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Old 04-29-2020, 10:16 AM
GaryK's Avatar
GaryK GaryK is offline
Join Date: Nov 2005
Location: Zeeland, Michigan
Posts: 411
Default Air on Ground fail

I've read through several of the posts on this subject but didn't see anything that fixed the issue. Lots of great suggestions but thought I would reach out again to those that have gotten past this.

Everything on the ADS-B Performance report is fine except "Air on Ground", 3.76%

Trig TT-22 with Trig head mounted on panel (S/W updated)
GRT Safe Fly GPS
GRT Sport SX (does not control the transponder)

There aren't many option to change on the Trig that deal with GPS stall speed and too low of a stall speed other than the SQUAT switch question.

There are 4 choices

I have it set on NOT CONNECTED as I don't have a squat switch or airspeed switch.

If I switch it to AUTO ON GPS DATA is there a fixed speed the FAA uses to determine when to interpret ground operation vs airborne?

I have tried some of the tips and tricks such as hold a steady 3 degree glide slope and come to a complete stop on the runway. Then taxi slowly back to the hangar.

Any help or suggestions would be appreciated.

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Old 04-29-2020, 10:54 AM
lr172 lr172 is offline
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 6,735

both my GRT and garmin installation go to grd mode automatically based upon air or GPS speed dropping below a pre-set threshhold. I would set it for auto based upon GPS. I am guessing it will ask for a threshhold speed. The GRT just sends the pre-configured threshhold speed to the trig, I believe, so there must be a setting for this field. You can't leave it as not conected, as it must have a way to enter grd mode to be compliant.
N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019

Last edited by lr172 : 04-29-2020 at 10:57 AM.
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Old 04-29-2020, 12:05 PM
GaryK's Avatar
GaryK GaryK is offline
Join Date: Nov 2005
Location: Zeeland, Michigan
Posts: 411

I was also thinking after I switched to auto on GPS I'd get another option to put in the speed, no such luck. Since the Sport doesn't control the Trig I have no option to set the speed.

I read some articles from 2016 when this was a major issue in certified installations. The article said the FAA set a speed of 25KTS but I can't find any info to verify that.

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Old 04-29-2020, 02:21 PM
Raymo's Avatar
Raymo Raymo is offline
Join Date: Nov 2014
Location: Richmond Hill, GA (KLHW)
Posts: 2,340

The install manual only says this:

"If no squat switch input is available, the transponder can automatically determine the air/ground status from the GPS input."
RV-7A - Slider - N495KL - First flt 27 Jan 17
O-360-A4M w/ AFP FM-150 FI, Dual PMags, Vetterman Trombone Exh, SkyTech starter, BandC Alt (PP failed after 226 hrs)
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Old 04-29-2020, 02:28 PM
JDA_BTR JDA_BTR is offline
Join Date: Dec 2013
Location: Colorado Springs, CO
Posts: 1,379

"Auto on GPS" is the only logical choice in your setup. I'd do that and see how it goes.
Ser 140142, RV-14A flying - N1463
Ser 83825, RV-8 building - N8638?
USN Ret, Urologist, AME, Repeat Offender
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Old 04-29-2020, 02:32 PM
BobTurner BobTurner is offline
Join Date: Dec 2011
Location: Livermore, CA
Posts: 7,863

I did use my GRT EFIS to control the Trig, and had the same issue. Changing the GRT settings to a higher stall speed, and aggressive braking to a full stop, got me a passing report. But then, I heard that some airports - even if within a mode C veil - do not have good ground level coverage of whatever the automated faa system uses for pass/fail data (how does it know you’re on the ground?). At my home field LVK has poor or no ground level radar coverage, even though within the mode C veil. I flew to another airport (several, actually) and easily passed every time. You might try a different airport.
And yes, try auto on gps.

Last edited by BobTurner : 04-29-2020 at 02:34 PM.
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Old 04-29-2020, 03:00 PM
GaryK's Avatar
GaryK GaryK is offline
Join Date: Nov 2005
Location: Zeeland, Michigan
Posts: 411

Thanks all
I'll try the Auto on GPS data, agree its the next choice. I'll keep digging to find out the magic speed since I don't know what triggers the "AUTO" part of the choice.

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Old 04-29-2020, 04:51 PM
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Carlos151 Carlos151 is offline
Join Date: Jan 2008
Location: Lebanon, TN
Posts: 427
Default Software update?

I?ve got a Trig TT31 that required a software update before ADSB worked properly. From installation to build completion was a couple of years and I was behind by about 5 software versions. Now it works great.
Sent it in to Mid Continent Avionics in Wichita and round trip was about 10 days from what I recall. You should see your latest software version displayed when you power up.

Straight from their support page:

17/04/2018 version 2.13
This software improves GPS-only air/ground determination algorithm for ADS-B Out.?
Karl Richcreek
N151TK "La Otra Chica"
Flying as of August 14, 2015
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Old 04-29-2020, 07:57 PM
GaryK's Avatar
GaryK GaryK is offline
Join Date: Nov 2005
Location: Zeeland, Michigan
Posts: 411

I did send the T-22 off to Mid Continent Avionics, they upgraded to the latest SW. Great group of people, quick turn and no charge other than the shipping cost.

Once the rain stops in Western MI I'll be testing the Auto on GPS setting.

Thanks again for the suggestions

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