Why are non precision approaches not lined up?

Greg Farris wrote in
:

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.

The term 'precision approach' refers to having vertical guidance (a
glideslope), not to the runway alignment. A precision approach does
have to be aligned relatively closely, but not precisely. I can't
recall the exact number of degrees off the top of my head, but it's not
exact. Even if a non-precision approach is perfectly aligned with the
runway, it's still a non-precision approach, because there is no
glideslope. An ILS without a glideslope, which becomes a localizer
approach, is a non-precision approach.

--
Regards,

Stan

"They that can give up essential liberty to obtain a little temporary
safety deserve neither liberty nor safety." B. Franklin

Greg Farris wrote:

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.

The VOR is on the centerline? I gotta get my eyes examined.

In a previous article, Greg Farris said:
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

The VOR most definitely is NOT on the centerline. Look at the airport
diagram on that approach - it's a hundred feet or more from the
centerline.

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.

Because then you would never cross the extended centerline, but would be
that same distance (a hundred feet or more) to one side. I'm guessing
that in a case like this they want the course to cross the runway
centerline some specific distance from the runway. Even ROC's VOR/DME 4
(an approach which I've never heard used in 10 years of being based at
ROC) is offset a tiny bit.


--
Paul Tomblin http://xcski.com/blogs/pt/
I read [.doc files] with "rm". All you lose is the microsoft-specific
font selections, the macro viruses and the luser babblings.
-- Gary "Wolf" Barnes

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.

This has little to do with non-precision / precision classification.

If you can get hold of them, get some ILS approach plated for
Norway. There are ILS:es with approach path 60 degrees off
runway direction.

The approach path has to fulfill separation requirements for
both other flight procedures with protection zones and for
obstacle celearance.

--

Tauno Voipio
tauno voipio (at) iki fi

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.

It is due, at least in the cases I've seen, to the location of the
associated navaid, be it VOR or NDB. Sometimes they can't be sited on
the extended centerline of a runway, or possibly the navaid existed
prior to the airport. Aren't most GPS approaches lined up with a runway?


Matt

Greg Farris wrote:

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.

No, the VOR is not on the runway centerline. It is several hundred feet
off to the side of the runway. Why they didn't use the runway heading
for this approach I don't know, but it could be for noise abatement,
obstruction clearance, or other reasons.


Matt

"Matt Whiting" wrote in message
news

No, the VOR is not on the runway centerline. It is several hundred feet
off to the side of the runway. Why they didn't use the runway heading for
this approach I don't know, but it could be for noise abatement,
obstruction clearance, or other reasons.


If they did that the MAP would be several hundred feet off to the side of
the runway.

"Greg Farris" wrote in message
...

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.


You're apparently looking at the wrong airport. If you look at the plate
for the VOR RWY 14 approach at ITH you'll see that the VOR is not on the
extended runway centerline. Here's a link to the plate:

http://www.myairplane.com/databases/.../00779VG14.PDF

Stan Gosnell wrote:
A precision approach does
have to be aligned relatively closely, but not precisely. I can't
recall the exact number of degrees off the top of my head, but it's not
exact.

Here's an example of a precision approach that's not aligned with the runway,
the LDA Rwy 6 at ROA, Roanoke, VA. Terrain appears to be the motivation for the
misalignment.

http://www.myairplane.com/databases/.../00349LDA6.PDF

In article .net,
says...



"Matt Whiting" wrote in message
news

No, the VOR is not on the runway centerline. It is several hundred feet
off to the side of the runway. Why they didn't use the runway heading for
this approach I don't know, but it could be for noise abatement,
obstruction clearance, or other reasons.


If they did that the MAP would be several hundred feet off to the side of
the runway.


OK - the VOR is not exactly on the runway centerline - maybe two runway
widths off. Is that the reason then? Are we sure, or just guessing?
Is it better to break out with two runway widths of sidestep, or with the MAP
"on" the extended centerline, but the runway visible out the side window?

My question is why it's done that way. If we're sure that the answer is "to
place the MAP on the centerline, regardless of heading" then that answers my
question.

Regarding Norwegian, Icelandic or lunar ILS' 30° off the centerline, I don't
know. I always see ILS' (and by implication LOC) aligned with the runway,
whereas VOR/DME/NDB approaches are very frequently not aligned.

G Faris