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The Avionics saga continues...

D

dbier99

Well Known Member
For those who have seen my recent posts you'll know that I took my recently acquired RV6A into a highly regarded avionics shop a couple weeks ago to have a Garmin G% installed (primarily) to gain an artificial horizon and do our bi-annual transponder check. Well after they moved the existing electronic/pulse tach to position the G5 - the tach stopped working. They ended up doing too much trouble shooting before just replacing the wire between the mag switch, tach and mag to get it working - and added $1,000 to my bill.

Yesterday, on our first flight since the 20 minute hop home on Thursday - the oil pressure gauge started fluctuating and dropping - which led to a quickly aborted flight. With some input from the mechanic who helped us with our recent annual condition inspection we replaced the wire to the oil pressure sensor and everything was fine on this morning's flight. BUT...

While climbing after T/O the tower told us our altitude was reporting very low. Turns out the Stratus transponder (which was working perfectly and had been recertified by the shop - is now reporting about 1500 feet low initially, then slowly creeps up within about 600 feet of actual (after 15 minutes) then lags greatly on our descent. OMG - talk about opening up a can of worms by installing the G5! (which by the way works beautifully).

The shop says they think they "may have missed a line of code" in the transponder - whatever that means - so for the time being we've turned off altitude reporting and are avoiding any Mode C airspace.

Anybody have similar experiences with shops or did we just have bad beginner's luck? Also any thoughts on how the transponder could be doing what it's doing?
 
The second thing, after what Dave suggested, I would do is to look for a different shop to do my avionics work and possibly ask for some of my money back.
 
This is the risk of taking an experimental plane to a spam can avionics shop.

I suggest that all builders (and for that matter non-builder owners) learn your systems and do all such work yourself. While you must have a certified shop for the biannual static/XPDR check NEVER hand over your plane before you verified no static or pitot leaks, XPDR getting GPS serial in and such.

You should know your plane much better than the avionics guy drawing the short straw to work on one of those #%!* experimentals….

Carl
 
another perspective...

some of this can be due to the original installation... for example poorly crimped connectors. I recently worked on an "A&P built" RV. After a few flights the autopilot servos went offline and wouldn't return. Issue? Loose connection.

Things are ok until someone gets under the panel trying to re-route wires and then everything that can get tugged on ... gets tugged.

That said my neighbor has shown me really poor electrical work that has been done by professionals. So this isn't just a home built risk.
 
Carl Froehlich said:
This is the risk of taking an experimental plane to a spam can avionics shop.

I suggest that all builders (and for that matter non-builder owners) learn your systems and do all such work yourself. While you must have a certified shop for the biannual static/XPDR check NEVER hand over your plane before you verified no static or pitot leaks, XPDR getting GPS serial in and such.

You should know your plane much better than the avionics guy drawing the short straw to work on one of those #%!* experimentals….

Carl
Click to expand...

+1. Except, it’s ‘biennial’.
Did you get a quote for the work first? Did they call you, and did you authorize additional work, when problems were found? If the answer is ‘no’, you need to find another shop. If the answer is ‘yes’, then you gave them a blank check. Trouble shooting can be time consuming ($$); it’s always best to do as much as you can yourself.
 
Carl Froehlich said:
...NEVER hand over your plane before you verified no static or pitot leaks, XPDR getting GPS serial in and such.

You should know your plane much better than the avionics guy drawing the short straw to work on one of those #%!* experimentals….
Click to expand...
In an ideal situation - you're absolutely correct. However, in our case my son and I did not yet feel comfortable/competent enough to monkey with the panel and avionics. Frankly, we wanted an experienced person/shop installing the G5 for fear we would hopelessly muck it up and/or cause the kind of issues that cropped up even with an experienced shop. Also, we wanted an experienced person taking a look behind our panel to determine if it was in decent shape - we likely would have no idea.

As for the pitot and static systems - they found several leaks in the pitot system which they repaired for very nominal charges. They also determined the static system was "wide open" - and quickly traced that to the airspeed indicator - which we declined to replace (at least yet) because our plane id VFR only. The shop indicateed the leaky A/I would not have any substantial impact on the plane. I will double check with them Monday to see if the leaky A/I could have anything to do with the transponder issue - however the A/I static leak was pre-existing and the transponder was working fine before the bi-annual check.
 
