Cost to install blind altitude encoder

[jaylw314]

I have problems with an intermittent altitude encoder signal loss from the built-in encoder in the factory altimeter.  I have it connected to an ADS-B transponder, a KAS-297 altitude preselector, and the GNS530W GPS.  As far as I can tell, it's either the encoder itself or the wiring upstream of where the signal connects, because all three instruments lose the altitude signal at the same time.

I've already asked my A&P to look into it last year, but he said the connections looked solid and more troubleshooting would probably require bench testing at an avionics shop, and even that might not even detect or solve an intermittent problem.  It works 95% of the time, but fails for a few minutes when it does.

Rather than throwing money at an avionics shop to troubleshoot it further, I suspect it will be more time and cost-efficient to just install a new blind encoder and disconnect the factory one.  Anyone have a rough guess as to how much such an install would cost?

 

[gacoon]

Which xpndr, Garmins got neat new encoder for the 335and345

[carusoam]

+1 for listing the hardware details if known...
 

Let’s see if Mr. @Baker Avionics is around... for guidance in troubleshooting encoder connections...

Best regards,

-a-

[Warren]

With all the upgrades going on, it is probably relatively easy to find an encoding altimeter for sale that could be swapped in and at least eliminate one potential problem.  Even better if you could borrow one.

Of course intermittent problems are painful and can be expensive to diagnose.  If you have the luxury of low cost parts to exchange it can be the most cost effective approach to start eliminating potential problems.  When they do the swap, have them check that the wiring is well secured and try to ensure nothing has the potential to chafe.

I had a similar problem with an ADF system.  Traced the wiring,...  Still intermittent after multiple attempts.  Finally removed the system during upgrades and then found there was a chafe mark on one of the wires deep behind the middle of the panel that would have been almost inaccessible without extensive component removal.

[RobertGary1]

Most of us have them holding doors open at this point since the new systems no longer require separate encoders. Should be hundreds on ebay. 

[PT20J]

Blind encoders are cheap. Working behind a Mooney panel - not so much. Best to call your favorite avionics shop for a quote, but I’d guess 4 hrs or less.

https://www.aircraftspruce.com/catalog/avpages/a30encoder.php

Skip

[Baker Avionics]

Encoders can go bad, especially the older ones and it may be time to replace.  One of the good things is a lot of them are wired the same with a 15 pin connector if you are going to keep using Gillham Code lines. The one in question is incorporated into the Altimeter which introduces a little bit more of a challenge.    @jaylw314you are in Corvallis and I am in Grants Pass.  If need be, I have one here in my desk that we can swap out for you and it shouldn't cost too much to do.  It is a SSD120 and depending on the one you currently have, it could just be as little as 2-3 hours to replace and check out, if the old one is truly bad.  My question is "What makes it seem intermittent?  Why are you suggesting it is intermittent?"  Are you seeing a difference on the transponder or the preselector not being reliable?    

[Ragsf15e]

When I had the G5s put in, shop asked if I wanted to get rid of my encoder.  I didn’t realize it was an option, but it’s in the current installation manual.  If you have at least one G5 (or gi275) or are thinking of getting one, just use that and dump the encoder.

[N201MKTurbo]

15 minutes ago, Ragsf15e said:

When I had the G5s put in, shop asked if I wanted to get rid of my encoder.  I didn’t realize it was an option, but it’s in the current installation manual.  If you have at least one G5 (or gi275) or are thinking of getting one, just use that and dump the encoder.

I’ll have to check that out. When I put in my system it prohibited that. I wired it up anyway, all I have to do is push a few buttons.

[Ragsf15e]

12 minutes ago, N201MKTurbo said:

I’ll have to check that out. When I put in my system it prohibited that. I wired it up anyway, all I have to do is push a few buttons.

Yeah I went in knowing about that previous restriction, but it’s no longer there.  I made my avionics shop check twice!

[RobertGary1]

57 minutes ago, Ragsf15e said:

When I had the G5s put in, shop asked if I wanted to get rid of my encoder.  I didn’t realize it was an option, but it’s in the current installation manual.  If you have at least one G5 (or gi275) or are thinking of getting one, just use that and dump the encoder.

