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freedomtofly
09-28-2019, 07:12 PM
I have a GRT HXr with a Trutrak vision 385. My GPS source is the Safefly 2020 from GRT. This morning while flying I loaded the SAP for our airport, highlighted ENAV and VNAV and Capt under SAP. Then I flew runway heading about 8 mile final and engaged the TT by pressing the mode button. GPSS was showing on my A/P. The autopilot flew the correct heading but would not maintain altitiude even though the "wings" of the flight director were below the intended altitude. Also the airplane was flying below the HITS boxes. I'm wondering what I am missing in the approach.

agirard7a
09-28-2019, 07:30 PM
Did you try switching to heading vs. nav?

agirard7a
09-28-2019, 07:38 PM
My GRT Sport will not fly VNAV on the SAP if I am in the Nav function. I need to fly the aprox runway heading using the Heading function first.

freedomtofly
09-28-2019, 08:20 PM
Are you saying I should push the HDG under LAT A/P and then leave ENAV under the VERT A/P? I then fly runway heading?

freedomtofly
09-28-2019, 08:24 PM
What should I set as my Sel Alt? Circuit height or runway height?

BobTurner
09-29-2019, 01:00 AM
What should I set as my Sel Alt? Circuit height or runway height?

Neither. Set the altitude to the current altitude, or the altitude at which you intend to begin the approach.
Do you have the ARINC pair installed between the GRT and the autopilot? You need them for this.
Make sure your TruTrak is in the mode where it will accept external arinc commands. I think that is GPSS SV on the TruTrak.
On the SAP key, select ARM.
When you reach the proper point (depends on the altitude; about 1 mile from the airport if you?re at 300? AGL; 10 miles if you?re at 3000? agl, etc) the autopilot should commence a descent. If you do nothing, the descent will end when you hit the runway, about 500-1000? from the threshold.

freedomtofly
09-29-2019, 12:51 PM
I have the arinc pair hooked between the HXr and the A/P. I will give it another try when the weather clears up a bit out here.

agirard7a
09-29-2019, 02:12 PM
Are you saying I should push the HDG under LAT A/P and then leave ENAV under the VERT A/P? I then fly runway heading?

Yes. Heading under the Lat A/P and fly the runway heading at the initial fix.
Set VNAV under the VERT A/P. I don’t have an ARINC. But this is how it works with my GRT auto pilot. Not sure about the TRutrak. Sorry for the confusion. AP captures the SAP after you confirm altitude.

jbDC9
09-29-2019, 02:48 PM
Duhhh. What?s SAP?

Too many acronyms here! And I thought as a 737 driver flying LNAV/VNAV and RNAV/RNP approaches all day long I?d heard them all...

RV8JD
09-29-2019, 02:55 PM
SAP = Synthetic Approach, for HITS guidance (Highway-in-the-Sky boxes):

http://grtavionics.com/media/Sport-Real-Quick-Ref.pdf