STEC 60-2 and RNAV approaches - what am I doing wrong?

[JamesMooney]

There's a few threads on similar topics out there, but I don't think any have answered this question head-on, so I'm going to try it here. 

I'm having issues getting my STEC 60-2 to switch into APR mode when flying LNAV/LNAV-VNAV/LPV approaches. It worked a few months ago, but I think that was by sheer luck, and I'm struggling to figure out the correct sequence of steps.

My equipment:  STEC 60-2, GPSS (STEC ST 901), GNS430W, and a Bendix-King HSI

Here's an example approach (approach plate included) - the RNAV Rwy 04 at KSBY. I arrive east of the airport at 3k feet, and am given direct to FEYKO and fly the procedure turn (hold). In this scenario, here's the steps I've followed:

- GNS430W: select the RNAV Rwy 04 with FEYKO as the IF fix. Activate approach.

- Autopilot: GPSS is selected and HDG + ALT on. 

- The aircraft flies to FEYKO and executes a parallel entry, and flies the procedure turn perfectly.

- Autopilot: While on the procedure turn inbound, outside of FEYKO, flying a 45 degree intercept to join the inbound course before FEYKO, I select NAV mode. (This makes GPSS irrelevant.) I see the usual combination of CAP, CAP+SOFT, then SOFT only to indicate that it has received the course tracking information (the GNS430W telling the HSI it is a localizer).

- The aircraft intercepts the inbound and crosses FEYKO. Shortly after, the glideslope appears on my HSI. There are no flags or cautions on my HSI. Everything is live and functioning.

However, the autopilot continues to track inbound on NAV mode only. The APR light does not illuminate. As I approach the glideslope, it does not illuminate GS / does not capture the glideslope.

That's the problem I can't figure out. This used to work (I believe), but for some reason it will not engage APR mode when I am aligned to the inbound course.

Possible issues:

- I'm not following the right buttonology

- The GPS is switching to LPV (or LNAV, or LNAV-VNAV) mode too late (I've noticed sometimes it does not switch until after passing the IAF - it remains in TERM until then)

- Something has happened to the ILS Energizer wire that sends a dummy ILS (LOC+GS) signal from the GPS to the autopilot

Thoughts?

Thanks!

[JamesMooney]

@David Lloyd - what do you think of the scenario I present here? In your experience, why isn't the STEC activating APR mode? Given it is on NAV mode, the GPS is recognizing the approach ("activated'), and I'm within all the degrees/deflection parameters on the inbound course. Thoughts? Buttonology? Issue between GPS<>Autopilot?

[David Lloyd]

Buttonology sounds good.  APR should activate almost as soon as you switch to NAV.  The GS will never arm or capture unless APR is active.  Once APR is active, GS should arm in 10 seconds.  You can force GS to arm if you get a close-in turn as long as still below the slope, within half scale nav and APR is active by pressing ALT once if already lit, twice if not.  Yes, I suspect something else, is the wire, 530 or Stec?  

Will the GS arm flying an ILS?

And oddly enough, several posts in the last week here and Beechtalk regarding Stec (various) not capturing a glideslope.  Is it because of new equipment and people have a renewed interest in a coupled approach or something else?

[carusoam]

Let’s bring @midlifeflyer along for the discussion…

Best regards,

-a-

[midlifeflyer]

9 hours ago, carusoam said:

Let’s bring @midlifeflyer along for the discussion…

Best regards,

-a-

LOL! I appreciate the confidence but I really don't know every GPS/AP combination. I might be able to figure it out but I'd have to see it happening. Only  WAG (assuming nothing broken) is APs have a sweet spot for capturing the glideslope/path and it's getting missed. 

 

18 hours ago, FlyingCanuck said:

The GPS is switching to LPV (or LNAV, or LNAV-VNAV) mode too late (I've noticed sometimes it does not switch until after passing the IAF - it remains in TERM until then)

That's normal. It should not switch from TERM until the FAF becomes the active waypoint.

If you want to try an experiment, do the HILO for the full 4 nm. Once you intercept inbound  activate either the FEYKO-EDITH leg or VTF. Either will make EDITH the active waypoint which should put you in LPV mode with the glidepath well above you. Try switching to APR and see what happens.

[carusoam]

Thanks Mark!

I always appreciate your input!

Best regards,

-a-

[Marauder]

On 10/31/2021 at 1:11 PM, FlyingCanuck said:

There's a few threads on similar topics out there, but I don't think any have answered this question head-on, so I'm going to try it here. 

I'm having issues getting my STEC 60-2 to switch into APR mode when flying LNAV/LNAV-VNAV/LPV approaches. It worked a few months ago, but I think that was by sheer luck, and I'm struggling to figure out the correct sequence of steps.

