Altimeter Bounce Issues

[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".

[juredd1]

There is no yellow tag but there is as Richard mentioned a 8130-3 form (Airworthiness Approval Tag) that states that "Item 2 was overhauled in accordance with the component maintenance manual TM5934 Rev 01/09 complies with approved specifications".

Justin

[n3833v]

Another note, check to make sure no lines are crossing and connecting lines to the altimeter that might inject vibration.

John

[canav8]

Justin, are you sure the instrument is hooked into the static line only and not a vacuum or suction line? Does the bounce change with RPM when running the engine? Just a thought.

[juredd1]

Another note, check to make sure no lines are crossing and connecting lines to the altimeter that might inject vibration.

John

John,

I have looked the best I can but there doesn't appear to be anything touching up close to the instrument. Now are there any lines crossing or touching 16 inches from the instrument, that is very well possible but that wouldn't be anything new. Those lines haven't been moved or rearranged in any way since I bought the plane. As for the past several flights there hasn't even been a line hooked into the instrument and I still get the bounce.

Justin, are you sure the instrument is hooked into the static line only and not a vacuum or suction line? Does the bounce change with RPM when running the engine? Just a thought.

Doug,

I would have to run the lines down to be 100% sure but it appears to be connected to a separate line than what the DG is hooked into and the suction gauge wouldn't work when the DG was out of the plane for repair.
I haven't noticed the bounce any worse with a change in RPM.
As I mentioned to John there is no lines hooked into it right now. When it was hooked up the altimeter and the VSI were hooked into the same line.

When the rain stops and the field get a bit more firm I'm going to take the altimeter out of my uncles Champ and place it in my plane. Take mine and place in his plane and take them for a ride and see what happens.

Thanks again for your much appreciated help,
Justin

[juredd1]

So I ran over and took a look under the dash and the tubing running from the altimeter loops around and connects to this. I have not idea what this is.

Now remember right now the altimeter is not hooked to anything but when it was hooked up it ran from the VSI to the Altimeter and then to this box.


Thanks,
Justin

[juredd1]

That's your Mode C encoder

I have so, so much to learn.

So I am guessing it's normal for the altimeter to be tied into that device? I can't be 100% certain but it looked to me like it went straight from the encoder to the altimeter and then to the VSI.

Justin

[cessna170bdriver]

My brain hurts because it's been so long since I've messed with mine. I think my encoder is connected to my transponder and not the altimeter. I'd have to double check, but logically thinking it through, that makes sense since the encoder has the ability to send pressure altitude to the transponder independent of the altimeter.

Have you had an avionics shop that does pitot static and transponder checks look at your plane? When was the last time you had your FAR 91.413 encoder/transponder check? (Due every 24 calendar months)

The encoder does connect to the transponder electrically, but it is (or should be) plumbed into the static system to be able to read pressure altitude. The encoder's job is to convert static pressure into an encoded altitude that your transponder understands, enabling it to operate in Mode C.