I really enjoy the new VNAV capability the Garmin has provided with the v6.5 update to the GTN, combined with the recent G3X update. However, the updated Pilot Guide states that for the G3X, VNAV capability is only for visual conditions. That actually makes sense, because in IFR flight, you’ll be on an assigned or prescribed altitude. In fact, my operational experience has found that if you pick a fix to start and approach, set the altitude constraint and hit “save” in the GTN, and then arm VNAV, the AP will not automatically transition to the approach; it will steer laterally to the inbound course, but vertically, altitude hold will take effect for the last constrained altitude - even if a GP or GS is prescribed in the approach. I wondered how I could get the VNAV feature to make IFR flight easier as it wasn’t obvious to me in either the GTN and G3X PG’s.
Well, if you have a GTN coupled to your G3X, I’m happy to report that there is a feature called VNAV Transition to Approach that works very well, but requires using the Direct to VNAV feature. A common occurrence for me is to have ATC say “proceed direct to XXXXX and cross at XXXX, cleared for blah, blah, blah” - direct to VNAV works great for this.
It wasn’t obvious to me how this all worked, and in the event that I’m not the only person who hasn’t got it all figured this out - after MUCH playing around with the system - I’ve come up with a way to use VNAV as part of my IFR flying and thought I’d share my process.
I have a GTN625, GMC307 AP controller and G3X dual displays - so this is applicable to that setup, or a similar one.
- Load my applicable flight plan in the GTN
- Be in NAV mode (on the GMC, select NAV); VNAV will not work in HDG mode.
- Load my approach and verify routing to the IAF is active.
- Verify the altitude constraint for the fix; the system automatically loads the published altitude, such as 4500’ for DOCAL on my local approach, but ATC often gives a different crossing altitude, such as 4700’, so I just update that. Then - and this is a key point - press the D-VNAV button on the GTN, not “SAVE”.
- Press the APR button on GMC (APPR on the G3X if you don’t have a GMC) to arm the approach. An option would be flying on vectors in heading mode and then activate this and then proceed on the approach once cleared.
- And then press the VNAV button. The APR button will stay lit - armed. You’ll also note that if the approach has a glide path (GPS) or glideslope (ILS) a GP or GS will also appear on the AP control panel showing armed in grey color.
- You’ll note a altitude constraint in magenta above the altitude tape appears and the VNAV magenta “<“ on the altitude tape starts descending.
The AP will guide descent to the waypoint at the constrained altitude and start the turn onto the approach leg. Once you are at the constraint altitude, (it seems to capture at about 50’ above), the VNAV will transition automatically to the GP or GS.
Enjoy watching the magic happen. It’s pretty slick.
Well, if you have a GTN coupled to your G3X, I’m happy to report that there is a feature called VNAV Transition to Approach that works very well, but requires using the Direct to VNAV feature. A common occurrence for me is to have ATC say “proceed direct to XXXXX and cross at XXXX, cleared for blah, blah, blah” - direct to VNAV works great for this.
It wasn’t obvious to me how this all worked, and in the event that I’m not the only person who hasn’t got it all figured this out - after MUCH playing around with the system - I’ve come up with a way to use VNAV as part of my IFR flying and thought I’d share my process.
I have a GTN625, GMC307 AP controller and G3X dual displays - so this is applicable to that setup, or a similar one.
- Load my applicable flight plan in the GTN
- Be in NAV mode (on the GMC, select NAV); VNAV will not work in HDG mode.
- Load my approach and verify routing to the IAF is active.
- Verify the altitude constraint for the fix; the system automatically loads the published altitude, such as 4500’ for DOCAL on my local approach, but ATC often gives a different crossing altitude, such as 4700’, so I just update that. Then - and this is a key point - press the D-VNAV button on the GTN, not “SAVE”.
- Press the APR button on GMC (APPR on the G3X if you don’t have a GMC) to arm the approach. An option would be flying on vectors in heading mode and then activate this and then proceed on the approach once cleared.
- And then press the VNAV button. The APR button will stay lit - armed. You’ll also note that if the approach has a glide path (GPS) or glideslope (ILS) a GP or GS will also appear on the AP control panel showing armed in grey color.
- You’ll note a altitude constraint in magenta above the altitude tape appears and the VNAV magenta “<“ on the altitude tape starts descending.
The AP will guide descent to the waypoint at the constrained altitude and start the turn onto the approach leg. Once you are at the constraint altitude, (it seems to capture at about 50’ above), the VNAV will transition automatically to the GP or GS.
Enjoy watching the magic happen. It’s pretty slick.
Last edited: