GTN Xi Hold Exit Legs

[PT20J]

Most stored procedures have hold exit legs; some don't. Garmin doesn't explain the rationale for including them. Since the navigator's lateral navigation when exiting a hold is the same whether there is an exit leg or not, it seems to me that the only reason for a hold exit leg is to allow an additional altitude constraint on the terminating inbound leg of a holding pattern. Anyone figured out another rationale?

[Marc_B]

My impression is that this is just the way the FMS was built allowing the navigator to sequence to the hold/hold entry, followed by a suspended hold, then a hold exit.  i.e. in a suspended hold the FMS sequences continued circling in hold, but unsuspended the FMS sequences through the exit. 

But the confusing part to me is that the Pilot Guide mentions in the discussion about approach holds that: "Not all published holds support a Hold Exit leg. Some show only Hold Entry and Hold legs. In this case, the Hold leg will remain active until crossing the hold fix for the final time."

I've never found an approach that didn't have all three legs yet.  Anyone know an example of approach without hold exit leg??

Initially I thought that maybe 3 hold legs was so you could have 3 vertical altitude constraints for VNAV so there would be a way to circle down inside a hold using VNAV, BUT the altitude constraints in the Hold (for hold entry, hold, and hold exit) don't sequence like that.  i.e. if hold entry is at or above 15,000, hold leg is at 7500, and hold exit leg is at 7000 --> it will sequence you to 15000 for entry, then vertical track will begin but you'll get a message that "cannot reach current vertical waypoint" since it's too steep of a descent for my VNAV parameter and it exits the hold WAY above your constraint.  If you "suspend" the hold (thinking this would give VNAV a chance to "catch up" and reach the vertical waypoint), VNAV will keep you at 15,000 and won't descend in the hold until you unsuspend.

Out of all the modes with the GTN and GFC500, VNAV is the least intuitive and seems to have very specific and limited purpose...descent on STARs using GPS.

[PT20J]

I don’t think it’s smart enough to project multiple turns if the hold entry altitude is very much greater than the hold exit.

[Marc_B]

@PT20J not needed to predict # of turns, but ability to suspend hold and it still descends to the hold altitude constraint and stays there. Suspend hold suspends the hold leg altitude constraint as well.

but surely it wouldn’t be much different than the logic of a departure procedure that follows a heading until “x” altitude then sequences to next waypoint. In departures like this it’s continually updating its prediction of where that altitude may be as the projection keeps changing as it climbs. 

[midlifeflyer]

22 hours ago, PT20J said:

Most stored procedures have hold exit legs; some don't. Garmin doesn't explain the rationale for including them. Since the navigator's lateral navigation when exiting a hold is the same whether there is an exit leg or not, it seems to me that the only reason for a hold exit leg is to allow an additional altitude constraint on the terminating inbound leg of a holding pattern. Anyone figured out another rationale?

I'm not sure what you mean, especially the part in bold . Do you have any examples? 

A hold in lieu has an exit leg because the hold is the intermediate leg of the instrument approach. It already knows what to do next and is prepared to sequence to it unless you tell it not to.

A missed approach hold does not have an exit leg because it's designed to be a stopping point at the end of the procedure. It's waiting to you to tell it what to do next and when.

 

[Marc_B]

2 minutes ago, midlifeflyer said:

A missed approach hold does not have an exit leg because it's designed to be a stopping point at the end

That would make sense.  But when I load the KGXY ILS35 or the KGXY RNAV35, both of the missed approach holds load a hold exit leg in the GTN flight plan.    Truly a missed approach hold when loaded on an approach is the "End of your flight plan" so you'd think no hold exit leg, right??  However when I load my own hold in the flight plan, it doesn't load a hold exit leg.

So the question remains, how does the hold exit leg differ?  What does it do besides add an altitude constraint (albeit a constraint that it won't try to sequence to unless you're unsuspended and the hold exit leg is the active leg)

My initial thought was one sequences through the hold to the holding fix and the other just sequences from present position when you unsuspend; however this isn't what's happening either.  So I thought maybe one automatically sequences through the hold vs loading in a suspended state if there isn't a hold exit leg...when I load my own hold it automatically suspends at the hold vs HILPT where it's sequences the hold, turns and flies inbound...HOWEVER, in the KGXY missed approach hold above, it's automatically suspended in the hold until you change it, so then why have a hold exit leg?

As an interesting aside, on the flight plan listing on my G500TXi, the Hold Exit Leg doesn't appear even when it's shown on the GTN.

[Marc_B]

56 minutes ago, midlifeflyer said:

I'm not sure what you mean, especially the part in bold . Do you have any examples? 

