Activate Missed Approach (GTN/GFC500)

[Marc_B]

Experimenting with different ways to go missed today...(edit) and I found a few different ways to sequence the missed, but found out that they DO NOT DO THE SAME THING to the GFC500, although act similarly for the GTN.  For reference, GFC500 with GTN750Xi.

1) TOGA Button:  most who have GFC500 are familiar with this.  It sequences the missed approach in the GTN, but it reverts the autopilot to roll/pitch mode which for me is wings level, 7 deg pitch up.  Then you have to finish your flow then reactivate the NAV mode for the GPS and if a stiff crosswind this may have pushed you off path a bit.  But close to the ground winds level and pitch up probably makes sense.

2) GTN "Activate Missed Approach":  if you select your approach from the GTN Flight Plan page, you can then select "Activate Missed Approach".  This also correctly sequences the missed approach, but is only "active" as a button once you're on the final approach course (i.e. it's greyed out when you are on a HILPT or a feeder route).  This maintains your GPS / NAV tracking mode on the GFC500, but reverts the vertical mode to pitch.  Surprisingly, I was navigating down towards FAF on VNAV with GP armed and the GFC500 kept the same pitch down and kept the GP armed.  Out of curiousity, I let it continue down to see if it would then capture GP, but once you have activated the "missed approach" in the GTN the GP will not capture.  However, it will keep pitch mode until it hits your altitude bug.

I'll have to try with an ILS to see what happens.  When I did this with the GTN trainer the GPS and AP automatically switched back from Green to Magenta needles and NAV, but I want to confirm that actually is what happens.  My suspicion is that when you "activate missed approach" from GTN while on an ILS that it 1) automatically changes CDI to magenta to sequence the missed, but 2) then reverts GFC500 to roll and pitch given the LOC to GPS switch.

I think this makes the most sense if you had to go missed early due to change in runway, winds, downgraded approach, or diversion while on the final approach course.  At least it maintains the GPS track and doesn't revert to Roll in an RNAV approach.  Past the FAF, it's too many button presses and screens to think its a good idea...in that case the TOGA makes way more sense.

[PT20J]

The reason that the GFC 500 does not go into NAV mode when TOGA is activated is that it has no idea what your missed approach clearance is. In a radar environment, it is common to get missed approach instructions from ATC which differ from the published procedure. Also, missed approach procedures that are based on ground based navaids will have an alternate procedure designed for the case where a ground based navaid is OTS and these alternate procedures are not in the navigator database. https://aerospace.honeywell.com/us/en/about-us/news/2023/05/alternate-missed-approach-procedures#:~:text=If a navaid used on,primary navaid is still available.

 

[midlifeflyer]

The “Activate Missed Approach” in your pic is really designed for only one situation -  going missed before the MAP, using the published missed. It’s the rough equivalent of activating the first leg of the missed. 

As @PT20J said, TOGA is designed to assist with a wings-level climb at climb pitch. You can use it for takeoff and VFR go-around too. It does not know and does not assume what your missed approach instructions are. It might be the published missed. Might be the NOTAM’d alternate missed you programmed. Might be a heading and altitude ATC-directed missed.

[Marc_B]

6 hours ago, midlifeflyer said:

The “Activate Missed Approach” in your pic is really designed for only one situation -  going missed before the MAP

Yup.  But the action is different than the TOGA button.  And the reaction from the GFC500 is different from the TOGA button.  That's my point.  TOGA and "Activate Missed Approach" in the GTN do similar things to the GTN, but much different things to the GFC500.

I understand that ATC gives alternate missed approach instructions quite frequently.  But when you push the TOGA button it activates the missed approach in the GTN and sequences the standard missed approach as well.  With both methods you have to program into your flight director what you want the AP to fly if given alternate instructions or "fly heading ... and climb to ..."

Activate Missed on GTN = GPS + current PITCH on GFC500

TOGA = Roll + 7 deg pitch up.

