marks bracket and move with the B-trace, and the antenna is controllable in azimuth. All symbols that were  present  in  automatic  search,  including  the artificial horizon, are present in manual search. The horizon line still functions to indicate aircraft attitude. It should also be reasonable to expect to see no targets other than the ones that appear on the range sweep line, since the antenna is no longer scanning. Fire Control (Lock on) The  lock  on  mode  is  a  momentary  mode  of operation between manual track and automatic track. Some   radars   combine   the   previously   described manual operations and lock on mode into one mode called “acquisition.”  The term acquisition,  as used in operation  of  a  radar  set,  refers  to  a  momentary  mode of operation. The time period for acquisition begins at the moment the operator depresses a control switch transferring antenna control from automatic search to manual search. During this period, the operator has complete  control  of  antenna  position,  both  in  azimuth and elevation, and may also control a symbol on the indicator  called  an  “acquisition  symbol.”  If  the operator   places   the   acquisition   symbol   over   the selected  target,  it  causes  coincidence  between  the tracking gate and the target in the range and tracking circuits  of  the  radar.  Acquisition  is  complete  when lock on occurs, and the system switches to automatic track.  Lock  on  is  accomplished  by  a  change  in  the B-scope  presentation  and  the  blanking  of  the  PPI scope. However, in the trainer, manual track may be continued  after  leek  on,  if  desired. On   the   B-scope,   the   acquisition   symbol   is removed and replaced with a range strobe or notch superimposed on the target, as shown in figure 3-13. The artificial horizon remains as before. Note there are two symbols present now that were not previously present. One of these is a small dot, called a steering dot.  The  purpose  of  the  steering  dot  is  to  indicate antenna  position,  which  also  presents  target  position with  respect  to  the  attacking  aircraft.  For  a  pure pursuit  course,  the  pilot  need  only  maneuver  the aircraft  to  cause  the  steering  dot  to  remain  in  the center of the scope. When the steering dot is in the center of the scope on a pure pursuit course, the target is dead ahead of the attacking aircraft. The  second  symbol,  which  was  not  present  in  the previous  modes,  is  a  circle.  This  circle  is  called  a “range   circle,”   and  its  diameter  is  proportional  to range.  Normally,  lock  on  occurs  at  near  maximum range,  which  produces  a  range  circle  of  maximum size.  As  the  range  between  the  attacking  aircraft  and the target decreases, the diameter of the circle also decreases,  keeping  the  operator  informed  of  the  range to the target. In addition to these symbols, two other indications of range are presented at the time the radar locks on. A light, known as the lock on or acquisition light, is illuminated when the target has been acquired and  lock  on  has  been  accomplished.  Range  is  also presented in digital form in a small window similar to the  mileage  counter  of  an  automobile. Fire Control (Automatic Track) The  automatic  track  submode  of  fire  control results from the manual track mode upon release of the  manual  controls  (range  and  azimuth).  Remember, prior  to  automatic  tracking,  the  antenna  had  been manually controlled in both elevation and azimuth, and the range strobe (notch) had been controlled by the range control. To initiate automatic tracking, the operator releases the manual controls, and the radar switches to automatic track. At this time, the antenna is  caused  to  track  the  target  by  the  antenna  servo system error circuits. Range  tracking  is  accomplished  in  the  range tracking circuits. Automatic tracking continues until one of three things occurs. First, lock on will be lost if the attacking aircraft is closing on the target at a rate greater than 700 knots, or if an opening rate greater than 200 knots should occur. Second, the target will be lost, and the radar will unlock if the target does not remain within the tracking window (antenna limits in azimuth and elevation). Finally, the target will be lost if  the  range  exceeds  maximum  tracking  range. Figure 3-13.-B-scan presentation after lock on. 3-14