Approaches with STEC 30+ Aspen PFD+GTN 650

[DXB]

I have an STEC 30 coupled to a GTN 650 and an Aspen pfd.  I realize the STEC 30 alone can't do intercepts for approaches but can track a VOR or localizer signal in trk-lo or trk-hi mode.  I also understand that having GPSS via the Aspen allows the STEC to use GTN 650 data to intercept.  I'm trying to figure out how to make the most of this setup during training and  real world IFR flying.   After poring through the STEC 30 and Aspen manuals, I'm left with two unanswered questions:

1.  After intercepting an LPV final approach course, the STEC manual says to use trk-hi mode to follow the course.  But if I use GPSS to intercept, why not just leave it in heading mode with GPSS? In the real world, I imagine one would even prefer to use GPSS to fly an ILS approach after switching the nav signal display to the ILS?  The STEC 30 autopilot's ability to track the localizer directly in trk-hi sounds more finicky than heading mode with GPSS.

2.  What am I left with if the Aspen fails?  This failure will likely be simulated on the check ride.  Obviously GPSS function and flying in heading mode will be gone.  But will the STEC 30 still be able to track a VOR or localizer in trk-lo or trk-hi mode based on the NAV signal from my GTN 650 or SL30?  I suspect not, but couldn't figure this out definitively from the manuals.  I'd like to have some clue what the answer should be before I try it.

[Marauder]

I have an STEC 30 coupled to a GTN 650 and an Aspen pfd.  I realize the STEC 30 alone can't do intercepts for approaches but can track a VOR or localizer signal in trk-lo or trk-hi mode.  I also understand that having GPSS via the Aspen allows the STEC to use GTN 650 data to intercept.  I'm trying to figure out how to make the most of this setup during training and  real world IFR flying.   After poring through the STEC 30 and Aspen manuals, I'm left with two unanswered questions:
1.  After intercepting an LPV final approach course, the STEC manual says to use trk-hi mode to follow the course.  But if I use GPSS to intercept, why not just leave it in heading mode with GPSS? In the real world, I imagine one would even prefer to use GPSS to fly an ILS approach after switching the nav signal display to the ILS?  The STEC 30 autopilot's ability to track the localizer directly in trk-hi sounds more finicky than heading mode with GPSS.
2.  What am I left with if the Aspen fails?  This failure will likely be simulated on the check ride.  Obviously GPSS function and flying in heading mode will be gone.  But will the STEC 30 still be able to track a VOR or localizer in trk-lo or trk-hi mode based on the NAV signal from my GTN 650 or SL30?  I suspect not, but couldn't figure this out definitively from the manuals.  I'd like to have some clue what the answer should be before I try it.

Dev - if I am flying an LPV approach, I would have the unit in heading mode and the Aspen GPSS flying the approach. I have altitude hold and automatic electric trim, so all I would do is switch from HDG to NAV on the STEC on the leg to the FAF. I have a 60-2 so your “approach” mode may be labeled different. If you don’t have the ability to fly a fully coupled approach (vertical), then once you go to “approach” mode, you would need to make the altitude adjustments by following the Aspen’s vertical course indicator.

For the second scenario, if you lost the Aspen, you would lose GPSS and heading mode (flying with the Aspen’s heading bug). The Aspen default mode during a failure is wing’s level.

The STEC manual was written during the dark ages. My 60-2 doesn’t even mention GPSS. I would go out and simulate the failures and see what it does or doesn’t do.


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[Marauder]

Also to add on to my first response, if I am flying an ILS, I would be using GPSS to fly any procedure turn and then when the unit switches to VLOC automatically, I hit the “NAV” button to put it into approach mode.

Same goes for the VOR approach except I would manually switch it to VLOC.


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[MIm20c]

I have a similar setup 430w/stec 50 and I use the gpss for the AP approaches. The 50, similar to the 30, will not couple vertically to the approach so I don’t see a reason to change it. IMO the stec AP’s are not the most precise and I feel the gpss is more consistent giving the AP the best input data available. 

You can switch the garmin to the vloc mode and still have the Aspen gpss output running in the background feeding the AP through the heading input.  

[DXB]

16 hours ago, Marauder said:

Also to add on to my first response, if I am flying an ILS, I would be using GPSS to fly any procedure turn and then when the unit switches to VLOC automatically, I hit the “NAV” button to put it into approach mode.

 

11 hours ago, MIm20c said:

You can switch the garmin to the vloc mode and still have the Aspen gpss output running in the background feeding the AP through the heading input.  

