Garmin G5/GTN650 with King KAP140 Autopilot (C172)

[Thunderbird83]

My flying club just upgraded their 172SP to a dual Garmin G5/ GTN650 combo. They kept the old King KAP140 autopilot. I have been trying to find info about flying approaches with this combination. I have figured out that I can put the G5 in GPSS mode and select heading on the autopilot to track the navigation course. But I can’t quite figure out how to capture a glideslope.

Anybody have experience with this combination? Are there any training videos or publications that describe the proper use of this combo for navigation and approaches?

 

[Baron62]

I believe the G5 only provides GPSS or Heading bug steer while your AP is in "Heading" mode only. When your AP is in NAV mode you should be able tune an ILS and get vertical guidance as you have in the past. I don't think you get vertical channel GPSS from the G5. Having said all that, I don't have this AP, but that is how my simple Century AP works with a G5/GTN650 combo.

 

[Stephen Shore]

I believe the G5 only provides GPSS or Heading bug steer while your AP is in "Heading" mode only. When your AP is in NAV mode you should be able tune an ILS and get vertical guidance as you have in the past. I don't think you get vertical channel GPSS from the G5. Having said all that, I don't have this AP, but that is how my simple Century AP works with a G5/GTN650 combo.

This is correct - no vertical guidance from the G5 to the King AP.

I went with an Aspen Evolution 1000 in my airplane when I updated to a GTN 750. I have a King KFC200 AP, and the G5 does not have the ability to fly a fully coupled GPS approach with an old legacy analog AP. With the Aspen you can purchase the EA 100 AP adapter (I also added the altitude preselect). This basically almost doubles the price of the Aspen unit, but it will get you where you want to be - a fully coupled GPS approach.

 

[flyingcheesehead]

I believe the G5 only provides GPSS or Heading bug steer while your AP is in "Heading" mode only. When your AP is in NAV mode you should be able tune an ILS and get vertical guidance as you have in the past. I don't think you get vertical channel GPSS from the G5. Having said all that, I don't have this AP, but that is how my simple Century AP works with a G5/GTN650 combo.

Correct - And this is true of any GPSS, not just the G5. "GPSS" (GPS Steering) is a function wherein the GPS can pretend to be a heading bug, and it will feed headings in that allow your autopilot to near-perfectly track a GPS course, do turn anticipation, etc. So, the autopilot needs to be in Heading mode for GPSS to work.

To capture and track a glideslope, you've gotta be in Approach mode, which is a more-sensitive Nav-based mode, not a heading-based mode. GPSS does not work in this mode, regardless of where it comes from.

To the OP: Once you're established on the final approach course, flip the autopilot into Approach mode ("APR" button). I can't remember with 100% certainty, but I think if you have a crosswind it may "hunt" for a moment - if it does, it'll turn to a heading matching the FAC, start correcting as it drifts off course momentarily, and then quickly reintercept and track the FAC). In any case, it should remain within a dot of course anyway. When the glideslope comes alive, it should intercept it and the vertical mode of the autopilot should switch from ALT to GS.

Once you've intercepted the FAC and switched to APR mode, it's really no different than it was before you had the G5. The autopilot is just tracking needles at that point, regardless of where they come from.

 

[arnoha]

This is the setup in my plane right now...G5s and KAP140. The way I fly it, I stay with HDG mode and GPSS until I note that the ILS receiver has captured the glideslope. I use VS mode extensively while in GPSS. If you have altitude preselect, that's quite useful. Once lined up on the runway, I switch to approach mode and turn off GPSS. Only with that can you actually follow a glideslope. This is true for an LPV approach as well.

It's a bit more button fiddling than I'd like, but it works well as long as you get on final a reasonable distance out. If you're in tight, it may take some manual flying to get things lined up.

 

[Thunderbird83]

Thanks for your responses, everyone. It turns out, that the shop that did the install didn't wire it correctly to the autopilot the first time, so it couldn't capture the glideslope. That part has been fixed, and now it works.

So, just so I understand the proper operation/sequence for using the autopilot with the G5...

1: Enroute, I should have GPSS enabled on the G5 and HDG selected on the autopilot.
2: Load my approach in the 650 and:
2(a) disable GPSS if I'm getting vectors and use the bug to set the heading, remain in HDG mode on the AP
or 2(b) if flying to an IAF stay in GPSS mode and HDG mode on autopilot.
3: After crossing the IAF or when given an intercept heading for the final approach course, is that when I disable GPSS and switch to APR on the autopilot?

 

[Stephen Shore]

In my setup, I don't have to "disable" the GPSS when I switch to APR - once I go to APR, the glideslope is captured (RNAV approaches).

Of course for an ILS approach (vectors), I am not in GPSS mode - I am in VLOC mode on my CDI and once the localizer is captured and glideslope, the AP flies the airplane on in.