I think what Skip means is that even if you don't have a hold exit leg (i.e. you loaded a hold on a fix in your waypoint) and it's flying the hold as built, it will continue to fly the hold to exit when unsuspended.  i.e. If you unsuspend the hold on the outbound leg, the GTN will still sequence around the hold and inbound on the hold back to the hold fix before sequencing to the next waypoint.  Meaning, even without a hold exit, it wouldn't be the case where if you unsuspended that it would immediately turn direct to the next fix from present position.

[PT20J]

2 hours ago, Marc_B said:

@PT20J not needed to predict # of turns, but ability to suspend hold and it still descends to the hold altitude constraint and stays there. Suspend hold suspends the hold leg altitude constraint as well.

but surely it wouldn’t be much different than the logic of a departure procedure that follows a heading until “x” altitude then sequences to next waypoint. In departures like this it’s continually updating its prediction of where that altitude may be as the projection keeps changing as it climbs. 

But VNAV calculates a distance between TOD and BOD. 

[PT20J]

I’m thought I had seen some procedures with a missed approach hold with no exit leg, but prowling around the simulator, I can’t find one. All the missed approach holds I found have entry, hold and exit legs. When entering the hold, the GTN suspends. To exit the hold you tap the hold leg on the flight plan and select exit hold which causes the GTN to sequence to the hold exit leg when you next turn inbound. Interestingly, you can delete the hold exit leg. If you do this, the hold exit button on the hold menu is unavailable and the unsuspend button on the 650Xi default nav page is also unavailable, so there is no way to unsuspend the GTN without deleting the hold.
 

 

[PT20J]

52 minutes ago, Marc_B said:

I think what Skip means is that even if you don't have a hold exit leg (i.e. you loaded a hold on a fix in your waypoint) and it's flying the hold as built, it will continue to fly the hold to exit when unsuspended.  i.e. If you unsuspend the hold on the outbound leg, the GTN will still sequence around the hold and inbound on the hold back to the hold fix before sequencing to the next waypoint.  Meaning, even without a hold exit, it wouldn't be the case where if you unsuspended that it would immediately turn direct to the next fix from present position.

Yes, that’s how it seems to work. The difference in operation seems to be that without a hold exit leg, you use the unsuspend button to resume sequencing and exit whereas if there is an exit leg, you use the exit hold button from the hold leg menu. 

[Marc_B]

17 minutes ago, PT20J said:

The difference in operation seems to be that without a hold exit leg, you use the unsuspend button to resume sequencing and exit whereas if there is an exit leg, you use the exit hold button from the hold leg menu. 

When I load an approach with a HILPT but want to use as a hold pattern, if you choose "Activate hold" it's the equivalent of a "direct to" hold fix but it doesn't keep you in the hold suspended.  However if you wait till you're in the hold you can select Suspend from the map page.  Then it appears you have two options: select Unsuspend, or from flight plan select the hold and select exit hold.  I don't think I've ever used "exit hold" to exit the hold as it's much easier to just unsuspend.

Usually what I've found is that holds with an exit leg just sequence a turn in the hold then exit, whereas no hold exit leg usually keeps you suspended in the hold, as the times I've seen this it's when I've built a hold from "Hold at waypoint"  The outlier is the missed approach holds that have hold exit legs, but are sequenced indefinitely in the hold until you manually exit the hold, use direct to, etc.

 

[hammdo]

Spot on - Same here on the GNC355 - enter hold In Lieu then suspend/unsuspend. I practice this with my CFII often…

-Don

[PT20J]

HILPT is different than MAPH. Upon entry the former defaults to unspended, latter defaults to suspended.

[Marc_B]

3 minutes ago, PT20J said:

HILPT is different than MAPH. Upon entry the former defaults to unspended, latter defaults to suspended.

Sure.  But just mentioning that in the context of the initial thought that holds with hold exit leg sequence automatically vs previously the only holds I found without hold exit legs were ones I loaded and they defaulted to suspended.  However as mentioned, MAPH have exit and default suspended counter to that.

As above though, Pilot Guide mentions in the discussion about approach holds that: "Not all published holds support a Hold Exit leg. Some show only Hold Entry and Hold legs. In this case, the Hold leg will remain active until crossing the hold fix for the final time."

Anyone know an example of approach or published hold that loads a hold without hold exit leg??