Thanks y'all  -  I gleaned similar info from my reading but was a little hesitant to try out without confirmation. I have no true "approach mode" - just TRK-hi mode, which can follow a localizer or GPS signal but will not intercept.  By contrast, having GPSS makes my basic STEC-30 autopilot much more capable, but the process of using it for approaches with an Aspen is not well delineated in the documentation - hence the need for this thread.  I think Mlm20c's setup is very similar.  I'm guessing the real world process for getting vectored to final for an ILS would be something like this:

1. Fly assigned vectors using the heading bug with the STEC-30 in heading mode.  Make sure the approach is activated in the Garmin. The Garmin NAV radio should be set to the localizer.  I guess the Aspen could set to GPS or VLOC - I"m not sure it matters? Alternately it could just stay in GPSS the whole time until the MAP if flying a full approach.

2.  When told to join the localizer from an assigned heading, is it ok to just hit GPSS on the Aspen or should I wait until within a certain distance of the localizer course?  When intercepting the localizer course, do the Garmin and the Aspen BOTH switch to VLOC automatically?   

3. The ILS CDI and glideslope should now be displayed on the Aspen.  However,  I would leave GPSS engaged and the STEC in HDG mode, allowing the autopilot to fly the localizer based on GPS.  Alternately I could turn GPSS off and switch the STEC to TRK-hi mode to allow it to follow the NAV signal directly, but I see no reason to do this.

An LPV approach seems to hold the advantage of less button pushing and risk of configuration error over an ILS. Both the Garmin and Aspen stay in GPS mode the whole time.  The GPSS button is pressed to intercept the final approach course, like in my ILS example.  The STEC manual however suggests switching from heading to Trk-hi mode after intercepting, which can follow the GPS signal for the final approach course - but again I fail to see the advantage.  The disadvantage is more button pushing while going missed.   I likely have misconceptions at my rudimentary stage of learning, so any further input is appreciated.

[Marauder]

4 minutes ago, DXB said:

 

Thanks y'all  -  I gleaned similar info from my reading but was a little hesitant to try out without confirmation. I have no true "approach mode" - just TRK-hi mode, which can follow a localizer or GPS signal but will not intercept.  By contrast, having GPSS makes my basic STEC-30 autopilot much more capable, but the process of using it for approaches with an Aspen is not well delineated in the documentation - hence the need for this thread.  I think Mlm20c's setup is very similar.  I'm guessing the real world process for getting vectored to final for an ILS would be something like this:

1. Fly assigned vectors using the heading bug with the STEC-30 in heading mode.  Make sure the approach is activated in the Garmin. The Garmin NAV radio should be set to the localizer.  I guess the Aspen could set to GPS or VLOC - I"m not sure it matters? Alternately it could just stay in GPSS the whole time until the MAP if flying a full approach.

2.  When told to join the localizer from an assigned heading, is it ok to just hit GPSS on the Aspen or should I wait until within a certain distance of the localizer course?  When intercepting the localizer course, do the Garmin and the Aspen BOTH switch to VLOC automatically?   

3. The ILS CDI and glideslope should now be displayed on the Aspen.  However,  I would leave GPSS engaged and the STEC in HDG mode, allowing the autopilot to fly the localizer based on GPS.  Alternately I could turn GPSS off and switch the STEC to TRK-hi mode to allow it to follow the NAV signal directly, but I see no reason to do this.

An LPV approach seems to hold the advantage of less button pushing and risk of configuration error over an ILS. Both the Garmin and Aspen stay in GPS mode the whole time.  The GPSS button is pressed to intercept the final approach course, like in my ILS example.  The STEC manual however suggests switching from heading to Trk-hi mode after intercepting, which can follow the GPS signal for the final approach course - but again I fail to see the advantage.  The disadvantage is more button pushing while going missed.   I likely have misconceptions at my rudimentary stage of learning, so any further input is appreciated.

1. GPSS is a GPS only function. Flying an ILS, the Garmin GTN will have the GPS overlay including the entire procedure loaded. It is just not legal for you to fly the ILS with the GPS. On an ILS, if you have the option set in the GTN, the GTN will convert to VLOC when certain conditions are met (distance to the FAF). These are described in your GTN manual. I would load the ILS approach, have the autopilot in HDG mode, the Aspen in GPSS mode. For GPSS to fly the full procedure, you would select an IAF.  The autopilot will fly to the IAF and follow the procedure. Once inside the "conversion" area for the VLOC change, the GTN would switch to VLOC and the GPSS is abandoned. The Aspen cannot be changed to "VLOC" mode. When the GTN changes it to VLOC, the Aspen will now show that as the Nav source.

2. If you are told to join the localizer, then the assumption is you are on a heading provided by the controller to allow you to intercept. There are two schools of thought on how to set up the approach. If you select Vectors to Final, all of the waypoints are removed and if you are by chance told to fly to a waypoint (like an IAF or IF) you will be scrambling to load it. If you load the full approach, you can follow the vectors and when on the localizer headed towards the FAF, your sequencing will continue. If you are using the autopilot, you would be in HDG mode and the GPSS is off. You fly the heading provided by ATC, when intercepting the localizer, the GTN will switch to VLOC. 

