Navigation  is  both  an  art  and  a  science.  The science part is the development of instruments and procedures   of   navigation,   along   with   the computations involved. The art is the skillful use of the instruments and the interpretation of the data. This combination has led some to call navigation a “scientific art.” The  beginning  navigators  practiced  the  science  of navigation, in that they gathered data and used it to solve a navigational problem in a mechanical way. It takes many hours of flying for navigators to realize that their total role involves not only the mechanics of navigation, but an integration based on judgement. They   build   accuracy   and   reliability   into   their performance  by  applying  sound  judgment  based  on experience.  Navy  navigators  must  be  able  to  plan missions covering every possible situation. In flight, they must evaluate the progress of the aircraft and plan  for  the  remainder  of  the  mission.  High-speed navigation  demands  that  they  have  the  ability  to anticipate changes in flight conditions and make the correct  decisions  immediately  ahead  of  those changes. The  purpose  of  air  navigation  is  to  determine  the direction  of  travel  needed  to  end  up  at  the  desired location, to locate positions, and to measure distance and time as a means to that end. This chapter deals with   the   various   types   of   navigation   and   the equipment used in aviation navigation. You must know  and  understand  this  information  in  order  to  train your  subordinates. METHODS OF NAVIGATION Learning Objective:    Recognize  the  various methods  of  navigation. There are certain terms that you must know to understand navigation. The  navigator  uses  these terms  to  express  and  accomplish  the  practical  aspects of air navigation. These terms are  position,   direction, distance,  and  time.  These  terms  are  defined  as follows: Position  is a point defined by stated or implied coordinates. It always refers to some place that can be identified. A navigator must know the aircraft’s immediate  position  before  he/she  can  direct  it  to another  position. Direction  is  the  position  of  one  point  in  space relative to another without reference to the distance between them. Direction is not in itself an angle, but it is measured in terms of its angular distance from a reference   direction. Distance  is  the  spatial  separation  between  two points  and  is  measured  by  the  length  of  a  line joining  them.  On  a  plane  surface,  this  is  a  simple problem.  However,  consider  distance  on  a  sphere, where   the   separation   between   points   may   be expressed  as  a  variety  of  curves.  The  navigator must  decide  how  the  distance  is  to  be  measured. This  distance  can  be  expressed  in  various  units; miles, yards, etc. Time  is  defined  in  many  ways,  but  for  our purposes, it is either the hour of the day or an elapsed interval. These   terms   represent   definite   quantities   or conditions   that   can   be   measured   in   several different   ways.    The  position  of  an  aircraft  may be  expressed  as  coordinates  such  as  latitude  and longitude,  or  as  being  10  miles  south  of  a  certain landmark.  It  is  vital  that  navigators  learn  how  to measure  quantities  and  how  to  apply  the  units  by which  they  are  expressed. EARTH’S SIZE AND SHAPE For navigational purposes, the earth is assumed to be a perfect sphere, although it is not. There is an approximate 12-mile difference between the highest point and the lowest point of the earth’s crust. The variations  in  the  surface  (valleys,  mountains,  oceans, etc.) give the earth an irregular appearance. Measured   at   the   equator,   the   earth   is approximately 6,887.91 nautical miles in diameter. The polar diameter is approximately 6,864.57 nautical miles. This difference of 23.34 nautical miles is used to express the ellipticity of the earth. Great Circles and Small Circles A great circle is defined as a circle on the surface of a sphere whose center and radius are those of the 2-2