If you are having RNAV or ILS malfunctions, try this.

I have begun a project to build 25 airports in Canada, in Northwest Territories and Nunavut, that Asobo doesn't include in MSFS2020 stock scenery. I ran into a problem with coding RNAV approaches for them; nothing fancy, just straight-in, 2-legs, IF>CF>Runway. The problem I had was that the plane I was testing this with, the Rheims FR-172 from flightsim.to, equipped with the PMS50 GTN750 and a Bendix Autopilot, was touching down right at the edge of the threshold instead of on the touchdown stripes. You code this in the XML source file by adding 50 feet to the runway elevation, like this:

<Approach

type="RNAV" runway="07" designator="NONE" gpsOverlay="FALSE" fixType="TERMINAL_WAYPOINT" fixRegion="CY" fixIdent="I07SY" altitude="4200.0F" heading="84.00000" missedAltitude="2100.0F" lnav="TRUE" lnavvnav="TRUE" lpv="TRUE" lp="FALSE" >

<ApproachLegs>

<Leg type="IF" fixType="TERMINAL_WAYPOINT" fixRegion="CY" fixIdent="I07SY" altitudeDescriptor="+" altitude1="4500.0F" />

<Leg type="TF" fixType="TERMINAL_WAYPOINT" fixRegion="CY" fixIdent="C07SY" flyOver="FALSE" recommendedType="RUNWAY" recommendedIdent="RW07" theta="3.0" rho="10.0N" altitudeDescriptor="A" altitude1="3800.0F" magneticCourse="65.3" distance="10.0N" isFAF="TRUE" />

<Leg type="TF" fixType="RUNWAY" fixRegion="CY" fixIdent="RW07" flyOver="TRUE" altitudeDescriptor="A" altitude1="359.00F" magneticCourse="65.3" theta="3.0" rho="10.0N" distance="10.0N" verticalAngle="3.0" />

</ApproachLegs>

In this example, the IF fix point is at 4,500 ft MSL, the FAF fix at the top of the glide path is at 3,800 ft, and the RW fix is shown at 359 feet, which is 50 feet above the threshold. The Theta, Rho, Distance, faf="TRUE", and verticalAngle tags are all designed to instruct the aircraft's GPS and Autopilot to provide a Glide Path of 3.0% from FAF to the runway, with the plane crossing the threshold 50 feet AGL, and setting the wheels down more or less exactly on the touchdown stripes.

So I spent about 20 hours struggling with this, and the plane kept touching down right on the threshold: it was doing this not only at my custom airport, but also at a couple of Asobo stock airports that I tried, too, and that gave me an idea: "maybe the problem is in the plane's hardware, and not in my Approach code?". So I rebooted the sim with the stock Asobo C-172, G-1000 version, and again with the Bonanza G-36 Turbo (also equipped with the G-1000), and my RNAV approach worked perfectly at both runway 07 and 25.

So lesson #1 learned: when designing custom scenery, Approaches are usually the hardest part of any custom airport, because the SDK scenery designer offers you very little assistance, if any; every ILS approach I've ever built, originated with XML code generated in Jon Masterson's ADE. But now I'm trying to work out how to build RNAV approaches, and had to find hints on how to do it from whatever examples I could find on the Internet, and a lot of them ultimately had bugs and didn't work. Lesson #2 learned: If the code for an approach isn't working, yet it compiles in the SDK without throwing an error message, try flying it in a different aircraft that uses a different GPS. If you are testing a new airport with a plane you got on the Marketplace, for example the C-182RG from Carenado, and something is not working as you expect, maybe you've found a previously undiscovered bug in the source code for that plane's avionics. Try a stock Asobo plane, and if your airport is now fully functional, you know the problem wasn't in your code, it was in the third-party aircraft. Good luck! There's nothing more satisfying than that first successful touch and go at an airport you designed from scratch, where you test all of the ILS and/or RNAV approaches, and everything works as it's supposed to.

Edited yesterday at 03:04 AM1 day by lgcharlot
Added GTN 750 in first paragraph.