vor radials vs mag variation -...

1

VOR RADIALS

VS

MAGNETIC VARIATION

FOR

MISSION PILOTS

MISSION CO-PILOTS

AND

MISSION OBSERVERS

FOR

CROSS TRACK FLIGHT PLAN

CROSS TRACK SINGLE LEG

AND

GARMIN SAR

METHODS

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VOR radials do not always = current magnetic course

MOT VOR 144 Radial (150 degrees magnetic), 5 to 15 nm, 10 nm legs,

1.0 nm spacing, start NW

When setting up the above creeping line search area, I first used the

MOT 150 degree radial instead of the MOT 144 degree radial. The

center line from the MOT VOR through V0 did not split the V3 to V4 leg,

and I could not figure out why. Then I realized the MOT 360 and 180

degree radials were 13 degrees off of true north and true south;

respectively, instead of 7 degrees. The current magnetic variation at

KMOT is 7.5 degrees east.

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The trainer was changed to true headings to convert the 150 degree

specifications to their true course values. The true radials constructing

user waypoints had a 6 degree difference between (V3 = V2 157T deg @

10nm plus V4 = V1 157T deg @ 10 nm) and (V0 = MOT 163T @ 5nm).

The simulated aircraft is over the MOT VOR headed true 180 degrees.

NOTE:

The inner compass rose is based on magnetic variation in 2011, trainer

data base. True 180 degrees = 173 degrees magnetic

The outer VOR compass rose is based on magnetic variation when the

MOT VOR was installed. True 180 degrees = 167 degree radial

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G1000 Screen Shot using MOT VOR 150 degree radial

NOTE:

The MOT 150 radial does not bisect the V3 to V4 flight plan leg. V3 and

V4 are 150 degrees magnetic from V2 and V1 respectively. The current

magnetic variation is 7.5 degrees east. The screen shot is 7 degrees east.

MOT VOR 150 Radial, 5 to 15 nm, 10 nm legs, 1.0 nm spacing, start NW

V0 = MOT VOR 150 degree radial at 5 nm (156 degrees magnetic)

V1 = V0 240 degrees magnetic at 5 nm (150 + 90 degrees)

V2 = V0 060 degrees magnetic at 5 nm (150 – 90 degrees)

V3 = V2 150 degrees magnetic at 10 nm


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G1000 Screen Shot using MOT VOR 144 degree radial

NOTE:

The MOT 144 radial does bisect the V3 to V4 flight plan leg. This change

translated the search area 6 degrees to the east. The Garmin G1000

database has the magnetic variation of 7 degrees east at KMOT, 6 degree

difference. The G1000 version 12 trainer database is dated 17 Nov 2011.

MOT VOR 144 Radial, 5 to 15 nm, 10 nm legs, 1.0 nm spacing, start NW

V0 = MOT VOR 144 degree radial at 5 nm (150 degrees magnetic)

V1 = V0 240 degrees magnetic at 5 nm (150 + 90 degrees)

V2 = V0 060 degrees magnetic at 5 nm (150 – 90 degrees)



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FLIGHT PLAN MOT (Minot, ND) to BIS (Bismarck, ND)

NOTE:

The simulated aircraft is departing MOT VOR on the MOT 151 radial;

however, the Desired Track is 157 degrees magnetic. The simulated

aircraft will arrive at the BIS VOR with a Desired Track of 158 degrees

magnetic. It will be arriving the BIS VOR on the 332 radial, which the

reciprocal is 152 degrees. The G1000 V12 Trainer has a 6 degree

difference between both the MOT and BIS VOR radials and the

magnetic courses at each in November 2011.

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Florida VOR radials do not equal current magnetic course

Lakeland (LAL) VOR

G1000 V12 Trainer Screen Shot – NAV Data Base 17 NOV 2011

The LAL VOR 360 degree radial is 1 degree east of true north.

The magnetic variation in November 2011 at LAL VOR is 5 degrees west.

From the AIRPORT/FACILITY DIRECTORY SOUTHEAST US, 21 AUG 2011,

the LAL 360 degree radial is 01E of true north. The 2010 magnetic

variation at KLAL is 5.1 degrees west; the annual rate of change is 0.1

degrees west. This is a 6 degree west difference.

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LAL VOR to OCF VOR V157 Flight Plan


V157 departs the LAL VOR on the 350 degree radial, and the Desired

Track is 356 degrees. This is a 6 degree west difference.

PENSACOLA:


the CEW 360 degree radial is 03E of true north. The 2010 magnetic

variation at KPNS is 2.0 degrees west; the annual rate of change is 0.1


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LAL VOR 350 radial circled, Jacksonville Sectional.

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Ocala (OCF) VOR


The OCF VOR 360 degree radial is equal to true north.

The magnetic variation in November 2011 at OCF VOR is 5 degrees west.


the 360 degree radial is 00E of true north. The 2010 magnetic variation

at KOCF is 5.2 degrees west; the annual rate of change is 0.1 degrees

west. This is a 5 degree west difference.

