TrueCourse
Line Up and Wait
- Joined
- Dec 10, 2019
- Messages
- 922
- Display Name
Display name:
TrueCourse
This may simply be an altitude encoder problem and we'll get an avionics shop involved after I check a few things, but I'll throw it on here with some background just to see if there is anything I'm missing. It's a Garmin GTX 327 xpdr in a Cherokee, a Trans-Cal encoder (which was in the airplane before the Garmin was installed), skyBeacon ADS-B out. Alt/Stat and transponder passed inspections last year.
Flew through some Class C airspace requesting flight following and ATC said there was no altitude being transmitted. This happened twice that day, so its not intermittent. I pulled the FAA's PAPR and it shows most of the ADS-B was working fine, but at the top of the page under the "Missing Elements" section it shows Mode 3A with no failures and Baro Altitude column with 100% Fail. OK, that makes sense. However, near the bottom of the page under the "Other Checks" it shows Mode 3A 100% fail. Anyone know more about this difference?
I was running skyBeacon in Anonymous mode which I don't think was an issue because, by design, after ATC gave me a squawk code they started receiving the code (after being told it was briefly one digit off?). The transponder is displaying a pressure altitude. The Reply light was occasionally displaying. Anyone have an issue using anonymous mode?
So, I'm thinking a dead encoder or other issue with the encoder. But if the encoder was dead, wouldn't the transponder not display a pressure altitude? Or, can the encoder be good, while the transponder is not delivering the altitude information?
I did read the uAvionix information about Resolve Failing Mode 3A on PAPR and the Transponder Threshold Adjustment, but that appears to be related to the squawk code in general, not necessarily the Mode C readout. Next flight I'll use the Monitor function to see if it is reporting as it should. This was the first time flying this airplane through Class C so don't know how long its not been working.
Flew through some Class C airspace requesting flight following and ATC said there was no altitude being transmitted. This happened twice that day, so its not intermittent. I pulled the FAA's PAPR and it shows most of the ADS-B was working fine, but at the top of the page under the "Missing Elements" section it shows Mode 3A with no failures and Baro Altitude column with 100% Fail. OK, that makes sense. However, near the bottom of the page under the "Other Checks" it shows Mode 3A 100% fail. Anyone know more about this difference?
I was running skyBeacon in Anonymous mode which I don't think was an issue because, by design, after ATC gave me a squawk code they started receiving the code (after being told it was briefly one digit off?). The transponder is displaying a pressure altitude. The Reply light was occasionally displaying. Anyone have an issue using anonymous mode?
So, I'm thinking a dead encoder or other issue with the encoder. But if the encoder was dead, wouldn't the transponder not display a pressure altitude? Or, can the encoder be good, while the transponder is not delivering the altitude information?
I did read the uAvionix information about Resolve Failing Mode 3A on PAPR and the Transponder Threshold Adjustment, but that appears to be related to the squawk code in general, not necessarily the Mode C readout. Next flight I'll use the Monitor function to see if it is reporting as it should. This was the first time flying this airplane through Class C so don't know how long its not been working.