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BobTurner said:
+1. Except, it’s ‘biennial’.
Did you get a quote for the work first? Did they call you, and did you authorize additional work, when problems were found? If the answer is ‘no’, you need to find another shop. If the answer is ‘yes’, then you gave them a blank check. Trouble shooting can be time consuming ($$); it’s always best to do as much as you can yourself.
Click to expand...
We needed an operating Tach so I told them it had to be fixed and provided suggestions from you guys and contacted the Tach maker to expidite things and reduce the amount of time they spent inestigating possible fixes - but NO they did not give any estimate because they said they had no idea how long it might take to repair. Basically, I had to trust their good reputation in our area. Live and learn I guess. :(
 
dbier99 said:
While climbing after T/O the tower told us our altitude was reporting very low. Turns out the Stratus transponder (which was working perfectly and had been recertified by the shop - is now reporting about 1500 feet low initially, then slowly creeps up within about 600 feet of actual (after 15 minutes) then lags greatly on our descent. OMG - talk about opening up a can of worms by installing the G5! (which by the way works beautifully).

The shop says they think they "may have missed a line of code" in the transponder - whatever that means - so for the time being we've turned off altitude reporting and are avoiding any Mode C airspace.

Anybody have similar experiences with shops or did we just have bad beginner's luck? Also any thoughts on how the transponder could be doing what it's doing?
Click to expand...

This seems unlikely to be a configuration issue or in the transponder itself, though most anything is possible. First determine where the altitude for the transponder is coming from. I assume this was just a 6 pack before the G5, so there is likely still an alt encoder in there somewhere. Shop probably did not replace that in favor of the G5 as an encoder and may not even be possible due to no RS-232 ports on xpdr or no remaining ports on G5. The shop would have had to cut up your pitot and static lines to add the G5 and am guessing that they created some type of blockage in the static line going to the encoder and that is why it is lagging. If the G5 is the source, still seems like it is not a config issue, as it is mostly lagging vs inaccurate. When the alt changes happen very slowly but ultimately get near the target, that is almost universally an issue of pnuematics. This kind of stuff is taught for your IFR rating to help diagnose static port and pitot port icing, which are very similar symptoms. Would think a shop would know that.

WHile not surprised, it is sad to hear that they would charge you $1000 to make up for their tech's inability to properly diagnose a tach issue.

FYI, this isssue (i.e. lagging indication) is NOT related to the leak, though the leak is likely the reason that your final target is 600' off actual, assuming the leak is significant. In most planes, getting static pressure from the cockpit instead of external (what a leak causes), will net a 500-1000' alt reporting difference from actual and it often varies with airspeed.

Larry
 
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lr172 said:
This seems unlikely to be a configuration issue or in the transponder itself, though most anything is possible. First determine where the altitude for the transponder is coming from. I assume this was just a 6 pack before the G5, so there is likely still an alt encoder in there somewhere. Shop probably did not replace that in favor of the G5 as an encoder and may not even be possible due to no RS-232 ports on xpdr or no remaining ports on G5. The shop would have had to cut up your pitot and static lines to add the G5 and am guessing that they created some type of blockage in the static line going to the encoder and that is why it is lagging. If the G5 is the source, still seems like it is not a config issue, as it is mostly lagging vs inaccurate. When the alt changes happen very slowly but ultimately get near the target, that is almost universally an issue of pnuematics. This kind of stuff is taught for your IFR rating to help diagnose static port and pitot port icing, which are very similar symptoms. Would think a shop would know that.

WHile not surprised, it is sad to hear that they would charge you $1000 to make up for their tech's inability to properly diagnose a tach issue.

FYI, this isssue (i.e. lagging indication) is NOT related to the leak, though the leak is likely the reason that your final target is 600' off actual, assuming the leak is significant. In most planes, getting static pressure from the cockpit instead of external (what a leak causes), will net a 500-1000' alt reporting difference from actual and it often varies with airspeed.

