Intermittent avionics

gprellwitz

gprellwitz

Touchdown! Greaser!
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Grant Prellwitz
Onwards' recent thread brought to mind a problem I 've been having in the C182S that I rent. We've squawked and the avionics shop has looked and been unable to reproduce a problem where the transmitter on COM1 just doesn't seem to want to be crystal clear. This is a standard 1999 C182S stack with King avionics.

What I don't think has gotten to the avionics folks is that this only happens after it's been flying a hour or two, and seems to be largely toward the left end of the spectrum, mainly between 119 and 120MHz, with a bit of fudge factor. If we switch over to COM2, everything is fine. We can receive on COM1 without problem, but transmitting is a real problem for the recipient. I was wondering if anyone had any suggestions on what to look at.
 
kgruber said:
Can you swap Com1 and Com2?
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Not sure what you mean. As a renter, there's very little I can do physically to the plane! Transmitting on COM2 tends to work fine. I can suggest that they swap the COM1 and COM2 radio heads, but that costs AMUs, and there's no guarantee that they'll be willing to do that. On the other hand, this plane is on a Part 135 certificate and the owner is aware of the difficulty. The avionics shop just hasn't been able to narrow it down yet!
 
Intermittent faults are the worst. If you cannot talk directly to the avionics tech yourself, I've found that nothing beats writing up a detailed squawk, even if it takes a page or two, explaining:

The problem. (Com 1 transmissions are reported as unclear by listeners)
When it happens (only appears to happen after flying for 2 hours or more)
What you think may be causing it (don't know, possibly heat related?)
Any troubleshooting you've done (Turned unit off and back on, no change?)
Any other observations (Comm 2 is OK).

At least then the tech may say "hmm let me put this thing on ground power and let it run for a couple of hours, and then try to test it".

Best wishes,
 
kgruber said:
Can you swap Com1 and Com2?
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gprellwitz said:
Not sure what you mean.
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He means have them pull the top and bottom radios and put each in each other's trays (top now bottom, bottom now top).
That will help determine if there's something wrong with the physical radio (if it now happens with the bottom radio), or an issue with trays, heating, or antennae (if the problem stays with the top position, not the actual radio).

Big, big help in determining the problem by narrowing down variables.
 
PilotAlan said:
He means have them pull the top and bottom radios and put each in each other's trays (top now bottom, bottom now top).
That will help determine if there's something wrong with the physical radio (if it now happens with the bottom radio), or an issue with trays, heating, or antennae (if the problem stays with the top position, not the actual radio).

Big, big help in determining the problem by narrowing down variables.
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Okay, makes sense. It also has the benefit of exercising any connections and possibly cleaning them. Unfortunately, as I noted, I'm a renter, so have limited access.

OTOH, I did fly with the owner down to the Bahamas earlier this month, so we were able to run through some basic troubleshooting over about 18 hours of flying. I'd already told him much of the details, but, of course, being able to see it himself over a long trip was helpful. And he has had it to the avionics shop for this before, but they always say "we can't reproduce it." That's why I was trying to give him the most detailed info I could.
 
gprellwitz said:
Okay, makes sense. It also has the benefit of exercising any connections and possibly cleaning them.
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Good point. Very true as well.
Unfortunately, as I noted, I'm a renter, so have limited access.
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Understood. But you never know when such a little tidbit of information may become handy.
 
Agreed, ask them to swap the radios in the stack.

Also climb under the dash and look for the big blast hose that the C182 uses for avionics cooling and see if someone's punched a big hole in it, or it's torn. If your rental C182 doesn't have an avionics cooling fan, you might convince them to invest in one.

Nothing kills electronics faster than heat... and the top of any stack is almost always where things are hottest.

It'd be interesting to pull that top radio and have a bench alignment done on it after heating it up significantly somehow, right before starting the procedure on the workbench.
 
He said it was a standard King stack in a late(r)-model C-182S. They're swappable in every config of that model I've seen. But it's really a question for the avionics shop... he's just here for advice.
 
denverpilot said:
He said it was a standard King stack in a late(r)-model C-182S. They're swappable in every config of that model I've seen. But it's really a question for the avionics shop... he's just here for advice.
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Well, maybe. We have a 172 with the king stack. The radios are not the same. Only #1 has a glideslope.
 
Skylane81E said:
Well, maybe. We have a 172 with the king stack. The radios are not the same. Only #1 has a glideslope.
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Yeah, I don't think the 182 had that difference... but... yeah... still up to the shop...

Big shops will have loaners on the shelves of just about all radio types, and they'll gladly rack the loaner and see if it behaves correctly. Small shops, won't have that luxury.
 
I just wanted to point it out because the radios can look the same but be different.
 
Does it have a Garmin audio panel? I had that failure mode on mine (and due to Garmin's absolutely crappy AOG policies, I had to just buy another one as there is no provision to get either fast turn around or a timely loaner, but hell they'll fedex you a new one if you want to buy it).
 
flyingron said:
Does it have a Garmin audio panel? I had that failure mode on mine (and due to Garmin's absolutely crappy AOG policies, I had to just buy another one as there is no provision to get either fast turn around or a timely loaner, but hell they'll fedex you a new one if you want to buy it).
Click to expand...

Or you could replace with a PS Engineering panel, plug-compatible with Garmin, and backed by PSE's stellar quality and service.
 
flyingron said:
Does it have a Garmin audio panel? I had that failure mode on mine (and due to Garmin's absolutely crappy AOG policies, I had to just buy another one as there is no provision to get either fast turn around or a timely loaner, but hell they'll fedex you a new one if you want to buy it).
Click to expand...
Nope, King. And, unfortunately, I haven't been near it since we got back from the Bahamas about 3 weeks ago.
 
SCCutler said:
Or you could replace with a PS Engineering panel, plug-compatible with Garmin, and backed by PSE's stellar quality and service.
Click to expand...
Well, it's King, not Garmin. But two of my wish list items are a 12V power plug and an Aux In. :) They've been conveyed to the owner!
 
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