This is with a GTN750, Aspen 1000 PRO, and KFC200.

 

[flyingcheesehead]

Thanks for your responses, everyone. It turns out, that the shop that did the install didn't wire it correctly to the autopilot the first time, so it couldn't capture the glideslope. That part has been fixed, and now it works.

So, just so I understand the proper operation/sequence for using the autopilot with the G5...

1: Enroute, I should have GPSS enabled on the G5 and HDG selected on the autopilot.
2: Load my approach in the 650 and:
2(a) disable GPSS if I'm getting vectors and use the bug to set the heading, remain in HDG mode on the AP
or 2(b) if flying to an IAF stay in GPSS mode and HDG mode on autopilot.
3: After crossing the IAF or when given an intercept heading for the final approach course, is that when I disable GPSS and switch to APR on the autopilot?

I think the most common scenarios in real-world IMC flying are vectors to an ILS or RNAV(GPS) final approach course, or an RNAV(GPS) "T" approach.

Try this out in VMC first, always. Here's how you would fly those two scenarios:

Vectors to final:
1) GPSS on and autopilot in HDG and ALT until you're on vectors
2) Once you get a vector, turn GPSS off to fly the bug. Autopilot will still be in HDG ALT.
3) After you get your approach clearance (ie, you're on the final vector to intercept), hit APR to arm approach mode. Display will say "HDG", "APR ARM", and "ALT"
4) The autopilot will intercept the final approach course automatically, at which point the display will say "APR ALT" and "GS ARM".
5) The autopilot will capture the glideslope automatically, at which point it'll say "APR GS".

T approach (RNAV LPV):
1) GPSS on and autopilot in HDG and ALT. This time, leave GPSS on for the moment since you're not on vectors.
2) After you cross the IAF, the autopilot will turn to fly the base leg automatically. Autopilot still in HDG ALT and GPSS on.
3) Approaching the IF, the GPSS will give you a perfect turn onto the final approach course for the intermediate leg. Autopilot still in HDG ALT and GPSS on.
4) After the autopilot has completed the turn onto the FAC and you're established on the intermediate leg, hit APR and turn GPSS off. Display should go straight to APR ALT and GS ARM.
5) The autopilot will capture the glideslope automatically and switch to APR GS.

For clarity's sake: The intermediate leg is the one where you're on the final approach course, before the FAF, flying level... After you've turned in from the base leg, but before the descent.

So, they're pretty similar, the difference is just when you hit APR and when you turn off the GPSS. They happen at different times on vectors to final, and at the same time on the T approach. The reason you disable GPSS once you're on vectors is because the autopilot will capture the final approach course on its own - If you try to leave it in HDG mode and intercept final prior to switching over to APR mode, well, you'll never do it as well as the autopilot will! On a GPS approach (without vectors), we use the GPSS to make the turn onto final because the autopilot will overshoot the final approach course big-time if you do a 90-degree intercept. In fact, it'll probably go full deflection to the other side quicker than it can even start the turn, and just start wandering off into space randomly (you can probably guess how I know this).

Hope this helps!

 

[Thunderbird83]

I think the most common scenarios in real-world IMC flying are vectors to an ILS or RNAV(GPS) final approach course, or an RNAV(GPS) "T" approach.
-snip-
Hope this helps!

Thanks Kent! This is an excellent write up, and I'm going to get in the plane this week and try it out! Thanks!

 

[Stephen Shore]

I think the most common scenarios in real-world IMC flying are vectors to an ILS or RNAV(GPS) final approach course, or an RNAV(GPS) "T" approach.

Try this out in VMC first, always. Here's how you would fly those two scenarios:

Vectors to final:
1) GPSS on and autopilot in HDG and ALT until you're on vectors
2) Once you get a vector, turn GPSS off to fly the bug. Autopilot will still be in HDG ALT.
3) After you get your approach clearance (ie, you're on the final vector to intercept), hit APR to arm approach mode. Display will say "HDG", "APR ARM", and "ALT"
4) The autopilot will intercept the final approach course automatically, at which point the display will say "APR ALT" and "GS ARM".
5) The autopilot will capture the glideslope automatically, at which point it'll say "APR GS".

T approach (RNAV LPV):
1) GPSS on and autopilot in HDG and ALT. This time, leave GPSS on for the moment since you're not on vectors.
2) After you cross the IAF, the autopilot will turn to fly the base leg automatically. Autopilot still in HDG ALT and GPSS on.
3) Approaching the IF, the GPSS will give you a perfect turn onto the final approach course for the intermediate leg. Autopilot still in HDG ALT and GPSS on.
4) After the autopilot has completed the turn onto the FAC and you're established on the intermediate leg, hit APR and turn GPSS off. Display should go straight to APR ALT and GS ARM.
5) The autopilot will capture the glideslope automatically and switch to APR GS.

