"Foggy" looking instruments

PilotRPI

PilotRPI

Line Up and Wait
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Jun 21, 2012
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PilotRPI
I'm looking at a few planes to buy, and on an instrument or two, they often have glass on the face that looks "foggy" or opaque, not nice and clear. What usually causes that, and is it something that is easy to fix? Is it a few minutes of a mechanics time, or an instrument rebuild, or somewhere in-between?
 
It's the same thing that happens to the headlights on your car. Just take some Off Backwoods mosquito spray and a dry cloth and wipe them down. They'll clear right up.
(Always remember to do a test area first)
 
Archammer said:
It's the same thing that happens to the headlights on your car. Just take some Off Backwoods mosquito spray and a dry cloth and wipe them down. They'll clear right up.
(Always remember to do a test area first)
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Really? That's a new one on me. I'll have to give that a try.
 
PilotRPI said:
I'm looking at a few planes to buy, and on an instrument or two, they often have glass on the face that looks "foggy" or opaque, not nice and clear. What usually causes that, and is it something that is easy to fix? Is it a few minutes of a mechanics time, or an instrument rebuild, or somewhere in-between?
Click to expand...

Is it he glass that is foggy or is there moisture behind the glass making a fog?
 
DEET is a mild plastic solvent, it'll do a great job etching screens on GPS units, etc... Many boaters won't allow folks to spray or use DEET bug spray near their instrument panels.

As far as it removing oxidation from headlights and/or instruments, it will, but it won't do as good a job as buffing and polishing the plastic exterior to remove the oxidized layer. I've done it to some crappy headlights and it'll take a layer of the crud off but it won't make them perfectly shiny like a proper buffing job will. I don't think I'd spray instruments with it unless it was a last resort because they were completely unreadable and I was in the boonies. Even then, avionics are too expensive for such experiments. On vehicles, most of them the bumper and surrounding area around headlights are subject to permanent damage. And if used on black plastic, it'll create white powdery swirls that never come off.

Also highly recommended to spray the rag, not the plastic, overspray will etch/damage any plastics around.
 
I don't think its moisture, from the pictures it looks more like the glass/plastic itself is hazy. Hard to tell exactly until I go see the planes.

I saw an altimeter once that had what looked like flour on the inside of the lens. No one had any idea what it could be.
 
If the plane was flown by smokers, it may be on the inside of the glass (and yes, it's usually glass, not plastic) and that can be dealt with only by disassembling the instrument, which is something requiring the attention of an instrument repair shop. If it's on the outside, any good glass cleaner will remove it.
 
Ok, lets go on a rabbit trail here. Attitude Indicator not foggy BUT the Captain calls in to the company and says that he needs maintenance to meet the airplane. (Twin Otter) His attitude indicator is working fine, the glass is clear so the mechanic says "What's the problem?" The Captain says watch.....and a cockroach climbs out from behind the blue side, across the airplane symbol and back down to the brown side and then disappears :yikes:

Mechanic says "it still works go fly". The Captain says "NO" and they watch as the instrument tumbles on the ground. Pull it and the inside of the mechanisms are gunked up with dead cockroach. I don't remember the write up and clearing of the write up.
 
I have an AI removed from our Cherokee 180 due to a foggy glass. It worked just fine.
Glass is fogged from the back side. and not condensation.
 
PilotRPI said:
I don't think its moisture, from the pictures it looks more like the glass/plastic itself is hazy. Hard to tell exactly until I go see the planes.

I saw an altimeter once that had what looked like flour on the inside of the lens. No one had any idea what it could be.
Click to expand...

Dust, allowed to be drawn into the instrument by a bad vac filter.
 
Ron Levy said:
If the plane was flown by smokers, it may be on the inside of the glass (and yes, it's usually glass, not plastic) and that can be dealt with only by disassembling the instrument, which is something requiring the attention of an instrument repair shop. If it's on the outside, any good glass cleaner will remove it.
Click to expand...

If it didn't have a bad filter how did the gunk get in there?
 
Tom-D said:
No, the instrument fairy can remove the glass, clean it, and put it back.
Click to expand...

Does the instrument fairy know how to freshen up a grungy looking dial? My homebuilt has a nasty looking airspeed and VSI dial.
 
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