I use a Garmin 300 IFR GPS .. and a Garmin 196 handheld. I keep the IFR
database
current and update the handheld about once a year. I've had no trouble
working
around and under the Class B shelves using them. When compared to prominent
landmarks (roads, etc) that help identify the boundaries, they seem to be
highly
accurate. Some Class B's have VFR waypoints shown on the TAC and those
help. An important thing is to keep the zoom set correctly so you can
identify
just where you're at in relation to the different B floors. If you're zoomed
in
too close .. you may think you're under the wrong one. I like to zoom so I
can
see the B space to it's outermost ring.


"John Bell" wrote in message
om...
It appears that a lot of pilots are violating airspace even with GPS on
board.

I would like to hear some feedback as to how pilots are violating airspace
with GPS. I address this in my online book, www.cockpitgps.com. I have
my
hypothesis, but I would like to hear your experience or scenarios that you
have heard involving this issue.

Also of interest is how you might be using GPS to successfully avoid
airspace violations.

Other hypothesis are also welcome.

Thanks,

John Bell
www.cockpitgps.com

Here is my hypothesis:

I have already mentioned in my discussion of database currency that you
should set up a routing around any airspace and check it with a current
chart before flight. Even with a current database, it is possible for the
GPS to get you into trouble with airspaces.
Aviation receivers can be setup to display airspace boundaries and to give
warnings before entering certain airspace classifications such as category
B
airspace. These warnings can be a great benefit or a nuisance depending on
the type of flying that you are doing. Thus, most receivers allow you to
turn them on or off. Additionally, which boundaries will display and at wh
at
point of zooming out they will disappear can be set. The ability to make
these settings is a good feature and I would not want to see this changed.
However, it is possible to have the GPS not display or not warn of an
impending airspace violation if you have the GPS set up incorrectly for
the
mission.
Even if the airspace boundary is displayed, it is often difficult to
decide
what boundary a given line applies to. On the Garmin aviation receivers it
is possible to cursor over the point to get a description. On a handheld
GPS
just press the rocker pad up, down, left, or right to start moving the
cursor. On the GPS 400 and 500 series, press in on the knob and then start
moving the cursor. Move the cursor to highlight the line and press the
ENTER
button to get information on the airspace. This is a great feature at the
planning stage and is occasionally useful in flight. When you have
preplanned the route and have a route line, the context of the border is
obvious. However, I think that it is possible to confuse borders and
violate
airspace without first creating a route using a chart before flight.