15 hours ago, PT20J said:

The reason that the GFC 500 does not go into NAV mode when TOGA is activated is that it has no idea what your missed approach clearance is.

Certainly makes sense.  But in both circumstances the GTN's idea of what you're doing in a missed approach is flying the published standard missed approach and that's what it loads and programs. 

A loosely similar example would be a departure procedure where the GTN and AP are coupled with a set plan and ATC gives you a short cut "direct to" a fix further along the way.  In that situation, in order to deviate from what is planned, the pilot has to change the GTN (press direct to) and AP adjusts automatically with the rest of the procedure.  The GFC500 doesn't then say "oh crap he's not on the plan so when he hits direct to another fix let's revert to roll pitch cause I'm not sure what he's doing!"   joking of course.

Activate Missed Approach assumes that you're flying the published missed it just doesn't know the altitude you want.  TOGA assumes nothing but you wanna get up and out (but still sequences the missed if you're on an approach).

My guess is that in order to make the TOGA work for go arounds as well as missed approaches, then you'd have to be careful with either commanding a heading (as you don't know where your heading bug may be) and careful with GPS (as you don't know where your magenta line may be).  So for a Go Around button it makes 100% sense for climb up and wings level.

[PT20J]

TOGA (Take Off and Go Around) is an autopilot function. It commands wings level and default climb pitch. (Note that Garmin actually calls this function "Go Around", not TOGA).

Missed approach navigation is a GTN function. 

There is an installation option to connect the GFC Go Around button to the GTN to cause the GTN to initiate missed approach guidance. But the two functions are otherwise unrelated.

[Marc_B]

11 minutes ago, PT20J said:

There is an installation option to connect the GFC Go Around button to the GTN to cause the GTN to initiate missed approach guidance. But the two functions are otherwise unrelated.

Mine must be interfaced as it does sequence the missed approach in the GTN.

[midlifeflyer]

1 hour ago, Marc_B said:

The GFC500 doesn't then say "oh crap he's not on the plan so when he hits direct to another fix let's revert to roll pitch cause I'm not sure what he's doing!"   joking of course.

Actually... it does exactly that for that reason when you change CDI source . Here's what the AFMS and it makes sense to me. Even if the GPS sequences to the the missed, you may not be doing it so the GFC should not automatically follow it in the wrong direction. All it's doing is getting you started on whatever missed you fly.

 

Edited March 2 by midlifeflyer

[donkaye]

12 minutes ago, Marc_B said:

Mine must be interfaced as it does sequence the missed approach in the GTN.

48 minutes ago, Marc_B said:

Mine must be interfaced as it does sequence the missed approach in the GTN.

If it is, I think it should be changed.  I'd want to control the missed approach function.  The scenarios below apply to my airplane.  Follow the AFMS in yours.

Scenario 1: Go missed before the missed approach point:  Push TOGO, Power Up, On positive rate Gear Up, CDI source to GPS, Push HDG, Preselect altitude, Announce.  Actions passing the MAP depend on ATC.  If flying the published missed, tap Activate missed Approach on the GTN and hit NAV.  If given alternate missed approach instructions, tap Activate missed Approach to enable the GTN to advance, but follow ATCs instructions in HDG mode and do not tap NAV.

Scenario 2. Go published missed at the MAP:  Push TOGO, Power Up, On positive rate Gear Up, CDI source to GPS, tap Activate missed Approach to enable the GTN to advance, tap NAV, Announce.  If given alternate missed approach instructions by ATC, Push TOGO, Power Up, On positive rate Gear Up, CDI source to GPS, tap Activate missed Approach, tap HDG and follow ATCs instructions.

Scenario 3. Go missed, but return for another approach to any airport:  Push TOGO, Power Up, On positive rate Gear Up, CDI source to GPS,  tap Activate missed Approach to enable the GTN, tap NAV.  On the flight plan page, tap the current approach, tap APT and select a new airport or keep the same one, select the approach you want.  When given a new clearance Activate the approach or follow ATCs instructions to the new airport.   One of the big benefits of the GTNs is the ability to load a new approach to any airport while still flying the original the missed approach.

