Mailing List lml@lancaironline.net Message #44780
From: <Sky2high@aol.com>
Sender: <marv@lancaironline.net>
Subject: Re: [LML] Re: Design for Circuit Breakers & Fuses?
Date: Wed, 07 Nov 2007 15:11:16 -0500
To: <lml@lancaironline.net>
In a message dated 11/7/2007 8:47:06 A.M. Central Standard Time, rpastusek@htii.com writes:

You have a good point if you intend/need to troubleshoot while still in the air. As I noted in my original post, many years of doing this in military fighters (as a weapon systems operator—with a well qualified pilot still flying the jet and typically swearing because his xyz was not working) convinced me that this was (in my experience) a totally pointless exercise. I’m pretty sure I never recovered a system by resetting a CB, and I once caused a fire in the cockpit, and killed a generator another time. Still, I’ve heard that others have successfully recovered systems by resetting CB’s. So in the end, you make your own tradeoffs/decisions. Everything is a compromise at some level…

Bob,
 
You are correct about the flight regime but I find certain breakers very useful during maintenance, especially if the Master Switch must be on during the work or for certain testing.
 
1. Hydraulic pump breaker (and the relay inline fuse wired after the breaker).  This eliminates the pump running or relays be being selected when one doesn't want it operating.
 
2. TC breaker - reduces load on battery when checking other things
 
3. Alt field breaker - reduces load.
 
4. Certain electronic flight instruments - reduces load.
 
5. Certain avionics components (no on-off switch) can be excluded.
 
Interestingly, occasionalIy have a use for the Facet pump (aux tank to header) breakers in flight with the automatic keep-the-header-full engaged.  I can disable one of the pumps for a while in order to balance the mistake of mis-fueling the aux tanks - more fuel in one than the other.
 
I certainly like fuses for most circuits - mine are accessible only if I remove the glare shield - a minor hassle.
 
 
Scott Krueger AKA Grayhawk
Lancair N92EX IO320 SB 89/96
Aurora, IL (KARR)

Darwinian culling phrase: Watch This!




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