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The north magnetic pole is located close to 71° N latitude, 96° W longitude and is about 1,300 miles from the geographic 63 or true north pole, as indicated in Figure 16-8. If the Earth 3 3 3 were uniformly magnetized, the compass needle would point 7 2 0 3 W W W N W N W N N W N N N E N E N E E N E 6 9 t T s i A S t o n h h t N c w t e a o e t t w u a r m e ( s r a a s n d e a l , s l c g b y t t s t h h n y , i h e o e e t o t h n t m h n i w e c e o e a E n e f m g p a d n t b o r a h l e t y l e g h e e t i n , t u c i m h e s b s p t e u n e u i o c r a o t g l i l t e m d e i l u t , y o i e a i n m g n p r n i r i f o s w a a d o . y i p i r h n a m h i t v n c s i a l c s h y ) i r a n y c l m c a o t m i s a h n u e g e e l n t d c r h g i e e d b e e t r i i e t n v z a a e a m e n i r n r d s a i e ) . a l a g I t a s n i d e o n u o i t n r d r h g e e e b r c M d a e U t p i a t N o w n h t n i i a e t c ( n e e o a a d y n s f l S S 2 4 W W 2 S W S S S E S S E 5 S E 1 2 l o S d o f i t c r a v e a te a c li s r t t i i i a o h e t n a s i o s b o n y b f e a m e t v n a t a h n r c o i y a a u t r d s i e e a o f g n n u r d , l e l s y e w o s h d . f e i C s c t e o e h l r n e m c s c e h t i e q n a d u e n d e g lo n . e c t T l a s y h t l , i e i o g t h n a h e m s t l e i y o n x u a f t n c h r t o t e m a a U m n d n t o i i u m t t e h n d e e t 1 1 to time, are shown on most aeronautical charts as broken 18 magenta lines called isogonic lines that connect points of equal magnetic variation. (The line connecting points at which there is no variation between TN and MN is the agonic Figure 16-6. Compass rose. line.) An isogonic chart is shown in Figure 16-9. Minor bends and turns in the isogonic and agonic lines are caused The true heading (TH) is the direction in which the nose of by unusual geological conditions affecting magnetic forces the aircraft points during a flight when measured in degrees in these areas. clockwise from TN. Usually, it is necessary to head the aircraft in a direction slightly different from the TC to offset On the west coast of the United States, the compass needle the effect of wind. Consequently, numerical value of the TH points to the east of TN; on the east coast, the compass needle may not correspond with that of the TC. This is discussed points to the west of TN. more fully in subsequent sections in this chapter. For the purpose of this discussion, assume a no-wind condition exists under which heading and course would coincide. Thus, for a TC of 065°, the TH would be 065°. To use the compass accurately, however, corrections must be made for magnetic variation and compass deviation. Variation Variation is the angle between TN and magnetic north (MN). It is expressed as east variation or west variation depending upon whether MN is to the east or west of TN. TN Course A to B 065° MN 065° B 245° A Course B to A 245° Figure 16-8. Magnetic meridians are in red while the lines of longitude and latitude are in blue. From these lines of variation Figure 16-7. Courses are determined by reference to meridians on (magnetic meridians), one can determine the effect of local magnetic aeronautical charts. variations on a magnetic compass. 16-6