GTN650xi and KAP150 Question

[Tim-37419]

I'm just now beginning my instrument training so if this is operating by design feel free to school me.

 

When departing an airport and the GTN is in terminal mode it will not fly the magenta line. 20 or so miles later, I forget the exact number but I read it in the manual, the GTN goes into  enroute mode and all is fine.

Am I doing something wrong?

 

I should add that’s nav mode on the KAP. Heading mode works as expected, I didn’t think to try GPSS. If it’s important, I have the Aspen 2500 Max.

Edited November 6, 2023 by Tim-37419
Added more information and made corrections

[Tim-37419]

Ah, I wrote that on my phone. 650xi. I’ll edit the post.

[Pinecone]

You want to leave your KAP-150 in Heading Mode, and turn on GPSS on your Aspen.   With this setup you don't use Nav mode on the KAP, ever.

I have an Aspen 1000 and KAP-150 in my plane.  I did not know this at first so had some weird things happen.

Terminal or Enroute mode only changes how far each dot left/right of course is in miles. 

[TheBearFlies]

I have GTX650XI with GFC500. After TO you have to activate or engage NAV mode. During pre-flight, make sure your GTN/Menu/OBS/GPS Not Nav 1 or LOC. Highly recommend Garmin GTN trainer for iPad.

[kortopates]

Terminal mode has nothing to do with it, but perhaps you are full scale deflection on your HSI. So start with heading mode to get you on a proper intercept for the current DTK and then arm NAV mode OR update the DTK by pressing Direct and then NAV mode should work fine.
TERMINAL mode just means 1 nm full scale deflection when you are within 30 nm of your departure or Destination, then it goes to Enroute mode which is 2nm full scale deflection.


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[Marc_B]

I think @Pinecone has the answer. I had GTN with KFC150 and I never used Nav mode, only heading mode. If I was being vectored then used heading bug and heading mode. If flying the magenta then hold heading bug button to turn on GPSS and still use heading mode. NAV was for flying VORs. 

[Tim-37419]

Yes, he was correct. Also correct on the AP does weird things in nav mode. Nav mode kept turning me back to the airport and I was like what the hell is going on. Hell was not the word I originally used.

[kortopates]

Yes, he was correct. Also correct on the AP does weird things in nav mode. Nav mode kept turning me back to the airport and I was like what the hell is going on. Hell was not the word I originally used.

You’ll still want to sort out the issue with Nav mode as i am sure it will re-appear in approach mode. Can’t use GPSS on approaches other than VOR.


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[PeteMc]

On 11/6/2023 at 6:51 AM, Pinecone said:

 With this setup you don't use Nav mode on the KAP, ever.

Always Heading?...  What do you do for a GS/GP?  I'm assuming you use APC Mode?

[PT20J]

Just now, PeteMc said:

Always Heading?...  What do you do for a GS/GP?  I'm assuming you use APC Mode?

With my Aspen/KAP 150/GNS 450W I used HDG for heading, HDG + GPSS for GPS Nav, NAV for VOR nav (rarely), and APR for approaches regardless of nav source.

[PeteMc]

2 minutes ago, PT20J said:

and APR for approaches regardless of nav source.

Should have added in the OP that I was just curious if there was something different with the KFC150 and the KFC200. 

 

[PT20J]

1 hour ago, PeteMc said:

Should have added in the OP that I was just curious if there was something different with the KFC150 and the KFC200. 

 

Should be the same. The logic was the same on my 200 and 150. GPSS is completely external to the autopilot and is just a converter to translate digital roll steering commands from a GPS navigator to analog heading for the autopilot. 

[larryb]

I have a similar setup, GTN650, Aspen, KFC150.  My understanding is that NAV mode works by keeping the deviation bar centered. So if you are navigating to a point, and you are on-course, this will work fine and keep you on-course.  The problem comes when you reach the waypoint and want to turn. In NAV mode you will keep going straight over the waypoint until the deviation bar shows off course, then the AP will try to correct and re-center the deviation bar. In Heading mode, combined with GPSS mode on the Aspen, the Aspen will direct the AP to turn before you get to the waypoint, anticipating the turn and flying a more accurate course. 

[PeteMc]

4 hours ago, larryb said:

the Aspen will direct the AP to turn before you get to the waypoint, anticipating the turn and flying a more accurate course. 

That actually should be your GTN that makes that determination.  And yes, Enroute the Wpt are "Fly-By" so you just need to be close and the GTN (and other Navigators) will anticipate and start the turn early.  Then there are "Fly-Over" Wpts where you actually have to cross the Wpt before you turn.  There are a few of these in the Enroute system and certainly on Approaches. You can tell a Fly-Over Wpt by the Circle around the typical Wpt ballooned cross or star.  A Missed Approach Point is and example of a Fly-Over Wpt with the Circle.

 

[PT20J]

GPSS does more than turn anticipation, i.e., not overshooting a Fly-By waypoint. It also allows a legacy autopilot to fly complex procedures in the GPS database such as missed approaches, DME arcs and holding patterns. 

[midlifeflyer]

19 hours ago, larryb said:

I have a similar setup, GTN650, Aspen, KFC150.  My understanding is that NAV mode works by keeping the deviation bar centered. So if you are navigating to a point, and you are on-course, this will work fine and keep you on-course.  The problem comes when you reach the waypoint and want to turn. In NAV mode you will keep going straight over the waypoint until the deviation bar shows off course, then the AP will try to correct and re-center the deviation bar. In Heading mode, combined with GPSS mode on the Aspen, the Aspen will direct the AP to turn before you get to the waypoint, anticipating the turn and flying a more accurate course. 

@PeteMcgave a good explanation. Said another way, your GTN650 provides turn anticipation. That’s the “turn 120 in 9-8-7…” annunciation you see. The “0, turn now “ is when to start the turn before the waypoint to a standard rate turn rolls out on course. 

In NAV mode, that “turn now” instruction  is meaningless to your KFC 150. All it knows is the VOR standard cross the fix, then turn (and with the original King HSI, which doesn’t auto-slew to the new course, you will have to manually turn the course needle too).

GPSS in your Aspen setup is basically a translator which converts that “turn now” GPS command into a heading instruction which the KAP 150 has no trouble following.