Activate Missed Approach (GTN/GFC500)

[Marc_B]

52 minutes ago, 201Mooniac said:

it looks like I reintercepted the course about 1 mile from IPDEW Hold Exit.  I can't tell when the switch occured though.

I'll have to pay better attention to that next time.  If the Garmin Aviation Trainer reflects IRL, it looked like the Hold Exit IPDEW sequenced once it was fully turned and on an intercept course to IPDEW.  (picture below was snapped right when waypoint sequenced which I think is when CDI would have switched (if in the box to autoswitch). But this was at 150kts and the GTN set up an intercept that was pretty much right before IPDEW. 

 

 

<-- "established inbound"

[201Mooniac]

3 hours ago, Marc_B said:

I'll have to pay better attention to that next time.  If the Garmin Aviation Trainer reflects IRL, it looked like the Hold Exit IPDEW sequenced once it was fully turned and on an intercept course to IPDEW.  (picture below was snapped right when waypoint sequenced which I think is when CDI would have switched (if in the box to autoswitch). But this was at 150kts and the GTN set up an intercept that was pretty much right before IPDEW. 

 

 

<-- "established inbound"

I usually to try enter the hold so I can slow to about 90 kts when turned inbound so I would have been closer but if the intercept was very close to IPDEW, it would depend on when I was within the lateral dimensions of the box I would think.

[Marc_B]

I think 1 minute holding at the FAF is an issue all the way around if you're entering parallel.  If you're below 104 kts then you're inside of the 2nm from the FAF and it could be problematic for autoswitch regardless depending on when the GTN sequences to FAF as active waypoint.

*** But the good part is that you can manually switch CDI yourself and if you have APR armed, then the GFC500 will then immediately capture LOC.  And if you don't switch manually, it flashes and lets you know your assistance is required!

Diameter = diameter of std rate turn 180 in hold (1min) = distance laterally from FAC on outside of hold

[donkaye]

I want to thank Marc for starting this thread.   Here are my takeaways.

Preface:

I've been flying with the GFC 500/GTN combination since 2019.  I've flown it a lot both doing approaches in Actual IMC and practice approaches in VMC.  I had not done missed approaches before the MAP, so this was a beneficial thread from that point if view.  The only issue I've had was with the autoswitch when running ILS approaches.

1.  Based on the "box" for accurate autoswitch, since I have no intention of taking the time to figure out whether I'm in the box or not, I will not be using autoswitch.  (I haven't been using it anyway after my issue with it.  At least now I know the reason for it). The monitoring whether it's going to switch or not and the actions to take if it doesn't switch takes more time than just doing the switching manually.  I've had the same issue as Adam when doing the Stockton ILS.  At least now I know the reason.

2.  When going missed after the MAP when the splash screen appears, I will continue to do it as I have in the past before going through all the machinations we have been discussing here, ie, aviate, navigate, communicate.  That means TOGA, Power, Cleanup, HDG or NAV, Talk.

4.  If I ever want to go missed before the MAP, it will be ALT, NAV, Preselect a new Altitude, Power, VS (or IAS), Roll up the Rate for either.  At the splash screen tap it and I'm off on the missed approach.  In this situation I wouldn't use TOGA.

Thanks for calling my attention to going missed before the MAP.

 

[midlifeflyer]

5 hours ago, donkaye said:

Based on the "box" for accurate autoswitch, since I have no intention of taking the time to figure out whether I'm in the box or not, I will not be using autoswitch.  (I haven't been using it anyway after my issue with it.  At least now I know the reason for it). The monitoring whether it's going to switch or not and the actions to take if it doesn't switch takes more time than just doing the switching manually.  I've had the same issue as Adam when doing the Stockton ILS.  At least now I know the reason

This is a key point. 

These boxes have incredible functionality. While I think it’s important to understand what they are capable of, it’s far more important to develop personal SOPs that work for us. The weird part to me is that in recurrent training, I see far more pilot errors in what I consider to be common tasks than those which involve getting into the more esoteric weeds.

With the possible exception of using TOGA on an early missed (I have to look at the downside a bit more), my SOPs for the missed are pretty much identical to yours. 
 

[donkaye]

3 hours ago, midlifeflyer said:

With the possible exception of using TOGA on an early missed (I have to look at the downside a bit more), my SOPs for the missed are pretty much identical to yours. 
 