Larry
Click to expand...
Thanks for the great info/insights - it will allow me to pose better questions to the shop on Monday. I don't like the idea of our leaky A/I continuing to cause a ~600ft or more discrepancy (even after the current lag issue is resolved) - so maybe I should start planning on replacing that too in the coming days.
 
One thought about the lagging altitude - if it's initially lagging more than it settles down at, is that during the climb when you have lower airspeed and a higher angle of attack? If the airspeed indicator is open to the cabin, the cabin pressure will change slightly depending on the angle of attack and airspeed, just wondering if that might be the difference you are seeing being 1500' and 600' low.
 
airguy said:
One thought about the lagging altitude - if it's initially lagging more than it settles down at, is that during the climb when you have lower airspeed and a higher angle of attack? If the airspeed indicator is open to the cabin, the cabin pressure will change slightly depending on the angle of attack and airspeed, just wondering if that might be the difference you are seeing being 1500' and 600' low.
Click to expand...
The lag didn't seem related to our climb rate as we weren't climbing all that quickly. Also the lag persisted on the descent - to the point that we crossed through the Transponder's stated altitude and then dropped below it. The Transponder slowly started desending but when we landed our actual Alt was 1700 and the Transponder read 3310.
 
In flight readings

Just for kicks, here's the text and readings I reported to the shop for their insight...

Transponder was showing 890 at taxi (field elevation is 808). At takeoff it sat while we climbed. Started moving up slowly. We were at 4000 but trans read 1250. At 5000 was at 1470. 5500 = 1800.
Results while cruising at level 5500:
@ 1min = 2160,
2min = 2410,
3 min = 2620,
4 min = 2820,
5 min = 3000,
7 min = 3290,
10 min = 3670
11 min = 3780
Then we started our descent...
@ 13 mins 4000 = 3900 trans.
@ 14 mins 3200 = 3800 trans,
@ 15 mins 2500 = 3780 trans,
@ 16 mins 1800 = 3650 trans
@ touchdown: 1700 = 3310 trans.
 
dbier99 said:
In an ideal situation - you're absolutely correct. However, in our case my son and I did not yet feel comfortable/competent enough to monkey with the panel and avionics. Frankly, we wanted an experienced person/shop installing the G5 for fear we would hopelessly muck it up and/or cause the kind of issues that cropped up even with an experienced shop. Also, we wanted an experienced person taking a look behind our panel to determine if it was in decent shape - we likely would have no idea.

As for the pitot and static systems - they found several leaks in the pitot system which they repaired for very nominal charges. They also determined the static system was "wide open" - and quickly traced that to the airspeed indicator - which we declined to replace (at least yet) because our plane id VFR only. The shop indicateed the leaky A/I would not have any substantial impact on the plane. I will double check with them Monday to see if the leaky A/I could have anything to do with the transponder issue - however the A/I static leak was pre-existing and the transponder was working fine before the bi-annual check.
Click to expand...

You have a G5, right?

Why are you still hauling around an antique airspeed indicator??
 
Unless the particular shop in question is an EAB specialist, this thread belongs on a Bonanza/Cirrus/Cessna forum...
 
Considering his avionics problems a steam airspeed indicator is a wise installation.
This is one of my problems I have with "expert" shops, they charge you top dollar for labor and then leave the work to a two year A&P making $20 a hour. That's if the worker even has a A&P.
 
Sam Buchanan said:
You have a G5, right?

Why are you still hauling around an antique airspeed indicator??
Click to expand...

Only needed to free up one space - so opted to lose the old Rate of Climb steam gauge instead. But your point is a good one - that admittedly hadn't crossed my mind: We could probably just remove the old airspeed indicator to eliminate its static leak - which could be what is causing the difference between the transponder and actual altitude (although we'd still need to figure out what is causing the transponder lag).
 
Tommy123 said:
Considering his avionics problems a steam airspeed indicator is a wise installation.
This is one of my problems I have with "expert" shops, they charge you top dollar for labor and then leave the work to a two year A&P making $20 a hour. That's if the worker even has a A&P.
Click to expand...
Just read your response about keeping the "steam" airspeed indicator - also a valid point. I won't remove it without careful consideration. Also am in more agreement than ever regarding "expert" shops. :(
 
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DanH said:
Unless the particular shop in question is an EAB specialist, this thread belongs on a Bonanza/Cirrus/Cessna forum...
Click to expand...