My equipment:  STEC 60-2, GPSS (STEC ST 901), GNS430W, and a Bendix-King HSI

Here's an example approach (approach plate included) - the RNAV Rwy 04 at KSBY. I arrive east of the airport at 3k feet, and am given direct to FEYKO and fly the procedure turn (hold). In this scenario, here's the steps I've followed:

- GNS430W: select the RNAV Rwy 04 with FEYKO as the IF fix. Activate approach.

- Autopilot: GPSS is selected and HDG + ALT on. 

- The aircraft flies to FEYKO and executes a parallel entry, and flies the procedure turn perfectly.

- Autopilot: While on the procedure turn inbound, outside of FEYKO, flying a 45 degree intercept to join the inbound course before FEYKO, I select NAV mode. (This makes GPSS irrelevant.) I see the usual combination of CAP, CAP+SOFT, then SOFT only to indicate that it has received the course tracking information (the GNS430W telling the HSI it is a localizer).

- The aircraft intercepts the inbound and crosses FEYKO. Shortly after, the glideslope appears on my HSI. There are no flags or cautions on my HSI. Everything is live and functioning.

However, the autopilot continues to track inbound on NAV mode only. The APR light does not illuminate. As I approach the glideslope, it does not illuminate GS / does not capture the glideslope.

That's the problem I can't figure out. This used to work (I believe), but for some reason it will not engage APR mode when I am aligned to the inbound course.

Possible issues:

- I'm not following the right buttonology

- The GPS is switching to LPV (or LNAV, or LNAV-VNAV) mode too late (I've noticed sometimes it does not switch until after passing the IAF - it remains in TERM until then)

- Something has happened to the ILS Energizer wire that sends a dummy ILS (LOC+GS) signal from the GPS to the autopilot

Thoughts?

Thanks!

I'm in a meeting and will look at your post closer when I get a minute. Just an initial thought is that you are trying to enter the approach mode too far out. I think you need to be within 3 miles of the FAF before you activate the APR mode. I'll look at it closer when I get a minute.

[JamesMooney]

Thanks @Marauder. Remember that with the STEC 60-2, there's no dedicated APR mode button. When in NAV mode, the APR mode automatically activates (at some mystery point, it seems)... This is part of the confusion... Appreciate your thoughts!

[Marauder]

21 minutes ago, FlyingCanuck said:

Thanks @Marauder. Remember that with the STEC 60-2, there's no dedicated APR mode button. When in NAV mode, the APR mode automatically activates (at some mystery point, it seems)... This is part of the confusion... Appreciate your thoughts!

This might help. An RNAV approach I shot a few years ago with my autopilot. Does your HSI's course need to be set to the inbound course? My Aspens have an autocourse capability so it is automatically set to the inbound course. 

 

[David Lloyd]

In the video a couple key things:  everything lined up, as soon as the Stec is switched from HDG to NAV, APR annunciates.  Count 'em off, 10 seconds the GS arms.  Crossing the FAF the GS centers and is captured, ALT goes out.  Nice video.

[JamesMooney]

One thing that's interesting. You stayed on HDG mode until much closer to the FAF than I normally do. I would have switched to NAV mode earlier, just before the IF/IAF and once I was set up inbound from the procedure turn. 

My HSI (course and heading bug) were pointed on the inbound course when I was having issues, so that wasn't it...

[midlifeflyer]

43 minutes ago, Marauder said:

This might help. An RNAV approach I shot a few years ago with my autopilot. Does your HSI's course need to be set to the inbound course? My Aspens have an autocourse capability so it is automatically set to the inbound course. 

 

That's a great point. Some  setups auto-slew the course needle and others require you to manually set it. And it reminds me of another possibility. While some APs do the HDG-NAV combo where it maintains the bugged intercept heading and automatically switches to NAV on intercept, others require you to turn the heading bug to match the course. I took a quick look at a manual online and it looks like that's the way the STEC 60 series does it - HDG bug all the way onto the FAC before switching to NAV.  

(It's an issue for my flying club. We have two Diamonds G1000s, one with GFC700, the other a KAP 140. Gotta do similar gyrations with the KAP)

Edited November 3, 2021 by midlifeflyer

[David Lloyd]

2 hours ago, midlifeflyer said:

That's a great point. Some  setups auto-slew the course needle and others require you to manually set it. And it reminds me of another possibility. While some APs do the HDG-NAV combo where it maintains the bugged intercept heading and automatically switches to NAV on intercept, others require you to turn the heading bug to match the course. I took a quick look at a manual online and it looks like that's the way the STEC 60 series does it - HDG bug all the way onto the FAC before switching to NAV.  