The reason I wouldn't use TOGA before the MAP is the lack of lateral control (this is momentary after the MAP).  The upside is guaranteed pitch up., but that is easily handled in a couple of seconds with ALT (stop the descent), NAV (to maintain lateral control), Altitude Preselect (set the missed approach altitude), and VS or IAS (to get the plane climbing).  I'm open to input if you can show me why TOGA is a better alternative in this situation.

[201Mooniac]

Just now, donkaye said:

1.  Based on the "box" for accurate autoswitch, since I have no intention of taking the time to figure out whether I'm in the box or not, I will not be using autoswitch.  (I haven't been using it anyway after my issue with it.  At least now I know the reason for it). The monitoring whether it's going to switch or not and the actions to take if it doesn't switch takes more time than just doing the switching manually.  I've had the same issue as Adam when doing the Stockton ILS.  At least now I know the reason.

This is really critical learning from this thread.  I guess I always just thought autoswitch was still flakey and while I have it enabled, I always plan to manually switch on IMC approaches and use the autoswitch as a pleasant surprise when it works.  Now that I understand it better, I think I will likely disable it and stick with manual switching so I am never surprised by what the automation is doing.

[PT20J]

I use Auto Switch, but my SOP is to always verify that I have the appropriate nav source as soon as I am established on the final approach course. That’s good to do whether you use Auto Switch or not. 

[donkaye]

48 minutes ago, 201Mooniac said:

This is really critical learning from this thread.  I guess I always just thought autoswitch was still flakey and while I have it enabled, I always plan to manually switch on IMC approaches and use the autoswitch as a pleasant surprise when it works.  Now that I understand it better, I think I will likely disable it and stick with manual switching so I am never surprised by what the automation is doing.

While I was always aware of the "box" for auto switch, I didn't give it that much attention.  I should have.  At least now I know why I don't want to use it.

[midlifeflyer]

4 hours ago, donkaye said:

The reason I wouldn't use TOGA before the MAP is the lack of lateral control (this is momentary after the MAP).  The upside is guaranteed pitch up., but that is easily handled in a couple of seconds with ALT (stop the descent), NAV (to maintain lateral control), Altitude Preselect (set the missed approach altitude), and VS or IAS (to get the plane climbing).  I'm open to input if you can show me why TOGA is a better alternative in this situation.

I'm not suggesting one alternative is inherently better than the other. More than one way to skin that particular cat. 

Unless the missed is way early and there is a howling crosswind, I'm not too worried about lateral control with TOGA wings level. Besides, if I can't follow NAV, a tap on HDG will follow the heading bug which has already been synced for wind correction. So it's seems to be just as momentary on an early missed as one at the MAP. Now I'm HDG or NAV for lateral and TOGA for the climb to the missed approach altitude. VS vs IAS is the last thing I deal with on the missed.

So, at least from my perspective, I don't see the disadvantage of TOGA outweighing the advantage.

 

[Marc_B]

Went of for a few approaches after work this evening for some testing using Activate Missed Approach from the GTN:

1)  Coupled ILS approach, Level:  LOC / ALT 7000 (GS armed), APR lit.  --> Activate Missed Approach = APR light off and AP in ROL (LOC flashing yellow) and ALT 7000.  Just to make sure the altitude bug had nothing to do with the ALT mode I was at 7000 but bugged the FAF 6600.

2) Coupled ILS approach, VS descent to FAF:  LOC / VS -500 (GS and ALTS armed), 6600 bugged, APR lit. --> AMA = APR light off and AP in ROL (LOC flashing yellow) and VS -500 active (ALTS armed).  It descended to and captured 6600 ft with ROL, ALT 6600.

3) Coupled ILS approach, past FAF with GS captured and descending:  LOC / GS --> AMA = APR light off and AP in ROL / PIT (with LOC and GS flashing yellow) but with ALTS still armed although bugged altitude was 7000 ft missed approach

4) Coupled RNAV approach, GPS / ALT 7000 (GP armed), APR lit --> AMA = APR light off and AP in GPS / ALT 7000.  I had to go back to the Activate Missed Approach to see if it actually did anything and now the AMA was greyed out.

 

So general gist:

Lateral Mode: if you're in GPS and hit AMA there is no reversion; but LOC reverts to ROL wings level.

Vertical Mode: if you're in ALT or VS and hit AMA there is no reversion, but GS/GP reverts to PIT and captures your current pitch.

