Van's Air Force
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ADS-B Performance Report
- Thread starter dpansier
- Start date
Your ADSB-out signal changes to different data once it 'detects' that you are on the ground (or vice-versa).The change over can be initiated by a squat switch if you have one, but for most RV's it's a combination of ground speed (gps) and IAS (pitot system), e.g., if well below stall speed you must be on the ground. The red data (air-ground) indicates that the FAA believes you were still sending the "airborne" data when you were in fact on the ground. Now, I have no idea how the FAA actually determines this. At my home airport (KLVK) there is no radar coverage at ground level (despite being within the SFO class B airspace). Is that the issue for me? At KLVK I also got a 'red' air-ground report while always passing at other airports. I played with the airspeed parameters a bit, then landed at LVK, hard breaking to a full stop on the runway. I passed. So there's something not quite right with how the testing is done. But I passed, and continue to pass, so I don't worry about it anymore.
Edit. I should have mentioned that I'm using a Trig TT-22 mode S (ES) transponder for adsb-out, and my GRT HX shows when it's in the ground mode, and every time I look it's in the correct mode. But of course I'm not looking at the panel at the most critical time: just after lift off or just after touch down. My feeling is that the FAA's tolerance on the switch over is pretty tight.
Edit. I should have mentioned that I'm using a Trig TT-22 mode S (ES) transponder for adsb-out, and my GRT HX shows when it's in the ground mode, and every time I look it's in the correct mode. But of course I'm not looking at the panel at the most critical time: just after lift off or just after touch down. My feeling is that the FAA's tolerance on the switch over is pretty tight.
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What system are you using? If it is determining air/ ground based upon groundspeed, what is the threshold? Possibly you were lingering right at the groundspeed set as the air/ground threshold, and the FAA monitor saw rapid repeated changes from ground status to air, and back.
For RVs, I set the threshold at 30 KTS groundspeed, and haven't one come back for a tune up yet...
Ed_Wischmeyer
Well Known Member
I recently proof-read a book and, if I recall correctly, the FAA / authors / somebody advised against using anything other than a squat switch to determine airplane on the ground due to unreliability of the algorithms...
I call foul. Squat switches fail, too. I'd sure like to see their engineering analysis of the algorithmic solution to back up this claim.
It's certainly true that if you're flying (or taxiing) in a near hurricane these airspeed/groundspeed measurements could give an incorrect indication of air/ground. But what's the alternative? Do you know of anyone, EAB or normally certified, with a fixed gear aircraft that has an actual squat switch? I actually thought about it but could not see any obvious way to do it with an RV. IMHO the FAA guys just blew it on this - the regs were written thinking only about air carrier type retractables with "weight on wheels" switches.
N804RV
Well Known Member
Maybe this will help?
https://stratusbyappareo.com/knowle...on on the ground,have acquired a GPS Position.)
https://stratusbyappareo.com/knowle...on on the ground,have acquired a GPS Position.)
dpansier
Well Known Member
Bob and OKAV8r, thanks for the detailed explanation.
I have a Stratus ESG Transponder, after reviewing the manual, I found no user defined parameters for the ground speed / flight set point. Not sure where that is set.
I do recall that flight ended with a downwind landing due to runway closure / construction so my groundspeed was higher than normal.
Ken W, thanks for the Stratus info, I have several ADS-B Performance Reports where I had no flags, I’m not sure what changed in the system as this is the first failure.
I have a Stratus ESG Transponder, after reviewing the manual, I found no user defined parameters for the ground speed / flight set point. Not sure where that is set.
I do recall that flight ended with a downwind landing due to runway closure / construction so my groundspeed was higher than normal.
Ken W, thanks for the Stratus info, I have several ADS-B Performance Reports where I had no flags, I’m not sure what changed in the system as this is the first failure.
Here are some suggestions for you, specific to the Stratus transponder.
https://stratusbyappareo.com/knowle...the-faa-public-ads-b-performance-report-papr/
This being said .. if this is your first air/ground failure, and your next flight shows a pass, I wouldn't worry about it.
https://stratusbyappareo.com/knowle...the-faa-public-ads-b-performance-report-papr/
This being said .. if this is your first air/ground failure, and your next flight shows a pass, I wouldn't worry about it.
FWIW, I've installed 62 ADS-B systems as of this date, and they ALL use groundspeed to determine air/ ground status
FAA AC20-165B section 3.10.2 addresses the FAA expectation for air/ ground determination. https://www.faa.gov/documentlibrary/media/advisory_circular/ac_20-165b.pdf#page38
Interesting that the faa expects fixed gear aircraft to do better than RG:
‘Retractable gear aircraft typically use a weight on wheels switch’
‘Fixed gear aircraft may use a weight on wheels switch AND GPS velocity.’