(It's an issue for my flying club. We have two Diamonds G1000s, one with GFC700, the other a KAP 140. Gotta do similar gyrations with the KAP)

I have done both ways with my 60-2.  Using the heading bug at first initially until turning to intercept the FAC, then pushing HDG and NAV it will follow heading (and GPSS) until the deviation indicator centers.  It will then sequence to NAV and APR.  It might be a little tricky, if flying a T shaped LPV, out at the end of the T needle is centered, not certain if it will sequence properly.  Usually I just use HDG until I want NAV.

With auto-slew, I'm spoiled.  I have forgotten on an ILS the 275 does not auto-slew.  Do I have a 100 knot cross wind?  Why am I tracking the localizer with 45 degrees of correction?  Doh! 

[JamesMooney]

@David Lloyd someone posted on the Beech forum with a similar process (HDG+NAV when on vectors; HDG then NAV when flying the whole approach with own navigation). Seems like thats the way the STEC 60-2 likes it, whether on an RNAV/GPS or ILS approach.

Question for you - do you know how far into the approach environment you normally are when you switch from HDG to NAV? Are you inside the IAF/IF? Or still outside (albeit directionally on the final approach course)? I'm wondering if that distance from FAF has something to do with when the 60-2 will pick up the APR signal (rather than just a NAV signal) from GPS. Maybe there's a too far / too close issue...

[David Lloyd]

I typically use HDG until on final approach course outside the fix.  Have some notes here from recent approaches at KAFP and KCQW.  KAFP LPV16 used heading to intercept the final approach course. 2.5 miles outside JORGA (IAF/IF) got APR, 10 seconds later GS.  KCQW LPV28 used GPSS/HDG to ZEDPI (IAF) then until in the turn to final approach course at IYPET (IF) punched the HDG & NAV buttons and right away HDG dropped, APR lit.  10 seconds later GS.  

Have you tried an ILS to see if the APR lights?  Fewer electronic hurdles to clear with the old-fashioned ILS.  

[Marauder]

I think your issue is either timing or the plane is not in the correct position when you push the Nav button to enter approach mode. The 60-2 manual hasn’t been updated for a while. And certainly not for some of the features like GPSS.

You need to have a glide slope signal and be within 50% of the centerline in order for the approach mode to activate. If you look at my video (~6:00 in) when I push the nav button, I have a glide slope indicator and I am on the centerline on the Aspen. It won’t activate automatically unless the glide slope is present and you are a certain position relative to the glide slope and centerline.



Another thing to look for is whether it truly couples or not. When you reach the FAF, the “APR” light extinguishes to signify that it is following the glide slope (6:05 in on the video).

If you don’t meet the coupling parameters, you can force it by doing the following:



As David pointed out, you can dual press the Nav/HDG buttons to have the AP follow your heading bug until it picks up the approach signal. I have used this a few times but never with an RNAV approach. It works great if you are being vectored for an ILS. I think it should work the same for an RNAV but I don’t think you can be in GPSS mode.

Hope this helps.


Sent from my iPad using Tapatalk Pro

[JamesMooney]

Update: went flying yesterday, did 6 approaches. The APR mode problem with RNAV approaches persists.

The ILS approach worked perfectly. HDG+NAV while on vectors to intercept the localizer. Near the LOC, the HDG light went out, and the autopilot began to intercept the LOC. Once established inbound, the APR light came on, and shortly after, the GS light. The autopilot flew the approach down to minimums in a 15 knot crosswind flawlessly.

However, the GPS approaches still will not work. The autopilot will not activate APR mode (remember: the STEC 60 does not have an APR button like the KFCs or STEC 55. Instead, you arm NAV mode, and it automatically activates APR mode when the AP receives a localizer signal, or a dummy localizer signal from the GPS in the case of RNAV approaches). 

I tried 4 RNAVs. Entered the approach at different points. Switched from GPSS/HDG to NAV mode at different points. There were no flags or issues with altitude relative to GS or deflection of localizer. Everything was centered. The STEC 60-2 just did not want to pick up the APR signal.

I'm wondering if the wiring between the AP and the GPS is wrong. There's another forum (https://www.pilotsofamerica.com/community/threads/s-tec-60-2-w-gpss-and-lpv-approaches.39267/) on this, where they pointed out:

"The wiring error possibility is that the wrong signal was interconnected to the autopilot. The autopilot has an input named "ILS Energize" and the 530W has an output of the same name on P5006 - pin 29. If these two pins are interconnected, you will be able to track an ILS GS but not a LPV GP. The correct 530W signal to wire to the autopilot is "ILS/GPS Approach" P5001 - pin 14. "

[David Lloyd]

ILS but not LPV.  Sounds like pilotsofamerica.com has it nailed. A trip to the shop is in order.  

