TM 1-1510-223-10 Change 3          3-77 doppler (DD) and time difference of arrival (TDOA) infor- mation  received  at  a  ground  facility  from  the  aircraft. CHALS receivers aboard the aircraft will receive and digi- tize emitter signals. The data will be transmitted over the data  link  to  the  GR/CS  integrated  processing  facility (IPF).  There,  CHALS  processors  will  perform  the  re- quired computations to produce accurate emitter loca- tions. The precise navigation required is provided by the inertial navigation system (INS) and the global position- ing system (GPS). GPS also provides the primary means of time synchronizing the CHALS receivers (signal condi- tioners or SC’s) aboard the aircraft. A backup for the GPS is provided by the data link. The resultant emitter reports will be sent to GR/CS by CHALS. b.   GPS (and INS) movement. The accurate and time- ly navigation (position and velocity) is provided by inte- grating an INS with a GPS, and integrating both (through a series of intermediaries) with a CHALS ground based navigation   processor   (NP).   The   SC,   data   link,   and CHALS HSSP (high speed signal processor) form the communication link. The critical airborne interfaces for CHALS navigation and time synchronization include the following: (1)    INS to GPS and CHALS: Acceleration Velocity Position Altitude (2)    GPS to CHALS: Time mark pulse (time synchronization) Navigation data block (position, velocity, and time) Error state vector data block (9 element ESV, time) TM/covariance data block (time, TM time, covarian- ce) Status data block (status including DOP’s and FOMN) Section  IV. RADAR AND TRANSPONDER 3-30.   RADAR   AND   TRANSPONDER   EQUIPMENT GROUP DESCRIPTION. The radar and transponder group consists of a weath- er radar, lightning sensor system, transponder, and en- coding  altimeter  indicator.  The  transponder  and  radar group  includes  an  identification,  position,  emergency tracking system, and a radar and lightning sensor system to locate potentially dangerous weather areas. 3-31.   WEATHER RADAR SYSTEM (WC-650). The weather radar system is a light weight, X-band digital radar with alphanumerics designed for weather detection and analysis and ground mapping. The radar system  is  controlled  from  the  radar  control  panel  (fig. 3-29), located on the pedestal extension (fig. 2-12). Ra- dar information is displayed on the pilot’s and copilot’s EHSI. NOTE The weather radar may display false echoes and spikes on all ranges when the VHF-FM (SINC- GARS) transceiver is transmitting. The primary purpose of the system is to detect storms along the flight path and give the pilot a color visual indi- cation of there rainfall intensity. After proper evaluation, the pilot can chart a course to avoid these storm areas. Figure 3-30 depicts a typical EFIS weather test pat- tern (120 degree scan). WARNING The   system   performs   only   the   functions   of weather detection or ground mapping. It should not be used nor relied upon for proximity warning or anti-collision protection. Output power is radiated during test mode. CAUTION If the radar system is to be operated in any mode other than standby while the aircraft is on the ground: Direct the nose of the aircraft so that the antenna scan sector is free of large metallic ob- jects such as hangars or other aircraft for a dis- tance of 100 feet (30 meters). Do not operate during refueling of aircraft or de- fueling operation within 100 feet (30 meters). Do  no  operate  if  personnel  are  standing  too close  to  the  270-degree  forward  sector  of  the aircraft (fig. 3-31). Operating personnel should be familiar with FAA AC 20-68B.