Activate Missed Approach (GTN/GFC500)

[donkaye]

21 hours ago, donkaye said:

It's sometimes helps to take a look at the PIlot's Guide.  Yellow highlight is mine.

 

So it occurs to me that the clarity I thought I had from the above was misplaced.  I've got a call into Garmin, but don't expect a callback in the near future.  Here's the question: If the missed approach is activated among other times before the MAP and guidance is provided along the extension of the final approach course and the TOGA button is pushed, which takes precedence, the TOGA button that only provides pitch and wings level, or the GTN which provides along course guidance?  It would appear TOGA, but that defeats the along track benefit of the GTN stated above.

[PT20J]

57 minutes ago, donkaye said:

So it occurs to me that the clarity I thought I had from the above was misplaced.  I've got a call into Garmin, but don't expect a callback in the near future.  Here's the question: If the missed approach is activated among other times before the MAP and guidance is provided along the extension of the final approach course and the TOGA button is pushed, which takes precedence, the TOGA button that only provides pitch and wings level, or the GTN which provides along course guidance?  It would appear TOGA, but that defeats the along track benefit of the GTN stated above.

If you activate the Missed Approach on the GTN before the MAP, it will switch the CDI to GPS (if it was in VLOC) and navigate along the final approach course to the MAP and then navigate along the missed approach track. This should not change the GFC vertical mode. I'm not sure what the lateral mode does. I think it would revert to ROL if the CDI was VLOC because of the navigation source change. It might also revert to ROL in any event to prompt you to hit NAV since it might have been in APR.

If you do not have the Go Around button connected to the GTN, pressing it only affects the autopilot causing it to command a wings level climb.

If the Go  Around button is connected to the GTN as well as the GFC, pressing it before the MAP should cause the autopilot to command a wings level climb and should cause the GTN do the same as if you initiated the missed approach from the GTN.

 

 

[PT20J]

3 hours ago, donkaye said:

I've got a call into Garmin, but don't expect a callback in the near future.

The problem with Garmin support is that sometimes I get wrong answers. They should hang this up in the tech support area:

[PT20J]

On 3/3/2024 at 9:28 AM, midlifeflyer said:

Keeping in mind donkaye's comment about not liking autoswitch, my SOP for receiving vectors to the ILS is, on the first vector,  (1) switch my NAV source to VLOC (I confirmed the ILS frequency was in active much earlier), (2) confirm the green course needle is pointing to the FAC, and (3) activate the leg to the FAF on the GPS.

That works fine for vectors because you are in HDG with APR armed. If you are on a GPS leg to an IAF, you can hit APR at any point and auto switch will make a seamless transition from the GPS to VLOC. I you don't have auto switch enabled and change the CDI to VLOC manually, I think it will cause the GFC to revert to ROL and you will have to hit APR. Not a big deal if you are expecting that.

 

[201Mooniac]

43 minutes ago, PT20J said:

That works fine for vectors because you are in HDG with APR armed. If you are on a GPS leg to an IAF, you can hit APR at any point and auto switch will make a seamless transition from the GPS to VLOC. I you don't have auto switch enabled and change the CDI to VLOC manually, I think it will cause the GFC to revert to ROL and you will have to hit APR. Not a big deal if you are expecting that.

 

I had the autoswitch fail to switch on the ILS 29R into KSCK the other day.  I was pilot nav to IPDEW for the HILPT and had APR armed.  The CDI flashed and no autoswitch.  I'm not sure if it was pilot error or not but I'm less confident in it now than I was previously.

[PT20J]

3 minutes ago, 201Mooniac said:

I had the autoswitch fail to switch on the ILS 29R into KSCK the other day.  I was pilot nav to IPDEW for the HILPT and had APR armed.  The CDI flashed and no autoswitch.  I'm not sure if it was pilot error or not but I'm less confident in it now than I was previously.

