How much protection on approach?

"Michael" wrote in message
m...
How much protection do we have on an off-field VOR approach? I was
always under the impression that as long as the equipment was within
tolerances for an airborne VOR receiver check (+/- 6 degrees) and the
approach was flown to PTS tolerances (no more than 3/4 scale
deflection) it was impossible to hit anything. I now know this is not
necessarily true.

The approach in question is the VOR-B to LVJ; the URL for the plate is
http://www.myairplane.com/databases/...ral/LVJ_vB.pdf

The long and the short of it is this. The Cat-A altitude minimum on
the approach is 520 MSL; there is a 1200 ft MSL tower less than 4 nm
South of the airport, and the FAC is 260. The VOR is 25.8 nm from the
MAP, which is over the field. No matter how you slice it, that's less
than 9 degrees off the FAC. 3/4 scale deflecion on a VOR is more than
7 degrees in itself.

From my reading of TERPS para 513, the primary area is defined by a
trapezium that is 2 miles wide at the facility and 5 miles wide at 30 miles
from the facility (which is the furthest permitted). The secondary area is
a mile wider on each side at 30 miles. So at 30 miles the deviation against
which you are protected is 3.5 miles. As you say, that's about 7 degrees.
Scary stuff!

Julian Scarfe

My take on this is that such specifications exist, but we, as pilots,
don't have access to them. This is due to their complexity. However,
if we pilots fly reasonable approaches, and don't get "too far" off
course, we will be safe. In this case, the tower is 4 miles away from
the field. THAT is a long way. If you take a look at the approach to
ERIE, Colorado, there is a tower that is less than a mile off course,
and only 100' below where you are supposed to be. Very scary. All it
would take is a combination of bad altimeter setting, or being a
little low, and flying a couple of dots off. I always am very, very
cautious flying approaches in IMC if I have never flown in visual
conditions to acertain the radio tower and hill situation. There are
some frightenly close obstructions out there. Nevertheless, we as
pilots seem to be doing a fairly good job, as we are not plowing into
such obstacles at a very high rate. So the system seems to be working.
Certainly you bring up a good point. I would like to see the zone of
protection marked on the charts in some way. This would obviously be a
major change from current charting system.

(Michael) wrote in message om...
How much protection do we have on an off-field VOR approach? I was
always under the impression that as long as the equipment was within
tolerances for an airborne VOR receiver check (+/- 6 degrees) and the
approach was flown to PTS tolerances (no more than 3/4 scale
deflection) it was impossible to hit anything. I now know this is not
necessarily true.

The approach in question is the VOR-B to LVJ; the URL for the plate is
http://www.myairplane.com/databases/...ral/LVJ_vB.pdf

The long and the short of it is this. The Cat-A altitude minimum on
the approach is 520 MSL; there is a 1200 ft MSL tower less than 4 nm
South of the airport, and the FAC is 260. The VOR is 25.8 nm from the
MAP, which is over the field. No matter how you slice it, that's less
than 9 degrees off the FAC. 3/4 scale deflecion on a VOR is more than
7 degrees in itself.

So what am I missing?

Michael