VNAV into Approach

[Marc_B]

Preface: using GTN750Xi/G5/GFC500 and sequencing coupled approach

Logged in to a Garmin Webinar today regarding VNAV.  The GTN Xi is set up to sequence VNAV for initial fixes into the FAF and then sequencing APR approach mode for Glidepath capture and descent.  My question is for those who have used this, how have you managed your power for the transition?

i.e. previously I've slowed down to gear speed by the FAF so that with the GP diamond 1 dot above capture I drop gear and configure for final approach.  What I've found is that with initial trial if the VNAV is descending me continuously from start of approach all the way to FAF and GP capture that my speed is typically much higher and doesn't have a chance to "settle down" to a gear speed without either speed brakes or dropping engine MP drastically.  Before use of VNAV I would typically choose a VS descent that would allow me to level off prior to FAF.  VNAV descends you TO the FAF.

Just wondering how others use this and sequence their power changes on an approach with continued descent like this (VNAV with bottom of descent at FAF with immediate GP capture and continued descent).

Thanks,

Marc

Edited April 4, 2023 by Marc_B
typos

[midlifeflyer]

You manage your power the same way as you would if you were hand flying the same profile. Same basic "fly by the numbers" principles. Keep in mind that the VNAV calcs are based in GS. If you descend without reducing power, the BOD will changed due to increased speed, or your descent rate will increase and might exceed VNAV parameters.

[donkaye]

23 hours ago, Marc_B said:

Preface: using GTN750Xi/G5/GFC500 and sequencing coupled approach

Logged in to a Garmin Webinar today regarding VNAV.  The GTN Xi is set up to sequence VNAV for initial fixes into the FAF and then sequencing APR approach mode for Glidepath capture and descent.  My question is for those who have used this, how have you managed your power for the transition?

i.e. previously I've slowed down to gear speed by the FAF so that with the GP diamond 1 dot above capture I drop gear and configure for final approach.  What I've found is that with initial trial if the VNAV is descending me continuously from start of approach all the way to FAF and GP capture that my speed is typically much higher and doesn't have a chance to "settle down" to a gear speed without either speed brakes or dropping engine speed drastically.  Before use of VNAV I would typically chose a VS descent that would allow me to level off prior to FAF.  VNAV descends you TO the FAF.

Just wondering how others use this and sequence their power changes on an approach with continued descent like this (VNAV with bottom of descent at FAF with immediate GP capture and continued descent).

Thanks,

Marc

VNAV with the GFC 500 is only certified to one waypoint before the final approach fix.  There is not "Transition to Approach" with it.  Only the GFC 600 has that capabiity.  Unless there is a large descent from that waypoint to the FAF, I would just wait to intercept the GP.  

From the below and further investigation, the above comment is no longer valid.

[Marc_B]

@donkaye You might double check next flight.  What was presented today at webinar, as well as what the Mooney was doing in the air yesterday, VNAV went up to FAF and APR went past FAF.  Meaning if you had vertical navigation altitude constraints selected/listed you could "activate" VNAV on the GFC500 and "arm" APR.  VNAV would function prior to FAF and when you hit the FAF the GP/GS would become active.

Here's a slide from the presentation.  Comment during this slide from Garmin: "VNAV ends at the final approach fix, and then approach vertical guidance is going to take over."

But it functions as Garmin VNAV is designed to do...create a smooth line from start altitude down to bottom constraint as smoothly as possible down to your lower constraint...in this case your FAF altitude.  So it's a continuous descent rather than step downs if that's possible.

So @midlifeflyer, it sounds like just anticipate slow down much earlier...I've usually only moderately dropped MP in level flight prior to FAF to slow down to gear speed, dropped gear just before FAF and that slows me to approach speed with fine tuning from there.  a 500-600 FPM descent is enough energy that I'll need to test out how far before FAF I need to drop MP to 1) avoid need for speed brakes, 2) keep speed up as long as possible, but 3) with being able to drop below 140kts before the FAF for gear. 