I think that GTN Activate Missed Approach makes a LOT of sense for an early missed, a missed with a mandatory descent (i.e Skip's comment about KBFI), and for a nonprecision approach where you are level in ALT and have time to get things set up exactly as you want.  If I was going missed at the DA/MAP you bet I'd already have my Missed approach altitude set, click TOGA, then would be clicking NAV (or HDG) after I'd powered up and cleaned up.

BIG GOTCHA though, I didn't realize there were some installs where TOGA was not set up to sequence the GPS missed approach.  If that is your set up then you have to make sure that you actually fly through the MAP before going missed.  Since I'm set up with TOGA sequencing the missed as long as I hit NAV it will fly me through a safe area.  There are plenty of mountain airports in Colorado where this is an absolute necessity.

 

Regarding Autoswitch CDI.  I've experimented with both enabled and disabled.  I certainly understand why you might want one vs the other.  Fortunately this is on the system page and you can change in flight at will.  I think it might change my perception if it was hard coded like transition to approach and permanently set one way or the other.  But that being said, I like that this allows automation and sequencing of several things at once (CDI switch/LOC capture), and also helps to focus my flow at that moment so I can check multiple things off all at once.  i.e. LOC freq is set, APR was armed, turning inbound and LOC captured.  You pick these things up not sequentially, but at common time when the AP sequences to the segment leading to the FAF.  In trying to squirrel around with this and figure out the faults, I've found that it pretty reliably sequences LOC, CDI Switch, and turning inbound at the same point on the approach.  So this makes it VERY obvious that its either 1) working as intended, or 2) I screwed something up.  And it's at a point usually where I can either adjust, hand fly, or decide to go missed early in the game.  Personally I'd rather not figure that out at the FAF when I don't capture GS cause then my best option is probably go missed.

BUT I think that the main problem with autoswitch is that it has rules.  Approach loaded, LOC tuned, APR armed, inside the "box", AND segment to FAF sequenced.  That's a lot of potential for error.  But once you understand the rules it makes much more sense.

HOWEVER, even if you mess it up, or would rather push CDI yourself...you can still manually change CDI at will, whenever you want.

[donkaye]

4 hours ago, Marc_B said:

 

BIG GOTCHA though, I didn't realize there were some installs where TOGA was not set up to sequence the GPS missed approach.  If that is your set up then you have to make sure that you actually fly through the MAP before going missed.  Since I'm set up with TOGA sequencing the missed as long as I hit NAV it will fly me through a safe area.  There are plenty of mountain airports in Colorado where this is an absolute necessity.

BUT I think that the main problem with autoswitch is that it has rules. 

I'm not sure I understand the underlined sentence.  When you say "TOGA was not set up to sequence the GPS missed approach", do you mean you don't have to push the NAV button?  Or do you mean you push TOGA then push the NAV button to execute the missed, the latter being the way I've seen all GTN/GFC 500s set up.

Sorry Marc, I know it was not you intention to convince either way, but you have not convinced me to enable autoswitch.

[Marc_B]

@donkaye I thought Skip's comment earlier in this thread made it sound like some installs the TOGA button is not linked to the GTN to also "Activate Missed Approach" in addition to Go Around Mode with wings level ROL and PIT up 7 deg?  If TOGA only ROL/PIT up, then the pilot has to make sure they activate missed and actually fly passed the missed.  i.e. if pilot just read missed instructions, went missed early by TOGA, then immediately started missed approach instructions that might be dangerous.  Having the GTN sequence makes it easier for me to 1) take care of vertical flight (climb, cram, cleanup) then 2) allow the GTN to take care of lateral course (press NAV/HDG) pretty easily...

With autoswitch, the thing you always must do is arm APR.  The most "disruptive" (but immediately informative) issue for me has been if I forget to press APR in GFC, then when the CDI changes the mode reverts to ROL PIT.  But again, this immediately shows me I goofed and I just press APR.  If I was manually switching CDI, I"d do it once I was established on FAC and if i switched CDI then without APR armed then the mode would still revert, but it would "seem" like I was still flying what I should (unless a lot of wind drift)...until I didn't capture GS.

[PT20J]

I gave this more thought and reread the documentation. I think the logic is pretty simple:

The Go Around button activates GFC Go Around mode (wings level, pitch up). If connected to the GTN, it also activates the missed approach per the GTN Pilot's Guide.