My shop didn't even ask. They just pulled the encoder. If you have a fancy GI-275 why would you keep the old encoder? I was also changing the transponder so it was less labor to just chuck it.

-Robert

[jaylw314]

3 hours ago, Baker Avionics said:

Encoders can go bad, especially the older ones and it may be time to replace.  One of the good things is a lot of them are wired the same with a 15 pin connector if you are going to keep using Gillham Code lines. The one in question is incorporated into the Altimeter which introduces a little bit more of a challenge.    @jaylw314you are in Corvallis and I am in Grants Pass.  If need be, I have one here in my desk that we can swap out for you and it shouldn't cost too much to do.  It is a SSD120 and depending on the one you currently have, it could just be as little as 2-3 hours to replace and check out, if the old one is truly bad.  My question is "What makes it seem intermittent?  Why are you suggesting it is intermittent?"  Are you seeing a difference on the transponder or the preselector not being reliable?    

Thanks, it was something I was considering looking into next fall when the static/IFR recert is due (assuming it doesn't get worse before then), since I assume changing it out will require a new recert anyway.

The encoding altimeter is a Gray code encoder (is that the same as Gilham code?).  The transponder it's hooked up to is a BK KT-74.

When I said intermittent, all 3 devices (the GNS530W, the KAS297 and the KT74) all show "no altitude input received" errors.  It randomly seems to occur for about 2-3 minutes, and then pops up again.  I've had flights where it doesn't happen at all, flights where it starts failed and comes up later, and flights where it happens in the middle.  Recycling the encoder circuit breaker occasionally seems to fix it, but most of the time it doesn't.

Yelling and harsh language doesn't seem to help either 

[EricJ]

35 minutes ago, jaylw314 said:

Thanks, it was something I was considering looking into next fall when the static/IFR recert is due (assuming it doesn't get worse before then), since I assume changing it out will require a new recert anyway.

The encoding altimeter is a Gray code encoder (is that the same as Gilham code?).  The transponder it's hooked up to is a BK KT-74.

When I said intermittent, all 3 devices (the GNS530W, the KAS297 and the KT74) all show "no altitude input received" errors.  It randomly seems to occur for about 2-3 minutes, and then pops up again.  I've had flights where it doesn't happen at all, flights where it starts failed and comes up later, and flights where it happens in the middle.  Recycling the encoder circuit breaker occasionally seems to fix it, but most of the time it doesn't.

Yelling and harsh language doesn't seem to help either 

Have you tried reseating any of the connectors?   One disadvantage of the old encoding schemes is that they need a lot of wires to carry all the bits of the code in parallel, so if any one of them is intermittent it could cause problems.

[Warren]

Gray and Gillam are the same output.

When you change an altimeter or add an encoder, you are breaking into the static system and this means to be legal, you need to update the pitot-static cert for IFR.

I stand corrected.  See below from Baker Avionics.  Only need to do a correlation to verify no leaks -- Thanks Greg

[Baker Avionics]

1 minute ago, Warren said:

Gray and Gillam are the same output.

When you change an altimeter or add an encoder, you are breaking into the static system and this means to be legal, you need to update the pitot-static cert for IFR.

You actually only need to do a correlation check to verify no leaks but not a full fledged IFR Cert.  

[Baker Avionics]

42 minutes ago, jaylw314 said:

Thanks, it was something I was considering looking into next fall when the static/IFR recert is due (assuming it doesn't get worse before then), since I assume changing it out will require a new recert anyway.

The encoding altimeter is a Gray code encoder (is that the same as Gilham code?).  The transponder it's hooked up to is a BK KT-74.

When I said intermittent, all 3 devices (the GNS530W, the KAS297 and the KT74) all show "no altitude input received" errors.  It randomly seems to occur for about 2-3 minutes, and then pops up again.  I've had flights where it doesn't happen at all, flights where it starts failed and comes up later, and flights where it happens in the middle.  Recycling the encoder circuit breaker occasionally seems to fix it, but most of the time it doesn't.