[donkaye]

1 hour ago, PT20J said:

There is an installation option to connect the GFC Go Around button to the GTN to cause the GTN to initiate missed approach guidance. But the two functions are otherwise unrelated.

I didn't know about that.  I'm glad mine wasn't hooked up that way.

[midlifeflyer]

10 minutes ago, donkaye said:

If it is, I think it should be changed.  I'd want to control the missed approach function.  The scenarios below apply to my airplane.  Follow the AFMS in yours.

Scenario 1: Go missed before the missed approach point:  Push TOGO, Power Up, On positive rate Gear Up, CDI source to GPS, Push HDG, Preselect altitude, Announce.  Actions passing the MAP depend on ATC.  If flying the published missed, tap Activate missed Approach on the GTN and hit NAV.  If given alternate missed approach instructions, tap Activate missed Approach to enable the GTN to advance, but follow ATCs instructions in HDG mode and do not tap NAV.

Scenario 2. Go published missed at the MAP:  Push TOGO, Power Up, On positive rate Gear Up, CDI source to GPS, tap Activate missed Approach to enable the GTN to advance, tap NAV, Announce.  If given alternate missed approach instructions by ATC, Push TOGO, Power Up, On positive rate Gear Up, CDI source to GPS, tap Activate missed Approach, tap HDG and follow ATCs instructions.

Scenario 3. Go missed, but return for another approach to any airport:  Push TOGO, Power Up, On positive rate Gear Up, CDI source to GPS,  tap Activate missed Approach to enable the GTN, tap NAV.  On the flight plan page, tap the current approach, tap APT and select a new airport or keep the same one, select the approach you want.  When given a new clearance Activate the approach or follow ATCs instructions to the new airport.   One of the big benefits of the GTNs is the ability to load a new approach to any airport while still flying the original the missed approach.

You and I are on exactly the same page. 

[Marc_B]

36 minutes ago, donkaye said:

If it is, I think it should be changed.  I'd want to control the missed approach function.

If the TOGA button ONLY results in ROLL - PITCH with AP, then why would you not want this to sequenced to squelch the splash screen of "remain suspended" or "activate missed approach" at the MAP?  I guess the other effect of linking is that it will change CDI to magenta (if your approach was LOC) as the missed approach is flown with GPS.  But again, you're still flying in Roll pitch with wings level in a climb configuring for your missed.

If you're going to be vectored in heading mode, no harm no foul; you'll have to set that up with heading bug and hit HDG.  If you're going to get sequenced to an alternate missed approach hold then that wouldn't be in your GTN anyways; probably given Vectors then direct to a fix and hold.  And if you're going to fly the published missed you are already one step ahead.

Not sure I understand the rationale of not wanting that to sequence the missed (in the GTN) if you hit TOGA...since it doesn't change the AP, it only avoids the splash screen. 

 

But my original post was pointing out that the logic behind TOGA and the logic behind the GTN Activate the Missed Approach are different in terms of the effects on the GFC500.  I think we are all on the same page with the process of TOGA, and my standard flow is pretty much same as @donkaye's above.

[donkaye]

29 minutes ago, Marc_B said:

If the TOGA button ONLY results in ROLL - PITCH with AP, then why would you not want this to sequenced to squelch the splash screen of "remain suspended" or "activate missed approach" at the MAP?  I guess the other effect of linking is that it will change CDI to magenta (if your approach was LOC) as the missed approach is flown with GPS.  But again, you're still flying in Roll pitch with wings level in a climb configuring for your missed.

Maybe I'm missing something, but at the MAP I may want to fly the published missed approach even it I wanted to go missed before it.  I've actually never looked at a menu Item "Activate the missed Approach".  In any even I wouldn't want to activate it prior to the MAP due to potential terrain issues.

