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Re: VNAV capture

Postby Bobturner » Fri Aug 11, 2017 11:55 pm

This is puzzling. I presume you 'armed' the approach in the GRT menu, then 'execute'. When it failed to capture the GS did you try 'VERT' in the grt menu, to force it to engage? Or have you tried an ILS? Something is off somewhere.
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Re: VNAV capture

Postby 1 Victor Fox » Sat Aug 12, 2017 2:13 pm

Bobturner wrote:This is puzzling. I presume you 'armed' the approach in the GRT menu, then 'execute'. When it failed to capture the GS did you try 'VERT' in the grt menu, to force it to engage? Or have you tried an ILS? Something is off somewhere.


Yes, quite puzzling. I am quite confident that I have all the button pushing correct and in the correct sequence. After loading and activating the approach in the GTN, my understanding is that you must arm "GPSV" to bring up "execute", and "missed" will only show after a successful capture and I have seen all of that except the autopilot doesn't physically fly the VNAV path. I suspected communication between the GRT and TruTrak via ARINC as perhaps suspect, but that's only two pins, and the fact that it performs other Vertical commands correctly means its communicating.

Your other question of "Did you try Vert" The options under Vert A/P are: AUTO, V/S, ASPD & VNAV. I have always had VNAV selected (although I left it in auto once to no avail). Not sure what you mean by force it. Usually when it fails to capture VNAV, I give it some more time until I'm two dots high then click it off. Ill fly it down to the path center things up and try to recouple the a/p. Never works.

I may double check the deep ARINC setup menus in the GTN today. (I have not done that) (Aerotronics did my install and they're very good at this stuff of course) I have looked over all my GRT settings many times & there are very few settings on the Vizion trutrak. All good as far as I can tell.
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Re: VNAV capture

Postby Bobturner » Sat Aug 12, 2017 5:19 pm

Yes, sorry, I meant VNAV. You shouldn't have to select this - it should be selected automatically, at GS capture, if the approach has been armed. What I meant to ask was, after the autopilot flies thru the glide slope, can you manually push VNAV and does the autopilot then try to track the GS?
I'm not sure what happens if you engage VNAV before ARM.
You said 2 wires, I'm sure you meant 3, between the efis and trutrak - 1 (plus ground) serial line, 2 (1 pair) arinc lines.
Edit: I re-read, and see you said 2 arinc wires, so that's correct. It's not unheard of for even the pros to make mistakes. You might check that your arinc lines are correct - A to A, B to B. And to the correct pins.
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Re: VNAV capture

Postby GRT_Jeff » Tue Aug 15, 2017 6:09 am

What doesn't make sense about this is the regular altitude controls use the same ARINC pitch commands. If you can dial in an altitude and vertical rate on the EFIS and the TruTrak follows it and matches the rate you selected, then I don't see how it wouldn't follow the GS capture. From the TruTrak's perspective it is getting the same pitch command as if you selected a lower altitude. It doesn't know that it's a GS capture. Our EFIS displays don't rely on the special GS capture modes that are used by some TruTrak's to directly follow the Garmin 430 compatible units.
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Re: VNAV capture

Postby Bobturner » Thu Aug 17, 2017 12:54 am

Any chance the glide slope gain (in the set up) is set to zero?
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Re: VNAV capture

Postby 1 Victor Fox » Thu Aug 17, 2017 7:53 pm

Ill check that one for sure Bob. Ive been away on a trip for the last few days so I haven't been able to get out to the Plane... Thanks for keeping your thinking cap on.
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