Thread: Altitude encoder

My 05 CTSW with 460 hours has been causing some confusion when travelling in and around controlled airspace with the ATC requesting confirmation that we are actually at 13500 - I don't remeber installing that O2 bottle.

Apparently it is adding an additional 10,000 feet to the broadcast altlitude. I did check and found the line to have worked its way loose.eattaching brought the discrepancy back to 400 feet but as of last friday it is back at 10,000.

A friend advised me that the Americking AE have about a 6 month life expectancy of about 6 months- I am not sure which I have without further inspection but I am guessing it needs replacing.

Any suggestions on a good reliable and inexpensive replacement??????


Peter

Have a good avionics guy look at it before you toss it. It may be just a glitch in the system somewhere. To buy another probably an Ameri-King encoder is as cheap and easy as any.

I did check and found the line to have worked its way loose.eattaching brought the discrepancy back to 400 feet but as of last friday it is back at 10,000.

If you mean the static line running into the encoder, then its being loose would lead to the encoder to measure cabin pressure. Normally, that's only slightly lower than ambient pressue (thank you, Mr. Bernoulli!). No way it could account for 9,600' of error.

I think your problem is either electronic or mechanical. If I had to guess, I'd guess mechanical - something causing the bellows mechanism to bind. Maybe reattaching the line freed things up temporarily.

Either way, it should be a simple fix - good luck!

I had a similar problem. We thought it was the encoder at first, but it would up being the transponder itself. If you've got a good local avionics shop, give them a try.

If you have a G327, you can enter the setup menu and have it display the grey code input from the encoder - start there. Then, if that shows Ok, check the grey code from the encoder to see if it's working. It sounds like you have one of the bits of the grey code stuck. Google for encoder grey code and you'll get a table of the bits and resulting altitudes.

When I had the problem, it turned out to be in the G327 iteslf. Garmin charges a flat $600 to service a G327, regardless of what is wrong. On mine, all they did was flash and upgrade the firmware and it's worked fine ever since. Strange.

Doug

Thanks guys - All useful suggestions.

I went out to the hangar this afternoon and pulled the two instument panels out to check on things only to find the other end of the Static tube goes nowhere anyway and the top port on the ASI has been closed with a piece of pinched rubber tube.

I would assume that there should be a Static and Pittot connection to the ASI and Auto Pilot as well as a static to the Altitude Encoder( AK-350) so I will replace the tubing and put in a couple of tees to supply a Static to the ASI and the AK 350. Of couse I will pull it out as well and check the "Bellows" for any malfunction before I go chasing any electrical issues.

Does anyone know what the little steel "T pieces" are called or who wouod supply them. I would rather use them if I can trrack them down but for the time being I will have to use some plastic T pieces and some rubber sleeve.

Thanks,

Peter

Hi Peter,

Are you talking about the little shinny plated compression fittings that the hose goes into? It has a compression nut on each end? You can get those at FD. Parker fittings has them too just in standard brass.

Originally Posted by Roger Lee

Hi Peter,

Are you talking about the little shinny plated compression fittings that the hose goes into? It has a compression nut on each end? You can get those at FD. Parker fittings has them too just in standard brass.

Hi Roger ,

Yes mate the little "Chromed T" fittings with the barb and the compression ferrule that cause the line to flare when done up. Sorry FD Australia carries minimal spares and I suspect the wait would be toooooo long. I am not familiar with Parker fitting- are they Hydraulic or Plumbing suppliers?. I f I knew what they were actually called I could search the net foor a local supplier

I recently had to plumb in a second Ice/water fridge which meant I had to track down a "T" piece for the 1/4" nylon line- One of the local plumbing places had a plastic fitting that they just pushed into and locked- No leaks yet - but that was not for a 6 mm hose so I am not sure if it would be good enough for this application but it sure would be light and compact.


Peter

Originally Posted by Fast Eddie B.

If you mean the static line running into the encoder, then its being loose would lead to the encoder to measure cabin pressure. Normally, that's only slightly lower than ambient pressue (thank you, Mr. Bernoulli!). No way it could account for 9,600' of error.

I think your problem is either electronic or mechanical. If I had to guess, I'd guess mechanical - something causing the bellows mechanism to bind. Maybe reattaching the line freed things up temporarily.

Either way, it should be a simple fix - good luck!

Hi Fast Eddie,

I have pulled the encoder from the plane to check the Bellows and opened it to find a plastic foam sandwich which I suspect houses the bellows. Is it worth trying to pull it apart to check the bellows or am I likely to cause more damage than I can repair?

Peter

There are some good online suppliers of the "T" with push-on fittings. You can get lots of different configurations, including 4-port crosses, 3-port "Y"s, 90 swivels, etc. Stein Air is one of my favored vendors for stuff like this.

Doug
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Is it worth trying to pull it apart to check the bellows or am I likely to cause more damage than I can repair?

Wow! I had no idea what one of those guys looked like opened up.

I, for one, would get it to an avionics shop for repair or replacement. I think you may be straying a bit beyond what and owner/operator can properly do involving avionics.

But taking a look never hurt!

A whole new AmeriKing encoder is only about $200, so I wouldn't throw a whole lot at repairing your unit.

Good luck!

BTW, just yesterday I had my biannual transponder check done on my Garmin 327. Mine's also fed by an AmeriKing encoder, which was off by about 300'. We brought it back into agreement, but the avionics tech really did not have anything good to say about Ameri-King products - though they've served me well over the years.