That's the problem with automation. It's very confusing if something doesn't work. And most of this stuff works 98% of the time and when it doesn't I usually don't know why. Sometimes I can figure it out later; often not. And, it is a big distraction to try to figure it out during the flight. I think it is a good idea, if choosing to use it, to set a limit by which point if it hasn't done it's thing then you do it manually. 

[Marc_B]

4 hours ago, 201Mooniac said:

The CDI flashed and no autoswitch. 

You might check your system page and see if autoswitch CDI is actually checked.  If it's NOT checked then that's exactly what it does...start flashing CDI and usually gives you a message to switch.

[Marc_B]

8 hours ago, donkaye said:

If the missed approach is activated among other times before the MAP and guidance is provided along the extension of the final approach course and the TOGA button is pushed, which takes precedence, the TOGA button that only provides pitch and wings level, or the GTN which provides along course guidance?

EDIT: rereading your question...if you Activated Missed Approach and have already sequenced the missed, then pressing toGA button (at any point really) activates go around mode and wings level ROLL, 7deg PITCH up.

From my testing and understanding, these are two separate issues and ultimately the reason I started the post:

1) RESPONSE OF GTN:  in the GTN you can select Activate missed approach from several ways (TOGA if linked, Splash screen at MAP, from procedures page, etc.); when you choose Activate Missed approach then the GTN sequences, via GPS, through the rest of the approach laterally all the way to the MAP, then starts the standard missed approach that was loaded from the database.  It will not arm the GP even if you have "GP" armed in white.  i.e. it will not capture a glidepath even if you select missed prior to the FAF at the FAF altitude.  From what I can tell, in the GTN the logic for Activate Missed Approach is the same regardless of how you activate it.

2) RESPONSE OF GFC500:  with a coupled GFC500, the response of the AP depends on the approach. 

          a)  If you press TOGA button then the GFC500 activates go around mode which is PITCH *UP 7deg* (depending on install), and ROLL wings level.  It will continue this until you change it and this is independent of the GTN, which for me TOGA also sequences/activates Missed Approach.  For me, toGA sequences the missed but doesn't automatically follow it, but rather goes into Go Around mode.

          b)  HOWEVER, if you use any other method in the GTN to Activate Missed Approach, then the response of the GFC500 is different.

                  1. if you are on an RNAV approach and select "Activate Missed Approach," the GTN sequences the Missed as above but the GFC stays in NAV mode and continues to fly the rest of the approach and missed coupled.  However the vertical mode reverts to PITCH capturing whatever your current pitch is.  So if you're on a VNAV descent and press Activate Missed, then the current descent path is continued until you hit Altitude bug.  If you're level then you maintain level PITCH.

                  2.  if you're on an green needle approach I have to confirm what happens.  In the GTN trainer it autoswitches CDI back to magenta but it also goes into NAV mode.  However I do not think this is what happens in real life.  My suspicion is due to change in CDI that the GFC500 reverts to ROLL and PITCH similar to as if you accidently hit CDI button on the GTN.  I'll check this next time I'm out flying approaches.

 

4 hours ago, PT20J said:

If you don't have auto switch enabled and change the CDI to VLOC manually, I think it will cause the GFC to revert to ROL and you will have to hit APR.

I think there are scenarios where when you have APR armed and THEN switch the CDI that it doesn't revert to ROLL PITCH.  But I think that if you don't have APR armed and you switch the CDI that it will absolutely revert to ROLL PITCH.  @midlifeflyer is that your experience?  I have autoswitch CDI on and typically let it autoswitch and monitor when it should be doing this on final approach course intercept.  If you have autoswitch on, it switches when the GTN sequences at/past the first waypoint along the final approach course. (usually FAF-1).

[201Mooniac]

1 hour ago, Marc_B said:

You might check your system page and see if autoswitch CDI is actually checked.  If it's NOT checked then that's exactly what it does...start flashing CDI and usually gives you a message to switch.

I did look at the setting and it was checked.  This is the first time since I set it up that it didn't autoswitch.  I flew the same approach (coming form the other side) in actual the day before and it worked fine on that approach.