Auto Switch ONLY works on an ILS; not a VOR or LOC approach. The GTN knows it is set for an ILS. The GFC normally reverts to ROL when the CDI source is changed. The reason you need to arm APR is that this is what tells the GFC that you shooting an approach with vertical guidance and then the logic prevents it from reverting to ROL. This implies that it should also not revert to ROL if you switch manually when the CDI is within the localizer capture range since the GFC doesn't know about GTN settings.

[Marc_B]

20 hours ago, PT20J said:

This implies that it should also not revert to ROL if you switch manually when the CDI is within the localizer capture range since the GFC doesn't know about GTN settings

I think this is spot on, and I’ve not had it revert when I switched manually with APR armed. 

EDIT: the more I think about it, I'm sure this has "rules" as well.  Pressing APR:

When I've manually switched the CDI, I've not got mode reversion, but I've also typically switched the CDI in an area where it goes to LOC capture.  I've never tried it far enough out (greater than half scale) that the LOC mode is armed. (my testing has either been on FAC or intercepting the FAC)

However, this still reads to me that if APR mode pressed and you're tracking on GPS, that LOC would be armed, mode not reverted, and it would automatically switch when less than half-scale deflection.

[PT20J]

Here is something interesting to ponder relative the GTN Auto Switch and the GFC 500 interaction:

ILS Auto Switch works with an ILS. I tried it with a localizer approach on the simulator and it works on a localizer also. 

However, the GFC 500 is set to APR for an ILS and NAV for a localizer-only approach.

So, there cannot be anything "special" about APR since NAV has to work the same way. It seems that the logic in the GTN and GFC will always do the Auto Switch without reverting to ROL.

According to the GFC 500 AFMS, if a localizer is the active navigation source, the GFC will "arm" if the CDI deflection is more than half scale and "capture" if the CDI is less than half scale deflection. So, I'm betting that if your are on a GPS leg and there is more than half scale deflection after you manually switch from GPS to VLOC that the GFC will revert to ROL and if there is half or less full scale deflection it will just smoothly capture the localizer. 

[Marc_B]

@PT20J The thing that made me think that APR is what prevents the mode reversion, is that if I load an ILS approach, am in NAV mode on a feeder route and forget to press APR on the GFC500, then it will revert to ROL PIT when I switch the CDI (or when CDI switches automatically) coming up to LOC course intercept.  It will blow right though the LOC.  This I know for sure.

If a LOC approach is loaded and it is left in NAV, would that prevent reversion??  Not sure.

But I think that it also depends on if the LOC course is armed...i.e. when you press APR it arms LOC in white.  From the AFMS it says press NAV key and verify LOC armed for a localizer approach.  So is it LOC is armed that prevents reversion or APR is armed?

But I don't find that the Aviation Trainer reflects the actual behavior of the GFC500 with this very well.

[PT20J]

16 minutes ago, Marc_B said:

If a LOC approach is loaded and it is left in NAV, would that prevent reversion??  Not sure.

It would be interesting to try. I’m betting that it will just capture without reverting to ROL because there is no confusion about your intent. 

There is a potential issue if you cannot capture the ILS localizer in NAV. Sometimes I get cleared to track the localizer, but not for the approach because there is an airplane ahead of me on the approach and I cannot be cleared until that aircraft lands or misses (the last time this happened, I was following an Army helicopter doing 60 kts!) In that case, I intercept the localizer in NAV and don’t hit APR until cleared to avoid accidentally capturing the GS and busting my assigned altitude. I’ve always had auto switch work without reverting to ROL, but I think I’ve always been on a vector in HDG with NAV armed so there was not a change in the active navigation source. 

[Marc_B]

So I think the LOC/GS armed in white is what avoids autopilot mode reversion.  You can arm LOC course by either pressing APR (which also arms GS) or by pressing NAV which just arms LOC.  But it would seem that if you don't have LOC armed and your CDI switches then you'll revert to ROL PIT.

I'll have to take a flight and go though Localizer only approaches.  Haven't done those in a while.  Certainly in HDG mode you could press NAV and arm LOC?...but what if you're on a feeder route in GPS...do you press NAV again to arm LOC?

[Marc_B]

Back course and VOR you can't use autoswitch CDI.

Back course, VOR, and LOC you don't use APR.

Without a proper mode armed, a change in CDI causes mode reversion with GFC500.

I don't fly LOC, VOR, or BC frequently enough to feel solid on the gotchas in these approaches.