GPSS testing

[Wingover]

Hi All,

Is it possible to test the GPSS on the ground or you have to fly it to see if it anticipates the turns? I can test the AP on the ground when I turn the heading bug and the AP turns but not sure about GPSS.

[PeteMc]

What kind of GPS and why do you think you need to test it?

Specifically on your question, I don't know if avionics shops have the gear to spoof your GPS to test this, but I sort of doubt it.  As for testing on the ground, you'd need a huge amount of space and a fair amount of speed.  So it would be so much easier to just go fly.

ADDED: Remember there are "Flyover Waypoint" so be sure not to choose one of those for your test.  They're the ones with the Circle around the Wpt symbol and your GPS should always fly OVER those, then turn.

Edited December 5 by PeteMc

[Wingover]

1 minute ago, PeteMc said:

What kind of GPS and why do you think you need to test it?

Specifically on your question, I don't know if avionics shops have the gear to spoof your GPS to test this, but I sort of doubt it.  As for testing on the ground, you'd need a huge amount of space and a fair amount of speed.  So it would be so much easier to just go fly.

 

It’s Garmin 175 connected to G5 with GAD29B.  I couldn’t get the GPSS option to come up on the G5 but after reading the installation instructions I  made the changes and can activate it now.  I was hoping to test on the ground first since you can’t make changes while flying and the weather is bad on top of that.   My avionics shop in an hour flight from me and too busy right now.

You say I need lots of space, do you mean taxing while testing?  I meant stationary on the ground.

[PeteMc]

1 minute ago, Wingover said:

You say I need lots of space, do you mean taxing while testing?  I meant stationary on the ground.

Probably more like a big desert or else you won't really see the early turn to the new heading. 

And I added a comment Flyover Wpts probably while you were replying.  And I'm pretty sure the GPS175 will anticipate turns as long as the Autopilot is following the GPS.  I think all the new Garmin Navigators will do it. 

 

 

[Wingover]

1 minute ago, PeteMc said:

Probably more like a big desert or else you won't really see the early turn to the new heading. 

And I added a comment Flyover Wpts probably while you were replying.  And I'm pretty sure the GPS175 will anticipate turns as long as the Autopilot is following the GPS.  I think all the new Garmin Navigators will do it. 

 

 

I am more interested to see if the AP even reacts to the GPSS in any shape or form.

[802flyer]

1 hour ago, Wingover said:

I am more interested to see if the AP even reacts to the GPSS in any shape or form.

What autopilot? Was the autopilot and/or G5 pre-existing?

If your autopilot previously followed a heading bug, and the G5 is allowing you to turn on GPSS, then you should be able to put the autopilot in heading mode, activate GPSS on the G5, and sit back while the plane flies the turns for you.


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[midlifeflyer]

1 hour ago, Wingover said:

I am more interested to see if the AP even reacts to the GPSS in any shape or form.

You may have to wait until you are in the air. Check your manual, some say that preflight tests for GPSS won’t work unless you have a good signal and the aircraft is in motion.

[Wingover]

35 minutes ago, 802flyer said:

What autopilot? Was the autopilot and/or G5 pre-existing?

If your autopilot previously followed a heading bug, and the G5 is allowing you to turn on GPSS, then you should be able to put the autopilot in heading mode, activate GPSS on the G5, and sit back while the plane flies the turns for you.


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KAP 150 - Yes AP and G5 were there prior to the GPS175 install.  AP (in heading mode) follows the heading bug on the G5 when I manually move it.  Theoretically should it also follow the glideslop on the G5 when in approach mode?

Edited December 5 by Wingover

[802flyer]

KAP 150 - Yes AP and G5 were there prior to the GPS175 install.  AP (in heading mode) follows the heading bug on the G5 when I manually move it.  Theoretically should it also follow the glideslop on the G5 when in approach mode?

Yes it should follow the lateral course of GPS approaches in GPSS mode (pedantic clarification: the glide slope is the vertical portion and would depend on the approach mode of your autopilot).

Just make sure you have the KAP 150 in heading mode to use GPSS, as GPSS will not change the performance of NAV mode.


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[802flyer]

I am more interested to see if the AP even reacts to the GPSS in any shape or form.