[PT20J]

23 minutes ago, 201Mooniac said:

I did look at the setting and it was checked.  This is the first time since I set it up that it didn't autoswitch.  I flew the same approach (coming form the other side) in actual the day before and it worked fine on that approach.

Were you in the “box”?

[midlifeflyer]

16 hours ago, PT20J said:

That works fine for vectors because you are in HDG with APR armed. If you are on a GPS leg to an IAF, you can hit APR at any point and auto switch will make a seamless transition from the GPS to VLOC. I you don't have auto switch enabled and change the CDI to VLOC manually, I think it will cause the GFC to revert to ROL and you will have to hit APR. Not a big deal if you are expecting that.

 

That’s why I said it was my procedure for vectors to final. 

Yes, manually switching  CDI when the AP is flying the flight plan sequence requires two buttons. As you say, not a big deal.

[midlifeflyer]

11 hours ago, Marc_B said:

 

I think there are scenarios where when you have APR armed and THEN switch the CDI that it doesn't revert to ROLL PITCH.  But I think that if you don't have APR armed and you switch the CDI that it will absolutely revert to ROLL PITCH.  @midlifeflyer is that your experience?  I have autoswitch CDI on and typically let it autoswitch and monitor when it should be doing this on final approach course intercept.  If you have autoswitch on, it switches when the GTN sequences at/past the first waypoint along the final approach course. (usually FAF-1).

The autoswitch traditionally occurs on sequence when the FAF becomes the active waypoint/leg. 

I say traditionally because I don’t yet know how “VNAV transition to approach” handles that because if the way it delays GS acquisition.  It’s one of the things I want to try when I have a chance. (I have access to but don’t regularly fly two GFC500 equipped airplanes. ) 

[Pinecone]

18 hours ago, PT20J said:

I you don't have auto switch enabled and change the CDI to VLOC manually, I think it will cause the GFC to revert to ROL and you will have to hit APR. Not a big deal if you are expecting that.

I think I read that if APR is armed, it will not kick off the autopilot when manually switching, but if APR is not armed, you will have to re-engage the AP.  Now have to find that in the manual.

 

[PT20J]

52 minutes ago, Pinecone said:

I think I read that if APR is armed, it will not kick off the autopilot when manually switching, but if APR is not armed, you will have to re-engage the AP.  Now have to find that in the manual.

 

Actually, I think it is the other way around 

The G5 Pilot's Guide (Rev J, p 65) states: "If the following occurs, the autopilot reverts to Roll Mode (wings rolled level): Approach Mode is active and the Navigation source is manually switched."

This makes sense for a couple of reasons. First, unlike most other autopilots, there is no difference in lateral mode operation between NAV and APR modes. APR merely enables the GP/GS. So LOC and VOR approaches are flown in NAV. If APR arming affected whether the autopilot reverted to ROL, then the behavior would be different for a LOC and an ILS.

Second, one feature of Auto Switch is that the GTN makes the switch gradually to avoid any "needle jump" which could cause the autopilot to roll abruptly to re-center the needle. This doesn't happen when you switch manually.

 

[Marc_B]

@PT20J I couldn't find my cell phone video of when I tested this out in December, when I had the autoswitch CDI disabled/off and was switching CDI manually from the G500Txi...when I had APR armed, the autopilot most definitely did not revert; instead when I manually switched the CDI, LOC captured immediately with CDI centered (I was on magenta with AP) and ALT stayed coupled with GS armed. (link to my flight results in post below)

Reading through page 65 you referenced, I think this was based on pilot selecting proper CDI, verifying frequency and then pressing APR to have LOC active on AP.  THEN mentioned if CDI switched away from LOC that the AP coupling would revert.  I don't think this page comment was describing switching TO the LOC.

 

 

 

 

 

<--I read this as if you have the LOC/GS active and for any reason that signal is lost then the AP will revert (i.e. loss of signal, accidently changing CDI, changing frequency on the NAV/COMM, etc.)

[Marc_B]

4 hours ago, midlifeflyer said:

The autoswitch traditionally occurs on sequence when the FAF becomes the active waypoint/leg.