Sorry - I'm new to aircraft ownership in general and to Vans in particular - so don't know what that means. However, hope what I'm experiencing and the eventual resolution (which I will be sure to share) will be of some assistance to others reading these posts. I know the responses are helping me. :)
 
dbier99 said:
Only needed to free up one space - so opted to lose the old Rate of Climb steam gauge instead. But your point is a good one - that admittedly hadn't crossed my mind: We could probably just remove the old airspeed indicator to eliminate its static leak - which could be what is causing the difference between the transponder and actual altitude (although we'd still need to figure out what is causing the transponder lag).
Click to expand...

dbier99 said:
Just read your response about keeping the "steam" airspeed indicator - also a valid point. I won't remove it without careful consideration.
Click to expand...

You stated you have a VFR aircraft and the G5 is working properly. It is definitely your decision but retaining a known faulty airspeed indicator is not a good way to troubleshoot a static problem. You need to eliminate as many variables as possible---after flying the G5 for a bit you won't ever use the clock gauge.
 
Just a minor comment - your problems are much larger than this - but when you get to small issues, don’t forget that your mode C is pressure altitude, not usually the same as indicated altitude.
 
BobTurner said:
Just a minor comment - your problems are much larger than this - but when you get to small issues, don’t forget that your mode C is pressure altitude, not usually the same as indicated altitude.
Click to expand...

Good point! If I'm remembering the difference between pressure and indicated altitude correctly - I think we'll need to do some level flight tests with our altimeter set to the standard 29.92 to determine the actual differential between our altimeter and the transponder once it has caught up as far as it's going to.
Or am I not thinking correctly? My private test was many years ago! :)
 
With the transponder, you need a static or maybe a pitot-static test on the system every two years for VFR use. If you have that test done by an outside vendor, that'll give you an independent check on that system.

There's a gotcha with this... it's another vendor. If they sign it off, then your current shop can't work on that without affecting that sign-off.

Out here, they come to my hangar and cost around $200. They do need electricity, but my hangar has that.

Dave
 
David Paule said:
With the transponder, you need a static or maybe a pitot-static test on the system every two years for VFR use. If you have that test done by an outside vendor, that'll give you an independent check on that system.

There's a gotcha with this... it's another vendor. If they sign it off, then your current shop can't work on that without affecting that sign-off.

Out here, they come to my hangar and cost around $200. They do need electricity, but my hangar has that.

Dave
Click to expand...

The shop that just installed the Garmin G5 also just performed our bi-annual transponder check - and certified it for use. So that apparantly means theycan work on it to fix it - but of course how did they pass it with the current issues?
 
I'd sure be curious to know if they did that before starting work on the plane, in its current state, or whether they merely wrote it in the log without doing the work.

Still - your question is an excellent one to ask them.

Dave
 
dbier99 said:
Good point! If I'm remembering the difference between pressure and indicated altitude correctly - I think we'll need to do some level flight tests with our altimeter set to the standard 29.92 to determine the actual differential between our altimeter and the transponder once it has caught up as far as it's going to.
Or am I not thinking correctly? My private test was many years ago! :)
Click to expand...

Yes, when setting alitimeter to 29.92, it should match the encoder alt. However, you mentioned ATC gave guidance of bad altitude and they convert it backto prevailing altimeter settings before comparing to the alt you gave them. Will need more of the story to resolve that. This test won't work with a leak however. When you have a static leak in the system, ALL altitude sources in the plane are compromised. Also possible that the xpndr obstruction will only allow it to get to within 600' of actual.
 
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There’s a difference..

dbier99 said:
The shop that just installed the Garmin G5 also just performed our bi-annual transponder check - and certified it for use. So that apparantly means theycan work on it to fix it - but of course how did they pass it with the current issues?
Click to expand...

The xpndr check required every two years for VFR is very different from the IFR check. For IFR they check you altimeter(s’) up to 20,000 feet, noting readings every 1,000 feet, to be within specified limits. Each altimeter installed is checked and signed off.
The VFR check is only to see if the xpndr is actually emitting the proper values.
 
dbier99 said:
The shop that just installed the Garmin G5 also just performed our bi-annual transponder check - and certified it for use. So that apparantly means theycan work on it to fix it - but of course how did they pass it with the current issues?
Click to expand...

