NOTE If  COLD  alternates  with  the  figure  of merit  display,  the  GPS  is  performing  a cold  start. 7. Data selector switch - STAT. NOTE The  number  of  satellites  (SAT)  being  ac- quired  and  tracked  can  be  observed.  Esti- mated  position  error  (EPE)  and  figure  of merit   (FM)   can   be   monitored.   The   GPS will be ready for use when SAT 3 or SAT 4  is  displayed  on  STAT  page  1. 8.    Select    page    2    of    STAT. Check   almanac   age   (ALM). If   greater   than   5000   hours, force  a  cold  start. 9.   While   the   GPS   is   acquiring satellites,   periodically   check STAT  page  1  for  SAT  3  or SAT   4   message.   Figure   of merit   (FM)   is   another   indi- cation  of  a  converging  posi- tion  fix  and  can  be  directly monitored  from  page  1  of any  data  selection,  where FM  alternates  with  the  sys- tem  map  datum  and  other alerts. 10. SAT  3  or  SAT  4  should  be displayed  within  five  min- utes.  If  not,  check  that  posi- tion, time, track, and groundspeed  have  been  en- tered   correctly.   Also   check that   satellites   are   available. If   all   information   is   correct and  satellites  are  available, force  a  cold  start. (b.)   GPS   Quick   Start. 1. Mode selector switch - Set to NAV  directly  from  OFF.  Af- ter  power-on  test  has  been completed,  the  GPS  uses  ve- locity  estimates  from  the  air- craft’s  sensors  (if  available). If   velocity   is   not   available from  the  aircraft,  zero  veloc- ity   is   assumed.   If   position and   time   are   not   available from  the  aircraft,  the  posi- tion   estimate   from   GPS 2. 3. 4. TM  55-1510-221-10 memory  is  used,  and  the  in- ternal  low  power  time  source (LPTS)   is   used   to   initialize time. As  the  GPS  is  acquiring  sat- ellites,  position,  time,  and velocity  estimates  can  be checked   to   ensure   that   they are  within  startup  error  lim- its.  If  so,  monitor  STAT page  1.  If  not,  a  normal  start is  required. After SAT 4 is achieved with good  EPE  (Estimated  Posi- tion  Error),  and  FM  (Figure of  Merit)  of  FM3  or  below, check  position,  velocity,  and time. GPS   is   now   ready   for   nor- mal   navigation. (c.)  GPS  Cold  Start. 1. Mode  selector  switch  -  INIT. 2.  Data  selector  switch  -  OPT. 3. Slew key - Select page 4. 4. Enter  04  on  line  1. 5. Line select key 2 - Press next to  COLD  START  to  initiate. 6. Line select key 3 - Press next to   COLD   START   to   clear cold   start   message   and   re- sume  normal  display. 7. Mode  selector  switch  -  NAV. e. CHAALS  Use  of  GPS  and  INS. (1.)  CHAALS  Concept.  CHAALS   (Coher- ent  High  Accuracy  Airborne  Location  System),  is  an emitter   location   system   that   provides   timely,   high accuracy  locations  required  for  targeting  and  to  sup- port  emitter  associations  and  battlefield  situation  as- sessment.  CHAALS  provides  this  capability  through coherent  processing  of  differential  doppler  (DD)  and time   difference   of   arrival   (TDOA)   information   re- ceived  at  a  ground  facility  from  the  aircraft. CHAALS   receivers   aboard   the   aircraft   will   re- ceive  and  digitize  emitter  signals.  The  data  will  be transmitted   over   the   data   link   to   the   GR/CS   inte- grated  processing  facility  (IPF).  There,  CHAALS processors   will   perform   the   required   computations to   produce   accurate   emitter   locations.   The   precise navigation  required  will  be  provided  by  the  inertial navigation  system  (INS)  and  the  global  positioning system  (GPS).  GPS  also  provides  the  primary  means Change  2 3-76E