Coupled ILS with GNS530 with S-TEC 60-2 and GPSS

[mtr84S]

I am having trouble with a coupled full procedure approach with a procedure turn/hold at the FAF. Basically here is what I see:
-Fly to IAF/FAF and conduct 1-turn course reversal with 530 on "GPS", 60-2 on "HDG and ALT" and GPSS "on". Fly's hold perfectly.
-Once at a good final approach course intercept at the cmpletion of the turn (just outside FAF), I convert to VLOC on 530 and hit the NAV button on the 60-2. Since I am so close to the FAF I hit the "ALT" button to manually arm GS intercept. All the proper annunciations on the 60-2 light-up.
-As I intercept the final approach course (albeit close to the FAF) the 60-2 fails to turn on-course and capture. In fact at that point the plane typically drives right through the final approach course and no decent is ever initiated.

I have successfully made the above work further outside the FAF and whith vectors to final (captures course and GS for both ILS and LPV) but the ILS where the hold course-reversal is right at the FAF has not worked.

Any advise?

 

[Checkout_my_Six]

select CDI....on the GNS? when performing GPS approaches?

I have a similar setup combo....but haven't done enough coupled approaches to be confident with the button-ology.

 

[flyingron]

select CDI....on the GNS? when performing GPS approaches?

The STEC will not fly vertical guideance in GPSS mode. You have to put it in normal chase-the-needle approach mode.

HDG+ALT will never intercept the approach. You want HDG+NAV together (that's HDG intercept of NAV course). You also want ALT or VS activated if you want it to capture the GS.

 

[iflyatiger]

I would agree with this.. Gpss will capture the glideslope but only on a rnav (gps) approach. When you hit the cdi to change to ils / loc mode then deselect gpss mode for the 60-2 to fly the ils.

The STEC will not fly vertical guideance in GPSS mode. You have to put it in normal chase-the-needle approach mode.

HDG+ALT will never intercept the approach. You want HDG+NAV together (that's HDG intercept of NAV course). You also want ALT or VS activated if you want it to capture the GS.

 

[wsuffa]

The STEC will not fly vertical guideance in GPSS mode. You have to put it in normal chase-the-needle approach mode.

HDG+ALT will never intercept the approach. You want HDG+NAV together (that's HDG intercept of NAV course). You also want ALT or VS activated if you want it to capture the GS.

I would agree with this.. Gpss will capture the glideslope but only on a rnav (gps) approach. When you hit the cdi to change to ils / loc mode then deselect gpss mode for the 60-2 to fly the ils.

Yep. One of the few shortcomings of the S-Tec 60 system... designed before there was GPSS.

 

[flyingron]

Yep. One of the few shortcomings of the S-Tec 60 system... designed before there was GPSS.

Even the 55X which has integrated GPSS won't do vertical guidance in GPSS mode.

 

[Checkout_my_Six]

Even the 55X which has integrated GPSS won't do vertical guidance in GPSS mode.

Was the OP in HDG- GPSS mode?.....I think not.

He was in NAV mode....with ALT hold.

I'm thinking the CDI is going to drive the STec in that mode.

 

[iflyatiger]

The 60-2 doesn't have built in gpss so you can be in any mode on it and still have gpss selected on the separate gpss button / annunciator.

Like this..

Was the OP in GPSS mode?.....I think not.

He was in NAV mode....with ALT hold.

I'm thinking the CDI is going to drive the STec in that mode.

 

[flyingron]

Was the OP in HDG- GPSS mode?.....I think not.

That's what he said.

He was in NAV mode....with ALT hold.

Then it would have eventually careened onto the course. My guess is was he was in HDG (without GPSS).

I'm thinking the CDI is going to drive the STec in that mode.

I have no idea what that means. However, it will NEVER capture the GS if you are not in NAV mode (HDG GPSS or not will not do it).

 

[flyingron]

In order for it to do GPSS the 60-2 controller must be in HDG mode and the GPSS unit must be punched in (GPSS). I suspect from his observation he was in HDG on the 60-2 and HDG on the GPSS unit. That's why it just flew through the course.

Again, the 60-2 will not capture the GS in HDG mode. It has to be in NAV with one of the vertical modes (ALT or VS) turned on.

 

[Checkout_my_Six]

keep reading Ron....he was in NAV mode....after he captured the approach.

CDI vs GPS .....button on the GPS.

 

[iflyatiger]

This is from the stec gpss manual

" Conduct all GPSS operations
with the autopilot in the HDG mode only. Selecting any lateral mode
besides HDG (NAV, APR, REV, etc.) will decouple the autopilot from
the GPSS function."

Maybe his gpss unit is not switching out of gpss mode automatically when he selects nav or hdg+nav on the 60-2..?

Or there is a chance that the OP forgot to press the cdi button on the garmin to change from gps navigation to vloc navigation?

 

[iflyatiger]

Ignore this.. Reread and OP says he hit the alt button when already in alt hold mode which should force the ap into gs capture.





And one more thing I remembered and looked up.. This from the 60-2 manual.

Intercepting and Coupling the Glideslope
To arm the automatic glideslope (GS) capture function, the following
conditions must be met:
1. NAV receiver must be tuned to the appropriate frequency.
2. The glideslope signal must be valid; no flag.
3. The autopilot must be in NAV/APR/ ALT modes.
4. The aircraft must be 60% or more below the GS centerline during
the approach to the intercept point, and within 50% needle deviation
of the localizer centerline at the point of intercept, usually the outer
marker.

Maybe he was at or above the glide slope when trying to intercept..

 

[mtr84S]

Thanks all for the feedback. Truth is I am clear it is not a GPSS issue as in my original post I turned this off and slectedd "VLOC" on the 530 and "NAV" on the 60-2 given it was an ILS I was trying to couple to. Also I know the GS arm needs special attention if < 60% below GS...which is why I hit the ALT button again (which should manually arm). I am relatively new to the avionics setup...so don't mean to sound like I know it all (in truth I have read a lot...and practiced a lot...but this one has stumpted me per the manuals and experience).

I did read (page 113 of the GNS 530W Manual) that "switching to VLOC late in the approach may not provide the AP enough time to respond and intercept the approach course prior to the FAF.....). Given this is a hold (in leui of PT) at the FAF....I am pretty much right at the FAF once intercepting the final approach course. I don't want to take the easy out...but maybe my issue is how close (<2nm) to the FAF when I am tryining to intercept?

As a reference...it is the KMOD ILS 28R approach I am referencing. I am 100+% happy to have someone point out my procedural issue (no embarassment points on my side).

Thank you all for your kind consideration. I actually joined the forum (having learned a lot from reading other threads) so I could ask this very question that was vexing me.

 

[MAKG1]

I fly that approach from time to time.

I find I'm always doing teardrop entries on that hold. That gives you an additional couple of miles to track the localizer before the FAF. A parallel entry would be problematic for the reasons you describe.

Note that the plate does not allow coupled approaches to proceed below 660 MSL. I suspect there is a reason for that….this may not be the best candidate for a coupled approach. It is very short, very low, and very close in.