Approach intersection displayed Altitude on G1000 FMS is different from that on Approach chart

When loading different ILS approaches in X-Plane using the current database 2401, I see an anomaly that I would like to better understand and hopefully that can be corrected.

It appears that on many ILS/LOC approaches, the minimum altitude at the fix just outside of the final approach fix on the localizer approach is being incorrectly displayed on the G1000 FMS Flight plan page. Each of these intersections, just prior to the final approach fix, is incorrectly showing the minimum altitude for the final approach fix.

An example of this is the ILS 20R at Santa Ana, CA (KSNA). The minimum altitude over Hukem intersection is correctly shown on the approach plate as 2,800’ but the altitude that is being loaded into the FMS in the G1000 is incorrectly shown as 2,200’ which is the minimum altitude over the final approach fix of Lemon. See the attached approach plate and the G1000 flight plan page of the same approach which shows the discrepancy in the minimum altitude over Hukem.

A review of several other approaches in the Los Angeles area indicate this same anomaly is on many other FMS displayed altitudes over the fix prior to the final approach segment. See the ILS 25L at LAX or the ILS 30 at LGB for this same issue. It appears this incorrect altitude issue may be the way your database is being processing and displayed on the G1000.

I hope that this issue is able to be corrected so the displayed minimum altitude over the fix prior to the final segment of the approach is correctly displayed on the FMS display.

Standing by for your thoughts…

Hi,
and welcome at Navigraph. Thank you very much for this posting and the details. Much appreciated …

I have checked our data and also what we offer X-Plane and I think the reason is the implementation in the G1000.

Here, what we have in our data and what we offer X-Plane:
APPCH:010,I,I20R, ,HUKEM,K2,P,C,E I, , ,IF, ,ISNA,K2,P,I, ,0159,0099, , ,J,02800,02200,18000, , , , , , , , , ,0,N,S;

Please look at the part ...,J,02800,02200, ... … these values are

  • J = altitude description code
  • 02800 = altitude 1
  • 02200 = altitude 2

So, what does J mean now:
Glideslope intercept altitude specified in altitude 2 field and at or above altitude specified in altitude 1 field on the FACF waypoint in precision approach coding with electronic glideslope

When you now compare it with your posted chart, you will see that the FACF is LEMON and the altitude 2200 feet is bold. HUKEM is on 2800 feet, which is corresponding with the coding line. So, the coding is correct in my view …

I don´t know anything about the G1000 and how this unit works in real, but it seems that Laminar shows in this case also the second altitude field from our data. Again, I´m not sure, if this is real also so but this implementation is made by Laminar. As you see, we offer both altitudes, possible they select the wrong one. When this is the case (or you mean this is the case), please report this to Laminar Research that they can fix it. The data looks ok so far - so not really a navdata issue from our side :wink:

Hope that helps,
Richard

Hello Richard,

Thanks so much for the detailed information regarding this anomaly.

I will take your advice and submit this as an issue to Laminar Research and see if they are able to come up with a resolution to the problem.

Thanks for your help.

Corey Ferguson

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