Their format allows them to depict navaids that would not be visible if the
whole thing was to scale....might have an IAF 20 miles out that would be off
the chart.

Bob Gardner

"Phil Verghese" wrote in message
.44...
I don't understand the point of the reference circle on the NACO
instrument charts. According to the FAA Instrument Flying Handbook:
"The majority of NACO charts contain a reference or distance circle
with a 10 NM radius. Normally, approach features within the plan view
are shown to scale; however, only the data within the reference circle
is always drawn to scale. The circle is centered on an approach fix
and has a radius of 10 NM, unless otherwise indicated. When a route
segment, outside of the circle, is drawn to scale, the symbol [wiggly
lines] interrupts the segment."

I understand the definition above, but how does the reference circle
help me at all? I think the charts would be easier to read without the
reference circle. Almost all charts I've seen are drawn to scale, and
when they are not the wiggly lines going through a route segment makes
it clear that something is not to scale. I feel like I'm missing
something about the reference circle, so please enlighten me.

I started flipping through some charts and noticed a few curious
things related to the reference circle. I guess the reference circle
would be less confusing to me if I understood when it would be there
or not, why it's centered in a certain fix, and why it's sometimes not
10 NM.

1) I could not find any standalone GPS approaches that had a reference
circle (unless there were enroute facilities that could not be shown
to scale). I certainly didn't miss the reference circle when it wasn't
there. Does anyone know of an example of this? I wonder why standalone
GPS approaches don't have reference circles.

2) Most of the time the reference circle is centered around the
procedure turn fix and the same size as the maximum PT size (or
centered on some other fix if there is no PT for the approach).
Exceptions:
a) Arcata, CA (ACV) ILS 32. The PT is w/in 10 NM of KNEES. The
reference circle is 15 NM centered on the ACV VOR.
b) Buffalo, WY (BYG) VOR/DME or GPS 30. The PT is w/in 10 NM of
INJUX. The reference circle is 10 NM centered on MIZNR.
c) Jackson, WY (JAC) VOR or GPS-A has a 10 NM reference circle and
the PT requires you to remain within 15 NM.
d) Hoquiam, WA (HQM) ILS/DME 24 has a 15 NM reference circle and
the PT requires you to remain within 10 NM.

If I just ignore the reference circle, will I be missing something
important? I don't see how it helps me interpret the chart or fly the
approach. I guess Jeppesen agrees with me, since they don't bother with
a reference circle on their charts.

Phil
www.pfactor.com