Why no stepdown fix in GPS?

[Roy Smith]

I flew the KFWN VOR or GPS-A (http://204.108.4.16/d-tpp/0506/05412VGA.PDF)
this morning with a CNX-80. Annoyingly, ANKLE (the stepdown fix) is not in
the database. You get SAX->MAGLV. It seems like SAX->ANKLE->MAGLV would
make a lot more sense. Is the some reason it's left out of the database?

[[email protected]]

Roy Smith wrote:

> I flew the KFWN VOR or GPS-A (http://204.108.4.16/d-tpp/0506/05412VGA.PDF)
> this morning with a CNX-80. Annoyingly, ANKLE (the stepdown fix) is not in
> the database. You get SAX->MAGLV. It seems like SAX->ANKLE->MAGLV would
> make a lot more sense. Is the some reason it's left out of the database?

It's an overlay, so someone at Jeppesen made a coding judgment to treat it as
an ATD stepdown fix. I believe that is the protocol agreed upon for GPS final
approach segment stepdowns, but having said that, I suspect they are treated
both ways.

[Roy Smith]

In article >, wrote:

> Roy Smith wrote:
>
> > I flew the KFWN VOR or GPS-A (http://204.108.4.16/d-tpp/0506/05412VGA.PDF)
> > this morning with a CNX-80. Annoyingly, ANKLE (the stepdown fix) is not in
> > the database. You get SAX->MAGLV. It seems like SAX->ANKLE->MAGLV would
> > make a lot more sense. Is the some reason it's left out of the database?
>
> It's an overlay, so someone at Jeppesen made a coding judgment to treat it as
> an ATD stepdown fix.

What's "ATD"?

[[email protected]]

Roy Smith wrote:

> In article >, wrote:
>
> > Roy Smith wrote:
> >
> > > I flew the KFWN VOR or GPS-A (http://204.108.4.16/d-tpp/0506/05412VGA.PDF)
> > > this morning with a CNX-80. Annoyingly, ANKLE (the stepdown fix) is not in
> > > the database. You get SAX->MAGLV. It seems like SAX->ANKLE->MAGLV would
> > > make a lot more sense. Is the some reason it's left out of the database?
> >
> > It's an overlay, so someone at Jeppesen made a coding judgment to treat it as
> > an ATD stepdown fix.
>
> What's "ATD"?

It's in the AIM (many times ;-) "Along track distance

From AIM 1-1-19.13:

13. Unnamed stepdown fixes in the final approach segment will not be coded in the
waypoint sequence of the aircraft's navigation database and must be identified
using ATD. Stepdown fixes in the final approach segment of RNAV (GPS) approaches
are being named, in addition to being identified by ATD. However, since most GPS
avionics do not accommodate waypoints between the FAF and MAP, even when the
waypoint is named, the waypoints for these stepdown fixes may not appear in the
sequence of waypoints in the navigation database. Pilots must continue to identify
these stepdown fixes using ATD.

[[email protected]]

Is it part of FAA's move to CANPA? I found it easier to read out
distances then fixes when doing CANPA on my FS2004 with
JeppView/FliteDeck connected on another computer, but not in real plane
yet.

[[email protected]]

Roy,

No comments on my helpful answer?

Roy Smith wrote:

> In article >, wrote:
>
> > Roy Smith wrote:
> >
> > > I flew the KFWN VOR or GPS-A (http://204.108.4.16/d-tpp/0506/05412VGA.PDF)
> > > this morning with a CNX-80. Annoyingly, ANKLE (the stepdown fix) is not in
> > > the database. You get SAX->MAGLV. It seems like SAX->ANKLE->MAGLV would
> > > make a lot more sense. Is the some reason it's left out of the database?
> >
> > It's an overlay, so someone at Jeppesen made a coding judgment to treat it as
> > an ATD stepdown fix.
>
> What's "ATD"?

[Roy Smith]

In article >, wrote:

> Roy,
>
> No comments on my helpful answer?

Um, well, it was helpful, thanks.

[[email protected]]

Roy Smith wrote:

> In article >, wrote:
>
> > Roy,
> >
> > No comments on my helpful answer?
>
> Um, well, it was helpful, thanks.

Why the ambivalence?

You were distraught beceause a final-segment fix wasn't in the
database. Also, you did not know what an ATD was.

I pointed you in the right direction for some information that should be
meaningful to your IFR operations.

So, why the "um, well, it was helpful...?"