Flying by hand is easier as I can briefly level off to slow, drop gear and start descending again.  Just looking to see if others have a squared away process with this automation.

[201Mooniac]

Garmin added the VNAV transition to approach sometime last year if I recall.  They didn't call it that in the notes but said something about arming two modes at once or something like that.  I did an approach like this on Sunday and I just slowed to 120kts in my decent from 6000 to 2800 where I intercepted the GP and lowered the gear.  Given a couple of minutes of VNAV decent it was easy to slow as I had slowed to about 125kts during the vectoring..

[RoundTwo]

If it’s truly a path, and not just points that are calculated once, slowing down nearing the FAF, should reduce VS to keep you on the same slope/mile. I was on the same webinar and was hoping for something new, but Mark pretty much rehashed his earlier presentations.

[midlifeflyer]

3 hours ago, Marc_B said:

@donkaye You might double check next flight.  What was presented today at webinar, as well as what the Mooney was doing in the air yesterday, VNAV went up to FAF and APR went past FAF.  Meaning if you had vertical navigation altitude constraints selected/listed you could "activate" VNAV on the GFC500 and "arm" APR.  VNAV would function prior to FAF and when you hit the FAF the GP/GS would become active.

Here's a slide from the presentation.  Comment during this slide from Garmin: "VNAV ends at the final approach fix, and then approach vertical guidance is going to take over."

But it functions as Garmin VNAV is designed to do...create a smooth line from start altitude down to bottom constraint as smoothly as possible down to your lower constraint...in this case your FAF altitude.  So it's a continuous descent rather than step downs if that's possible.

So @midlifeflyer, it sounds like just anticipate slow down much earlier...I've usually only moderately dropped MP in level flight prior to FAF to slow down to gear speed, dropped gear just before FAF and that slows me to approach speed with fine tuning from there.  a 500-600 FPM descent is enough energy that I'll need to test out how far before FAF I need to drop MP to 1) avoid need for speed brakes, 2) keep speed up as long as possible, but 3) with being able to drop below 140kts before the FAF for gear. 

Flying by hand is easier as I can briefly level off to slow, drop gear and start descending again.  Just looking to see if others have a squared away process with this automation.

The profile is following the FAA's recent emphasis on a stable continuous descent final approach (CDFA). The concept is that you make only one configuration change. Like a lot of things, it's not ideal for every situation. 

[carusoam]

This is where the MAPA training book is really helpful…

It has all the great details of every step and power adjustment…

A great place to start, so you can adjust for your plane and personal choices…

 

+1 for Don and Mark’s input… they are actual Mooney CFIIs…. 

Best regards,

-a-

[midlifeflyer]

12 hours ago, donkaye said:

VNAV with the GFC 500 is only certified to one waypoint before the final approach fix.  There is not "Transition to Approach" with it.  Only the GFC 600 has that capabiity.  Unless there is a large descent from that waypoint to the FAF, I would just wait to intercept the GP.  

VNAV terminates when the FAF becomes the active waypoint in all the GFCs I'm aware of. 

When the GFC500 first came out, it would not allow you to arm both VNAV and GS/GP at the same time. I think you had to wait until VNAV was already active before arming GP. But, at least with the latest software, you can arm both LNAV and GP/GS at the same time just like in the GFC 600 and 700. It's one of the things I check for in transition training. 
 

 

 

[midlifeflyer]

12 hours ago, Marc_B said:

 

But it functions as Garmin VNAV is designed to do...create a smooth line from start altitude down to bottom constraint as smoothly as possible down to your lower constraint...in this case your FAF altitude.  So it's a continuous descent rather than step downs if that's possible.

So @midlifeflyer, it sounds like just anticipate slow down much earlier...I've usually only moderately dropped MP in level flight prior to FAF to slow down to gear speed, dropped gear just before FAF and that slows me to approach speed with fine tuning from there.  a 500-600 FPM descent is enough energy that I'll need to test out how far before FAF I need to drop MP to 1) avoid need for speed brakes, 2) keep speed up as long as possible, but 3) with being able to drop below 140kts before the FAF for gear. 

