GRT Avionics

gdtrfb58 wrote:Many airports are now requiring Transponders on "ALT" at all times on the ground.

How will this affect the ADS-b compliance?

This IS for ADSB-out compliance. The rules require that if the box is set to ALT, then the box itself will switch between ground mode and airborn mode, using either a squat switch or other data. The pilot is out of the loop. The current issue when you see a 'air on ground' red box is that the transponder did not make the switch to ground mode fast enough to keep the FAA happy.

Another question for Jeff: Exactly what should be the squat switch setting in the set up menu? There are 3 choices: "no squat switch", "closed on ground", and "closed in air". I chose "no squat switch" which is what the Trig manual says, but I'm not sure what exactly goes on in the adaptor. Does the software override the switch position choice, or vice versa? I could, if needed figure out some way to install a switch.
More information from my ADSB reports: It looks like a delay of 22 seconds (this includes take off and landing) before switching to the correct mode results in a "pass". A delay of 49 seconds gave me a fail. Because the RV accelerates very well, on take off it switches to "air" just a few (5 ?) seconds early; but on landing it switches to "ground" well late, depending on how hard I brake. As I noted above, it looks to me like the switching threshold needs to be higher - maybe 50 KIAS? At that speed I am certainly not in the air.

One more ADS-B complication.

We don't have a setting for the speeds. Currently the air/ground mode uses the main air/ground function used for everything in the EFIS. It's hard-coded to 30 knots airspeed or 25 knots ground speed. We could add a setting.

Mode S ADS-B Out transponders have 4 modes: Standby (STBY), Ground (GND), ON, and ALT. In Ground mode, the transponder replies to Mode S and sends "on-ground" messages in ADS-B Out. When XPDR is set to Auto (the default), the EFIS automatically switches between Ground and ALT mode based on airspeed and ground speed. If you force it to ALT mode, I assume you will get a red box.

The squat switch setting is only for a real squat switch. The adapter doesn't interfere with that. The speed-based switching should be OK, or at least the FAA expects some installations are only using speed-based modes.

A software update recently delayed the air-to-ground (landing) switch for 20 seconds for other purposes. The delay was added to the software before the FAA added that box to the report. In the beta updates I removed the delay for the transponder mode, so you should see the mode switch as soon as you cross that airspeed.

Bobturner wrote:

gdtrfb58 wrote:Many airports are now requiring Transponders on "ALT" at all times on the ground.

How will this affect the ADS-b compliance?

This IS for ADSB-out compliance. The rules require that if the box is set to ALT, then the box itself will switch between ground mode and airborn mode, using either a squat switch or other data. The pilot is out of the loop. The current issue when you see a 'air on ground' red box is that the transponder did not make the switch to ground mode fast enough to keep the FAA happy.

Jeff explained this better than I did. The FAA requires the air-ground mode switching to be done automatically. Note there is no 'ground' screen option. Some transponders will do the switching when in ALT, but with the HX to TT22 link here you must run the transponder in AUTO if you are using it for ADSB-out.

Okay, today I got an 'all passed' test report from the FAA for the ADSB-out. My previous issue was simple: on landing I was letting it roll down to my exit at maybe 20-25 knots. But with a 12 knot headwind, ias was over 30 so it didn't switch soon enough. I don't know what the FAA allows but it isn't too long. Maybe 30 seconds total, landing and takeoff? At any rate, today I kept braking moderately until I saw the transponder flip to ground mode. So it works.
Jeff, any chance of making the changeover speed user selectable? For the RV10 45 or even 50 kias would work better.

I got my $500 FAA check today - much quicker than promised.

Hi Guys,

I have just purchased the TT22 and the companion TN70 GPS/Antenna. I have the Sport SX 200A unit (new). Am I going to have potentially the same problem on the air/ground lag as the HXr and others? If so, will my Sport SX 200A be able to use the software patch?

Thanks,

John W.
Cuyler Airpark (FD27)

If you're using the SX to control the TT22, then yes you may have the same issue. This update includes the patch. The next update will add a configurable transition speed to all HX, HXr, SX, EX, and Mini models.

SX software version 12b-beta20 2016-12-09

Thank, Jeff,

I will be sure to get the new SX update installed as soon as my avionics tech installs my new system. OR..... do I need to go ahead in pre-install it in the Sport SX 200A before the TT22 is installed?

(Sorry for the add on question... I just thought of it to ask)

Regards,

John Wanamaker
N701SY
Cuyler Airpark (FD27)

GRT_Jeff wrote:If you're using the SX to control the TT22, then yes you may have the same issue. This update includes the patch. The next update will add a configurable transition speed to all HX, HXr, SX, EX, and Mini models.

SX software version 12b-beta20 2016-12-09

Thanks Jeff, I think the configurable transition speeds will help a lot. Although I got a pass, and my $500, I continue to get air on ground fails if I let it roll down the runway without braking.