.



Dan

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mmayfield

Joined: 09 Oct 2009
Posts: 40
Location: NSW Central Coast, Australia

Posted: Tue Oct 14, 2014 1:04 pm Post subject: Re: Should a tripped circuit breaker be reset in flight?

Same in our airline. There are good reasons for not resetting tripped breakers, eg., causing the production of smoke when before there was none. FWIW in the never-ending "fuses versus breakers" debate, my design goals were:



1. The circuit protection shall be checked during preflight (a principle beaten into me during both military flying and airline training), and so tripped circuit protection devices must be easy to distinguish on the ground, and must be investigated before getting airborne.



2. In the air, tripped circuit protection shall be easily identifiable but not be reset/replaced unless I have a damn good reason for it.



3. In the air, circuit protection shall be easily reachable by system, such that if things produce unauthorised smoke, corresponding circuit protection can be manually tripped (as a backup to actually switching the system off, or in the case of items not having their own power switch).



I achieved these goals, slightly more easily IMHO, by using CBs rather than fuses although with the advent of illuminated fuses there's probably no reason why they couldn't achieve them too.



I do actually know of a couple of instances when I was in the military where boxes produced smoke airborne and CBs had to be pulled.

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Mike

jluckey(at)pacbell.net
Guest

Posted: Tue Oct 14, 2014 2:00 pm Post subject: Should a tripped circuit breaker be reset in flight?

Mike,

All excellent points and it's good to hear from people who've had exposure to different organizations.  I'm not an airline pilot & never served in the military.

I would like to clarify one point.  In this and other posts, people have referred to fuse panels which have "fuse blown" indicators in the form of red LEDs mounted next to the fuse.  I think these are really neat!

But, keep in mind that the LED is only lit when the fuse is blown AND the device on the other end is  turned-on or at least capable of conducting a few milli-amps to ground.  This means that if the circuit w/ the blown fuse is turned-off, the LED will not light and the blown fuse may go unnoticed.



An example will help illustrate.  Let's say that while taxing back to your hangar one night, the landing light fuse blows.  No big deal - you're on the ground & home - you'll fix it next weekend.  Then, next weekend you get out to the plane and you forget about the inop landing light.  The "fuse blown" LED will not light up when you power-up  the buss because there is no path to ground for the LED.

This is really not a big deal, however, if that had been a breaker instead of a fuse, the breaker would still be 'popped' and sticking up when you got back to the plane.  The point being that a popped circuit breaker can be a conspicuous reminder of a problem.

The argument could be made that a popped breaker is easier to detect than a blown fuse as Mike points out.



-Jeff





 

     On Tuesday, October 14, 2014 2:17 PM, mmayfield <mmayfield(at)ozemail.com.au> wrote:

  

  



 --> AeroElectric-List message posted by: "mmayfield" <mmayfield(at)ozemail.com.au (mmayfield(at)ozemail.com.au)>



Same in our airline. There are good reasons for not resetting tripped breakers, eg., causing the production of smoke when before there was  none. FWIW in the never-ending "fuses versus breakers" debate, my design goals were:



1. The circuit protection shall be checked during preflight (a principle beaten into me during both military flying and airline training), and so tripped circuit protection devices must be easy to distinguish on the ground, and must be investigated before getting airborne.



2. In the air, tripped circuit protection shall be easily identifiable but not be reset/replaced unless I have a damn good reason for it.



3. In the air, circuit protection shall be easily reachable by system, such that if things produce unauthorised smoke , corresponding circuit protection can be manually tripped (as a backup to actually switching the system off).



I achieved these goals, slightly more easily IMHO, by using CBs rather than fuses although with the advent of illuminated fuses there's probably no reason why they couldn't achieve them too.



I do actually  

 

  

 

 [quote][b]

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stuart(at)stuarthutchison
Guest

Posted: Mon Oct 20, 2014 4:54 am Post subject: Should a tripped circuit breaker be reset in flight?

G’day Mike,



There might be a few chuckles over your remark … not even Bob has a patent on good ideas, but mortals are on a hiding to nothing arguing electrical architectures with him   I have a long P3 Orion background where CBs are used (and sometimes abused) by the hundreds too, but it never ceases to amaze me how much common sense and experience Bob has in his head and how well he can describe it !



We’re in your debt … onya Bob.



Cheers, Stu

On 20 Oct 2014, at 9:39 pm, mmayfield <mmayfield(at)ozemail.com.au> wrote:



 	  Quote: 	
		   

 

 Well Bob, you need to write to Boeing about addressing those issues and their system design or poorly conceived procedures because they are direct from the Boeing FCOM. Best of luck with that!

 

 The "tea and biscuits" metaphor was just that. Yes he was called to explain what happened but in this particular case I don't believe it was actually an inquisitorial meeting (notwithstanding that it can be). However there was a reminder issued that checking the breaker panels is a preflight requirement and it was a big deal.

 

 Even in my small plane, the breakers are there. They should all be in for engine start. Just like every other switch position I check before engine start in a standard panel scan, the breakers are part of that scan.

 

 As an interesting aside, the Airbus A330 has all its physical breakers down in the electronics compartment. Technically it's accessible, but not within arms reach. However Airbus needed a way of allowing pilots to pull and reset power to systems so they created an overhead panel with "breaker-like" switches - they do not function as circuit protection but look exactly like breakers, and physically pull and push in the same manner!

 

 It is quite common on the Airbus to use these to reset a system, both on the ground and in the air.

 

 --------

 Mike

 

 

 

 

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