[midlifeflyer]

4 hours ago, Marc_B said:

That would make sense.  But when I load the KGXY ILS35 or the KGXY RNAV35, both of the missed approach holds load a hold exit leg in the GTN flight plan.    Truly a missed approach hold when loaded on an approach is the "End of your flight plan" so you'd think no hold exit leg, right??  However when I load my own hold in the flight plan, it doesn't load a hold exit leg.

So the question remains, how does the hold exit leg differ?  What does it do besides add an altitude constraint (albeit a constraint that it won't try to sequence to unless you're unsuspended and the hold exit leg is the active leg)

My initial thought was one sequences through the hold to the holding fix and the other just sequences from present position when you unsuspend; however this isn't what's happening either.  So I thought maybe one automatically sequences through the hold vs loading in a suspended state if there isn't a hold exit leg...when I load my own hold it automatically suspends at the hold vs HILPT where it's sequences the hold, turns and flies inbound...HOWEVER, in the KGXY missed approach hold above, it's automatically suspended in the hold until you change it, so then why have a hold exit leg?

As an interesting aside, on the flight plan listing on my G500TXi, the Hold Exit Leg doesn't appear even when it's shown on the GTN.

Where does it go?

[Marc_B]

20 minutes ago, midlifeflyer said:

Where does it go?

@midlifeflyer Where does what go?

[PT20J]

4 hours ago, Marc_B said:

@midlifeflyer Where does what go?

If the question is, "What happens when you have a holding pattern with an exit leg and you tap exit hold on the hold menu?", the answer depends on whether there is a waypoint after the holding pattern. If yes, then it sequences to that waypoint. If no, then it continues on the same track as the inbound leg of the holding pattern.

If you have a holding pattern with an exit leg, you can also terminate the holding pattern and cause it to sequence to the next waypoint by tapping the unsuspend key IF there is a waypoint entered after the holding pattern. If there is no waypoint after the holding pattern, the unsuspend key is greyed out.

There are a lot of details left out of the manuals that remain an exercise for the user 

[midlifeflyer]

6 hours ago, Marc_B said:

@midlifeflyer Where does what go?

To me “Exit Hold” means “I’m done holding.” Or “bypass the hold.” Either way the whole idea of an “exit hold” to me is that you have somewhere to go afterward. Unless I had somewhere to go, whether another waypoint or a heading, why would I tap it. 

I guess I’m just thinking about what it’s used for and am missing something. 

[midlifeflyer]

On 9/13/2024 at 2:12 PM, Marc_B said:

Out of all the modes with the GTN and GFC500,

VNAV

is the least intuitive and seems to have very specific and limited purpose...descent on STARs using GPS.

Many simply don’t use VNAV, but I think it’s fun.

There are a few uses for VNAV aside from STAR descents. Any situation where you want to create a descent profile with targets. Most common IFR GA use is probably a crossing restriction - “cross FXNAM at 4000” when you are cruising at 8,000.  VNAV will create and fly the profile on those PD descents. Second, probably step-downs outside the FAF/PFAF on an approach. VNAV will meet each of them in turn before switching to the glidepath.

Most common VFR use is probably descent planning to the airport - “I want to be X feet above pattern altitude Y miles from the airport.”

(“intuitive” is in the mind of the beholder)

 

[Marc_B]

@midlifeflyer Basic use of VNAV for a GPS nav descent to automate when you need to start down without manual calculation, yes agreed.  I use it routinely more to just see where it has issues; but it's got several gotchas and is like walking your 4 year old across the street...you have to hold hands and watch closely to make sure they're safe.   But I only mentioned VNAV regarding hold altitude constraints.

@PT20J's original question was about the hold exit leg and why some holds have it and others don't other than allowing the input of one additional altitude constraint.  It would seem one basic use of holding pattern is descent from altitude.  So in that context, how do you utilize those constraints with VNAV?  I don't think you can reliably.  The behavior of VNAV with respect to holds is not instinctive.  Suspended it stays at the hold entry altitude (not the hold leg constraint that you're currently on), unsuspended it only takes one lap in the hold and will likely not meet your hold constraint; and the hold exit constraint only becomes active on the inbound leg exiting the hold (which is short enough that no meaningful descent could usually be attained).  So VNAV would work reliably to get you to the hold entry altitude, but not reliably past that point.

And I'm still curious what Garmin means by some published holds don't support hold exit legs...because that implies that there is something unique about the hold exit leg.  However with or without a hold exit leg, the GTN still completes the race track back to the hold fix before going to the next waypoint if there is one.  So if the behavior is the same, why do some holds have exit legs and others do not?

