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