Mode C Died

[Skates97]

For a little while now every so often the Mode C on my transponder will stop reporting. Cycling the transponder has previously got it working again. Today I was flying to my plane's new home (KFUL, will post in the today's flight thread on it) the tower reported that my Mode C was not working and asked me to cycle the transponder. I did, and it still wasn't working. The transponder was broadcasting position because when I initially called up tower he came back with "Are you next to the water treatment plant?" which I affirmed that was me. That was when he asked me to cycle it, after doing so and inquiring if it was working he told me negative, get it fixed when you get on the ground.

Not knowing enough about the workings and relationship between the transponder and encoder my question is which is it, or both? My thought would be that it was the encoder that gave up the ghost.

Transponder is a Narco AT 150 and encoder is a Narco AR 850 both of which could be had fairly cheap to swap one out and kick the can a little further down the road. (Yes, I know ADS-B is less than a year away and there is something to be said for not throwing money after bad/old/worthless components).

[carusoam]

I had a similar challenge.... When asking for flight following once...

But I could see my blinking light not blinking any longer...

Got one of those on your Narco?

I bought a different blinking light in a used BK box from @Alan Fox... and it displays the encoder altitude too.

Atc gets a couple pieces of information...

• where you are
• altitude you are reporting

If the encoder croaks, they still know where you are, sort of....

Best regards,

-a-

[Skates97]

14 minutes ago, carusoam said:

I had a similar challenge.... When asking for flight following once...

But I could see my blinking light not blinking any longer...

Got one of those on your Narco?

I bought a different blinking light in a used BK box from @Alan Fox... and it displays the encoder altitude too.

Atc gets a couple pieces of information...

• where you are
• altitude you are reporting

If the encoder croaks, they still know where you are, sort of....

Best regards,

-a-

Blinking light works fine. He knew where I was, just not how high I was, which is why I am thinking it is the encoder that died.

[Marauder]

For a little while now every so often the Mode C on my transponder will stop reporting. Cycling the transponder has previously got it working again. Today I was flying to my plane's new home (KFUL, will post in the today's flight thread on it) the tower reported that my Mode C was not working and asked me to cycle the transponder. I did, and it still wasn't working. The transponder was broadcasting position because when I initially called up tower he came back with "Are you next to the water treatment plant?" which I affirmed that was me. That was when he asked me to cycle it, after doing so and inquiring if it was working he told me negative, get it fixed when you get on the ground.
Not knowing enough about the workings and relationship between the transponder and encoder my question is which is it, or both? My thought would be that it was the encoder that gave up the ghost.
Transponder is a Narco AT 150 and encoder is a Narco AR 850 both of which could be had fairly cheap to swap one out and kick the can a little further down the road. (Yes, I know ADS-B is less than a year away and there is something to be said for not throwing money after bad/old/worthless components).

The transponder is doing the code reporting and the encoder is providing the pressure altitude through the transponder. Since the encoder transmits altitude through the transponder, it may be hard to tell if the encoder is not providing altitude or the transponder is not sending it. But if they can’t see your transponder at all, I’m of the belief it is the transponder.

The fact you could get it back by cycling it, suggests it could be an indication it is the transponder and not the antenna. I had a Narco AT-150 married to an old encoder. Never had an issue with it.

Personally, considering Narco is gone, I would either locate a working AT-150 to bide you over or spend the money to get a working transponder installed. It sounds like you are flying in an area where you need to be ADS-B compliant. You may find it hard to get one installed if you wait too long.




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[Alan Fox]

Skates , the time is now to upgrade , If you don't have a WAAS gps , I would suggest a beacon , and a GTX327 ,  I sell GTX 327 transponders with solid state encoders for about 600.00  complete....The beacon is approx. 1800.00 depending on where you buy it..     ,   Keep in mind  the deadline is MONTHS now , and any money tou spend on the transponder is purely a waste....   Good luck..

[Jerry 5TJ]

The wiring between the encoder and transponder has 12 conductors.  That wiring and the two connectors are possible trouble spots when you have intermittent mode C reports from ATC.  

[Marauder]

Listen to Jerry. He knows a thing or two about transponders...


