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Garmin GDL39-3D Showing weird traffic altitudes in Garmin Pilot

1001001

Well Known Member
Has anyone experienced this? My GDL39-3D (portable) is reporting traffic with wrong altitudes. Everything shows up as being significantly higher than it really is. Even though I have ownship detection set on, it shows my airplane as being a variable height higher than my actual altitude, and this discrepancy increases with increasing altitude. For instance, when I am at, say, 2200 ft MSL (Pressure altitude 1900 on the particular flight), my ownship is reported as a target 7500 feet above me. Other traffic shows similarly. As I climb, the difference between actual altitude and the reported traffic altitude increases.

I see this both on my iPad and my Android phone, both running Garmin Pilot. I have an Appareo Stratus ESG transponder with ADS-B out, and it is running correctly (passed its tests just fine and ATC never gives me any flak about my transponder showing wrong altitude). I also recently re-ran an ADSB out report with the FAA and it came back with no problems.

Any ideas? I want to contact Garmin about it, but I never think to on a weekday, and I mostly fly on weekends or after hours on weekdays. I'll have to make a note to call them, but in the mean time, can anyone else shed light on this?
 
Pressurized Cockpit?

While I would guess most people on this forum are flying RVs, many of us are flying other aircraft as well. Is this by chance happening in a pressurized aircraft? I believe the GDL 39 has a built in barometric sensor. If you are in a pressurized airplane, it is going to think you are at a much lower altitude.

If you are not in a pressurized airplane, there is a chance that the barometric sensor is damaged. I would reach out to Garmin using the [email protected] email address. They sometimes even respond to that on the weekend.
 
I don't use a 39 or garmin pilot, but I do have the symptoms you do. I believe that FF gets a GPS alititude from the IPAD OS and not a baro altitude. This is the reason for the discrepancy. The relative distance will change based upon how far off the altimeter setting leaves the altimeter from actual as well as how for off the pressure is from the "standard atmosphere." Compare your GPS altitude and altimeter. See if the difference doesn't match the altitude discrepancy on reported traffic.

Larry
 
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While I would guess most people on this forum are flying RVs, many of us are flying other aircraft as well. Is this by chance happening in a pressurized aircraft? I believe the GDL 39 has a built in barometric sensor. If you are in a pressurized airplane, it is going to think you are at a much lower altitude.

If you are not in a pressurized airplane, there is a chance that the barometric sensor is damaged. I would reach out to Garmin using the [email protected] email address. They sometimes even respond to that on the weekend.

Nope, not pressurized. I had thought there might be a problem with the gdl's baro sensor too but have no way to verify. I will have to look into this.
 
Set to "pressurized"

There is a setting in Garmin Pilot and probably most interfaces to the GDL 39 allowing you to tell it you are in a pressurized airplane. I believe this transitions the altitude alerts from using the baro pressure to using GPS. You could try setting that differently and see if the problem still occurs.
 
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