[Marc_B]

Missed approach point begins the missed approach (in the GTN), regardless of if you sequence with 1) toga button, 2) activate missed approach from approach button screen, or 3) selecting activate missed approach from the splash screen.  (edit: for clarity see Don Kaye's post below from pilot guide...activating missed follows the final approach course to the MAP)

Definitely not suggesting sequencing something that does not include flying over the MAP first; definitely a dangerous no no.  However if you hit TOGA you might actually drift laterally and you aren't actually following anything other than wings level until the pilot reconfigures or turns off AP and hand flies.

By activating approach, the GTN flys the proper approach and missed approach lateral course but will not sequence down the GP vertically.

i.e. I flew RNAV17 into KGXY from the southeast at 7600ft, flew the HILPT, and "Activate Missed Approach" was greyed out until after the crossing BLEEU (second time) past the procedure turn inbound.  I was using VNAV so it started a descent to 6600 down to GOHLD. As soon as I crossed BLEEU I pressed the Activate Missed Approach.  The AP maintained GPS course, but VNAV then reverted to pitch (in a descent to the bugged 6600 ft).  It continued the sequence through GOHLD, BAYYR, to RW17 MAP; since i was at my bugged 6600 ft (above 5400 missed instruction), at the MAP it began left turn direct CEDUK for hold.  (If I was at, for example 5000 feet then it would have kept me straight until climbing to 5400ft then climbing left turn to CEDUK.)

So pressing "Activate Missed Approach" right past BLEEU, the lateral course finished the approach to the MAP, and because I was already on GPS (since it's an RNAV approach) the lateral mode on GFC500 didn't revert, but stayed coupled to GPS.  The vertical mode reverted to PITCH (I was descending; PITCH green, VNAV flashed yellow and GP white) and since I had FAF altitude 6600 bugged it captured altitude at 6600 feet and leveled off.  "GP" was still armed vertically (white), but since missed approach was active it did not capture. 

 

[PT20J]

Don, I marked up your scenarios to show what happens if the Remote Go Around is connected on the GTN Xi:

3 hours ago, donkaye said:

Scenario 1: Go missed before the missed approach point:  Push TOGO, Power Up, On positive rate Gear Up, CDI source to GPS, Push HDG, tap NAV, Preselect altitude (I usually have preset the missed approach altitude after passing the FAF), Announce.  Actions passing the MAP depend on ATC.  If flying the published missed no action is required, tap Activate missed Approach on the GTN and hit NAV.  If given alternate missed approach instructions, tap Activate missed Approach to enable the GTN to advance, but tap HDG and follow ATCs instructions in HDG mode and do not tap NAV.

Scenario 2. Go published missed at the MAP:  Push TOGO, Power Up, On positive rate Gear Up, CDI source to GPS, tap Activate missed Approach to enable the GTN to advance, tap NAV, Announce.  If given alternate missed approach instructions by ATC, Push TOGO, Power Up, On positive rate Gear Up, CDI source to GPS, tap Activate missed Approach, tap HDG and follow ATCs instructions.

Scenario 3. Go missed, but return for another approach to any airport:  Push TOGO, Power Up, On positive rate Gear Up, CDI source to GPS,  tap Activate missed Approach to enable the GTN, tap NAV.  On the flight plan page, tap the current approach, tap APT and select a new airport or keep the same one, select the approach you want.  When given a new clearance Activate the approach or follow ATCs instructions to the new airport.   One of the big benefits of the GTNs is the ability to load a new approach to any airport while still flying the original the missed approach.

 

[donkaye]

7 hours ago, PT20J said:

Don, I marked up your scenarios to show what happens if the Remote Go Around is connected on the GTN Xi:

 

Thanks, Skip.  I put in the "CDI source to GPS" because I couldn't remember if the CDI autoswitched when flying the missed after an ILS approach.  Of course it wouldn't be necessary when flying GPS approaches.  When given the option, and assuming the minimums are the same, I'll always fly the GPS approach over an ILS now.