I believe the GPSS algorithm makes the steering commands based on real-time parameters such as speed (i.e. start the turn earlier if you’re going faster), so I doubt you can test it on the ground.


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[bigmo]

What navigator do you have? I do know that if I put my navigator in test mode (or maybe it’s called simulation mode) it sends commands just the same as if we’re flying. If you have that option, try that, build a short flight plan. You can turn on the AP and GPSS and you should see it trying to fly the flight plan.

[PeteMc]

2 hours ago, Wingover said:

Theoretically should it also follow the glideslop on the G5 when in approach mode?

Just so we're on the same page...  Depending upon what the GPS175 is replacing in your plane, no more "Glide Slope" as in an ILS.  The 175 is GPS only, so no ILS.

I believe the KAP150 should be able to follow the "Glide Path" of a RNAV Approach.  Subtle difference, but I've seen people load an ILS Approach and wonder why they're getting the "NOT APPROVED FOR GPS" warning message. 

 

[midlifeflyer]

14 hours ago, 802flyer said:

I believe the GPSS algorithm makes the steering commands based on real-time parameters such as speed (i.e. start the turn earlier if you’re going faster), so I doubt you can test it on the ground.


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I think you are correct. One thing to look at is the manual for the AP (as modified by any GPSS add-on). I’ve seen AP preflight checklists indicating that GPS functionality cannot be tested at all unless the aircraft is in motion.

[midlifeflyer]

12 hours ago, PeteMc said:

Just so we're on the same page...  Depending upon what the GPS175 is replacing in your plane, no more "Glide Slope" as in an ILS.  The 175 is GPS only, so no ILS.

I believe the KAP150 should be able to follow the "Glide Path" of a RNAV Approach.  Subtle difference, but I've seen people load an ILS Approach and wonder why they're getting the "NOT APPROVED FOR GPS" warning message. 

 

Do you mean this? Because you can’t substitute GPS for a localizer.

 

[Wingover]

I believe you can use the GPS for an ILS until the FAF but not 100% sure.  Anyway, I can use the NAV (Garmin 255A) with the CDI to track the ILS down.

[PeteMc]

9 hours ago, midlifeflyer said:

Do you mean this? Because you can’t substitute GPS for a localizer.

CORRECTION: I was thinking of a ILS/LOC Approach below.  Not sure if they even still have those, but if LOC is not in the Title, then you can not use GPS, it must be a NAV radio.  So for those with GPS only, anything with ILS only in the Title you can't use. 

Actually, No.... You can use GPS in lieu of the Localizer.  That warning is telling you that you can't fly the "ILS" Approach, or more specifically it is the Glide Slope you can't use the GPS for.

So if you were going to fly it as a LOC Approach with the Step Downs, you'd be legal.  Say the winds were howling and that was the only Approach to the best Rwy, go ahead and fly it as if the GS was out.  But if you followed your GPS generated Glide Path (vs GS) down and something happened, you'd be doing the carpet dance (which they'd probably see on radar at a lot of airports).  

 

 

Edited December 6 by PeteMc

[Vance Harral]

Getting back to the question of ground testing... you should be able to do this using the OBS mode of your GPS.  I'm not going to give a blow-by-blow detail of OBS mode here - you can read about it elsewhere - but in short it's the GPS equivalent of a VOR.  You select a waypoint on the GPS, and a course relative to that waypoint, and your CDI needle (and the data fed to the navigation system) will indicate your position relative to that course.  By selecting different courses, you can make your present position be "on course" or "left of course" or "right of course", without moving the airplane at all.  If you enable your autopilot, it should move the control wheel to make a left or right turn accordingly, to intercept the selected course.  As others have said, to test roll steering (GPSS), you'll want to have the autopilot in heading mode while you're doing this.

[midlifeflyer]

51 minutes ago, PeteMc said:

Actually, No.... You can use GPS in lieu of the Localizer. 

Not according to the FAA's guidelines on substitution of GPS for ground-based navaids in AIM 1-2-3 and AC 90-108. Not even the same permissive "monitoring" language as for VOR, TACAN or NDB.

You may disagree, but you asked the reason for the Garmin warning.