Gnc 420 "no altitude input is being received"

[Aaron H]

Hi all,

My ,new to me, plane keeps giving me... "no altitude input is being received".

Has anyone had this or can some of the experts give me something to check?

Any help would be appreciated!
Thanks
Aaron

 

[Aaron H]

It feels like the msg flashes every 10 minutes.

 

[Floyd]

The 420 is not receiving an altitude input from the encoder. Has it always done this since you got the plane?
Should be a wire from GTX 327 Pin 20 to 420 P4001 pin 57 and GTX 327 pin 13 to 420 P4001 pin 60.
Also check the 420 RS 232 input 1 is setup to receive the altitude .

 

[Aaron H]

Thx Floyd,
I don't remember it doing it when I went out to test fly it, but it could have been. It has been doing it for sure since ferry pilot dropped it off and signed me off.

This will be the first time I am touching avionics so please forgive any stupid questions.
(I used to build computers from scratch so I am familiar with electronics)

420 p4001 is the encoder I assume?
Is the encoder attached to the transponder?
Are the pins labeled or do I have to count from one side?

Thanks for the help!

 

[Ryan Klems]

If the 420 was setup for RS232 altitude feed, and it wasn’t getting it, I’d expect the “Not receiving RS232 #1” or something like that (can’t recall the exact verbiage). I wonder if it’s setup for gray code....

If you power off the 420, then power it up holding down ENT, you’ll enter config mode, scroll through with the small knob until you get to a page listing RS232 configs, take a picture, then scroll a few more pages until you get to the main discretes page, which shows the Gray code, take a picture of that. Post those pics

 

[Floyd]

Thx Floyd,
I don't remember it doing it when I went out to test fly it, but it could have been. It has been doing it for sure since ferry pilot dropped it off and signed me off.

This will be the first time I am touching avionics so please forgive any stupid questions.
(I used to build computers from scratch so I am familiar with electronics)

420 p4001 is the encoder I assume?
Is the encoder attached to the transponder?
Are the pins labeled or do I have to count from one side?

Thanks for the help!

The P4001 is a plug on the back of the 420. There are a couple ways the encoder could be wired to the transponder and 420. My manual shows the encoder wired via grey code to the transponder then RS 232 from the transponder to the 420. Might be worth a trip to the avionics shop.

 

[Aaron H]

Thx Ryan,

I believe I got what u were asking for

 

[Floyd]

Thx Ryan,

I believe I got what u were asking for

That shows the RS232 is turned off and you are not getting altitude to the 420.
Is there paper work with the install (a 337) showing that it was ifr certified?
You could try turning the RS232 input to channel 1 ON.
If the wires mentioned above are there that should fix it.
If not, you will get the message no input on RS232 channel 1.

 

[Ryan Klems]

Yeah, as Floyd says, you don't appear to have any altitude configured for your 420. You don't have G5's do you? It could potentially have been configured over 429 EFIS Airdata if so.

Could you power off the GTX327, then power it on while holding the FUNC key. This will get in to the 327 config. Then press func repeatedly until you get to it's RS232 input / output page and then take a picture of that, then press func several time again and you'll get to the RS232 status page, take a picture of that, and then func again to get to the Gray code page and take a picture of that. Curious how the 327 is configured, and if it's configured to output alt on its RS232 out. If so, then perhaps someone just turned off the RS232 in on the 420 for some reason.

If you pull the 420 from the rack, and look at the main connector (the biggest one, 4 rows of male pins) 2nd row down, pins all the way to the left are 59,58 (RS232 2 In/Out), 57,56 (RS232 1 In/Out), 55,54 (RS232 4 In/Out) and then very nearly the last puns on the right of that row 41,42 (RS232 3 In/Out) ... are any of those populated with pins? And then the top row, all the way to the left, are any of the first 11 pins populated (those are the Gray code inputs)?

 

[Aaron H]

That shows the RS232 is turned off and you are not getting altitude to the 420.
Is there paper work with the install (a 337) showing that it was ifr certified?
You could try turning the RS232 input to channel 1 ON.
If the wires mentioned above are there that should fix it.
If not, you will get the message no input on RS232 channel 1.

Thx Floyd,

I didn't see any 337 paperwork, but I will double check. The owner was a cfi and did plan on training in it before he started a pilot job and was to busy to teach.
It's an experimental LSA. It does have the standard six pack vacuum gauges and all the lights for night flying.

I will check the wire and turn on and let u knoe

Thx again Floyd!

 

[Aaron H]

Yeah, as Floyd says, you don't appear to have any altitude configured for your 420. You don't have G5's do you? It could potentially have been configured over 429 EFIS Airdata if so.

Could you power off the GTX327, then power it on while holding the FUNC key. This will get in to the 327 config. Then press func repeatedly until you get to it's RS232 input / output page and then take a picture of that, then press func several time again and you'll get to the RS232 status page, take a picture of that, and then func again to get to the Gray code page and take a picture of that. Curious how the 327 is configured, and if it's configured to output alt on its RS232 out. If so, then perhaps someone just turned off the RS232 in on the 420 for some reason.