Since Marc's posts both here and in another thread, I have experimented extensively with approaches using the GTN in conjunction with the GFC 500.  Some of my conclusions:  I don't like "autoswitch" when running an ILS approach.  Sometimes it works and sometimes it doesn't.  When it gives up the ghost when flying a HILPT, It establishes a 45° intercept angle and blows through the Final.  I have much better control when I am established on final in GPS mode and then switch myself.  This is especially true when flying a VNAV descent in the HLPT, and it switches before the descent is completed.   Let me say that "Transition to Approach" will be a nice addition when it is approved for the GFC 500.

I absolutely LOVE the ability to switch approaches and airports when on a missed approach.  This has allowed me solo to ping pong off of 4 very close airports (KSNS, KOAR, KMRY, KWVI) doing multiple different approaches to each airport, while having the time to pick up either ATIS or AWOS, change frequencies, write down new clearances to different airports, monitor the flight, and communicate with ATC without going into overload.  I have to add that a big reason for being able to do all this reasonably effortlessly is by making heavy use of the Aera 760 on the yoke for frequencies, runways, and approach charts, all things can can be done much faster on the 760 than on the GTN.

[midlifeflyer]

15 hours ago, Marc_B said:

However if you hit TOGA you might actually drift laterally and you aren't actually following anything other than wings level until the pilot reconfigures or turns off AP and hand flies.

I think there are two opposite things at work.

One is delaying navigating along the proper path when there is actually enough wind to blow you outside the lateral area protected for the missed.  (That sentence tells you exactly how worried I am about drift in TOGA AP mode).

The opposite is what I see far too often in recurrent training. Less likely with the GFC500 which does not disconnect the AP, but it's a rush to get back to the AP and NAV or HDG mode and miss the "aviate" part of the equation. I've seen partial power, failure to retract gear or flaps, and with the AP disconnected, turns away from the path - even if it's a straight climb to the MAHP - far greater than TOGA wings level would give one, even if they completely let go of the yoke.

This approach, even pure VNAV with less than a 300' initial climb segment before the turn, you are not drifting much in TOGA until hitting confirming CDI source and sequence and touching NAV for the turn. 

I actually talk about this briefly in an upcoming IFR Magazine article. 

[midlifeflyer]

12 hours ago, donkaye said:

 I don't like "autoswitch" when running an ILS approach.

Me neither. I keep it on but when I teach it, i tell my trainees that "autoswitch" is a backup for screwing up and not doing it manually.

[Marc_B]

Just to be clear...If I'm going missed, I'm a "click, cram, climb, clean, communicate" pilot.  And this wasn't an attempt to change that.  Not saying TOGA is unsafe, or shouldn't be used.  (wind drift was mentioned as a pro/con not a safety concern as Mark pointed out above).  Just finding new ways to do something and trying to figure out "what does that do?"  My whole intent with this thread was not to convince someone to alter IFR flow.  But Garmin has multiple ways to do the same thing and they don't always all do the same thing. 

Here are the two other ways to "Activate Missed Approach" that I've found.  You can go to procedures page and click "Activate Missed Approach."

...and this is what every GTN pilot sees filling the screen on landing when they cross the MAP and it asks if you want to activate missed.

The interesting thing is how the splash screen at the MAP actually states "Activate GPS Missed Approach" and the other methods don't.  I thought that Garmin always uses GPS for the missed approaches and I'm not aware of any other type. 

My point was, this is similar to activating an approach (i.e. you can: load and activate, direct to a fix on the approach, activate vectors, have it sequence automatically with flight plan, etc.).  Each method does something specific and while they are all similar, they are NOT all the same.  This is accentuated if you have a coupled GFC where the effect on the autopilot is completely different.  Really the main reason for my original post was to note that these are NOT the same with the GFC500.  I agree with you all that there is one main way that we ALL have in common that makes the most sense.  But I was just curious what these other methods do and if it's different from each other or an apples to apples button push (it's definitely not apples to apples!).

I always love the discussion and feedback from @midlifeflyer, @PT20J, and @donkaye.  Your discussions and nuance are always great food for thought and great learning!