[midlifeflyer]

3 hours ago, Marc_B said:

idlifeflyer Basic use of VNAV for a GPS nav descent to automate when you need to start down without manual calculation, yes agreed.  I use it routinely more to just see where it has issues; but it's got several gotchas and is like walking your 4 year old across the street...you have to hold hands and watch closely to make sure they're safe.   But I only mentioned VNAV regarding hold altitude constraints.

Everything has gotchas. Using a function properly requires knowing them.  And I treat most autopilots like a 4 year old  

[midlifeflyer]

3 hours ago, Marc_B said:

And I'm still curious what Garmin means by some published holds don't support hold exit legs...because that implies that there is something unique about the hold exit leg.  However with or without a hold exit leg, the GTN still completes the race track back to the hold fix before going to the next waypoint if there is one.  So if the behavior is the same, why do some holds have exit legs and others do not?

I guess we need to find one and look at it. 

[PT20J]

3 hours ago, Marc_B said:

The behavior of VNAV with respect to holds is not instinctive.  Suspended it stays at the hold entry altitude (not the hold leg constraint that you're currently on), unsuspended it only takes one lap in the hold and will likely not meet your hold constraint; and the hold exit constraint only becomes active on the inbound leg exiting the hold (which is short enough that no meaningful descent could usually be attained).  So VNAV would work reliably to get you to the hold entry altitude, but not reliably past that point.

My experience is slightly different. No problem with the hold entry constraint. On the simulator, I cannot get it to descend to a lower hold leg constraint - in fact, the simulator actually climbs back to the demo altitude setting after passing the holding fix the first time. I have never tried this in the airplane. However, in both the airplane and the sim, if I unsuspend after passing the hold fix it will calculate a TOD anywhere within the remaining turn of the holding pattern to meet the hold exit leg constraint.

@Pinecone took the live Garmin class -- maybe they explained it there?

[midlifeflyer]

50 minutes ago, PT20J said:

My experience is slightly different. No problem with the hold entry constraint. On the simulator, I cannot get it to descend to a lower hold leg constraint - in fact, the simulator actually climbs back to the demo altitude setting after passing the holding fix the first time. I have never tried this in the airplane. However, in both the airplane and the sim, if I unsuspend after passing the hold fix it will calculate a TOD anywhere within the remaining turn of the holding pattern to meet the hold exit leg constraint.

@Pinecone took the live Garmin class -- maybe they explained it there?

I think I got lost along the way.  What sim? If we're talking about that mini-autopilot on the Garmin trainer, while it emulates things pretty well, I never think of it as being a full GFC 500 or 600 emulator. That said, I did try to use it to do a VNAV in a published hold. I have no idea if this is what you are referring to. I did the RNAV 3 into my home base.  The default altitude constraint for the Hold Entry at IKTOW is 2100, which carries through to glidepath intercept at HEDYY. You can see how I adjusted the constraints in the picture. I started at 3,000.

The result was the trainer descended in the hold.

1. The trainer crossed IKTOW at 3,000.
2. The trainer ignored the "at or above" constraint in the hold (I have not tried making it a hard "at." but I wouldn't be surprise if it ignored that also).
3. The trainer did a normal VNAV descent to exit the hold at 2100.

[PT20J]

11 minutes ago, midlifeflyer said:

I think I got lost along the way.  What sim? If we're talking about that mini-autopilot on the Garmin trainer, while it emulates things pretty well, I never think of it as being a full GFC 500 or 600 emulator. That said, I did try to use it to do a VNAV in a published hold. I have no idea if this is what you are referring to. I did the RNAV 3 into my home base.  The default altitude constraint for the Hold Entry at IKTOW is 2100, which carries through to glidepath intercept at HEDYY. You can see how I adjusted the constraints in the picture. I started at 3,000.

The result was the trainer descended in the hold.

1. The trainer crossed IKTOW at 3,000.
2. The trainer ignored the "at or above" constraint in the hold (I have not tried making it a hard "at." but I wouldn't be surprise if it ignored that also).
3. The trainer did a normal VNAV descent to exit the hold at 2100.

Yep. I did something similar, only I made the hold entry 5000, hold 4000, hold exit 3000. All were hard "At" constraints. I monitored the altitude of the simulator by setting one of the user fields on the map to GPS Alt (GSL). I started the simulator at 6000 and activated the hold. It set a TOD and descended to 5000. Upon crossing the holding fix I selected SUSPEND and it climbed back to 6000 which I take as a bug in the sim, but I believe that the real system will probably just ignore the hold leg constraint and maintain altitude. Just after passing the holding fix again, I selected UNSUSPEND and it created a TOD and descended to 3000 at the holding fix before proceeding to the BOD at the next waypoint.