Garmin GNS530W, LOC BC Approach Messageor

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rhscholz

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When a LOC BC (BACKCOURSE) approach is loaded in my Garmin GNS530W and the course has not been selected yet in the HSI, I get the usual Garmin message "SET COURSE TO xxx deg", where xxx is the BACK COURSE.

I have raised this issue to Garmin to say they need the fix the algorithm in these units so that the message directs the pilot to set the FRONT COURSE when a LOC BC approach has been loaded.
Garmin responded by e-mail that this was due to having selected a "GPS approach" which doesn't make any sense since the only choice is to load the LOC BC approach from the Jeppesen data base.

Has anybody noticed this problem and found a remedy for it ?
 
When you load a LOC/BC approach, what's driving your CDI? The GPS or the LOC signal?

I know that quite a few operators fly a LOC/BC with the GPS driving the autopilot and flight director while monitoring the raw loc data on another CDI.

So, depending on whether you're in VOR/LOC or GPS mode on your CDI, the message could be correct.
 
When you select VLOC (as you must before crossing the FAF of a SIAP using a localizer for lateral guidance on the final segment), the message will go away. Until then, with GPS selected for CDI, you really do want the reverse course set on the OBS anyway, since the needle will be giving normal steering. Only when you punch the CDI button to shift to VLOC will you start getting "backwards" steering, and then a) you really do want the OBS twisted to the forward direction so you can look at the bottom of the CDI for headings to fly, and b) the message will go away. This is equally true any time you're flying the localizer backwards, whether it be inbound on the back course or outbound on the front course (say, for a PT for a front course approach or straight out on the missed for a BC approach).
 
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Ron Levy said:
When you select VLOC (as you must before crossing the FAF of a SIAP using a localizer for lateral guidance on the final segment), the message will go away. Until then, with GPS selected for CDI, you really do want the reverse course set on the OBS anyway, since the needle will be giving normal steering. Only when you punch the CDI button to shift to VLOC will you start getting "backwards" steering, and then a) you really do want the OBS twisted to the forward direction so you can look at the bottom of the CDI for headings to fly, and b) the message will go away. This is equally true any time you're flying the localizer backwards, whether it be inbound on the back course or outbound on the front course (say, for a PT for a front course approach or straight out on the missed for a BC approach).
Click to expand...

Ron, as I said I know (by having read their manuals) that more than 1 part 121 operator will load the BC approach into their FMS and will navigate using the GPS/INS guidance for the whole thing, while having the localizer tuned into a second radio and monitoring the raw data. This is only for BCs though, regular localizers and ILS are flown with the automation coupled to the Localizer.

Is there a regulatory statement that they are getting waived in their OpSpecs, or can us 91 fliers do the same thing?

I'll have to go see what the G1000 does on BC approaches, I don't know if it automatically switches to the localizer or not. It does on localizer procedures and ILS but it's been so long since I've flown a BC I don't know.
 
TMetzinger said:
Ron, as I said I know (by having read their manuals) that more than 1 part 121 operator will load the BC approach into their FMS and will navigate using the GPS/INS guidance for the whole thing, while having the localizer tuned into a second radio and monitoring the raw data. This is only for BCs though, regular localizers and ILS are flown with the automation coupled to the Localizer.

Is there a regulatory statement that they are getting waived in their OpSpecs, or can us 91 fliers do the same thing?
Click to expand...
I don't see why we couldn't, as long as we have that second CDI and VOR/LOC receiver on which to receive and display the "real" LOC data, and don't mind having that MSG light glaring at you all the way down.
 
TMetzinger said:
Is there a regulatory statement that they are getting waived in their OpSpecs, or can us 91 fliers do the same thing
Click to expand...

There's no waiver of any sort that I know of. As long as the raw data is presented and the needles remain within tolerance, then you're legal. If you're using GPS coupled to a FD to fly the procedure that's fine as long as the raw data is displayed and you're within tolerances.
 
Ron Levy said:
I don't see why we couldn't, as long as we have that second CDI and VOR/LOC receiver on which to receive and display the "real" LOC data, and don't mind having that MSG light glaring at you all the way down.
Click to expand...
Hmm My previous response to this is missing. In my scenario, the msg light would go out because either:

You remain in GPS mode and have the course pointer on the GPS-driven CDI set to the back course (while having a second CDI showing the localizer).

You put the 530 in VOR/LOC and the MSG light goes out because it no longer cares about the discrepancy between the GPS course and the CDI.
 
TMetzinger said:
Hmm My previous response to this is missing. In my scenario, the msg light would go out because either:

You remain in GPS mode and have the course pointer on the GPS-driven CDI set to the back course (while having a second CDI showing the localizer).
Click to expand...
If you do that, the MSG light will come back on approaching the FAF and stay on to the MAP because you have GPS selected on the CDI inside the FAF on an LOC/ILS approach. The message will be "Select VLOC for this type approach," or words to that effect.

You put the 530 in VOR/LOC and the MSG light goes out because it no longer cares about the discrepancy between the GPS course and the CDI.
Click to expand...
If you do that, you aren't doing what the poster suggested (leaving the #1 in GPS and using the #2 nav as your "legal" localizer indication).
 