3. When your GTN switches to VLOC, all of the GPS/GPSS stuff is ignored. your autopilot will be flying a heading and you should activate the "approach" mode on your autopilot. Sorry -- I am not that familiar with the 30 to say what buttons to push.

As for the STEC, on my 60-2, putting the unit in "approach" mode changes how the autopilot reacts to the nav signal. You don't want the autopilot to chase a bunch of signal deviations. My unit goes into a "soft" mode. At around 8:00 in this video, you can see the autopilot in HDG mode (GPSS off) where I am intercepting the final approach course for the LPV at KMQS. Once I get close to the final approach course, I active the approach mode on the autopilot and you will see the unit in approach mode.

 

[TWinter]

Wow..Can't believe this question has come up..and so timely. I too have been trying to figure out the same scenario. I've looked at every Youtube video, re-watched my Aspen training CD, re-read the STec 30 manual several times and even went back through the GTN 750 videos and guides. Finally after exhausting all those resources I asked my avionics shop last week what was I was doing wrong. When I was trying to set up for the approaches I was leaving it set on GPSS mode. Problem was over flying the fixes and usually ended up parallel to where I expected the pick up the GS.

Long story short.. My shop explained it as Chris and others have. I continue with GPSS until getting close to fix points or the GS. Then we go from GPSS mode on the STec 30 to heading bug mode, or Hi/Lo track and make adjustment from there to intercept.

I've spent gallons upon gallons of Avgas trying to figure out why we kept missing the fixes. I have not tried it yet since the weather had been poor, but at least we have the answers or at least steered in the right direction. Great question.. Glad I was not the only trying to understand the proper sequence.

 

-Tom

[MIm20c]

1 hour ago, Marauder said:

1. GPSS is a GPS only function. Flying an ILS, the Garmin GTN will have the GPS overlay including the entire procedure loaded. It is just not legal for you to fly the ILS with the GPS. 

......

3. When your GTN switches to VLOC, all of the GPS/GPSS stuff is ignored. your autopilot will be flying a heading and you should activate the "approach" mode on your autopilot. Sorry -- I am not that familiar with the 30 to say what buttons to push.

To be honest most of my flying has been without the AP as I train for my IR.  However, I think all of the gpss output information from the gtn/gns is still available to the Aspen. I think it would be legal to use the gpss steering from the ILS gps overlay if you have the Garmin in vloc mode and it is referenced on the aspen display. If there was a discrepancy you would need to disengage the AP and follow the ILS signal. 

The nice thing about this is you can use the heading bug until cleared for the approach at which time you could push the gpss button on the aspen. The Garmin would already be in the vloc mode. 

I need to do some more testing but my initial impression was the stec did a better job with the gpss signal. 

[carusoam]

Interesting.....

For comparison....

I get a few points from this discussion....

1) Using The AP during training for the IR... doesn't happen as often as expected.  I never got to use the AP in the school plane...

2) APs are imperfect like process controllers...  they are old computers at best... slow to react, with a touch of over controlling...

3) With APs, you get to choose from two modes.

• Tight accuracy and a more choppy ride...
• Smoother ride, but less accuracy...

On final approach, most people would choose the tighter accuracy and forego the ride comfort...

What counts in IMC is being closest to the magenta line/ILS.  Measured in feet on short final...

3) You May want to look up what the difference in accuracy is for trk hi and trk lo are... got the book?

4) On the KAP150 the accuracy vs comfort discussion is hidden by a button marked 'apch'...

You don't have to remember or debate the details... you are on an approach, so use the apch mode, It is the highest accuracy.   

5) Accuracy and jerkiness are typical of process control provided by small, old, slow, computer processors.  They just don’t have the computing power to process the data fine enough to provide a smooth and accurate flight path.

Hope this supplies the why this happens...  make sure you are using the highest accuracy you can get from your system...

Some GPSS systems may provide enough data points that will cover for the APs computing weakness.  It may provide enough points close enough together that the jerkiness is tiny...

Then test all the failure modes in VMC before going in IMC...

PP thoughts only. Not a computer specialist or CFI...

Best regards,

-a-

[DXB]

6 hours ago, Marauder said:

1. GPSS is a GPS only function. Flying an ILS, the Garmin GTN will have the GPS overlay including the entire procedure loaded. It is just not legal for you to fly the ILS with the GPS. On an ILS, if you have the option set in the GTN, the GTN will convert to VLOC when certain conditions are met (distance to the FAF). These are described in your GTN manual. I would load the ILS approach, have the autopilot in HDG mode, the Aspen in GPSS mode. For GPSS to fly the full procedure, you would select an IAF.  The autopilot will fly to the IAF and follow the procedure. Once inside the "conversion" area for the VLOC change, the GTN would switch to VLOC and the GPSS is abandoned. The Aspen cannot be changed to "VLOC" mode. When the GTN changes it to VLOC, the Aspen will now show that as the Nav source.

