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blakealbers

GtN 750 procedure turn

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Hi all, recently had a 750 installed coupled to a KFC 150 on my Mooney Bravo. The GTN will lay out the proper entry into to the procedure turn but once over the initial fix it will just veer off on its own without following the elected course. Was heading south and entering the EHROS way point on RNAV 36 for KLCG Wayne airport. Haven't had a chance to talk to the avionics guy yet but guessing an install problem ??

 

 

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Not enough detail to begin here. If you want to describe how you set things up? e.g., was the AP tracking the course as it approached the hold and how were you flying the hold? Do you have GPSS? etc.

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Not enough detail to begin here. If you want to describe how you set things up? e.g., was the AP tracking the course as it approached the hold and how were you flying the hold? Do you have GPSS? etc.


GPSS yes, was tracking the course into the IAF, tried NAV mode and approach mode


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Expect a discussion on using the AP / gpss in heading mode.

mostly because that is how many GPSSs work.

nav is good for going point to point.  Gpss creates a bunch of points to follow and delivers them to the AP as needed.  The AP uses heading mode that gets adjusted continuously by the GPS.

 

PP thoughts only, not an instrument guy or CFI...

Best regards,

-a-

Edited by carusoam
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Expect a discussion on using the AP / gpss in heading mode.
mostly because that is how many GPSSs work.
nav is good for going point to point.  Gpss creates a bunch of points to follow and delivers them to the AP as needed.  The AP uses heading mode that gets adjusted continuously by the GPS.
 
PP thoughts only, not an instrument guy or CFI...
Best regards,
-a-



No that's great, this is all new equipment to me and I only began my instrument training two weeks ago. Was curious if it was a problem I created or a problem via the install. All of this is during VFR no hood, trying to get my speeds settings and nuances of new equipment and such down so I'll do that


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It might be helpful to know what is providing the GPSS?

But with GPSS, the GPSS needs to be GPS mode (versus) heading and your AP needs to be in Heading mode as well. GPSS in GPS mode allows the GPS to provide steering information as heading inputs to the KFC 150, in lieu of just following your heading bug.

After you completed the procedure turn and captures final then you would have to engage APPR mode on the KFC 150 to track both lateral and vertical guidance and GPSS is then no longer being used. In effect, GPSS mode and APPR mode are mutually exclusive. 

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In heading mode the AP should follow the whole flight plan without any button pushing. From my fuzzy aged memory. I don't have a gtn or gpss...

This is one of the good things about transition training. If you get the chance... MAPA has some good training and trainers too.

Best regards,

-a-

Edited by carusoam
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It might be helpful to know what is providing the GPSS?
But with GPSS, the GPSS needs to be GPS mode (versus) heading and your AP needs to be in Heading mode as well. GPSS in GPS mode allows the GPS to provide steering information as heading inputs to the KFC 150, in lieu of just following your heading bug.
After you completed the procedure turn and captures final then you would have to engage APPR mode on the KFC 150 to track both lateral and vertical guidance and GPSS is then no longer being used. In effect, GPSS mode and APPR mode are mutually exclusive. 



Appreciate the help!


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Don Kaye has an article on his website (donkaye.com) in the flight training section on GPS approaches using GPSS.  I found it very helpful. I too have a GTN 750 and KFC 150.

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8 hours ago, carusoam said:

Expect a discussion on using the AP / gpss in heading mode.

mostly because that is how many GPSSs work.

nav is good for going point to point.  Gpss creates a bunch of points to follow and delivers them to the AP as needed.  The AP uses heading mode that gets adjusted continuously by the GPS.

 

PP thoughts only, not an instrument guy or CFI...

Best regards,

-a-

This.

Unless you have a newfangled digital autopilot which reads GPS data directly, and the 150 is definitely not one of them, GPSS operates in HDG (not NAV or APR) mode.  In simplistic terms, GPSS takes GPS data and converts it into a series of heading (as opposed to course) inputs fed to your HSI.

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Here is a quote from our GTN650 manual and I assume the same applies to the GTN750.

"CAUTION: Not all autopilots will follow guidance when on a heading leg using NAV, GPSS, or APR mode on the autopilot. Heading legs for procedures
can be identified by “HDG XXX°” in white on the Flight Plan page, as well as the procedure chart indicating that the aircraft must fly a particular
heading. Certain autopilots will revert to a “Roll Only” or “Wings Level” mode on these leg types and the pilot must engage the heading (HDG)
mode of the autopilot and set the heading bug appropriately in order to use the autopilot on these legs."

And I assume you mean the Hold In Lieu of Procedure Turn holding pattern.  When entering a holding pattern, we turn to a heading, not a course.

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Most everything has been discussed above, but here is my summary:

For the GTN 750 to follow GPSS inputs you first need some sort of converter to convert the GPS output to a Heading that feeds a GPSS/Heading switch connected to the KFC 150.  This is usually the G500, or Aspen, or DAC 31.