Flying by hand is easier as I can briefly level off to slow, drop gear and start descending again.  Just looking to see if others have a squared away process with this automation.

The automation gives choices.

1.  I can take full advantage of combined VNAV/GP arming, select 4300 (or lower) as my bottom altitude, take advantage of early approach configuration and ride it down. One configuration change and I'm done. In effect, VNAV is doing the same thing as activating the leg to the FAF (GARYC is the intermediate fix, albeit further out than usual with stepdowns between it and the FAF).
2. I can take partial advantage and select 4800 as my bottom altitude, keep my speed up to that level off, begin my slowdown there, and wait at 4800 for FAYUB to become the active waypoint and intercept the glidepath. Three configuration changes.
3. I can disregard VNAV guidance and dive and drive to 4800 and level off, dive and drive to 4300 and level off (as we were taught to do with ILS in ancient days) and then configure for the approach. Five configuration changes.

#2 is probably my most common setup with or without VNAV, although, looking at the plate, I'd choose #1 for this one because if the stepdowns inside the IF. I've pretty much given up #3's unnecessary diving and driving to GP/GS intercept altitude. I have a friend who still likes #3.

[PT20J]

15 hours ago, donkaye said:

VNAV with the GFC 500 is only certified to one waypoint before the final approach fix.  There is not "Transition to Approach" with it.  Only the GFC 600 has that capabiity.  Unless there is a large descent from that waypoint to the FAF, I would just wait to intercept the GP.  

Don, that used to be true and the Pilot’s Guide still states that because with a GFC 500 autopilot, transition to approach is not supposed to be enabled in configuration mode. However, I believe that the 20.23 GTN software update fixed this so that it will VNAV to the FAF without changing the configuration mode setting. I’ll try to find the software change history to confirm this, but Garmin doesn’t make them easy to find.

Skip

[donkaye]

I don't usually miss important changes like this, and when I called Garmin they couldn't point me the a section that indicated the change, but said they couldn't find anything that said VNAV wouldn't work to the FAF.  I didn't think that was very helpful.  @201Mooniac pointed me to a G5 change from software version 7.1 to 8.0 that states you can arm both VNAV and APP at the same  time, but I hadn't related that to removal of the "VNAV good only to one waypoint before the FAF" limitation for the GFC 500.

I went back and listened to a webinar given a year ago by Garmin and confirmed in that webinar the instructor discussed that limitation.   I'd like to hear the latest webinar where this was changed.  Is it posted?

[RoundTwo]

1 hour ago, donkaye said:

I don't usually miss important changes like this, and when I called Garmin they couldn't point me the a section that indicated the change, but said they couldn't find anything that said VNAV wouldn't work to the FAF.  I didn't think that was very helpful.  @201Mooniac pointed me to a G5 change from software version 7.1 to 8.0 that states you can arm both VNAV and APP at the same  time, but I hadn't related that to removal of the "VNAV good only to one waypoint before the FAF" limitation for the GFC 500.

I went back and listened to a webinar given a year ago by Garmin and confirmed in that webinar the instructor discussed that limitation.   I'd like to hear the latest webinar where this was changed.  Is it posted?

I posted a link but it looks to be personalized for me. Here’s the nugget. VNAV all the way to FAF and Approach Vertical Guidance from FAF inward.

[midlifeflyer]

48 minutes ago, donkaye said:

I don't usually miss important changes like this, and when I called Garmin they couldn't point me the a section that indicated the change, but said they couldn't find anything that said VNAV wouldn't work to the FAF.  I didn't think that was very helpful.  @201Mooniac pointed me to a G5 change from software version 7.1 to 8.0 that states you can arm both VNAV and APP at the same  time, but I hadn't related that to removal of the "VNAV good only to one waypoint before the FAF" limitation for the GFC 500.

I went back and listened to a webinar given a year ago by Garmin and confirmed in that webinar the instructor discussed that limitation.   I'd like to hear the latest webinar where this was changed.  Is it posted?

