I was flying this weekend to maintain my instrument currency and came
across a GPS approach unlike any I'd seen thus far. Then again, I'm
pretty new to GPS approaches so I'm still finding new stuff fairly often.

I was flying approaches into Wellsvill, NY (ELZ) and was setting up for
the GPS RWY 28. I hadn't studied the approaches in advance, which is my
norm for instrument practice as I like to simulate having to divert to
an unplanned destination and thus find and brief the approach while also
flying the airplane.

I saw the two "waypoints" as I scanned the plan view and then selected
the GPS 28 approach on the King KLN 89B. I don't remember the details
exactly now, but the GPS didn't act as I expected in leg mode. It
wouldn't sequence the approach so I put it in OBS mode and flew the
approach in that manner. Looking at the plate later on the ground, I'm
pretty sure I understand what was wrong.

I mistakenly thought that RW28 was the MAP waypoint, but it appears that
this isn't the case. I don't have the GPS handy at home so I can't pull
up the approach again to see what waypoints it lists, but there is no
MAP WP symbol beside RW28. It looks like the MAP is simply the point
2.9 NM from HALOS and isn't a GPS waypoint at all. I'm also thus
assuming that this type of overlay approach can only be flown in OBS
mode with no automatic sequencing. Is this correct?

I also flew the VOR-A approach, but not its overlaid GPS-A approach. I
see that the chart shows what appears to be a MAP wapoint, MAGNV. This
is listed in parens at the location of the runway. I don't find this in
the terminal procedures legend, so can someone confirm that (MAGNV)
really is intended to indicate a GPS waypoint? However, again it has no
MAP WP symbol beside it, but if it isn't the MAP waypoint I can't figure
out what it is.

I also checked the GPS approaches into ELM and they do have the same
waypoint names RW06, RW28, etc., but they DO have the symbol for the MAP
WP as shown in the legend. I'd only flown GPS approaches into ELM
previously and thus I guess that is why when I saw RW28 at ELZ I assumed
it was the MAP waypoint.

It seems odd that there would be such subtle variations in the symbology
of various GPS approaches. Can anyone explain this briefly or refer me
to a good reference for GPS approaches? It is clear that reading the
King manual and my last ICC didn't yet cover all of the bases. I've not
yet flown a GPS approach in actual as I still don't feel comfortable
that I understand both the approaches and the 89B sufficiently to be
safe. However, I would like to get to that point before warm weather
returns to the northeast. :-)


Matt