Assuming you have one of the 3 converters, then the switch should be set to GPSS and Heading on the KFC 150 should be enabled.  GPSS is for LATERAL navigation only, no vertical navigation is provided.  If you have the G500 and GAD 43e, you can still preselect your altitude and rate of climb/descent while tracking the GPSS course.

As Paul mentioned, when flying an approach you select APPR mode once on the final approach course and the KFC 150 will change from Heading Mode to Approach Mode and follow both course deviation and vertical navigation just like an ILS approach.

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Most everything has been discussed above, but here is my summary:
For the GTN 750 to follow GPSS inputs you first need some sort of converter to convert the GPS output to a Heading that feeds a GPSS/Heading switch connected to the KFC 150.  This is usually the G500, or Aspen, or DAC 31.
Assuming you have one of the 3 converters, then the switch should be set to GPSS and Heading on the KFC 150 should be enabled.  GPSS is for LATERAL navigation only, no vertical navigation is provided.  If you have the G500 and GAD 43e, you can still preselect your altitude and rate of climb/descent while tracking the GPSS course.
As Paul mentioned, when flying an approach you select APPR mode once on the final approach course and the KFC 150 will change from Heading Mode to Approach Mode and follow both course deviation and vertical navigation just like an ILS approach.

I totally agree with Don, but I want to mention that that the Icarus SAM GPSS works the same way as the other GPSS converters mentioned. I really like the SAM unit which verbally announces entering and leaving GPSS mode. Flys intercepts better than I can hand fly them.


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I can confirm that with an Aspen GPSS, GTN and STEC 60-2, it works the same.

If I am being vectored, I will be in HDG mode on the STEC (and ALT if holding altitude). Once I engage GPSS the real magic happens. I can descend if needed by going into VS mode and re-engage ALT as needed while all of the lateral control is being managed by the GPSS.

Here is an LPV approach flown using GPSS.




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Here is a video I took tonight trying out a coupled LPV approach with a G500, GAD 43e, GTN 750, and a KFC 150 autopilot.  

After it captured the glideslope and started down I ended the video so I could fly the plane.

 

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I have a 430AW, Icarus SAM, and the KFC200, basically they are the same set up.  I have found that you have to switch to APPR mode before the FAF, if that helps.  I had the same symptom as you until I figured that out.  I did some research and consulted a couple of people who are experts on the King AP's.  I don't really recall all the detail, it has been awhile, but what I remember is this:  The KFC autopilots (the old ones, the 150 and 200s), were designed to fly an ILS using the heading bug to intersect the final approach course.  One puts the AP in APPR mode and the AP flies the course set in the bug until it intercepts the final approach course, where it couples to the course.  To do the intercept, it computes a rate of closure to the course.  If you are directly on what the AP views as the final approach course when you switch to APPR, it usually couples immediately.  If you are off the course a good distance it uses the closure algorithm, computes and executes an intercept.  But there is narrow window near but not directly on the course, where you are not precisely on the course and where the computer is unable to develop a rate of closure, and without that it does not recognize the final approach course.  It flies off on what it thinks is an intercept, and can be quite persistent about it.  Where there is a GPSS, the GPSS is fooling the AP into thinking the commands coming from the GPS are the heading bug setting. I think the GPSS exacerbates the issue.  I believe there is a variance between what the GPSS views as the final approach course, and what the AP views as being on the course, and if the GPSS believes it is on the course it does not attempt to close to the APs view of the final approach course, because it does not know what that is or that it even exists.  The difference between the two is not that great, there is only a narrow window where this happens but it can happen.   If you switch to APPR mode far enough before the FAF, this does not seem to happen.  If you wait until the FAF or close to the FAF, it can.  I usually switch a few miles before the FAF and just have not seen the problem for a few years now.  I encountered the problem when I first had the Icarus and 430 installed, which was several years ago now.

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On 4/19/2017 at 7:34 PM, blakealbers said:

What do you all like using for power settings in the approach


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I fly 25/24 while being vectored and once glide scope is centered gear down appr flaps only if coupled...My AP is an KFC 225 which is digital so it doesn't need the converter

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I use 24+ and whatever RPM's I have the plane set at when I come into the approach, usually 2450.  I have a 231.  I am more concerned about TAS than power setting.  I fly the approach to the FAF at 120.  The 24+ power setting means that most days, 24.5 will give me that speed, but in the winter it is probably in the 23's.  Whether its 24.5 or 24.3 I don't really care, it is too much messing around to get to that degree of accuracy in a 231.

At the FAF I want slow to 90 for the final approach (that's knots).  Gear down plus half flaps and a power setting of about 16 does it, but sometimes I need a lower power setting.  I use 90 because that matches the "B" groundspeed in the time table, so all I have to worry about is adjusting a little for headwinds or tailwinds to the TAS.  

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