756 



AIRBORNE NAVIGATION AND GROUND SURVEILLANCE 



100% 



90% 



70% 



60% 



i!Z 50% 

 o 



30% 



20% 



10% 



0% 



0.2 0.4 0.6 0.8 1.0 1.2 



ERROR IN%OF DISTANCE TRAVELED, LESS THAN 



1.4 



Fig. 14-13 Cumulative Frequencies of Radial Position Errors AN/APN-66. 



Over water the mean position error of the AN /APN-66(XA-2) was 1.17 

 per cent of distance traveled, in contrast to the mean error over land of 

 0.51 per cent of distance traveled. The largest position error experienced 

 over water in this series was 2 per cent. It is interesting to note that the 

 AN/APN-66 has a beamwidth, in the 7 direction, of near 3°, but does not 

 have a land-sea switch facility. Most later systems have a wider beamwidth 

 (usually near 5°), but they have a land-sea switch incorporated in them, 

 which removes a large part of the over-water bias error. 



One interesting and important aspect of doppler navigation system 

 performance is the fact that the position accuracy (in percentage of distance 

 traveled) improves for longer flight distances. Apparently the additional 



