Why are non precision approaches not lined up?

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

Many VORs are used for approaches to multiple airports (CGT for
example) - it would be a bit much to expect that every one will line up
perfectly. I'm surprised at how close they usually are.

In article .com,
says...


Many VORs are used for approaches to multiple airports (CGT for
example) - it would be a bit much to expect that every one will line up
perfectly. I'm surprised at how close they usually are.


Nah - happens just as often with the VOR or NDB right on the field!

GF

"Greg Farris" wrote in message
...

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.


Because the navaid is not on the extended runway centerline.

In article . net,
says...


Because the navaid is not on the extended runway centerline.



Nope - Look at the VOR 14 approach to ITH (Ithaca New York - Just
grabbed the book and picked that one by chance). The VOR is on the
centerline, the runwya heading is 144.6° and the VOR approach is 133°. When
you break out, you have to turn 11.6° right to land. I don't see why they
couldn't have published it right on the 145° radial.

GF

"Greg Farris" wrote in message
...
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



There are numerous reasons. Off field navaids often serve serveral roles in
both the enroute and approach environment for several airports. On field
navaids may not be straight in as the approach coarse must lead to the
runway, and unless the navaid is at the end of a runway, the course would
either be parallel to the extended centerline of the runway, or offset to
intersect with the runway or runway threshold. Finally, obstructions along
the approach path or missed approach may be a fact in offsetting the
approach course. Lastly, air traffic considerations may be a factor,
especially with smaller airports situated close to busy airports.

On 10/6/2005 10:42, 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


I can think of a couple reasons. First, as other have said, the VOR
will not always be lined-up with the runway.

Secondly, it may be that the approach path has to come in at an
angle to avoid something, like high terrain, housing communities,
etc. (so they may have placed the VOR off center to facilitate
that).

Also, you shouldn't think of the difference between precision and
non-precision approaches as being lined-up or not with the runway.

Precision approaches are those that provide vertical guidance. Non-
precision approaches do not. That's the difference.

The fact that the typical precision approach uses a localizer which
is lined up with the runway (because the antenna is situated at the
field) does not make the approach 'precision' - the fact that it
provides vertical guidance does.


--
Mark Hansen, PP-ASEL, Instrument Airplane
Sacramento, CA

"Steven P. McNicoll" wrote in message =
ink.net...
=20
"Greg Farris" wrote in message=20
...

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.

=20
Because the navaid is not on the extended runway centerline.=20
=20


Furthermore, those alignments usually are not to the airport reference =
point,
but instead cross that centerline somewhere near the approach end of the =
runway,
just far enough out to turn and land if the runway environment comes =
into view.

"Greg Farris" wrote in message
...
In article . net,
says...


Because the navaid is not on the extended runway centerline.



Nope - Look at the VOR 14 approach to ITH (Ithaca New York - Just
grabbed the book and picked that one by chance). The VOR is on the
centerline, the runwya heading is 144.6° and the VOR approach is 133°.
When
you break out, you have to turn 11.6° right to land. I don't see why they
couldn't have published it right on the 145° radial.

GF

Because if they had you flying the 145 radial, you'd be flying parallel to
the extended centerline of runway 14 and would still have to sidestep to be
aligned.

"Greg Farris" wrote in message =
...
In article . net,=20
says...
=20

Because the navaid is not on the extended runway centerline.=20


=20
Nope - Look at the VOR 14 approach to ITH (Ithaca New York - Just=20
grabbed the book and picked that one by chance). The VOR is on the=20
centerline, the runwya heading is 144.6=B0 and the VOR approach is =
133=B0. When=20
you break out, you have to turn 11.6=B0 right to land. I don't see why =
they=20
couldn't have published it right on the 145=B0 radial.
=20
GF


Don't just say "no", Greg.
Examine the airport surface chart, and see where the VOR 14 course must =
lie
in order to cross the approach end of Runway 14.
Looks like about 133=B0 to me.
Then check the VOR 32 approach to see the corresponding offset the =
opposite way.