Non-Reciprocal LOC & BC

This was from another group.

At KBOI, until the current release, the approach charts showed, for the
ILS10R and LOC BC 28L approaches magnetic courses of 100° and 278°
respectively.

The JEPP charts were changed with the current release; but the NACO charts
probably still show it:

http://naco.faa.gov/d-tpp/0610/00057IL10R.PDF
http://naco.faa.gov/d-tpp/0610/00057LBC28L.PDF


Could this have to do with the changes in magnetic variation when the
charts were issued?

In other words, if the charting method for a LOC course merely takes the
true course, and then applies magnetic variation; and if the source showed
different values for these two approaches, could that result in this
apparent discrepancy?

www.airnav.com does show (at least as of this morning) a two degree
difference between the mag var for the airport, and that for the ILS10R
approach.
Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

Ron Rosenfeld wrote:

www.airnav.com does show (at least as of this morning) a two degree
difference between the mag var for the airport, and that for the ILS10R
approach.

Might be magnetic variation changes (the pole does wobble around)
and the approaches surveyed at different times. It's also possible
that there is some ground (terrain or buildings) that causes the
localizer to get bent.

2 degrees isn't much.

On Thu, 28 Sep 2006 06:44:58 -0400, Ron Rosenfeld
wrote:

This was from another group.

At KBOI, until the current release, the approach charts showed, for the
ILS10R and LOC BC 28L approaches magnetic courses of 100° and 278°
respectively.

The JEPP charts were changed with the current release; but the NACO charts
probably still show it:

http://naco.faa.gov/d-tpp/0610/00057IL10R.PDF
http://naco.faa.gov/d-tpp/0610/00057LBC28L.PDF


Could this have to do with the changes in magnetic variation when the
charts were issued?

In other words, if the charting method for a LOC course merely takes the
true course, and then applies magnetic variation; and if the source showed
different values for these two approaches, could that result in this
apparent discrepancy?

www.airnav.com does show (at least as of this morning) a two degree
difference between the mag var for the airport, and that for the ILS10R
approach.

I notice that KBOI HI-ILS10R, which is pretty much the same as ILS10R
except that it starts at FL200, has an approach course of 098 instead
of 100. Both approaches use the same localizer. It must be a charting
change and they haven't gotten around to redoing ILS10R yet. So much
for using current charts.

RK Henry

The ILS 10R approach was last ammended on the 159th day of 2006. The
LOC BC 28L was created on the 271th day of 2006. That's less than 4
months apart.

Maybe a magnetic survey was done between these two days and the LOC BC
approach has the most recent variation data.

Or, it's possible that the localizer signal bends slightly due to local
conditions :-)


Ron Natalie wrote:
Ron Rosenfeld wrote:

www.airnav.com does show (at least as of this morning) a two degree
difference between the mag var for the airport, and that for the ILS10R
approach.

Might be magnetic variation changes (the pole does wobble around)
and the approaches surveyed at different times. It's also possible
that there is some ground (terrain or buildings) that causes the
localizer to get bent.

2 degrees isn't much.

Ron Rosenfeld wrote:
This was from another group.

At KBOI, until the current release, the approach charts showed, for the
ILS10R and LOC BC 28L approaches magnetic courses of 100° and 278°
respectively.

The JEPP charts were changed with the current release; but the NACO charts
probably still show it:

http://naco.faa.gov/d-tpp/0610/00057IL10R.PDF
http://naco.faa.gov/d-tpp/0610/00057LBC28L.PDF


Could this have to do with the changes in magnetic variation when the
charts were issued?