I don't think there's a Garmin webinar that discusses it directly. But that's typical. When the Garmin PFDs began to show the the phantom localizer, there wasn't some big announcement, I've come to expect the unexpected every time I get into someone's airplane for avionics work. 

I knew about it because of a friend who whet through the configuration change process with Garmin. I check for it because people's upgrade speeds tend to differ. I know of it because it worked in the last G5/GFC500 airplane I taught it.

[LANCECASPER]

27 minutes ago, midlifeflyer said:

I don't think there's a Garmin webinar that discusses it directly.

@donkaye I think the webinar that @Marc_B was referring to was on yesterday. It looks like they are doing it again later today. 

https://www.garmin.com/en-US/aviation/webinars/americas/

[PT20J]

I'm not a VNAV expert because I don't get to use it that often. Usually, I get vectors just outside the FAF and intercept the final approach course and then capture the GS with the GFC 500 in APR. However, Monday, I found myself in San Jose planning the RNAV Y 30L and was cleared to GILRO at 5000 and then "Cross KLIDE at or above 5000, maintain 140 knots to KLIDE, best forward speed to HIVAK, cleared for the RNAV Y 30L approach." KLIDE has a published minimum altitude of 4000, so this put me above the VNAV glideslope. I could have gone into the flight plan and changed the constraint, but it was bumpy and I was busy because I was going fast so I just decided to hand fly the approach. Sometimes that's easier than trying to program the automation.

It's not that hard to slow a Mooney down while going down hill. You just have to plan ahead because it doesn't slow down quickly which translates to a lot of distance travelled while decelerating. Doing it mechanically doesn't work well because each situation is different. I taught myself to do this when I had my 1978 M20J without speed brakes by doing practice ILSs starting at high speed and letting the autopilot fly while I managed power and configuration to arrive at 500' AGL on speed and properly configured. 

Skip

[donkaye]

I have edited my first post above to account for the software update changes made by Garmin.  Personally, I think they should have better clarified the change, as that was a pretty important change in my opinion.

[donkaye]

10 hours ago, LANCECASPER said:

@donkaye I think the webinar that @Marc_B was referring to was on yesterday. It looks like they are doing it again later today. 

https://www.garmin.com/en-US/aviation/webinars/americas/

Thanks, Lance, I attended and asked the question.  It was specifically, fully and well answered.  As discussed, the legacy software has been updated and VNAV is active up to the  FAF where "Transition to Approach" takes over.  I went to the hangar and enabled "Transition to Approach on both the 750 and 650.

Thanks all for the input!

[PT20J]

10 hours ago, donkaye said:

I have edited my first post above to account for the software update changes made by Garmin.  Personally, I think they should have better clarified the change, as that was a pretty important change in my opinion.

Garmin should clarify a lot of things.

To be fair it’s difficult because they write the documentation for individual products which can be installed in various combinations to create a myriad of systems with capabilities depending on the configuration. But, you’ll find no manuals for your system. All you have are the individual manuals and you have to know which things work which way in your particular configuration. The AFMSes often have check boxes to show which options are configured for your system if your installer bothered to check them all correctly. 

Skip

[donkaye]

On 4/5/2023 at 9:54 PM, PT20J said:

Garmin should clarify a lot of things.

To be fair it’s difficult because they write the documentation for individual products which can be installed in various combinations to create a myriad of systems with capabilities depending on the configuration. But, you’ll find no manuals for your system. All you have are the individual manuals and you have to know which things work which way in your particular configuration. The AFMSes often have check boxes to show which options are configured for your system if your installer bothered to check them all correctly. 

Skip

Finally, I think I can speak with some finality about the current VNAV setup.  Both Skip and I have been communicating with each other and with Trek Lawler from Garmin.  Trek is the final word and basically he said that with the latest software updates to BOTH the GTN legacy and GTN Xi and GFC 500 that VNAV works up to the FAF now.  The important part, though, is that the  "Transition to Approach" setting on the GTN's must still be set to disable "Transition to Approach".  That is counterintuitive, but based on satisfying the STC that is what is required and you will still get VNAV to the FAF.

