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Figure 2-5.-Numerical system used in air navigation
AIRBORNE NAVIGATION SYSTEMS

Aviation Electronics Technician 1 (Organizational)
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. Course is the intended horizontal direction of travel. . Heading is the horizontal direction in which an aircraft is pointed. Heading is the actual orientation of the longitudinal axis of the aircraft at any instant, while the course is the direction intended to be made good. . Track is the actual horizontal direction made by the aircraft over the earth. . Bearing is the horizontal direction of one point to another (fig. 2-6). The direction of the island from the aircraft is marked by the line of sight (visual bearing). Bearings are usually expressed in terms of one of two reference directions: (1) true north, or (2) the direction in which the aircraft is pointed. If true north is being used as the reference, the bearing is called a true bearing. If the heading of the aircraft is the reference, the bearing is called a relative bearing. DEAD RECKONING Dead reckoning (DR) navigation is a very simple way of navigating. It uses speed and heading measurements to compute position changes from an initial position fix. One of the oldest automatic navigation systems is the dead reckoning analyzer, which takes its speed from the ship’s log and its heading from the ship’s gyrocompass to compute latitude and longitude. The error in dead reckoning, as a percentage of distance traveled, commonly reaches 2 to 5 percent. As the distance between fixes increases, the accuracy of the dead reckoning must be increased to maintain a small absolute position error. The two major causes of error in position computed by dead reckoning are errors in the measurements of heading and speed. A heading error of 1 degree introduces an error of 1.75 percent of distance traveled. A speed error of 1 percent introduces an error of 1 percent of distance traveled. The total system error becomes about 2 percent of distance traveled. Increasing the accuracy of the speed and heading measurements will increase the system accuracy. The various methods of dead reckoning and the devices that are used are described in detail in Aviation Electronics Technician 2 (Organizational), NAVEDTRA 12330. It is strongly recommended that you take the AT2(0) Nonresident Training Course, NAVEDTRA 82330, to get a better understanding of the above information. ELECTRONIC ASSISTED NAVIGATION While a navigator can successfully navigate an aircraft using basic mechanical instruments and the dead reckoning procedures, the use of electronic positioning equipment will greatly increase the accuracy of the navigation. The various fixing devices such as loran, TACAN, omega, VOR, etc., will be discussed in detail later in this chapter. Figure 2-6.-Measuring true and relative bearing. 2-6







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