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[steingar]

My Stratus 2020 transponder was I think 5 AMUs all in, and that includes the weather and traffics on my iPad running off ship’s power. That’s about what the original mode C transponders cost. For Odin’s Sale. 2020 is now months away. And there’s another damn rebate. I can’t believe there isn’t a clustefuck full of controlled airspace where you are. If not now, when?  Mooney’s are fast. You’re going to hit controlled airspace somewhere, and it’s going to suck going around it, especially if you have to fly way out to sea to do it

[Skates97]

1 hour ago, steingar said:

My Stratus 2020 transponder was I think 5 AMUs all in, and that includes the weather and traffics on my iPad running off ship’s power. That’s about what the original mode C transponders cost. For Odin’s Sale. 2020 is now months away. And there’s another damn rebate. I can’t believe there isn’t a clustefuck full of controlled airspace where you are. If not now, when?  Mooney’s are fast. You’re going to hit controlled airspace somewhere, and it’s going to suck going around it, especially if you have to fly way out to sea to do it

Yes, Mooneys are fast and I regularly fly to Phoenix and Salt Lake, not short little breakfast hops. And yes, everywhere around here you need ADS-B, things I already know. My question was about what might have failed, not how to spend my money or make a plan. 

If it's the encoder I can have one for $50 and the Skybeacon less the rebate has me complaint for about 1 AMU. Given all the upgrades going on I can pick up a spare transponder for not much if I want to down the road just in case it goes belly up. 

5 hours ago, Jerry 5TJ said:

The wiring between the encoder and transponder has 12 conductors.  That wiring and the two connectors are possible trouble spots when you have intermittent mode C reports from ATC.  

Thanks for this, will take a look at connections and wires and have my guy do a transponder check to see if we can narrow this down. 

14 hours ago, Marauder said:

The transponder is doing the code reporting and the encoder is providing the pressure altitude through the transponder. Since the encoder transmits altitude through the transponder, it may be hard to tell if the encoder is not providing altitude or the transponder is not sending it. But if they can’t see your transponder at all, I’m of the belief it is the transponder.

 

They could see the transponder (location) there was just no mode C (altitude) in the reporting. 

[ZuluZulu]

Skates, I’ve been talking with a few of the local avionics shops recently. High Desert is probably booked into June by now if not later. Leading Edge might have more immediate availability, but no doubt filling up fast. Might be worth thinking about making a reservation now if you’re thinking anything more involved than a SkyBeacon ... just my 2 cents. There are a ton of airplanes flying around SoCal that aren’t compliant yet. It’s the perfect storm. 

[Skates97]

On 1/20/2019 at 7:58 PM, ZuluZulu said:

Skates, I’ve been talking with a few of the local avionics shops recently. High Desert is probably booked into June by now if not later. Leading Edge might have more immediate availability, but no doubt filling up fast. Might be worth thinking about making a reservation now if you’re thinking anything more involved than a SkyBeacon ... just my 2 cents. There are a ton of airplanes flying around SoCal that aren’t compliant yet. It’s the perfect storm. 

Current plan is to put the SkyBeacon in, most likely next month.

Update from a few weeks back:

Pulled the right side of the panel out to get a better look at all the wiring. With the windshield mod even though I have the little access panels from the outside it is much easier to see with the panel out a few inches. Found a very loose ground and fixed that. Taxied out to run-up and called up Ground who said he won't be able to see anything on my Mode C until I am a few hundred feet up. I finished run-up and checklists, then received clearance to taxi and take off for right closed traffic.

Climbing out tower called up and said my Mode C was reporting 700', I glanced at the altimeter that was also at 700'. On downwind I received landing clearance and told that my Mode C was showing 1,100', perfect, that is exactly what my altimeter was showing. After landing and getting taxi clearance back to my hangar I thanked the tower for their help.

Side note, you never know what you are going to find when you start looking around. When I pulled the panel out I saw what looked like a hairline crack in one of the breakers, the one for the stall warning horn. Sure enough, when it was loosened a little it fell apart. Horn has always worked in preflight check and though I don't always get it on landing I do most of the time. However, I wonder at what point it might have just fallen apart on it's own. Fortunately Aircraft Spruce is not very far away from even my new hangar at Fullerton so a replacement was obtained the same day it was discovered.

[rbridges]

glad you got it working.  Cheap fixes are the best!

[bob865]

Just to throw this out since there are several pieces of incorect info in this thread.  The Mode C transponder does not report position.  It only reports altitude and squawk.  ATC can see your position with your transponder completely off, that's primary RADAR.  Now this position has no other info with it other than this your position on the ground, but not how high over the ground.  The squawk and altitude comes from your transponder and is part of the secondary survailence RADAR.  The screen the controller is looking at marries these two pieces of info together and displays your squawk, altitidude, and position.  The system has a database that relates your swawk to your tail number so your tail number will show up in your data block.

So if ATC can see you and your position but is only missing your altitude, it is likely you encoder or the connections related to.  If they can't see a squawk or an altitude, then it is likely the transponder.