KLAS GIDGT 1 departure using RWY 1L/R. X-Plane 11.55. Boeing 737-800 (default X-plane aircraft). Navigraph-provided AIRAC 2113 rev 1.
I’m noticing minor course discrepancies between the published departure and the actual departure data that is being fed into the FMS. Per my understanding, the course (DTK) in the FMS should line up with the course specified in the published departure procedure.
The GIDGT 1 departure using RWY 1L/R calls for “climb on heading 014 to intercept course 072 to KYBAD, then on track 072 to HAIDN, then on track 073 to cross AIRRO…”. This is slightly different from the data that is being fed to the 737-800 FMS. Specifically, instead of the 072 course to KYBAD, the FMS data shows a 075 course to KYBAD. Instead of the 072 course to HAIDN, the FMS data shows a *071 course to HAIDN. Finally, instead of the 073 course to AIRRO, the FMS data shows a 072 course to AIRRO.
Can you please clarify why there is a discrepancy and how to remedy it. Thanks.
A discrepancy of 1 degree is generally considered acceptable and will not necessarily trigger an immediate change to the chart. Corrections like this are usually made to the charts within a larger timeframe, which might cause temporary discrepancies between the FMC and chart.
There is a discrepancy of 3 degrees for the first waypoint on the SID ( instead of the published 072 course to KYBAD, the FMS data shows a 075 course to KYBAD). Based on your reply, I would expect that the discrepancy is sufficiently large to trigger a review of the Navigraph FMS data that accompanies the SID. Also, the Navigraph SID chart matches the FAA-published SID chart - so no issues with the chart itself.
Hi Dennis,
your understanding is correct but that doesn’t mean it’s not calculated. I have now looked into the procedure file and here you see the CF-leg (course to fix) with 72° … so, as I have suspected the FMC calculates this values and doesn´t take it from the data.
Here the corresponding lines in the KLAS-procedure file:
The yellow markers are the important one´s … all following leg types are TF-legs (track to a fix) and don´t have any course information - also here, will be calculated via the FMC.
Sorry, but that´s not a navdata issue - the data are correct so far.
Richard,
Thanks for looking into this. Ok, so the correct (Navigraph) data is being fed to the FMS but the FMS is ignoring it and calculating the course to KYBAD instead. I thought the course in the FMS was the DTK (Desired Track i.e. the published course to fix as per the published DP). Bottom line is that the plane does not fly the SID as published. I will reach out to Laminar for clarification. Thank you.