[rbp]

I will try it.
 

Can you describe the sequence of operations on the GTN/GFC ? 

[Marc_B]

@rbp There's enough to it that the Garmin video (linked below) does a pretty good job explaining it.  * *and I'm not an instructor, so I'd recommend the video and VFR practice before using it in IMC**  Below are my personal thoughts only.

The gotcha's I've found are:

1) make sure you have a TOD mark on your map in front of you...if your selected TOD is behind you then the GTN won't sequence.  Your clue is that you won't find a TOD on the map.  In that case you chose VNAV direct so that it puts your TOD 1 min in front of you.

2) make sure you set your altitude target select below your current altitude...I've forgotten to drop my target and the AP just stays where it is.  This should be the lowest assigned altitude given by ATC; or in the case you're VFR and using it to step you down on a descent or under a bravo shelf, then it should be the lowest altitude you want the AP to descend.

3) if you want to set a 1000' AGL pattern altitude target, then you have to first open the altitude constraint on the destination, set 1000' AGL, THEN choose along track "-5 miles" (or whatever you choose).  If you create the along track first, it will not give you ability to choose AGL. 

4) a slick feature is from your flight plan page on the GTN you can click "Menu" then "VNAV" and you can change your VS target or flight path angle % easily from there.  i.e. if you want a 500 fpm vs standard 3% flight path angle.  It's easy to get to the VNAV page this way than Home --> Utilities --> VNAV I think; partly because I spend plenty of time routinely in the Flight Plan page.

So for me, it's verify altitude constraints on GTN, roll down my altitude target bug, arm VNAV, verify TOD on map and wait for the descent.  If you're using it to sequence into the approach, then same as above but when cleared for approach I'll tap altitude bug and select "sync minimums" on the altitude constraint on the G500 then arm APR.  Once you capture the GS/GP then you can then set your altitude target select for the missed approach top altitude so that it's ready to go for the missed.

 

[Rmag]

See 22:40 in this video, I demonstrate a RNAV approach that has double step down VNAV descent, and then transition to a LPV Glidepath.  I am using a G500 TXi, GFC 600, and GTN 650 Xi in the video.

In this approach, I also talk about the GFC 500 not being able to do a VNAV descent to the FAF.  As previously discussed in this thread, that is no longer true due to a software update to the GFC 500 that added that capability.

 

[Marc_B]

@Rmag I don't think I noticed that to use VNAV you must be in GPS mode but this makes sense...I came across this Garmin support FAQ helpful:

COMMON ERRORS

Enhanced VNAV will not function if any of the following conditions are true.

    -Navigation source is not set to GPS

    -VNAV not enabled on VNAV profile page

    -No waypoints exist in the flight plan with appropriate altitude constraints

    -Lateral mode is not actively engaged to GPS

    -OBS mode is active

    -Dead reckoning mode is active

    -Parallel Track is active

    -Aircraft is on the ground

    -Aircraft is between the FAF and MAP of an approach

https://support.garmin.com/en-US/?faq=W7RRdCYWC04hI8kxfraxf7

[PT20J]

54 minutes ago, Marc_B said:

@Rmag I don't think I noticed that to use VNAV you must be in GPS mode but this makes sense...I came across this Garmin support FAQ helpful:

COMMON ERRORS

Enhanced VNAV will not function if any of the following conditions are true.

    -Navigation source is not set to GPS

    -VNAV not enabled on VNAV profile page

    -No waypoints exist in the flight plan with appropriate altitude constraints

    -Lateral mode is not actively engaged to GPS

    -OBS mode is active

    -Dead reckoning mode is active

    -Parallel Track is active

    -Aircraft is on the ground

    -Aircraft is between the FAF and MAP of an approach

https://support.garmin.com/en-US/?faq=W7RRdCYWC04hI8kxfraxf7

Yep, a lot of ways to screw it up