 

4 hours ago, TWinter said:

When I was trying to set up for the approaches I was leaving it set on GPSS mode. Problem was over flying the fixes and usually ended up parallel to where I expected the pick up the GS.

 

3 hours ago, MIm20c said:

The nice thing about this is you can use the heading bug until cleared for the approach at which time you could push the gpss button on the aspen. The Garmin would already be in the vloc mode. 

I need to do some more testing but my initial impression was the stec did a better job with the gpss signal. 

I'm surprised to hear it may be illegal to let the autopilot track the GPS overlay of the localizer on  an ILS approach even if one is displaying the CDI and glideslope derived from the real nav signals to confirm positional accuracy. But my grasp of this issue is admittedly rudimentary, and I will have to dig further.  My reading on GPSS in the Aspen PFD manual does seem to indicate that the autopilot can still use that function based on GPS even if the HSI is set to VLOC and displaying the CDI from the Nav signal.  This notion seems consistent with Mlm20c's experience.  I thought the beauty of adding GPSS to the STEC-30 was that it could capture any GPS course like a champ.  This has certainly been my experience in using it for vfr flying. So I don't know why it wouldn't do the same for the GPS overlay for an ILS - yet Tom's experience would indicate otherwise. Regardless, I appreciate all the input. It will be great fodder for discussion with my  instructor tomorrow.  He's a very experienced individual, but not so much with my particular setup, so we are trying to learn it together.

[MIm20c]

Please report back with his recommendation. It’s a tough call with the ILS/loc as they have very tight tolerances.  The approach phase is one area the BK AP’s have a leg up vs the stec. I hope the new generations of AP’s are even better. 

[TWinter]

So in simple terms. We will fly the approach and procedure turns with the Aspen in GPSS. At the IAP since we don't have a "approach mode" on the Stec30 we go to Track Hi or Track Low. I would also think you could leave it set on heading and use the heading bug on the inbound course and adjust if necessary? The Hi mode is supposed to be the preferred setting for ILS and Track Low preferred for VOR.

Keep us "me' posted on the results.

-Tom

[Marauder]

2 hours ago, DXB said:

I'm surprised to hear it may be illegal to let the autopilot track the GPS overlay of the localizer on  an ILS approach even if one is displaying the CDI and glideslope derived from the real nav signals to confirm positional accuracy. But my grasp of this issue is admittedly rudimentary, and I will have to dig further.  My reading on GPSS in the Aspen PFD manual does seem to indicate that the autopilot can still use that function based on GPS even if the HSI is set to VLOC and displaying the CDI from the Nav signal.  This notion seems consistent with Mlm20c's experience.  I thought the beauty of adding GPSS to the STEC-30 was that it could capture any GPS course like a champ.  This has certainly been my experience in using it for vfr flying. So I don't know why it wouldn't do the same for the GPS overlay for an ILS - yet Tom's experience would indicate otherwise. Regardless, I appreciate all the input. It will be great fodder for discussion with my  instructor tomorrow.  He's a very experienced individual, but not so much with my particular setup, so we are trying to learn it together.

 

There is a difference between using it as guidance and flying it as the Nav source. Good example is my home airport N57. The VOR 24 approach is based on the Modena VORTAC. There is no GPS approach but there is an overlay from the GPS depicting the VOR approach. It is illegal to fly this approach based on the GPS overlay. In other words, I can’t legally leave the GPS in GPS mode and fly the approach without the VOR being the primary source of Nav information.

Nothing wrong to use the GPS overlay as additional information for the approach.

I wouldn’t try to fly the approach using the autopilot in GPS mode and monitoring the ILS on a checkride.


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[MIm20c]

9 minutes ago, Marauder said:

I wouldn’t try to fly the approach using the autopilot in GPS mode and monitoring the ILS on a check ride 

 

+1

[Cruiser]

A couple of clarifications...as I understand them.......

GPSS is a function of the gps signal and computer wizardry. 

Track lo and track hi are pre gps functions of sensitivity to course errors

I don't know the accuracy off the top of my head but for comparative purposes GPSS will be better

The GPSS uses gps signal and your flight plane to look AHEAD and correct your heading based on what correction is needed to STAY on course

With GPSS off the navigation becomes based on what has ALREADY happened and the correction becomes what is needed to get BACK ON course

[Stanton R]

As far as GPS approaches go, leave it in GPS steer. The Stec manual assumes that you don't have GPS steering and the only way to track the approach would be changing to trk mode. You will be much closer to being on course using GPS steering, especially with a cross win.