 

[Marc_B]

The other thing worth noting is that I've found that the Garmin Aviation Trainer is not a completely accurate reflection of the behavior of a coupled GFC500 autopilot with several scenarios such as this and with VNAV.  What happens IRL is not what is seen with the trainer.  Hence, why I find it interesting to go fly these different ways of doing things to see what it does.

[midlifeflyer]

44 minutes ago, Marc_B said:

Just to be clear...If I'm going missed, I'm a "click, cram, climb, clean, communicate" pilot.  And this wasn't an attempt to change that.  Not saying TOGA is unsafe, or shouldn't be used.  (wind drift was mentioned as a pro/con not a safety concern as Mark pointed out above).  Just finding new ways to do something and trying to figure out "what does that do?"  My whole intent with this thread was not to convince someone to alter IFR flow.  But Garmin has multiple ways to do the same thing and they don't always all do the same thing. 

***

The interesting thing is how the splash screen at the MAP actually states "Activate GPS Missed Approach" and the other methods don't.  I thought that Garmin always uses GPS for the missed approaches and I'm not aware of any other type. 

 

Like every computer program, there are multiple ways. I'm not suer any of us ever really know all of them - we find the method that works and stick with it. I think consistent repeatable SOPs are essential. They become habits and actually free the mind for the variations that inevitable occur.

This one is dedicated to when you reach the nonprecision MAP. The others are bypasses for an early missed - that might be because of a problem like being unstable on the approach. Or it may be normal. Since the one in the photo doesn't come up until crossing the MAPWP, there is a delay when going missed off an ILS or LPV. I've seen pilots activate early as soon as they clean up on the missed of an approach with vertical guidance. I think it's a bit of overkill. 

 

Edited March 3 by midlifeflyer

[PT20J]

The Garmin avionics can be confusing because the documentation doesn't usually explain the underlying theory of operation and also because Garmin avionics can be used in a variety of configurations and with different installed options.

One thing to keep in mind is that the GTN is ALWAYS a GPS navigator. Even on a VOR or ILS, the GTN is using GPS and the missed approach is always GPS. The GTN includes a Nav receiver, and if you switch the CDI to VLOC the external CDI will display the VOR or ILS and the autopilot will track it, but the GTN is still using GPS and that's why the map course line is magenta and the distances are valid and why the GTN presents a splash screen when you select a non-GPS approach warning that it is advisory only. In other words, the GTN is not supplying navigation, the Nav receiver within the GTN box is supplying navigation.

Also, the GFC 500 requires a valid GPS source even to fly a ILS or VOR approach. In my airplane, I have a G3X, G5 and GTN Xi. If the GTN fails, the G3X GPS will drive the autopilot and if the G3X fails the GTN will drive the autopilot via the G5. It would be good to make sure that any installation has more than one GPS source.

[midlifeflyer]

21 minutes ago, PT20J said:

One thing to keep in mind is that the GTN is ALWAYS a GPS navigator. Even on a VOR or ILS, the GTN is using GPS and the missed approach is always GPS. The GTN includes a Nav receiver, and if you switch the CDI to VLOC the external CDI will display the VOR or ILS and the autopilot will track it, but the GTN is still using GPS

That's why it's essential to make sure the appropriate leg is active on the GPS - to ensure proper sequencing.  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.

Edited March 3 by midlifeflyer

[donkaye]

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

 

[PT20J]

Sometimes you might want to activate the GTN missed approach, but not the autopilot Go Around (TOGA). If you miss early on this approach you may need to descend rather than climb. The KBFI published missed approach procedure underlies the KSEA final approach course, hence the altitude restriction. It’s important to plan this sort of thing during preflight planning and to review it during the approach briefing.

 

[Marc_B]

5 minutes ago, PT20J said:

The KBFI published missed approach procedure underlies the KSEA final approach course

I don't think I've ever come across a note like this.  Looks like KSEA has all of their final approach fixes right over KBFI at 1900 feet; even their visual approaches show overflying KBFI at or above 1900.  Thanks for sharing!