+1.  This makes sense for what I've seen.  I've been thinking that it was sequencing though the first waypoint on the Final Approach Course, but it makes more sense that this happens when the FAF becomes active waypoint (leg leading to the FAF) becomes active.  I DO have autoswitch CDI enabled, and this HAS been the behavior I've seen.

3 hours ago, Pinecone said:

I think I read that if APR is armed, it will not kick off the autopilot when manually switching, but if APR is not armed, you will have to re-engage the AP.

+1.  This is what I've seen.  If I do not arm APR and change the CDI, the GFC500 reverts to roll/pitch.  But if APR is armed and I switch the CDI along the FAC, the LOC captures and GFC500 does not revert.  Additionally, with Autoswitch CDI enabled if the CDI changes before I have armed APR (or if you forget to press APR), then the AP reverts to roll/pitch as well.

[Marc_B]

 

 

[PT20J]

1 hour ago, Marc_B said:

@PT20J I couldn't find my cell phone video of when I tested this out in December, when I had the autoswitch CDI disabled/off and was switching CDI manually from the G500Txi...when I had APR armed, the autopilot most definitely did not revert; instead when I manually switched the CDI, LOC captured immediately with CDI centered (I was on magenta with AP) and ALT stayed coupled with GS armed. (link to my flight results in post below)

Reading through page 65 you referenced, I think this was based on pilot selecting proper CDI, verifying frequency and then pressing APR to have LOC active on AP.  THEN mentioned if CDI switched away from LOC that the AP coupling would revert.  I don't think this page comment was describing switching TO the LOC.

 

 

 

 

 

<--I read this as if you have the LOC/GS active and for any reason that signal is lost then the AP will revert (i.e. loss of signal, accidently changing CDI, changing frequency on the NAV/COMM, etc.)

OK, but try this  Auto Switch off. Be on a feeder route headed to an IAF in NAV with the CDI on GPS. Hit APR. Switch the CDI to VLOC. The CDI is off scale. What can the autopilot reasonably do? It’s got to go to ROL. Only if you wait until you are within a dot of centered on the localizer will it capture. 

[Marc_B]

27 minutes ago, PT20J said:

OK, but try this

I think this goes back to are you in the "box" you showed a few posts back.  I'm trying to fine tune the logic of the GFC500/GTN and it's not that clear in manuals.  I think that if:

1) Approach is loaded in GTN, 2) APR is armed, 3) LOC is tuned in radio, and 4) you're in the "box", THEN your CDI is switched (either manually or automatically) = the GFC500 captures and you don't revert.  The problem is if you don't have all the boxes checked, if you switch your CDI it reverts to ROLL/PITCH.

The times I've been flight testing with this have been on an approach flying it the way I'd likely fly it and I have the LOC shown in background in grey on the HSI.  So when I've switched CDI manually my LOC needle has always been "active" (usually either centered or a dot or two off at most).  I don't think I've ever tried changing CDI outside the "box" manually and the autoswitch won't switch it unless it's in the "box."  Autoswitch behavior is that it switches when the FAF becomes active waypoint which is usually along final approach course within the box.

* I have autoslew and autoswitch CDI enabled. That can possibly make a difference as well...i.e. if you have wrong course set...

[Marc_B]

The gotcha for this would be Vectors to FInal.  But ATC should be vectoring you at least 3 miles outside the FAF (approach gate is 1nm outside of FAF + standard 2 miles outside of gate).

From 7110:

HOWEVER, if I was flying an approach being vectored to final I'd be in HDG mode and I would have already manually switched my CDI and be monitoring LOC course.  So I'm not sure that I'd have to worry about the autoswitch or manual switch reverting the autopilot at all.  But there may be a scenario where a pilot requests final intercept inside of 2nm (outside the box of the autoswitch) and the autoswitch would not occur.

i.e being vectored in HDG mode, monitoring LOC, given PTAC (position, turn heading, altitude, and clearance) clearance for ILS approach, then turn to directed heading, Arm APR, and the GFC500 would sequence inbound with LOC course (AP would not revert).  But if you did not change the CDI manually and you were still in GPS mode on GTN then the autoswitch and subsequent LOC mode capture would only occur if your course flew though the box.

