VOR RADIALS VS MAGNETIC VARIATION

Transcription

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 1

2 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. 2

3 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 10nm plus V4 = V1 157T 10 nm) and (V0 = MOT 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 3

4 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 ( degrees) V2 = V0 060 degrees magnetic at 5 nm ( degrees) V3 = V2 150 degrees magnetic at 10 nm V4 = V1 150 degrees magnetic at 10 nm 4

5 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 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 ( degrees) V2 = V0 060 degrees magnetic at 5 nm ( degrees) V3 = V2 150 degrees magnetic at 10 nm V4 = V1 150 degrees magnetic at 10 nm 5

6 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

7 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. 7

8 LAL VOR to OCF VOR V157 Flight Plan G1000 V12 Trainer Screen Shot NAV Data Base 17 NOV 2011 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: From the AIRPORT/FACILITY DIRECTORY SOUTHEAST US, 21 AUG 2011, 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 degrees west. This is a 5 degree west difference. 8

9 LAL VOR 350 radial circled, Jacksonville Sectional. 9

10 Ocala (OCF) VOR G1000 V12 Trainer Screen Shot NAV Data Base 17 NOV 2011 The OCF VOR 360 degree radial is equal to true north. The magnetic variation in November 2011 at OCF VOR is 5 degrees west. From the AIRPORT/FACILITY DIRECTORY SOUTHEAST US, 21 AUG 2011, 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. 10

11 OCF VOR to TAY VOR V157 Flight Plan G1000 V12 Trainer Screen Shot NAV Data Base 17 NOV 2011 V157 departs the OCF VOR on the 351 degree radial, and the Desired Track is 346 degrees. This is a 5 degree west difference. TALLAHASSEE RGNL: From the AIRPORT/FACILITY DIRECTORY SOUTHEAST US, 21 AUG 2011, 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 degrees west. This is a 6 degree west difference. 11

12 OCF VOR 346 radial circled, Jacksonville Sectional. 12

13 Ormond Beach (OMN) VOR G1000 V12 Trainer Screen Shot NAV Data Base 17 NOV 2011 The OMN VOR 360 degree radial is equal to true north. The magnetic variation in November 2011 at OMN VOR is 6 degrees west. From the AIRPORT/FACILITY DIRECTORY SOUTHEAST US, 21 AUG 2011, the 360 degree radial is 00E of true north. The 2010 magnetic variation at KDAB is 6.0 degrees west; the annual rate of change is 0.1 degrees west. This is a 6 degree west difference. 13

14 OMN VOR to AMG VOR V51 Flight Plan G1000 V12 Trainer Screen Shot NAV Data Base 17 NOV 2011 V51 departs the OMN VOR on the 342 degree radial, and the Desired Track is 348 degrees. This is a 6 degree west difference. JACKSONVILLE CRAIG: From the AIRPORT/FACILITY DIRECTORY SOUTHEAST US, 21 AUG 2011, 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. 14

15 OMN VOR 342 radial circled, Jacksonville Sectional. 15

16 La Belle (LBV) VOR G1000 V12 Trainer Screen Shot NAV Data Base 17 NOV 2011 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. From the AIRPORT/FACILITY DIRECTORY SOUTHEAST US, 21 AUG 2011, the 360 degree radial is 01E of true north. The 2010 magnetic variation at KRSW is 5.1 degrees west; the annual rate of change is 0.1 degrees west. This is a 6 degree west difference. 16

17 LBV VOR to LAL VOR V157 Flight Plan G1000 V12 Trainer Screen Shot NAV Data Base 17 NOV 2011 V157 departs the LBV VOR on the 334 degree radial, and the Desired Track is 340 degrees. This is a 6 degree west difference. NAPLES: From the AIRPORT/FACILITY DIRECTORY SOUTHEAST US, 21 AUG 2011, 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 degrees west. This is a 2 degree west difference. 17

18 LBV VOR 334 radial circled, Jacksonville Sectional. 18

19 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 5 to 15 nm, 10 nm legs, 1.0 nm spacing, start NW LAL VOR 194 radial (200 degrees 10 to 5 nm, 10 nm legs, 0.5 nm spacing, start SW MHT VOR 060 radial (060 degrees 15 to 10nm, 10nm legs, 0.5 nm spacing, start NE MHT VOR 315 radial (315 degrees 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 5 to 15nm, 10 nm legs, 1.0 nm spacing, start NW KLAL 200 deg 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. 19

20 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. 20