C172 with KTN750 basic and premier installed with the C172 package.  The screen shot is simultaneous for my flight screen and my Navigraph screen. 

Flying the KSAN LOC RWY 27 approach as loaded into the AP and activated.  The flight plan page in the MFD shows the correct sequence of waypoints and the correct bearing and distance for each pair in sequence.  The AP flew me to PGY correctly and then the AP advanced the waypoint to be PGY -> LYNDI but the plane just kept going east. 

The PFD screen does NOT show the correct bearing and distance to fly from PGY To LYNDI and the plane does NOT turn toward LYNDI - it just keeps flying about 124°M, which is the magenta line course shown on the CDI.  The bearing to LYNDI never changes in the PFD information area.  You can see on the chart above the bearing from PGY to LYNDI should be about 34°M.

What am I doing wrong?  In the prior flight I did the same flight plan and approach using the C172 and WT1000 AP and had no problems. 

 

Edited May 22, 20215 yr by TacomaSailor

I'm wondering why you're starting the approach from LYNDI?  Should be from VYDDA (IF or IAF is a legal point to comence the approach).

Regardless the PMS GTN and any other default based Garmin stuff, it's not very reliable for RNAV(GPS) navigation.

You definitely would not fly from PGY to LYNDI and shoot the approach.   If you absolutely had to shoot it from LYNDI you'd be vectored to the NE and be abeam LYNDI when ATC clears you.

FWIW, I believe the TDS GTN Xi would be able to shoot that approach...even though, as I said above, it's not a realistic place to start.

Edited May 22, 20215 yr by ryanbatcund

Never mind...

 

Edited May 23, 20215 yr by b1bmsgt

2 hours ago, TacomaSailor said:

What am I doing wrong? 

Did you activate the approach in the GNT750?

Al

26 minutes ago, b1bmsgt said:

Is it because he is south of VYDDA?

Yes, to me VYDDA makes more sense once you are at PGY. If in contact with ATC, I would expect them to vector you to VYDDA with an assigned altitude. If not in contact with ATC you could still go direct from PGY to VYDDA, but would have to do so at the MSA since there is no 'bold' course line with a depicted altitude shown between PGY and VYDDA.

Al

Edited May 23, 20215 yr by ark

9 minutes ago, ark said:

Did you activate the approach in the GNT750?

Al

I thought that too but the leg is from PGY to LYNDI (on the g1000 PFD)....which doesn't make sense looking at the DTK. PGY to LYNDI is not a 110 track....MSFS default gremlins at work.

Flying the same combination earlier today (C172 & GTN750) to a similar approach.  When I passed the last enroute WP, the flight plan switched to the approach but added circling waypoints.

With your KSAN plate as an example, I immediately hit Direct To on the 750, chose the approach tab, selected the VYDDA waypoint as the transition and activated.  She turned and followed the approach perfectly.

MSFS will often throw in some extra WPs or sometimes send you in the wrong direction, but the neat thing about the GTN750 is you can instantly regain control when that happens.  When I pass that last WP I am always ready to over-ride - when it does the right thing, great.  When it doesn't I'm ready to get her back on track.

I understand the flight plan is unrealistic! 

My question is WHY does the PFD show the correct from->to waypoints but incorrect bearing and distance?

The flight plan shown in the MFD contains the proper sequence of PGY->LYNDI->VYYDA->OKAIN...ETC.   AND...LYNDI is the IAF!

I know all about added waypoints, and duplicated waypoints in the approach - but in this case none of that occurred.  The waypoint sequence (after LOAD & ACTIVATE) is correct in the MFD but the CDI/PFD never updates the bearing or distance.

Unrealistic or not - the AP should be able to fly to the IAF when the PFD and MFD show that as the next waypoint. 

 

24 minutes ago, TacomaSailor said:

My question is WHY does the PFD show the correct from->to waypoints but incorrect bearing and distance?

I think you have to start with the realization that the MSFS flightplan system is presently badly broken.. so it is not a question of WHY, but rather WHEN will this get fixed..

I understand.  At times there appears to be a disconnect between the Approach Procedure, the FP and the displays - the most common for me is when the next WP is the IAF for the approach.  I've come to expect the AP will NOT fly to that WP in that case.  Usually, close in, activating the approach cures this, but not always.

I had a fairly basic FP today and the next WP was the IAF.  However, the PFD showed the next WP as the airport and was flying to it instead of the IAF.  So, in this case, the MFD was correct and the PFD was wrong.  I first tried activating the approach procedure WAY OUT (something I normally wouldn't do) and the flight began the dreaded 180 - I immediately set a Direct To and still got no response.  I repeated the Direct To and reset the AP to Nav mode - the AP then turned me back on course and headed to the IAF.  When close to the IAF, I reactivated the approach and it worked properly - shouldn't have had to do any of that.

6 minutes ago, RandallR said:

shouldn't have had to do any of that.

Indeed... and I hate waiting.. but it is all we can do, at present 🤔

Edited May 23, 20215 yr by Bert Pieke

1 hour ago, Bert Pieke said:

Indeed... and I hate waiting.. but it is all we can do, at present 🤔

......and fly previous platforms that with the available enhancements are not so lacking.

Not to be rude but I did answer you right away @TacomaSailor .

The flight plan system is screwed up...it's unreliable.  It might work one time, then be completely different the next time.

 

36 minutes ago, ryanbatcund said:

Not to be rude but I did answer you right away @TacomaSailor .

The flight plan system is screwed up...it's unreliable.  It might work one time, then be completely different the next time.

 

I've been working with fairly sophisticated GPS/Autopilot/Navigation equipment for at least 20-years. I've spent many days operating many different GPS (and LORAN before that) systems in all kinds of weird situations. 

I have never seen a GPS or Autopilot make the decision "The flight plan system is screwed up...it's unreliable." and then set a course at right angles to the displayed waypoint.    The GPS/Autopilot displays the next waypoint correctly - that is ALL it does on any particular leg.  The GPS does not anticipate the next leg down the road and then say to itself "nope that can't be right - so let's go somewhere else."

Not to be rude - but your explanation defies logic. 

Again - I am not asking about the flight plan or procedure (arrival or approach).  I am asking about one particular leg in which the MFD shows the correct waypoint, bearing, distance but the PFD shows an incorrect and never changing bearing and distance.  It has nothing to do with the flight plan.  

Hmm, I am not sure about that particular issue with that addon, but I suggest to try different waypoints and see if it occurs still, or try a different airport. There are a lot of variables and things that can sometimes throw off these systems in the game due to interoperability and conflicts between the default auto-pilot, third party GPS, and the plane specific systems implementation. It could purely be a bug with this particular addon for some X reason that is unique to your path, no idea.

If you have a stuck leg, maybe try manually flying that leg and see if it becomes unstuck, if not I'd just try a different path entirely.

Edited May 23, 20215 yr by Alpine Scenery