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PAR instrument

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Precision Approach Radar Addon
Started in 02/2018
Description PAR addon
Contributor(s) Rodolfo
Status under active development as of 02/2018
Precision Approach Radar screen

Precision Approach Radar (PAR) is a ground instrument conceived primarily to provide the GCA service.

WIP.png Work in progress
This article or section will be worked on in the upcoming hours or days.
Note: Although still incomplete, the information it contains is valid and available.
See history for the latest developments.

PAR allows the Ground Controlled Approach (GCA) controller to deliver approach directives to the requesting aircraft.
(see Howto:Implementing_a_simple_GCA_system)


Cquote1.png Is there any work on GCA (ground controlled approach) in progress, or have missed it? GCA is surprisingly accurate and easy to use, both as a pilot and a controller.
— Alant (Sun Ago 13). Re: Spoken ATC.
(powered by Instant-Cquotes)

What PAR and GCA are

What can you expect from GCA

Horizontal trajectory when pilot follows GCA instructions
Arriving in the vicinity of the airport with little or no visibility, the pilot can request the GCA service. The Controller, assisted by a PAR (Precision Approach Radar), will guide you through a safe path (both in heading and in altitude) that will take you to the head of the used runway.
Vertical trajectory when pilot follows GCA instructions

How to install

{{note | This is the latest version (Feb 22, 2018)
If your FGFS version accepts Addons, you can download this feature from the Addons Repository. Download all the 12 files into the directory of your choice.

Launch FlightGear including --addon argument, eg.:

 fgfs <usual args> --addon=/path/to/PARaddon/
Note  From version 2017.4.0, the FG launcher accepts the --addon option in his Settings/Additional Settings tab.

Otherwise, you can install it as a submodule. Contact the author for further instructions.

And that's all !

How to use it

When you are about 15 or 20 miles from your destination, tune Comm1 to an available ATC frequency (you can find them at Menu/Location/Airfield information or at the F12 dialog).
Press the > key to see the PAR instrument (you can open as many as you want). Verify the airport and runway destination.
On the screen you should see not only your plane but all the flying MP/AI in range. Adjust Zoom if necessary.
Click the GCA button to request GCA assistance.
You will hear the GCA's answer "<callsign>, this will be a PAR approach to <airport> runway <rwy>."
Now, as you do not want to cheat, you should click the hide button. (Remember: this PAR is a ground instrument, not a flying one).
But not worry, once you have landed (or anytime, indeed) you can press the > key again to visualize and analyze your plotted trajectory.

Depending on your position and altitude, the GCA will give you a vector towards the base leg or towards the final one. Also will instruct to climb or descend if necessary.
Follow closely those instructions making standard turns first, and half standard ones when indicated. Adopt about 90 to 110 kts IAS until you hear "Begin descent", and configure a "final" atitude then.
If you are adviced "<Well/Slightly> <left/right> of course." then make "S" turns to fix that. Little ones if "Slightly", big ones if "Well".
Correct your vertical speed if you hear "<Above/Below> glidepath."

Phraseology customization

You can customize the phraseology by editing the "phraseology.xml" file.
There you can find groups of tags like:

    . . . . 
  <foo type="string">Hello world. </foo>
  <foo type="string">It is a good </foo>
  <foo type="string">day </foo>
  <foo type="string">to fly. </foo>
    . . . .

which will be read as a single sentence ("Hello world. It is a good day to fly. ").


Those in the example above are literal sentences that you can change by the strings you want.

  • You should not include either " or ' .
  • Punctuation is meaningfull.


Strings starting by % will call some property value. In the example above replace "day" by "% /sim/startup/time-offset-type".
Now the sentence will be read as "Hello world. It is a good morning to fly. " or "Hello world. It is a good evening to fly. " depending on the time.

  • The called property must be a string.


Strings starting by ~ will append the sentence with another one.
Try this:

    . . . . 
  <short type="string">% /satc/callsign-fmt</short>	
  <short type="string">, </short>

  <foo type="string">Have a nice fly, </foo>
  <foo type="string">~short</foo>
    . . . .
when calling foo you should hear "Have a nice fly, <your-callsign> , "

Word Replacement

If you find that the word Wind is not pronounced clearly, you can change it by Winnded or similar to increase its intelligibility..
Better? Fine, but what about the message on the screen? Include a tag with the pattern <replace type="string">old:new</replace> :

    . . . . 
  <replace type="string">Winnded:Wind</replace> 
    . . . .


  • To implement a setting dialog (binded to the set button) allowing further customizations.(as glideslope, TTS arguments, etc.)
  • To improve the terrain getVertProfilefunction when unloaded tiles are needed.
  • General improvements & optimizations

Behind the scene

Supporting all the graphic work:

  • Canvas-API
  • plot2D.nas
  • graph.nas
  • skinnable.nas

( to be continued ... )