Going over to the link you had has given me a clue to check for my problem.  Intermittent GS/GS capture on some LPV approaches.  Seems like every problem is at an airport where I have the KX165 tuned to the ILS frequency.  That may be interfering with the GS energize in the GI275.  I will know that answer tomorrow.  Might be grasping at straws but do have another trip to a radio shop Tuesday scheduled to try to decode what's going on.

[JamesMooney]

Update: Diagnosed!

Turns out the wiring is incorrect - as suspected in the thread above.

But along the way, I learned about a work-around for this problem. If the NAV radio in the GNS430 is programmed with any ILS frequency (whether it is active or not - could be an ILS frequency on the other side of the country!), then it will fool the GNS430W into sending a 'ground' signal via the wiring. This will allow the STEC 60-2 to activate the APR mode.

My options now are ~8 hours of labour to fix the wiring, or remember to always have a 'dummy' ILS frequency set in the NAV radio whenever flying GPS approaches.

I tried this out and it worked successfully on ~6 approaches, including at airports without any ILS facility and with an ILS frequency corresponding to an airport that was hundreds of miles away. (In my particular case, I had programmed the ILS Rwy 8 at CYTZ, freq 110.15, into my 430W. For three weeks after, it remained the nav freq in my GNS430 - and that's what enabled the STEC 60-2 to interpret RNAV approaches as an approach, and to activate APR mode)

[vorlon1]

On 12/6/2021 at 10:39 AM, FlyingCanuck said:

If the NAV radio in the GNS430 is programmed with any ILS frequency (whether it is active or not - could be an ILS frequency on the other side of the country!), then it will fool the GNS430W into sending a 'ground' signal via the wiring. This will allow the STEC 60-2 to activate the APR mode.

Question: Does the GTN 650/750 function in the same way?

[JamesMooney]

I'm not sure - depends on the wiring.

For the GNS430W, there are two output options to wire it to the STEC 60-2 to achieve Approach functionality - pin 29 or pin 14. I quoted that in the thread earlier: "The wiring error possibility is that the wrong signal was interconnected to the autopilot. The autopilot has an input named "ILS Energize" and the 530W has an output of the same name on P5006 - pin 29. If these two pins are interconnected, you will be able to track an ILS GS but not a LPV GP. The correct 530W signal to wire to the autopilot is "ILS/GPS Approach" P5001 - pin 14.

If the GTN series have the same wiring (an ILS Energize pin and an ILS/GPS Approach pin), then the issue could be the same - and presumably the work-around will also work (of putting any ILS frequency in the NAV radio of the GTN).

I'd say it depends firstly on whether the wiring out of the GTN is the same as out of the GNS series. My hunch is yes.

[Marauder]

On 12/6/2021 at 10:39 AM, FlyingCanuck said:

Update: Diagnosed!

Turns out the wiring is incorrect - as suspected in the thread above.

But along the way, I learned about a work-around for this problem. If the NAV radio in the GNS430 is programmed with any ILS frequency (whether it is active or not - could be an ILS frequency on the other side of the country!), then it will fool the GNS430W into sending a 'ground' signal via the wiring. This will allow the STEC 60-2 to activate the APR mode.

My options now are ~8 hours of labour to fix the wiring, or remember to always have a 'dummy' ILS frequency set in the NAV radio whenever flying GPS approaches.

I tried this out and it worked successfully on ~6 approaches, including at airports without any ILS facility and with an ILS frequency corresponding to an airport that was hundreds of miles away. (In my particular case, I had programmed the ILS Rwy 8 at CYTZ, freq 110.15, into my 430W. For three weeks after, it remained the nav freq in my GNS430 - and that's what enabled the STEC 60-2 to interpret RNAV approaches as an approach, and to activate APR mode)

It's good to hear you were able to find a cause. What confused me was you saying that out of sheer luck it worked a few months back. I would definitely get the wiring sorted out. You don't want an additional step in your AP setup, especially if you are dealing with high workload on an approach.

[JamesMooney]

7 hours ago, Marauder said:

It's good to hear you were able to find a cause. What confused me was you saying that out of sheer luck it worked a few months back. I would definitely get the wiring sorted out. You don't want an additional step in your AP setup, especially if you are dealing with high workload on an approach.

Ya, I think the 'sheer luck' was that I probably had an ILS freq in the NAV#1 freq window.

At the moment I'm not really treating it as a safety issue. The GNS430W reads the approach correctly, and my HSI receives all the right signals. The only thing that isn't working (without this work-around or the wiring being fixed) is arming the autopilot APR mode. If that happens on an approach, I'll know why now. I'm going to add it to my approach checklist (I'm a checklist-oriented pilot).

For now, its 1amu+ to fix. I think I'm going to wait until either annual or my next avionics upgrade to do this.