Capturing Glideslope w/KFC 225

[CaptainBen]

Hi folks. I have a question about using the KFC225 autopilot (2004 Ovation) on instrument approaches. Everything seems to be working, except when I press the "APR" button, it's not capturing the glideslope (ILS or RNAV LPV). I'm sure it's user error and I'm probably just not using the right sequence. The KFC 225 user manual isn't very helpful, so reaching out here to see if I can get some insights from y'all. Here's the sequence I've been following:

1) With the flight plan and approach activated on my Garmin 430, press "FD", NAV", and "AP" on the autopilot and use altitude pre-select for IAF altitude. The autopilot tracks the GPS course to the IAF, levels off at altitude, and turns on the approach course.

2) Use altitude pre-select and VS/DOWN buttons to descend to step-down altitudes between fixes. The airplane descends and levels off as appropriate.

3) At last waypoint / fix BEFORE the FAF, use the VS/DOWN button to continue descent to FAF altitude

4) When I see the glideslope come alive above me, press "APR"

When following the above sequence, the airplane just continues descending right through the glideslope after crossing the FAF.

Any suggestions? Appreciate your help!

[midlifeflyer]

I haven't flown the 225, so I'm going to assume it's operation is consistent with other King autopilots.

There are a few techniques involved there. Just for one, it is unnecessary to VS down to the FAF altitude. The unit will capture the GS just fine at the intermediate fix altitude. For the other, to most, it is a best practice to press APR upon hearing the words, "cleared for the approach."

Based on your technique, a question. In your step 3, are you leveling off at the the FAF altitude in ALT mode? There are several concerns here. One is that you have to be at or below PFAF altitude and some autopilots  have a limitation of how close you can be to intercept. Another is that your description of the AP continuing down through the GS suggests you never leveled off. And where are you when you switch to APR? And I think this is one of the autopilots that requires you to already be in ALT in order to capture the GS. Basically I think you are trying to time a transition from ALT to APR that doesn't need to be timed in that way. 

Unless someone has a better suggestion, I'd try one of two things:

Using your technique of diving down to PFAF altitude:

3) At last waypoint / fix BEFORE the FAF, use the VS/DOWN and altitude preselect to to dive down and level off. 

4) If you have not already armed APR mode (as many of the photos in the manual show, ARP can be armed while in ALT mode) do it as soo as you level off.

The only thing I would do differently as a technique is that (assuming I were cleared for the approach), I would have armed GS no later than in ALT mode at the the crossing altitude for the intermediate fix, but that strictly a personal technique issue.

If that doesn't make too much sense, I suggest giving us a specific approach to use as an example.

 

 

[Jerry 5TJ]

The KFC225 has two lines on the display. The top line indicates the present mode, the lower line shows upcoming mode(s) that are armed.  

The simplest way to use the APR mode is probably to use autopilot in HDG to intercept the localizer and then to switch to the APR mode when the localizer begins to move.  The GS Arm message should appear on the lower line of the KFC225 display.  When the glideslope is intercepted and the needle centers the KFC225 display should show GS on the upper line indicating the AP has captured the GS. 
 

If your 430W is in GPS tracking and you switch it to VLOC to fly an ILS the KFC225 cancels the active mode and reverts to ROL function.  Select VLOC on the 430W first and then set the KFC225.  
 

If the approach is RNAV GPS then you leave the 430W set to GPS for the entire approach.   
 

if you have a Garmin 650/750 instead of the 430//530 then there is an extra step:  A message prompt will appear on the navigator, and you must open the message page and then press the “activate approach guidance” soft key before you can set the KFC225 to APR mode. 
 

I’m not sure if the KFC225 can be in VS mode to a preset altitude below the GS intercept altitude and simultaneously be armed in APR mode. I suspect not.  
 

in any case—If you don’t see the “GS Arm” message on the lower line line of the KFC225 then it will not capture the GS. 

[midlifeflyer]

 

18 hours ago, Jerry 5TJ said:

The simplest way to use the APR mode is probably to use autopilot in HDG to intercept the localizer and then to switch to the APR mode when the localizer begins to move.  The GS Arm message should appear on the lower line of the KFC225 display.  When the glideslope is intercepted and the needle centers the KFC225 display should show GS on the upper line indicating the AP has captured the GS. 

Is there a reason you seem to assume vectors to final? But that's kind of why I asked for more detail - the approach involved and what happened.

Other than that, yes, if you manually switch CDI source from GPS to VLOC while in NAV mode, the AP will revert to ROL. But that's not the case with VTF. If you are in HDG mode and switch the source, it remains in HDG mode and does not revert to ROL. I'd be in APR as soon as I heard "cleared for the approach," and not delay until intercept. The screen would look like this picture  from the Pilot Guide: HDG mode for the vectors, ALT mode to hold altitude until glideslope intercept, APR mode armed for both lateral and vertical guidance after intercept.

The piece I am not at all sure about is whether the unit can be in VS mode with APR armed or whether it already has to be holding in ALT.

[CaptainBen]

Thanks for all the good info, folks. It seems like the autopilot won't intercept the glideslope when in Nav mode (after activating the approach in my 430, I set the autopilot mode to NAV). It tracks to the waypoints and then turns and tracks the localizer perfectly, but after pressing APR it won't intercept the GS, even if I'm at level altitude below the GS. Also, as a couple of you pointed out, using VS to descend to step-down altitudes doesn't work either, even if I'm above the glideslope initially, then press APR after I'm below the GS (the autopilot just continues descending right through the GS).

Seems like the autopilot prioritizes the VS setting over GS, and maybe it wasn't designed to use NAV on approaches. I was able to get the autopilot to capture the glideslope just by using HDG mode and ensuring I was leveled off below the glideslope when I turned onto the final approach course. I guess this is more realistic anyway, since I'll be getting vectors to the final approach course from ATC most of the time.