Altimeter Bounce Issues

[juredd1]

I had never noticed my altimeter bouncing as much as it did on my next flight after my annual inspection. I was headed for my BFR, during my BFR flight my instructor also notice there was about a 100 ft. bounce either side of the mark. No really knowing what to do I sent the instrument off for inspection/repair some months after that. I was told it was very dirty and needed work. After getting it back and reinstalled in the plane I noticed the 100 feet bounce was gone but was still bouncing about 20 feet either direction. After some discussion with the instrument repair place they sent me a replacement, but even after installing the second one that did not resolve my issue.

The repair guy asked if anything was touching the back of the instrument and I said no. He asked me if any of my rubber shock absorbers were out in the panel. Well I'm not sure but it wasn't doing this before my annual or that is my story as I never recall seeing this type of activity before. He stated that he has seen this when there is extra vibration in the panel from I suppose a variety of reason.

Well I had noticed since the annual (which included having the 500 hr inspection done on the mag) there seemed to be more vibration in the pedals and just what sounded like a rougher running engine. I had noticed one mag dropped roughly 20rpm and the other 100rpm during the mag check. Not sure if that is normal or not. Anyway I had discussed with my IA and he agreed to recheck things. Please forgive the correct technical terms as I am not a mechanic but one mag was not checking right with his tester. Took it apart and there was some oil or something on the points. Fixed, reinstalled and tested good this time and was re-timed. Maybe there was a reduction in the roughness that I think I am hearing and feeling but by this time months has passed since the annual and I am second guessing myself. However the altimeter is still bouncing that 20 feet either direction. It does not have to be rough air either it can be smooth sailing and I still see the movement.

So I guess I'm asking for some input from this community. Is the 20 foot bounce reasonable or not? Do I need to push my IA or find someone else for second opinion?

I know after you get used to something it seems normal, so maybe I am wrong, it has been 6 months since my annual but it just seems like I feel more vibrations in the pedals and even in my knee as it lays against the door post than was there before the annual.

What could be causing the altimeter to bounce if that movement is not normal?

Thanks for any input or advice,
Justin

[bagarre]

Stick an ice pick in your static port and give it a twist. (not really)

I've read where the smooth flat hole on the side of the airframe for a static port can pick up turbulence or other oddities and deforming the hole can stop this. Mine has a kink in the hole like someone, well, stuck and ice pick in it and gave it a twist.

Pretty sure that's why modern static ports are raised off the surface.

All of that is speculation as I don't have a source to refer to and I doubt it's listed as an approved method anywhere.

[juredd1]

Ice pick in hand and in route. (not really)

I never thought of that as I do remember on my 1980 model 152 that it was raised. It took me several attempts to locate the port on the 170 after I first got it, I keep looking for the raised part.

Thanks for your input David.


Justin

[hilltop170]

Is there any chance water might have gotten into the tubing?

[edbooth]

Ice pick in hand and in route. (not really)

I never thought of that as I do remember on my 1980 model 152 that it was raised. It took me several attempts to locate the port on the 170 after I first got it, I keep looking for the raised part.

Thanks for your input David.


Justin

Take the tubing off back of instrument, go fly and see if it still bounces. That will eliminate any problems with your static source.

[juredd1]

I apologize guys for my slow response. I'm on a computer 5 days a week for work so I try to stay away from it on the weekends.

Richard,

Your suggestion is the first thing the instrument repair place suggested.

Ed,

Your suggestion was the second thing the repair place suggested I do.

So after talking the tubing off the back it was still bouncing so the guy said it's likely the instrument. So sent it in for the repair. As I told above after I got it back it still had a bounce but just not as bad, same result with tubing on or off. Now what i don't think I mentioned in my original post is when I had both instruments (my original one overhauled and replacement sent to me) I placed them in the seat beside of me. Not a single bounce that I could notice on a 60mile flight. I put the replacement instrument in the panel and my bounce is back.

I am at a lose on what to do about it.

Thanks you very much for your input.

Justin

[n3833v]

It sounds like a vibration migrating into the gauge from somewhere.

John

[juredd1]

It sounds like a vibration migrating into the gauge from somewhere.

John

It seems more and more like that could be the issue. Is there no other instruments that would be affected by the vibration. The repair guy seemed to think the altimeter would be the most affected.

Now what? Somehow convince my AI we have an issue?


Thanks,
Justin

[canav8]

It sounds like a vibration migrating into the gauge from somewhere.

John

It seems more and more like that could be the issue. Is there no other instruments that would be affected by the vibration. The repair guy seemed to think the altimeter would be the most affected.

Now what? Somehow convince my AI we have an issue?


Thanks,
Justin

The altimeter has a weak anerod or billows and the Altimeter needs to be replaced.

[juredd1]

Try another altimeter?

I have already tried two rebuilt altimeters with the same result.

It sounds like a vibration migrating into the gauge from somewhere.

John

It seems more and more like that could be the issue. Is there no other instruments that would be affected by the vibration. The repair guy seemed to think the altimeter would be the most affected.

Now what? Somehow convince my AI we have an issue?


Thanks,
Justin

The altimeter has a weak anerod or billows and the Altimeter needs to be replaced.

Doug,

Is this not something that would have been replace during the rebuild/overhaul?

Thanks,
Justin

[canav8]

Justin, was the altimeter yellow tagged? or returned and said overhauled on an invoice? Who did the work? the next thing I would check if you believe the altimeter is good is the air filter high up in the back side of the panel for moisture in the filter.

[juredd1]

Doug,

I won't be back in town until late tonight to check my paperwork but don't recall seeing a yellow tag with it. as for the air filter, not sure there is a way to word this without sounding unlearned but I don't know about this air filter thing. What am I looking for there? Is it enclosed in some sort of filter box?

The second altimeter that I put in the panel was never hooked up to anything. I just took the plug out of the back and didn't hook up any hoses. That should rule out moisture getting in the instrument...right?

Thanks to everyone for your willingness to help and teach us less knowledgeable.

Justin

[DaveF]

Is this not something that would have been replace during the rebuild/overhaul?

There's no guarantee what parts get replaced in an overhaul. Component overhaul shops only do what the manufacturer's manual tells them to do. Mandatory replacement parts probably include seals, gaskets, high-wear parts, and parts required by service bulletin, but beyond that, if the unit meets performance testing, apply a nice coat of paint and ship it. I've run into this issue several times with fuel and turbocharger system components. The thing doesn't seem to work, so I sent it out, but it acts the same when I get it back. "Did you check the aneroid?" "No, we don't normally do that."

[canav8]

Justin, as Dave F mentioned. Rebuilt is not Overhauled and Yellow tagged. Sounds like Ebay Altimeter syndrome. If the Altimeter has a recent Yellow tag not something from 30 years ago then the filter I mention is somewhere inline of the static line. I am going to be as forward as saying your problem is your altimeter, and you need to have the Altimeter replaced or Overhauled with a current Yellow tag. You can ship your altimeter to Keystone Instruments in PA or there is an instrument guy closer to you in MO, I believe but not sure. He advertises on facebook frequently for instrument overhaul. You may check him out to. Regards, D

[hilltop170]

Do they still give out "yellow tags"? I have not seen a new one in several years. What I get now is an "8130 form".