Looking at the OZZIE FOUR departure off APC (first page shown) the instructions are, e.g.,

TAKEOFF RUNWAY 19L: Climb on heading 186° to intercept course 269° to KLARK, then on track 342° to FIRTO at or above 2700, then on track 350° to OZIEE at or above 6000, thence...

I know the first step can be done with GPS equipment by using the OBS setting with KLARK as the reference, but is this what the design intends? I've never seen the OBS mode used for anything except runway centerlines and the like. Using it for IFR nav relative to a GPS waypoint never came up in training. I would have expected the procedure to include a flyby waypoint where the 89° radial off KLARK meets the 186° radial off APC, which would make the first turn work like any other. How do people program & fly something like this in practice? (Also - more of a TERPS question - why are the courses to KLARK off 19R/L not the same & likewise for 1R/L first turns?)

ETA: this is not in reference to any specific equipment beyond RNAV capability. I'm just puzzled by the specificity of the courses to the first waypoint, and the SID charting showing turns at specific points in space not associated with a waypoint. It says specifically "intercept course 269 to KLARK". I can use OBS mode to do this, but is that what's intended?


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    $\begingroup$ "How do people program & fly" will obviously depend on the aircraft and the installed equipment. Can you narrow that down a bit? $\endgroup$
    – Bianfable
    May 25, 2022 at 15:17
  • $\begingroup$ See edits - I'm asking about the specificity of "intercept course 269 to KLARK". The GTN6xx/7xx series can certainly do this with OBS mode, but that seems like a non-standard use case. I used "radial" which I guess technically applies only to VORs, but I'm just referring to the course being specified relative to a waypoint. $\endgroup$ May 25, 2022 at 15:29
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    $\begingroup$ Related: What is the operational advantage of starting an RNAV SID with a VI-CF leg combination? What you describe here is VI (heading to intercept) followed by CF (course to fix). $\endgroup$
    – Bianfable
    May 25, 2022 at 15:29
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    $\begingroup$ Yes, you should be intercepting the specified "radial" to KLARK just as if it was a VOR station. This is a relatively common way to begin a SID. $\endgroup$
    – randomhead
    May 25, 2022 at 19:57
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    $\begingroup$ I understand puzzlement over there not being a waypoint at the almost 90 degree dogleg from takeoff course to KLARK, but I'm not sure what you mean by "you would have to switch"... Have you actually loaded this procedure to see what it looks like in map mode? $\endgroup$ May 26, 2022 at 2:27

1 Answer 1


Depending on your aircraft equipment, when you load a SID, as STAR, or any route, (whether manually or from a database) all the legs will simply be there. You may review them in map mode if you have it. In fact it is encouraged, and may even be required, that you scale out on the display and review the general shape of the procedure against what the chart shows to verify that the points are correct.

Once loaded, you can fly in either map mode, or OBS. Either way, your deviation left or right of course will be show on the CDI. Additionally, the active leg to your next waypoint will be displayed as a magenta line. So even without a CDI, in map mode you simply put your aircraft symbol on the line and follow it.

  • $\begingroup$ That's correct (I just tested it in a GTN750) but it seems like an odd design. The 750 appears to put in an "uncharted" waypoint at the intersection of the two courses and do a standard flyby turn past it. I am still puzzled by what the benefit is here to not putting in an explicit waypoint and why it's done this way. $\endgroup$ May 26, 2022 at 2:26
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    $\begingroup$ @FosterBoondoggle, I typed my last comment above before I read this... I get that it seems odd, but as long as the "uncharted waypoint" leads you to fly the procedure as published it must have passed muster by those who approve such things. $\endgroup$ May 26, 2022 at 2:28
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    $\begingroup$ The "uncharted waypoint" is known as a 'Floating Waypoint' in the FMS. The reason is that it isn't at a fixed point. The reason it isn't fixed is that the initial departure leg is a VI leg (heading to intercept). Heading legs don't correct for wind so when you depart "Fly runway heading" your course will drift left or right depending on the wind. That will change the point where you intercept the CF leg. As you fly the leg, the FMS (or GPS navigator) will be using your actual track to predict the intercept and generate the fly-by turn at the appropriate point. $\endgroup$
    – Gerry
    May 27, 2022 at 17:34
  • $\begingroup$ @Gerry - that is a really great observation. Thanks. I fly bugsmashers, not big iron, so I'm not familiar with a lot of the subtleties of SIDs & STARs, particularly that apply primarily to jets. $\endgroup$ May 29, 2022 at 0:11

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