# How do you encode a radial to radial turn in ARINC-424?

I am building my own ATC simulator and for that purpose I need to include several instrument procedures. I have a problem with that particular one:

My problem is on KEA transition, the leg between "RDL 256 KEA" and "RDL 192 ATV" how should the transition be encoded in terms of ARINC-424 path terminator sequences.

Specifically it's the turn from the one leg to the other that bothers me: "RDL 256 KEA" seems to terminate on either 27 DME KEA or RDL 187 ATV. But then what? There is a 20 DME ATV on the next leg that spoils everything. CD (or Course to DME) is not a specific route over the ground so the previous turn won't be able to intercept it. I could either omit the CD part or insert another CR (course to radial) before the CD leg but then I'm not doing what the map says, I improvise. So my question is am I conceiving this wrong, or the IAC is ambiguous in this particular point?

• The IAC is not ambiguous, but the translation to ARINC 424 Path Terminators is ambiguous. There are often multiple ways to do it, and sometimes none match exactly the procedure on the chart. Mar 19 '14 at 14:23

So you fly the KEA transition like this:

• Track RDL 265 KEA until crossing RDL 187 ATV or 27 DME KEA
• Start a right turn and intercept RDL 192 ATV
• Fly RDL192 until intercepting final

As egid said, RDL 187 ATV is a lead radial which is a radial used only to tell you when to start a turn.

As far as 20 DME ATV, it is actually only used for the PELAG transition so you can ignore it in this case.

• Lead radial is now understood. The chart has a DME mark right at the same point. Does that mean it can be flown "either way"? As I see it, it can be both course to radial termination and fix to DME. As for the 20 DME ATV, what makes me believe it's part of KEA and not PELAG transition, is the fact that the DME mark is placed slightly before the point the 339 track intersects the RDL 192 ATV. Mar 19 '14 at 7:29
• @SteliosAdamantidis Yes, the start of the turn can be determined determined either way. Generally I find DME to be easier if the aircraft is equipped with it, but will use the lead radial if not. As far as the 20 DME, it shows the turn being completed before it as well, so possibly they use it as a reporting point. Mar 19 '14 at 12:59
• I emailed an ATCO of Athens APP and while he claimed the 20 DME is used by both transitions, he didn't rule out the possibility of the chart being slightly wrong. Anyway the answer covers me, I just wanted to eliminate all doubts. Mar 19 '14 at 18:22

Just create a PC waypoint at the 20DME and use a Righturn DF with an FO requirement. Once the CR leg is completed the box with initiate a turn direct to the point and be certain of hitting it. From there you can TF to the station. I used to do this for a living.....this is how I would code it for real aircraft.

PC: Airport Terminal Waypoint.
FO: Fly over or overfly.
DF: Direct Fix.

• You may extend the acronyms PC, DF and FO Jan 13 '20 at 8:23
• I took the liberty to explain some of the acronyms, feel free to edit if I was wrong. Sep 11 at 10:41
• With all the respect to your professional experience -I'm not here to doubt it- I would like to refrain from doing so. Although I was many times tempted to do this. Code all turning points as Lat/Lon, mark as FO the fly overs and you are done. But then I'm afraid that maintaining the file will be a nightmare. Please note that I'm not coding for real aircraft but for simulation purposes. Sep 11 at 10:48