Sorry, but that is strike three for that shop. It would seem from your experience with the plane, post installation, that no one performed the the test, or at least not a complete test, even though they signed it off as done. Though I suppose it is possible that they did the cert test BEFORE the installation work that they botched. The technician would have seen the lagging on the transponder, as confirming that data moves with the test set altitude is part of the test. There are two key parts to the VFR test - first is that the reported altitude correctly reflects atmo pressure conditions and second that the transponder is sending data that matches those same conditions. The FAA doesn't really care that you don't know the correct altitude via the altimeter (at least for the VFR check). They REALLY care about the accuracy of the altitude that you report to the ATC system, via your transponder, so that they can resolve traffic conflicts. If your leak makes the reported altitude 600' off of actual is should NOT have passed the test, but at this point we cannot conclude that it is off with the data at hand. I don't know the particulars, but there are methods to compensate for small leaks during the test and some of that is allowed for the tester and still pass.
 
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Have a go . . . you still pay for the mistakes

dbier99 said:
In an ideal situation - you're absolutely correct. However, in our case my son and I did not yet feel comfortable/competent enough to monkey with the panel and avionics.
Click to expand...

I reasoned this about 60 yrs ago - - if I do it, there is time for education and broken parts/mistakes - but if they do it . . the same is true, so - have a go at it.

I had many issues with my pitot/static leaking. I made an EAA test manometer with a printed scale. Mostly the gauge leaked, but after solving that the rest was pretty straight forward. Is is not that hard, so if you have the time it truly is a learning experience and confidence builder - -one step at a time.

"The Avionics Place" is pretty good at KRFD if need something else.
 
First, I'll apologize and admit I haven't read every post or for too much detail.

What encoder is installed; possibly one of the ancient ones that requires an internal heater element for reference? The slow drift makes me think said reference could be drifting.

This is from the way (way) back machine so I'll again apologize if my memory of the tech details is off.

A TransCal may be in your future.
 
Tommy123 said:
Considering his avionics problems a steam airspeed indicator is a wise installation.
This is one of my problems I have with "expert" shops, they charge you top dollar for labor and then leave the work to a two year A&P making $20 a hour. That's if the worker even has a A&P.
Click to expand...

That's called maximizing shareholder return. :-(
 
dbier99 said:
Sorry - I'm new to aircraft ownership in general and to Vans in particular - so don't know what that means. However, hope what I'm experiencing and the eventual resolution (which I will be sure to share) will be of some assistance to others reading these posts. I know the responses are helping me. :)
Click to expand...

I was too cryptic, and I apologize for that.

The bedrock fundamental of EAB is education and recreation. Put another way, the EAB option (as compared to certified) works because we learn to do things ourselves, and enjoy doing it well. Thus "What the shop did to me" is a story more commonly heard in the certified world. Here discussion tends more toward "Help me learn how".

There are a number of good shops catering to EAB, and many good reasons to use them. However, even in that environment you'll find a strong push toward proactive owner involvement. If there is a fault with your EAB aircraft, in our world, generally speaking, owners take the blame, not A&P's, even if it was a hired A&P who made the error.

So, jump in. This bunch will bend over backwards to help you stay safe and enjoy your RV, but most will expect you to embrace the learning, and get your hands dirty.
 
Freemasm said:
First, I'll apologize and admit I haven't read every post or for too much detail.

What encoder is installed; possibly one of the ancient ones that requires an internal heater element for reference? The slow drift makes me think said reference could be drifting.

This is from the way (way) back machine so I'll again apologize if my memory of the tech details is off.

A TransCal may be in your future.
Click to expand...

A careful reading of the original post reveals he is using a Stratus transponder which is a contemporary ADS-B device.
 
Sam Buchanan said:
A careful reading of the original post reveals he is using a Stratus transponder which is a contemporary ADS-B device.
Click to expand...

I was focusing on altitude reporting as that seems to be the issue. This is encoded from a direct pressure reading vs GPS receiver output.
 
Shop suggestion...