For clarity's sake: The intermediate leg is the one where you're on the final approach course, before the FAF, flying level... After you've turned in from the base leg, but before the descent.

So, they're pretty similar, the difference is just when you hit APR and when you turn off the GPSS. They happen at different times on vectors to final, and at the same time on the T approach. The reason you disable GPSS once you're on vectors is because the autopilot will capture the final approach course on its own - If you try to leave it in HDG mode and intercept final prior to switching over to APR mode, well, you'll never do it as well as the autopilot will! On a GPS approach (without vectors), we use the GPSS to make the turn onto final because the autopilot will overshoot the final approach course big-time if you do a 90-degree intercept. In fact, it'll probably go full deflection to the other side quicker than it can even start the turn, and just start wandering off into space randomly (you can probably guess how I know this).

Hope this helps!

One question - when the GS is captured (the "diamond" becomes solid green on the Aspen 1000PRO), do you need to turn "off" the ALT on the AP or just leave it on and the GS takes over? I found yesterday that I had to turn the ALT off on my KFC200 in order for my AP to follow the GS. I did not think that was required (turning the ALT off on the KFC200).

 

[flyingcheesehead]

Thanks Kent! This is an excellent write up, and I'm going to get in the plane this week and try it out! Thanks!

Great! Let us know how it goes!

One question - when the GS is captured (the "diamond" becomes solid green on the Aspen 1000PRO), do you need to turn "off" the ALT on the AP or just leave it on and the GS takes over? I found yesterday that I had to turn the ALT off on my KFC200 in order for my AP to follow the GS. I did not think that was required (turning the ALT off on the KFC200).

That's weird. I've never flown a 200, but I've got about 900 hours combined behind the KAP 140 and KFC 150, and you don't have to turn off ALT in either of those. When you put it in APR mode, it should still be in ALT mode with the glideslope armed (140 actually says ALT and GS ARM, the 150 has the GS light blinking). When you capture the glideslope, I would think it would automatically track it and get rid of the altitude hold.

Are you leaving GPSS on, by chance? GPSS requires the autopilot to be in HDG mode, and if it's in HDG mode it doesn't know to capture the glideslope. You'll need to make sure it's in Approach mode before the glideslope comes alive to get it to capture properly.

 

[Stephen Shore]

Great! Let us know how it goes!



That's weird. I've never flown a 200, but I've got about 900 hours combined behind the KAP 140 and KFC 150, and you don't have to turn off ALT in either of those. When you put it in APR mode, it should still be in ALT mode with the glideslope armed (140 actually says ALT and GS ARM, the 150 has the GS light blinking). When you capture the glideslope, I would think it would automatically track it and get rid of the altitude hold.

Are you leaving GPSS on, by chance? GPSS requires the autopilot to be in HDG mode, and if it's in HDG mode it doesn't know to capture the glideslope. You'll need to make sure it's in Approach mode before the glideslope comes alive to get it to capture properly.

So....when the glideslope comes alive, disconnect the GPSS but don't bother the ALT button? I have had my airplane for one week and am still trying to figure it out. The ILS was easy...but I am having a little trouble on the RNAV approaches figuring out the correct sequences.

 

[flyingcheesehead]

So....when the glideslope comes alive, disconnect the GPSS but don't bother the ALT button? I have had my airplane for one week and am still trying to figure it out. The ILS was easy...but I am having a little trouble on the RNAV approaches figuring out the correct sequences.

*Before* the glideslope comes alive. If you're on a GPS "T" approach, for example, once the plane turns from base to final (the intermediate leg, lined up with final but the part that's usually 5-10 miles from the runway) so you're tracking the final approach course, flip the autopilot from HDG to APR right away. Since you're already on final, it should also arm the glideslope pretty much right away, and capture it once it comes alive. If you wait to flip to approach mode until after the glideslope is already alive, it may not work.

Keep in mind that all of these King autopilots came out before GPS approaches with vertical guidance (LPV) even existed. They're complex analog devices. All they know is the bug, the CDI, the static pressure and the attitude (or rates). GPSS merely fools them by converting a digital signal into an automatic analog heading bug.

 

[flyingcheesehead]

OK, I googled for the KFC 200 manual, which says this:

"Upon interception of the Glideslope, capture occurs and GS is lighted on the Annunciator Panel. A smooth capture pitch command is displayed by the Command V-bar. The pilot (or Autopilot) controls the aircraft to satisfy the Command V-bar. Slewing ALT at time of GS centering will inhibit GS capture.

"Upon GS capture, the ALT HOLD mode (if active) is cancelled. However, ALT HOLD may be manually reselected to maintain altitude upon reaching MDA if visual contact is not established."

So yeah, you shouldn't have to manually disable ALT. Maybe just try it in VMC and just don't do anything at glideslope capture, I know I've seen it where the glideslope is centered and it still says ALT until I decide I'm going to take over, and it suddenly switches to GS.