Greg Farris wrote:
The title just about says it - I've always wondered WHY many
non-precision approaches (not talking about LOC only here, but VOR,
VOR/DME, NDB etc) are not lined up with the runway heading. Sometimes it
looks as though the approach desginers have gone out of their way to
make sure the non-precision approach is just a few degrees off - as if
to say - "look stupid - this is not a precision approach . . ." But if
this were so, then we would have to wonder why SOME of these approaches
ARE lined up and straight-in. I'm surev there's a simple explanation
that will be pointed out here.

thanks,
G Faris


Alignment is not what defines precision vs nonprecision; vertical
guidance is the defining difference.
As for alignment, the only way to get an "on-airport" NAVAID to provide
a course right down the runway centerline is to place the NAVAID right
on the centerline of the runway, but then that would be a hazard to
airplanes as they had to swerve to avoid it as they were rolling out.
Seriously, though, the reason the course is not lined up is that the
TERPS criteria requires that it be aligned so as to cross the extended
runway centerline at a point optimally 3000' from the threshold. There
is some flexibility in this, as it can be aligned to cross the
centerline anywhere from over the threshold itself, out to 5200 ft from
the threshold, and in some cases can be aligned so it doesn't even cross
the threshold as long as it's within 500' of the centerline at the 3000'
point. Most on field NAVAIDS are a minimum of 500 ft from the runway
centerline. The further the NAVAID is from the edge of the runway, the
greater the difference between the course and the runway alignment. If
the procedure had the same course as the runway, then it would parallel
the centerline all the way down final, requiring an "S" turn rather than
one gentle turn to lign up.
At KITH, there's also a difference of 2 degrees between the airport
magnetic variation (12W) and the ITH VOR/DME magnetic variation (10W),
so even if the courses were parallel, the displayed headings would be 2
degrees apart.

JPH