The shop owner talked to the tech who worked on our plane and sent me the following suggestion - which we will try this evening....
"Hi David, Tom and I spoke. The remote altitude encoder is an ACK A30-9 . We had tracked it on the bench iaw. FAR 43 App. E(c) to comply with FAR 91.411. it is a serial connection to the transponder. So a wiring issue is most likely NOT the case. Tom suggests to potentially look at the hose going to
it. Maybe it got kinked. Unit is mounted on the firewall behind the pedestal. Lower half center . It connects to a T in the static system behind the panel . Maybe during the course of troubleshooting the tach issue, the hose got kinked? Or temporarily disconnect the hose at the encoder and fly it . It will be vented to ambient cabin pressure . Unless cabin vent is blowing on it it should be pretty accurate. That would tell you if it's a hose issue.
 
This doesn't rule out my theorized possibility.

As mentioned and IIRC, the (at least older) ACKs had a heater to set a reference and thus "stabilize" the circuitry. This is at least one of the reasons why these units had to warm-up before they would output. The way you describe the unit's output drifting makes me suspect the aforementioned (bad heating element). GA aircraft cockpits tend to be dynamic environments in regards to temperature (ambient and localized), air movement, etc. Aircraft Avionics, especially temperature sensitive ones, aren't immune from these effects. Would also help explain why it would pass a bench or in-situ functional test yet behave the way it does in operation.

That's all I can recall from geeking-up on my ACK installation when Mode C became a thing (~30 years ago?).

Don't know what the actual root cause may be but my theory does seem to follow some of the behavior you've explained. If it is the encoder proper, it could have been worse. They might be the cheapest Avionics piece in the game.

Let us know and best of luck.
 
see this old post:
I finally bit the bullet and installed ADSB-out in our RV-6A this weekend. I also put two Garmin G5's in and pulled the vacuum pump, directional gyro and attitude gyro. Pretty easy all around except hooking up the G5 altitude encoder function to the Stratus ESG. I got the wires right (single line from RS232 TX - pin 5 - on the G5 to RS232 RX Altitude - pin 5 - on the Stratus). When I fired up the boxes, I got ----- for altitude on the Stratus, and field elevation on the G5, so I knew they weren't talking.

I called Garmin and experimental support guy told me it wouldn't work. I argued that RS232 is a standard, and it "should" work. Called Greg at the Stratus installation support line and he didn't know how to hook the two boxes together . . .

So, I started looking for a way to change communications settings.

Turns out you have to scroll to the bottom of the G5 configuration menu to "RS232 Configuration" and change Output Format to "Altitude" and the Baud Rate to "9600". Works fine and saved me the cost of an altitude encoder.

I wish more experimental guys worked at these companies. It's not the first time I've had to figure out things about their products that they should know, but haven't played around enough to discover.
 
This from google:
The G5 has one RS232 bi-directional interface with one receive pin and one transmit pin (RX1, TX1). Each of these can be configured under different formats. For example TX1 can be used to send pressure altitude to a transponder while RX1 can take data navigation input from a GPS.
 
Resolved?

Was finally able to get to the hanger a little bit ago and take a look behind the panel and sure enough the static line from the altitude encoder had a major kink (see picture).

The plastic static tube was zip tied to some wires that I think got pulled while they were troubleshooting the airspeed indicator after the G5 install and apparently they didn't notice that it caused the kink.

Our airport is IFR right now so we can't take it up to fully test right now but when we did some taxiing just now and set the altimeter to 29.92 standard pressure the G5 indicated field altitude matched the transponder pressure altitude so I think we're in good shape. But of course we will monitor it closely on our next flight.

Although it's all been a bit frustrating, it has been a great learning process and I learned a lot just from the input/suggestions that you folks have provided and we really appreciate it! I'm coming along slowly but surely with my knowledge as a new owner! :)
 
Tommy123 said:
Did those clowns sign off your plane as airworthy?
Click to expand...
It seems they bench tested the transponder and all was fine there but there was no flight test or further testing done after it was installed. I guess that's standard with a VFR only plane transponder certification - or at least that's what they're indicating.
 
Just realized the picture of the kinked static line did not come through. Hopefully it does now...
 

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