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OCF VOR to TAY VOR V157 Flight Plan


V157 departs the OCF VOR on the 351 degree radial, and the Desired


TALLAHASSEE RGNL:


the SZW 360 degree radial is 02E of true north. The 2010 magnetic

variation at KTLH is 4.0 degrees west; the annual rate of change is 0.1


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OCF VOR 346 radial circled, Jacksonville Sectional.

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Ormond Beach (OMN) VOR


The OMN VOR 360 degree radial is equal to true north.

The magnetic variation in November 2011 at OMN VOR is 6 degrees west.



at KDAB is 6.0 degrees west; the annual rate of change is 0.1 degrees


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OMN VOR to AMG VOR V51 Flight Plan


V51 departs the OMN VOR on the 342 degree radial, and the Desired


JACKSONVILLE CRAIG:


the CRG 360 degree radial is 03E of true north. The 2010 magnetic

variation at KCRG is 5.9 degrees west; the annual rate of change is 0.1

degrees west. This is an 8 degree west difference.

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OMN VOR 342 radial circled, Jacksonville Sectional.

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La Belle (LBV) VOR


The LBV VOR 360 degree radial is 1 degree west of true north.

The magnetic variation in November 2011 at LAL VOR is 5 degrees west.



at KRSW is 5.1 degrees west; the annual rate of change is 0.1 degrees


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LBV VOR to LAL VOR V157 Flight Plan


V157 departs the LBV VOR on the 334 degree radial, and the Desired


NAPLES:


the CYY 360 degree radial is 03W of true north. The 2010 magnetic

variation at KAPF is 5.0 degrees west; the annual rate of change is 0.1


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LBV VOR 334 radial circled, Jacksonville Sectional.

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Examples of Creeping line searches relative to a VOR where the VOR

radials are not aligned with the current magnetic variation and where

they are aligned:

MOT VOR 144 Radial (150 degrees magnetic) @ 5 to 15 nm,

10 nm legs, 1.0 nm spacing, start NW

LAL VOR 194 radial (200 degrees magnetic) @ 10 to 5 nm,

10 nm legs, 0.5 nm spacing, start SW

MHT VOR 060 radial (060 degrees magnetic) @ 15 to 10nm,

10nm legs, 0.5 nm spacing, start NE

MHT VOR 315 radial (315 degrees magnetic) @ 18 to 23 nm,

8 nm legs, 0.5 nm spacing, start NE

NOTE:

When specifying a radial off a VOR, add in parenthesis the magnetic

course of that radial, even if it is the same. The MOT and LAL VORs are

on the airport, and basing the creeping line search off the airport will

simplify the specification. Radials off of airports, user waypoints, and

intersection are based on the current GPS data base magnetic variation.

MHT VOR is several miles away from the KMHT airport; therefore,

basing off the KMHT airport when the VOR is intended will not work.

KMOT 150 deg radial @ 5 to 15nm,

10 nm legs, 1.0 nm spacing, start NW

KLAL 200 deg radial @ 10 to 5 nm,

10 nm legs, 0.5 nm spacing, start SW

Airport radials do not always correspond to the VOR on the airport or

near the airport. Airport radials are always based on the magnetic

variation when the GPS data base was created.

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CONCLUSION:

The magnetic courses used in VOR compass roses are based on the

magnetic variation when the VOR was installed. In the Minot North

Dakota area, the magnetic variation apparently changes over time. In

two years, the magnetic variation in the Minot area changed by 0.6

degrees. In 1990, the magnetic variation at Minot was 10 degrees. In

2011, it was 6.9 degrees, and in 2013, it is 7.5 degrees. Of the 8 Florida

VORs evaluated, 3 had a current difference of 6 degrees W, 3 had 5

degrees W, 1 had 8 degrees W, and 1 had 2 degrees W. Of the 3 New

England VORs, GDM, MHT, and LWM, evaluated, all were aligned with

the current magnetic variation.

It would be too costly to adjust VOR antennas every time the magnetic

variation changes. This is not a problem using the published VOR radial

on your OBS setting. You are going to adjust your heading until the CDI

centers. The difference in magnetic heading to OBS setting may not be

all due to wind correction. Some of the difference may be due the

difference in magnetic variation now and when the VOR was installed.

When specifying a creeping line search based on a VOR radial,

determine the actual magnetic course. If the VOR is on a major airport,

this is easy to determine using the applicable Airport/Facilities

Directory. The nearest airport to the VOR will provide the latitude /

longitude, elevation, and the number of degrees east or west of the

VOR 360 radial from true north. The directory for major airports has

the magnetic variation listed on the airport diagram in the back of the

directory. Airport, Intersection, and User Waypoint GPS radials are

always based on the magnetic variation when the GPS data base was

created. For Garmin GPSs, this is when magnetic heading is selected.

vor radials vs mag variation -...

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