If you pull the 420 from the rack, and look at the main connector (the biggest one, 4 rows of male pins) 2nd row down, pins all the way to the left are 59,58 (RS232 2 In/Out), 57,56 (RS232 1 In/Out), 55,54 (RS232 4 In/Out) and then very nearly the last puns on the right of that row 41,42 (RS232 3 In/Out) ... are any of those populated with pins? And then the top row, all the way to the left, are any of the first 11 pins populated (those are the Gray code inputs)?

Thx Ryan,

GOT and 429 EFIS? No clue, sorry.
This is the first time I'm trying to figure out an issue with any avionics.

I will get pics of the 327 and try to take pics of the main plug into the 420.

Thx again!

 

[Floyd]

Do you have a nav indicator?
Sounds like he just did a minimal install.
For vfr, the encoder connection is not necessary. You will just get the no alt message. Just an annoyance. To make it go away, you will need to add the wires I mentioned earlier but it may not be worth the trouble.

Sent from my SM-G950U1 using Tapatalk

 

[Ryan Klems]

Thx Ryan,

GOT and 429 EFIS? No clue, sorry.
This is the first time I'm trying to figure out an issue with any avionics.

I will get pics of the 327 and try to take pics of the main plug into the 420.

Thx again!

Cool, pictures should help determine if the wiring is there or not. I'm kinda guessing not being an LSA, I don't think it could be flown IFR anyway, so no real need to baro-aid the GPS. Though if it's not wired, it would certainly be very easy for a shop to add it to get it to stop complaining. Also based on your description of 6-pack, you aren't going to have a something sending the 429 airdata either.

 

[Aaron H]

Thx Floyd,
No nav.

No other way to get that message to go away then to add those wires?

 

[Floyd]

I do not think so.

Sent from my SM-G950U1 using Tapatalk

 

[Aaron H]

Not sure where the encoder is...so I took a video.

https://photos.app.goo.gl/Cgp3QRzCk4yq1sNp8

 

[Aaron H]

Thx Floyd,

Found it...the static tube made it easy to find.
I did not see any wires going from the transponder to the 420.

I did set the input 1 on the 420 to what u said and I received an error.

I have the card out right now to get it updated.
Thx for the offer and I'm in pa.

Thx for all the help!

 

[Floyd]

I think we have beat the dead horse enough. You probably need the wires from the transponder. You might call Garmin and ask them as the install manual says it can be installed without encoder input so I would think the message could be turned off, but I cannot find it mentioned in the install manual.
Have you thought about putting in ADS-B? Depending on your plans have the shop put the wires in when you do the upgrade.

 

[Aaron H]

Depending on how the lawsuit with Garmin goes, I wast thinking the sky beacon from uavionics for adsb.

Why are those wires needed?
I'm assuming that those wires are needed for ifr approaches?
If so, I think I will call Garmin and see if there is a way to stop the message from coming up.

Thx

 

[Ryan Klems]

Yeah, doesn’t look like you have anything other than power and ground connected to P4001. They didn’t even bother putting the backshell on! The encoder input is really for IFR approaches for baro-aiding, not really useful in your setup, but I’m not aware of a setting for VFR only or whatever on the gps itself, certainly an install can be, as your is. The pressure altitude device and a CDI are listed as minimum installation requirements in the manual, so likely there is no setting to turn off the warning.

 

[Aaron H]

Thx Ryan,

Maybe a dumb question, but what's the backshell?

Good info about the minimum requirements.
Was going to get the wires installed, but if it needs cdi also, probably will just live with the message because I have no room to add it.

Will call Garmin to double check though.

Thx again!

 

[Ryan Klems]

The backshell is the shell that goes over the back of the d-sub connector (where all those pins go in) covering the holes and providing the clamping of the wires so they don’t flex on the pins. If you notice the connector on the back of the transponder, and the other connector on the gps both have the backshell on. Being an experimental, and a VFR install, I wouldn’t worry about the CDI. The wire to the GPS from the transponder should be a very simple job for a shop, to get the message to go away. I’m curious on one of your pictures, what the random pressure gauge hooked to?

 

[Aaron H]

Thanks Ryan!

Would installing those wires help me out at all being vfr?

Ah, u noticed the guage...
I noticed that the oil pressure was falling into the yellow 2 out of 3 takeoffs.
I hooked the mechanical oil pressure guage in line with the electronic guage to see if it was a pump issue or an electronic issue.

Did 6 takeoffs yesterday and they were both perfect....uuuggghhh
Only good thing is I'm pretty sure it's an electrical issue since I cant get it to do it again. Most likey the crappy vdo oil sender.

 

[Ryan Klems]

About the only thing it might be nice for, other than eliminating the message, would be for vnav calculations (you have have it remind you when to start down based on distance and altitude from destination ... see section 3.9 of the GNS430 pilot's guide ... though I think it can do this using GPS altitude as well). Otherwise it's used in RAIM and to help compute a location solution with fewer satellites by using the altitude input, which are really only needed for IFR, but I suppose could be useful to still have a GPS lock if you have fewer visible satellites.

 

[Aaron H]

Thx Ryan appreciate all the help!