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Ron Levy said:
When you select VLOC (as you must before crossing the FAF of a SIAP using a localizer for lateral guidance on the final segment), the message will go away. Until then, with GPS selected for CDI, you really do want the reverse course set on the OBS anyway, since the needle will be giving normal steering. Only when you punch the CDI button to shift to VLOC will you start getting "backwards" steering, and then a) you really do want the OBS twisted to the forward direction so you can look at the bottom of the CDI for headings to fly, and b) the message will go away. This is equally true any time you're flying the localizer backwards, whether it be inbound on the back course or outbound on the front course (say, for a PT for a front course approach or straight out on the missed for a BC approach).
Click to expand...

Ron,

thank you very much for your explanation; I really appreciate this.
This all now makes sense, i.e. the "SET COURSE TO xxx DEG" message only appears as long as GPS is the navigation source; with VLOC selected as navigation source this message will never come up, even if the pilot were to misset the cource on the CDI or HSI.
I wish Garmins would mention this in their Pilot Guide because on a LOC/BC
approach (while still using GPS as navigation source) this message can really be misleading
 
Ron Levy said:
If you do that, the MSG light will come back on approaching the FAF and stay on to the MAP because you have GPS selected on the CDI inside the FAF on an LOC/ILS approach. The message will be "Select VLOC for this type approach," or words to that effect.
.
Click to expand...

Will that happen on a BC? I agree it will on a LOC or ILS, just not sure about the BC.
 
TMetzinger said:
Will that happen on a BC? I agree it will on a LOC or ILS, just not sure about the BC.
Click to expand...
A BC approach is a LOC approach -- just flown the other way. And yes, you must use the localizer as your primary source of lateral nav data on a LOC(BC) approach, so yes, you'll get the message.
 
rhscholz said:
I wish Garmins would mention this in their Pilot Guide because on a LOC/BC
approach (while still using GPS as navigation source) this message can really be misleading
Click to expand...
Since there are only 15 BC approaches left in the US, and 3 are already scheduled for decomissioning, this issue is not going to be a big priority for Garmin to fix.
 
Plenty of holds depicted on localizers that you'll have to fly backwards to get to them, though, for a published missed.

Just out of curiosity, how do the GPSs handle that? (Since I don't have a GPS.) Does it revert back to GPS Nav on the missed to the waypoint, or must you stay in LOC mode?

It's fun to read the GPS threads. I'll have some studying to do if/when we add one.
 
Ron Levy said:
Since there are only 15 BC approaches left in the US, and 3 are already scheduled for decomissioning, this issue is not going to be a big priority for Garmin to fix.
Click to expand...

You are probably thinking of the 15 VOR/DME RNAV approaches remaining with 3 scheduled for cancellation, there are 78 of the LOC BC approaches in the inventory.

Since the message only relates to GPS guidance, I am of the opinion that there is nothing for Garmin to correct, the pilot has to understand that the different navigation sources depict differently on the CDI.

With a HSI, if VLOC is the source, the course pointer has to point towards the front course direction and you fly to the course pointer head for outbound and to the tail when tracking inbound on the back course.

If GPS is the source, the desired track will be the same as the front course when flying outbound and will switch to the back course direction for the inbound leg. So with GPS as the source you always fly to the head of the course pointer to get correct sensing.

The same is true with respect to using an APR mode or a BC mode on the autopilot. If GPS is the source, use APR mode for tracking inbound or outbound and HDG mode to perform the PT. If VLOC is the source use APR mode for tracking the back course outbound, use HDG for the PT, and then use BC mode to track the back course inbound on the final approach.

To minimize errors, I would recommend that you switch to VLOC and set the front course direction on the HSI, fly the head outbound and the tail inbound for the back course.
 
Ron Levy said:
Since there are only 15 BC approaches left in the US, and 3 are already scheduled for decomissioning,
Click to expand...

Is that for real?

I live about 50 miles from two BC approaches, one each at KOTM and KALO, and I've flown them both. I figured they were a common thing -- I had no idea they were rare.
 
NoHeat said:
Is that for real?

I live about 50 miles from two BC approaches, one each at KOTM and KALO, and I've flown them both. I figured they were a common thing -- I had no idea they were rare.
Click to expand...
Read John's post above. I was confused. However, even for 78 out of 22,000 approaches, and the FAA drawing them down slowly, I don't see Garmin making it a high priority.
 
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denverpilot said:
Plenty of holds depicted on localizers that you'll have to fly backwards to get to them, though, for a published missed.

Just out of curiosity, how do the GPSs handle that? (Since I don't have a GPS.) Does it revert back to GPS Nav on the missed to the waypoint, or must you stay in LOC mode?
Click to expand...
The GPS does whatever you tell it to do. However, since there is no requirement to use the "real" localizer for tracking on the missed approach segment, it's a good idea to kick the CDI back out of VLOC into GPS when you hit the OBS to get out of SUSP so you don't have to worry about reverser tracking.
 
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