[Pinecone]

53 minutes ago, PT20J said:

OK, but try this  Auto Switch off. Be on a feeder route headed to an IAF in NAV with the CDI on GPS. Hit APR. Switch the CDI to VLOC. The CDI is off scale. What can the autopilot reasonably do? It’s got to go to ROL. Only if you wait until you are within a dot of centered on the localizer will it capture. 

The difference is we are saying APR is ARMED, not ACTIVE.

[Marc_B]

I think this note from the AFMS for the GFC500 summarizes this behavior pretty well.  Pressing APR button = pilot does vs. Arming APR or Activating APR = something that the AP does automatically.  This is why it's always said to make sure you are Cleared for Approach before you press the APR button, as this will automatically sequence.

Basically if CDI is off scale it's the pilots responsibility to ensure the heading will result in capture, otherwise it won't capture.

On my flights it seems that Autoswitch CDI and activate APR (capture LOC) happen simultaneously.  So it's difficult to background logic...BUT I THINK that autoswitch CDI is the limiting factor and when this switches the CDI then the APR "activates" immediately as you're certainly within half scale deflection on a coupled approach when this happens.

*** here is also a note that GA button will not disconnect autopilot, it just reverts to ROLL/PITCH.

[201Mooniac]

18 hours ago, PT20J said:

Were you in the “box”?

I believe I was as I flew the HILPT and this course has worked previously.

[Marc_B]

On 3/4/2024 at 1:30 PM, 201Mooniac said:

I was pilot nav to IPDEW for the HILPT and had APR armed.

The KSCK ILS29R approach is a little different in that the HILPT is off of the FAF, so it would completely depend on where you intercepted/where the GTN sequenced to the FAF as the active waypoint, and if you flew a parallel entry on a 1min holding pattern there is a VERY GOOD chance that the GTN sequenced to FAF inside of the 2nm from FAF (area where the CDI would not autoswitch).  This is my best guess of what may have happened.

Heck, I think ~105kts = 2 miles per minute.  Depending on how fast you were going, the majority of your HILPT may have been inside 2nm from the FAF where Autoswitch wouldn't happen.

I don't think that the CDI will autoswitch until "Hold Exit" IPDEW is the active waypoint and depending on where you are when this happens it may or may not switch CDI automatically.  It could be that the last time it worked you had a different hold entry (i.e. teardrop or direct) + a faster approach speed that lined you up and sequenced to "Hold Exit" IPDEW much earlier??

[201Mooniac]

14 minutes ago, Marc_B said:

The KSCK ILS29R approach is a little different in that the HILPT is off of the FAF, so it would completely depend on where you intercepted/where the GTN sequenced to the FAF as the active waypoint, and if you flew a parallel entry on a 1min holding pattern there is a VERY GOOD chance that the GTN sequenced to FAF inside of the 2nm from FAF (area where the CDI would not autoswitch).  This is my best guess of what may have happened.

Heck, I think ~105kts = 2 miles per minute.  Depending on how fast you were going, the majority of your HILPT may have been inside 2nm from the FAF where Autoswitch wouldn't happen.

I don't think that the CDI will autoswitch until "Hold Exit" IPDEW is the active waypoint and depending on where you are when this happens it may or may not switch CDI automatically.  It could be that the last time it worked you had a different hold entry (i.e. teardrop or direct) + a faster approach speed that lined you up and sequenced to "Hold Exit" IPDEW much earlier??

Looking at the chart I think you are correct.  I typically approach from the west and have a teardrop entry.  This time I was coming from the northeast and had a parallel entry.  It didn't occur to me that this would make such a big different in how the automation works but looking at my ground track from that flight it looks like I reintercepted the course about 1 mile from IPDEW Hold Exit.  I can't tell when the switch occured though.