the outputs is used for the automatic frequency control (AFC) circuits. The other output is routed to the summing network, which provides a composite video output to the display indicator. The display indicator displays the video on the CRT. The operator can then set the position by aligning the master and slave pulses and reading the time delay. This information is then plotted on a chart to determine aircraft position. Loran-D uses the same theory of operation,but it is used in conjunction with the navigational computer. With this system, the indicator automatically displays the latitude and longitude of the aircraft. The operator just has to plot this information on a chart to determine position. OMEGA The omega navigation system is an outgrowth of the loran A and loran C systems. It is a worldwide network of eight transmitting stations that provide a means of navigation accurate to within 4 nautical miles anywhere in the world. Theory of Operation The AN/ARN-99(V) omega navigation set provides digital data representative of aircraft phase displacement to any combination of eight selected omega ground stations.    These eight ground stations broadcast 10 kW in the VLF band at 10.2 kHz, 11.3 kHz, and 13.6 kHz. These stations are strategically positioned around the world so their combined propagation will cover the entire surface of the earth. Each station transmits burst of the three different frequencies during a 10-second period, which are multiplexed so that only one station is on at one time on one frequency. All signals are transmitted starting at zero time (omega time), and maintained at the exact starting time by using atomic clocks at each station. The omega system in an aircraft must synchronize itself to this pattern. Synchronization is done by analyzing all the signals received in the 10.2-kHz frequency over one 10-second period. This period is broken up into 100 intervals of 0.1 second each. The beginning of each of these 0.1-second intervals is then considered a possible starting point. The signal levels are averaged over small intervals during the remaining 9.9 seconds of the pattern for each of the 100 intervals, and then all are compared with the predicted levels. Only one start time fits into the predicted pattern. When this start time is found, the omega system knows where each frequency is originating from during each burst. It can then make the proper measurements from each station. If the system cannot synchronize at 10.2 kHz, it will try to synchronize at 11.3 kHz and then at 13.6 kHz. The omega system uses the great circle distances to all stations. This is done to ensure that the effects of modal interference (interference between the primary wave and the sky wave and/or ground wave) and wrong way propagation do not bias the measurements. The stations less than 600 or more than 7,200 nautical miles from the aircraft are not used for the measurements. They are deselected and their strength readings indicate zero. Station range and bearings are recomputed every 10 seconds in the burst filter routine, and station selection/reselections correspondingly made. The omega system can use either the hyperbolic or the circular (RHO-RHO) method to process this data. The P-3C uses the circular measurement process, which measures phase from each station directly. With RHO-RHO processing, a line of position is generated from each station by direct measurement of the omega signal received from that station. Using another station and again generating another line of position, the position fix is found. The advantage of this method is that only two stations are required to establish a geographical fix. The disadvantage of this method is its need to establish the oscillator error of its receiver before the omega signals can be used. Since circular processing measures phase directly, it must subtract oscillator error from the measurement to be accurate. The RHO-RHO method uses a software routine based on many measurements to solve for this error. The omega on the P-3C is totally dependent on the central computer for operation. There are no operating controls or indicators other than the elapsed time meter and the power control panel. Components The AN/ARN-99(V) consists of three major components. These components are a control panel, an antenna coupler, and a receiver-converter. OMEGA POWER CONTROL PANEL.— The 960767 omega power control panel (fig. 2-15) controls the power to the omega system. When 2-16