A pilot is using a polar stereographic
chart whose grid is parallel to the zero meridian,
with Grid North in the direction of the North geographic pole. In polar regions, the pilot stops navigation in free-gyro mode
after leaving the 6 microteslas zone, and the grid
heading controlled by information from the inertial navigation system (INS) is
045°. After switching to "magnetic mode", the compass heading is
220°. The INS position at this moment is 76°N 180°W. The magnetic variation on
the chart is 10°E. The compass shift on this heading at this point in time is:
Answer:
Aircraft position is 76°N 180°W, GRID
heading 045°G
G = T ± Convergency, so we can rearrange, T = G ± Convergency
With the GRID aligned to the zero
meridian, Convergency = Aircraft longitude = 180
So, T = 045
± 180 = 225°T or 135°T (draw the diagram to confirm)
True Heading 225°T, VARIATION 10E,
so Magnetic Heading = 215°M
In the 6 microteslas
zone the MAG compass is no good – you will be in DG (gyro) mode, when you leave
the 6 microteslas zone, you switch back to MAG mode.
When you switch back to MAGNETIC MODE, the
compass heading is 220°M, the compass will now align
correctly to 215°M, in other words, -5°