In other words, if the charting method for a LOC course merely takes the
true course, and then applies magnetic variation; and if the source showed
different values for these two approaches, could that result in this
apparent discrepancy?

www.airnav.com does show (at least as of this morning) a two degree
difference between the mag var for the airport, and that for the ILS10R
approach.
Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

Whenever the published LOC course on a CAT II or III procedure is more
than 1 degree off the actual mag course, the mag var value is supposed
to be updated so that the depicted mag course is no more than a degree
off. 100 course is correct because the true LOC course is 115.13 minus
15 E variation = 100.13.
(If you want more information than you ever wanted about LOC values at
BOI, go to this link;
http://avnwww.jccbi.gov/pls/datashee...LOC&v_format=F
This 1 degree tolerance doesn't apply to CAT I procedures (3 degrees is
OK for them), but since the MAG VAR for BOI ILS was updated from 17E to
15E, they had to amend the CAT I procedure since it's on the same form
as the CAT II procedure. The problem appears to be that although they
updated the mag var for BOI LOC, someone forgot that the facility is
also used at the other end of the runway as a back course procedure and
it appears they should have amended that procedure at the same time, or
else they decided it was still in tolerance and did not need to be
changed. The true back course alignment is considered to be 295.15 minus
15E = 280.15 magnetic. They're still using 295.15T minus 17 = 278.15M.
ILS or LOC Rwy 10 was amended this year and the Final Approach (FAC) mag
course and mag variation can be found on page 1 at the below link.
http://avn.faa.gov/acifp/20050829155...EPLACEMENT.pdf
The ILS Rwy 10 course is based on using 15E variation, while the Rwy 28
procedure uses 17E variation from the same facility. The actual flight
path above the ground remains the same no matter what magnetic course
they publish, since the LOC signal does not move.

JPH

On Thu, 28 Sep 2006 21:24:13 -0500, JPH wrote:

Ron Rosenfeld wrote:
This was from another group.

At KBOI, until the current release, the approach charts showed, for the
ILS10R and LOC BC 28L approaches magnetic courses of 100° and 278°
respectively.

The JEPP charts were changed with the current release; but the NACO charts
probably still show it:

http://naco.faa.gov/d-tpp/0610/00057IL10R.PDF
http://naco.faa.gov/d-tpp/0610/00057LBC28L.PDF


Could this have to do with the changes in magnetic variation when the
charts were issued?

In other words, if the charting method for a LOC course merely takes the
true course, and then applies magnetic variation; and if the source showed
different values for these two approaches, could that result in this
apparent discrepancy?

www.airnav.com does show (at least as of this morning) a two degree
difference between the mag var for the airport, and that for the ILS10R
approach.
Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

Whenever the published LOC course on a CAT II or III procedure is more
than 1 degree off the actual mag course, the mag var value is supposed
to be updated so that the depicted mag course is no more than a degree
off. 100 course is correct because the true LOC course is 115.13 minus
15 E variation = 100.13.
(If you want more information than you ever wanted about LOC values at
BOI, go to this link;
http://avnwww.jccbi.gov/pls/datashee...LOC&v_format=F
This 1 degree tolerance doesn't apply to CAT I procedures (3 degrees is
OK for them), but since the MAG VAR for BOI ILS was updated from 17E to
15E, they had to amend the CAT I procedure since it's on the same form
as the CAT II procedure. The problem appears to be that although they
updated the mag var for BOI LOC, someone forgot that the facility is
also used at the other end of the runway as a back course procedure and
it appears they should have amended that procedure at the same time, or
else they decided it was still in tolerance and did not need to be
changed. The true back course alignment is considered to be 295.15 minus
15E = 280.15 magnetic. They're still using 295.15T minus 17 = 278.15M.
ILS or LOC Rwy 10 was amended this year and the Final Approach (FAC) mag
course and mag variation can be found on page 1 at the below link.
http://avn.faa.gov/acifp/20050829155...EPLACEMENT.pdf
The ILS Rwy 10 course is based on using 15E variation, while the Rwy 28
procedure uses 17E variation from the same facility. The actual flight
path above the ground remains the same no matter what magnetic course
they publish, since the LOC signal does not move.

JPH

Thank you for clarifying and amplifying the details of what I suspected to
be the case.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)