Yelling and harsh language doesn't seem to help either 

Did you happen to bang on the top like we used to do with our old TV sets?  That seems to work 12% of the time for us.  LOL.  Let me know if you need a hand and we fit you in.  You are not far so buzzing down here to 3S8 would be a quick trip

[RobertGary1]

14 minutes ago, Warren said:

Gray and Gillam are the same output.

When you change an altimeter or add an encoder, you are breaking into the static system and this means to be legal, you need to update the pitot-static cert for IFR.

I stand corrected.  See below from Baker Avionics.  Only need to do a correlation to verify no leaks -- Thanks Greg

Also my understanding is that any A&P can sign off RTS after opening the static system, even though they cannot sign a pitot static cert.

-Robert

[EricJ]

11 minutes ago, RobertGary1 said:

Also my understanding is that any A&P can sign off RTS after opening the static system, even though they cannot sign a pitot static cert.

-Robert

An A&P can do the system static/pressure tests, which are essentially leak checks, but not the altimeter/transponder cert for IFR. 

 

[RobertGary1]

22 minutes ago, EricJ said:

An A&P can do the system static/pressure tests, which are essentially leak checks, but not the altimeter/transponder cert for IFR. 

 

That's what pilots mean when we say "pitot static test". Its a colloquialism that means the altimeter and transponder test for IFR. Not sure why its called "pitot static" but it always has been.

-Robert

[EricJ]

56 minutes ago, RobertGary1 said:

That's what pilots mean when we say "pitot static test". Its a colloquialism that means the altimeter and transponder test for IFR. Not sure why its called "pitot static" but it always has been.

-Robert

Yeah, there's a distinction that isn't always recognized.   A basic "pitot static test" is essentially a leak check with a standard of how to perform it and how much leak is allowed.   Any A&P can do it with some electrical tape and a length of rubber hose.   The altimeter/transponder cert requires calibrated equipment that allows the altimeter and transponder outputs to be compared against the calibrated reference, which has to be operated by an authorized repair station.   I suspect more than once people have thought they were getting one done and got the other.

[RobertGary1]

7 minutes ago, EricJ said:

Yeah, there's a distinction that isn't always recognized.   A basic "pitot static test" is essentially a leak check with a standard of how to perform it and how much leak is allowed.   Any A&P can do it with some electrical tape and a length of rubber hose.   The altimeter/transponder cert requires calibrated equipment that allows the altimeter and transponder outputs to be compared against the calibrated reference, which has to be operated by an authorized repair station.   I suspect more than once people have thought they were getting one done and got the other.

The term I'm more familiar with is "pitot static cert". That seems to always mean the altimeter/transponder test required of IFR.

 

-Robert

[tmo]

12 hours ago, EricJ said:

One disadvantage of the old encoding schemes is that they need a lot of wires to carry all the bits of the code in parallel, so if any one of them is intermittent it could cause problems.

Those problems would be more likely to appear as nonsensical altitude values being presented (flipped bit), right?

[EricJ]

7 hours ago, tmo said:

Those problems would be more likely to appear as nonsensical altitude values being presented (flipped bit), right?

Potentially so depending on the implementation.   There are implementations on the receiver side that could detect an open circuit as opposed to driven high or low.    So I'm just speculating whether that's the cause, but it's something fairly easy to check.

 

[geoffb]

Jay,

If you end up needing a gray code encoder, my old one is sitting on a shelf.  Free to good home.

[jaylw314]

On 12/10/2020 at 1:13 PM, Baker Avionics said:

You actually only need to do a correlation check to verify no leaks but not a full fledged IFR Cert.  

I hadn't realized that--if so, I'll probably give you guys a call once the weather gets a little better. Thank you!

 

On 12/10/2020 at 1:09 PM, EricJ said:

Have you tried reseating any of the connectors?   One disadvantage of the old encoding schemes is that they need a lot of wires to carry all the bits of the code in parallel, so if any one of them is intermittent it could cause problems.

Yup, a couple years ago at annual I asked them to reseat it because I thought I was having an autopilot problem.  In retrospect, I think I was starting to have it back then.