At startup, the crew programs the aircraft location, departure  runway, DP (if applicable), WPs defining the route, approach  procedure, approach to be used, and routing to alternate. This  may be entered manually, be in the form of a stored flight  plan, or be a flight plan developed in another computer and  transferred by disk or electronically to the FMS computer.  The crew enters this basic information in the control/display  unit (CDU).  [Figure 9-42] Once airborne, the FMS computer channels the appropriate  NAVAIDs and takes radial/distance information or  channels two NAVAIDs, taking the more accurate distance  information. FMS then indicates position, track, desired  heading, groundspeed, and position relative to desired track.  Position information from the FMS updates the INS. In more  sophisticated aircraft, the FMS provides inputs to the HSI,  RMI, glass flight deck navigation displays, head-up display  (HUD), autopilot, and autothrottle systems. a target is precisely timed. From this, the distance traveled  by the pulse and its echo is determined and displayed on a  radar screen in such a manner that the distance and bearing to  this target can be instantly determined. The radar transmitter  must be capable of delivering extremely high power levels  toward the airspace under surveillance, and the associated  radar receiver must be able to detect extremely small signal  levels of the returning echoes. The radar display system provides the controller with a map- like presentation upon which appear all the radar echoes  of aircraft within detection range of the radar facility. By  means of electronically-generated range marks and azimuth- indicating devices, the controller can locate each radar target  with respect to the radar facility, or can locate one radar target  with respect to another. Another device, a video-mapping unit, generates an actual  airway or airport map and presents it on the radar display  equipment. Using the video-mapping feature, the air traffic  controller not only can view the aircraft targets, but can see  these targets in relation to runways, navigation aids, and  hazardous ground obstructions in the area. Therefore, radar  becomes a NAVAID, as well as the most significant means  of traffic separation. In a display presenting perhaps a dozen or more targets,  a primary surveillance radar system cannot identify one  specific radar target, and it may have difficulty “seeing” a  small target at considerable distance—especially if there is  a rain shower or thunderstorm between the radar site and  the aircraft. This problem is solved with the Air Traffic  Control Radar Beacon System (ATCRBS), sometimes  called secondary surveillance radar (SSR), which utilizes  a transponder in the aircraft. The ground equipment is an  interrogating unit, in which the beacon antenna is mounted  so it rotates with the surveillance antenna. The interrogating  The HUD is a display system that provides a projection of  navigation and air data (airspeed in relation to approach  reference speed, altitude, left/right and up/down GS) on a  transparent screen between the pilot and the windshield.  Other information may be displayed, including a runway  target in relation to the nose of the aircraft. This allows the  pilot to see the information necessary to make the approach  while also being able to see out the windshield, which  diminishes the need to shift between looking at the panel to  looking outside. Virtually any information desired can be  displayed on the HUD if it is available in the aircraft’s flight  computer and if the display is user definable.  [Figure 9-43] Radar works by transmitting a pulse of RF energy in a specific  direction. The return of the echo or bounce of that pulse from  Head-Up Display (HUD) Radar Navigation (Ground-Based) Function of FMS Figure9-42 .  Typical display and control unit(s) in general aviation. The Universal UNS-1 (left) controls and integrates all other systems. The  Avidyne (center) and Garmin systems (right) illustrate and are typical of completely integrated systems. Although the Universal CDU is not  typically found on smaller general aviation aircraft, the difference in capabilities of the CDUs and stand-alone sytems is diminishing each year. The Universal UNS-1 The Avidyne The Garmin system 9-46