Radio and Transponder problems

Robert G. White · Post by **Robert G. White** » Sun Mar 09, 2003 7:40 pm

I installed a new avionics package in my plane last year. In doing so, I rewired the entire avionics system, with an individual (pull for off) circuit breaker for each component. I have a avioics master switch AND a standby avionics master switch, as recommended in the handbooks. This was endorsed by both the IA and the FAA guy. This was the one bottleneck or failure point that is common to all. By putting in a second source of power I have redundancy in this critical spot. This is much perferred to not having way to isolate the avionics, other than pulling each CB, if possible. Component on-off switch failure, a grounded lead or any number of faults can be isolated and overcome in flight, rather than pulling THE master switch for the entire electrical system.
Blue skies to all, Bob

russfarris · Post by **russfarris** » Mon Mar 10, 2003 6:20 am

Hi Bob, I'm not sure I understand exactly what you have done. You have TWO seperate avionics master switches, wired in series? In other words, either switch, when turned on will power the avionics bus? I get the bit about the CB's. Explain your setup a little more, if you please! Russ Farris

P.S. I've been to Oregon, and it was anything but Boring

(I couldn't resist it!)

russfarris · Post by **russfarris** » Mon Mar 10, 2003 6:45 am

I think it's laudeable to have redundant systems, and I suppose one's own comfort level has alot to do with it, but the way most 170's are operated, worrying about radio master switch failures is a little over the top, IMHO. I fly mine IFR when conditions require it, and a battery powered hand-held VHF is all I need to feel comfortable.

To really give you guys something to worry about, if the master switch itself should fail, or the ground wire to it breaks, you have lost your entire electrical system! Talk about your single point failures...Russ Farris

Robert G. White · Post by **Robert G. White** » Mon Mar 10, 2003 7:45 am

Russ: Both avionic master switches have a lead from the main bus, then a lead from the switch to the avionics bus bar. You may have one or both on to supply power to the avionics bus. The regular switch is a CB switch combination. The standby is plain switch. The theory is that if something heats up and burns the avionics master switch, the pilot can pull the standby master and recycle things and isolate the problem. Yes, the battery gen master can itself fail, although that seems less likely than the avionics switch as they are very heavy duty. However, having a standby avionic master means one less thing to worry about... and the IA and FAA guys insisted. Yes, our town gets on TV now and then... a Boring school, a Boring fire station, etc.
Blue skies to you, Bob

zero.one.victor · Post by **zero.one.victor** » Mon Mar 10, 2003 6:06 pm

Number one,Russ,I believe that the switch wiring you describe is "in parallel",not "in series". In series would require that BOTH switches be on to power the remainder of the circuit.
Secondly,Bob,I would personally think long & hard about turning on the #2 avionics master,after the primary avionics master switch/CB had failed (or "burns",as you put it). Seems like that's tempting lightning to strike twice! But it's your plane,not mine.
What all radio gear do you have installed? Like I said,I have just a navcom,txp,and intercom. I check each anyway (for frequency,squawk,and mode) as part of my start-up checklist,so I turn them on as I go. An avionics master wouldn't really save me any time,and I consider it a possible problem area,so out it went!

Eric

Robert G. White · Post by **Robert G. White** » Mon Mar 10, 2003 7:13 pm

Eric: I am not too sure either, about powering things up after a failure... but as I said the IA and FAA guys said to put it in. I was appalled by all the sloopiness and splices and such... when I removed everything to make up my new panel. So decided to do my own installation... under the close supervision of an IA, of course.... I have a UPS Apollo (they are nearby in Salem) GX60 GPS/COM with a Mid Con. MD200-306 indicator and a UPS annuciator; UPS SL30 NAV/COM with a KI-209 indicator; KX-76A; and an audio panel. 12 CB and over 200 wire runs. "Heck... I couldn't even spell aveeonicker, now I are one" is the way it turned out. The handbooks and wire diagrams were a piece of cake to follow... did it all on my kitchen table. The FAA guy was very decent... I made a new panel and reorangized the instruments (replumbed and new gyro's, too) to the FAA reg standard for IFR layout. I did not alter controls and they clear the center stack with the audio panel at the bottom, as it is shorter. Of course this all took about two months of evenings and odd weekends, but I am very pleased and the FAA guy was, too. Forgive long story and also, I have a square tail 182. I'll send you a picture if you wish... email me. BobWhite@pcez.com
Blue skies to you, Bob

Dave Clark · Post by **Dave Clark** » Mon Mar 10, 2003 7:32 pm

Hey Bob, post the picture on the instrument panel thread I started for that purpose. My photo is feeling kinda lonely there.

russfarris · Post by **russfarris** » Mon Mar 10, 2003 9:42 pm

Eric, yeah that's the ticket! I did mean parallel. What came out of my brain was series. I continue to be mystfied by electricity and women. Russ Farris

Post by **GAHorn** » Sat Mar 15, 2003 7:24 pm

Two avionics power (master) switches, one an ordinary switch and one a CB/switch, wired in parallel,...with both on...defeats the purpose/function of the CB/switch. With the ordinary switch closed, sufficient power is allowed to bypass the CB that a fire is possible in the event of a short. In this type installation, it would be far better to install both as CB/switches, and use only one at any given time, using the other as a "backup" avionics power source.

Robert G. White · Post by **Robert G. White** » Sat Mar 15, 2003 9:07 pm

George:
Good point! The intent in practice is to have only the master with the CB "on" under normal conditions. Should if fail, then go thru and shut the individual units off, perhaps checking if one of them has caused the problem, then power up with the stand-by switch. I bought a new CB switch and used the original factory avionic switch for the stand-by. Now that you have pointed out the danger of having both on, I think I will change the stand-by to a CB switch, too. As I said, both the IA and FAA insisted that I have a standby avionics master. Thanks for the tip.
Blue skies to all, Bob

Post by **GAHorn** » Sun Mar 16, 2003 4:52 pm

The concept of a standy avionics master is good, but just to "give 'em hell"

you might point out the both the FAA and the IA that their idea/design is contrary to the original manufacturer's design, which had an ordinary pull-switch as a radio master. (See the Owner's Manual)

Robert G. White · Post by **Robert G. White** » Sun Mar 16, 2003 7:02 pm

George: Actually, I thought it was a good idea, too... and it's been over a year now since all done. Plus, I sorta needed to be careful for what I wished for... esp when it comes to original equipment... I made an entirely new panel which was approved, besides the avionics changes.
Blue skies to you, Bob

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Radio and Transponder problems

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