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wsieffert

How to write (GPS) approaches from scratch?!?

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I'm trying to "translate" approach plates to the XML approach format, but I'm a bit lost. For starters, I did some research using google and I know what the leg types, etc, are (don't necessarily understand them though). All in all, I have a rough understanding, but still can't add everything up to write my approach for a new airport...Other people must struggle with this as well, so maybe this thread will develop into a resource of help (there are other threads I have read, but none of them seem to come up with a clear strategy). BTW, DME arc approaches seem straight forward if one disassembles an example. I'm struggling with the more simple approaches.First of all, I gather that non-ILS approaches are only of cosmetic value, since AI/agents don't use them. correct?Here's my strategy. I posted 3 approach plates. For the first one I have matching decompiled code. I roughly understand the decompiled code, but some things I don't understand. Maybe someone has useful insights and has any ideas how to write approaches for the other 2 examples. The 2 most urgent questions I have:- Do I have to create my own waypoints? How do I know where to place them and how to name them?- Which approach type do I have to use? Sometimes a choice is obvious, but sometimes I seem to have a choice of three (or better, I could think of several ways to combine different leg types to describe the same approach plate). Are there some rules?Here are the plates and the xml code for Penrhyn/Tongareva... Cheers, Christianhttp://forums.avsim.net/user_files/71237.jpghttp://forums.avsim.net/user_files/71238.jpghttp://forums.avsim.net/user_files/71239.jpg

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Hi Christian,It all depends on what you intend to do with the approaches. ATC only uses a visual approach or an ILS approach to control AI or User aircraft to an airport. All the remaining approaches defined for an airport are there for the User to practice those approaches via the GPS. Therefore, it is up to you to determine how many of the practice approaches you want to define.The GPS approaches are limited to directional control when used with the autopilot. Altitude control is up to the User pilot since GPS will not cause the aircraft to descent on the glideslope. The setup for this event: A/P - ON, NAV/GPS - GPS, A/P NAV - ENABLED. Prior to setting the above the proper approach must be selected, loaded, and activated in the GPS.The User can select an ILS approach using the NAV1 radio and have the same approach activated in the GPS. In this case, the GPS only shows the approach and doesn't control the approach. The setup for this event: A/P - ON, NAV/GPS - NAV, A/P NAV - ENABLED, NAV1 radio tuned to proper ILS approach for the selected runway. Again the proper approach must be selected, loaded, and activated in the GPS for it to show the various legs.If you want ATC to control AI and the User Aircraft to a defined ILS, then the ILS must be defined for the airport runway and the approach legs must be defined for the approach. Otherwise, ATC will assume a visual approach even if the airport runway states it has an ILS. The legs have to be complete, i.e., approach legs, missed approach legs, and transition legs.Waypoints should be listed on your charts. Waypoint names can have up to five alphanumeric characters. If a new runway has been opened, you may have to define waypoints. Waypoints are normally defined by other NAVAIDs, such as, VORs. One waypoint is generated automatically by the system:When you use the above, the system will automatically place the fixIdent at the beginning of the runway as a waypoint. In all other cases you must define the waypoints.W. Sieffert

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Thanks for that. That didn't really help me though. To get more concrete, let's take the Penrhyn example from above...The only waypoint on the plate is NC PY. However, MS is also using FF14, CF14, and PY8NM. These aren't defined in the file (maybe somewhere else, but in an example I saw using DME arcs the waypoints were defined in the same file). Does this mean that FS2004 is defining waypoints itself? FF14 and CF14 are obviously refering to runway 14, and PY8NM could refer to 8NM away from PY?I'm starting to understand the example, I really have to check if those waypoints are defined somewhere or if FS2004 auto generates them.The only things unclear to me now are: - MS is using 8NM for the 'turn' to 134deg. The plate is using 2min instead. Can this be done? (Hmm, giving some more thought to this, maybe this is only used for the GPS graph anyway, since AI isn't using this approach. Then 2min would be of no use.)- why altitudes 650 and 508? They aren't on the plates.- There is a holding leg type available. Can that be used to incorporate the holding pattern on the plate?- Are the approach commands used to ONLY draw the graph in the GPS view? In this case it probably doesn't matter much which leg type combination to use as long as the graph shows up ok.Thanks for the help,Christian

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ok, I'm blind. The waypoints ARE defined in the same file, but they seem to be way out. Could be a coordinate transformation problem though...Christian

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Yes, MS does define some waypoints that are not on the charts. Have you actually loaded the Tongavera approach into the GPS to see what it looks like?If not, go to NCPY airport, open the GPS and stretch the GPS across your screen. Press the PROC button, press ENT if the Select Approach is highlighted. If NCPY is highlighted in the APT box, turn the outer knob to the right to move the highlight to the APPROACH box, turn the inner knob to the right to open the list of approaches (In this case, there is only one). Press ENT to select the NDB 14 approach. Turn the inner knob to PY. Press ENT to make your selection. Press ENT to LOAD the approach or use the outer knob to move the highlight to the ACTIVATE selection to LOAD/ACTIVATE the approach then press ENT. You will return to the Active Flight Plan List. Press the FPL button to return to the graphic picture. Notice the big differences in the charts and the installed approach.Is this caused by your charts being out of date or how MS designed the approach. I am pretty sure MS uses Jeppesen or other actual digital data and would have no reason to modify the actual approach to fit the flightsim.W. Sieffert

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>Have you actually loaded the Tongavera approach into>the GPS to see what it looks like?Yes, I did.>Notice the big differences in the charts and the>installed approach.I guess this is why I started this thread. My charts are up to date, so MS must have either changed the approach, or Jeppesen has some flawed data. Or this is the way MS implements approaches like this...I'm a bit lost which leg types to use to recreate the approach on the plate, but I'll keep fiddling. I think I understand the xml files a bit better already...Cheers, Christian

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