NOTE If  fourth  digit  from  right  is  blank,  a  valid heading  has  not  been  stored.  Proceed  with normal   preflight   procedure. TM  55-1510-221-10 NOTE 8. Monitor  data  display  for  sys- tem  alignment  state  “9“  to alignment  state  “8“.  Observe right data display will be “--- 184“. 9.   Monitor   data   display   for malfunction  codes.  Observe if  the  26V  400  Hz  power  is off,  “.03184“  will  appear  in the  right  data  display  and WARN  light  illuminates.  If magnetic  compass  system  is off,  “.03184“  will  appear  in r i g h t    d a t a    d i s p l a y    a nd WARN  light  is  extinguished. 10.   If   there   are   malfunction codes,   proceed   to   ABNOR- MAL  PROCEDURES  in this   chapter. NOTE To  achieve  best  accuracy,  engine  start  and heavy   loading   activity   should   be   delayed until  entry  into  NAV  mode. NOTE Waypoint   data   and   TACAN   station   data may  be  loaded  any  time  after  turn-on. (3.) Verify UTM Grid Coefficients: 1. Data  selector  (CDU)  -  UTM  WY PT. 2. Keys  “5”  and  “9“  -  Press  simulta- neously.   Observe   FROM-TO   dis- play  is  blank.  Earth  flatness  coef- ficient  appears  in  left  display.  The relative   earth   radius,   in   meters, appears  in  right  display. NOTE These  values  are  retained  from  turn-on  to turn-on  unless  changed  by  operator. 3.   Verify   that   values   correspond   to those  required  for  spheroid  being used. Values  for  various  spheroids  are  listed  in table 3-1. 4. If  values  are  correct,  return  CDU to   normal   display   mode   by momentarily   setting   data   selector to  any  position  except  UTM  WY PT.  If  values  are  to  be  changed, continue  with  following  steps: (4.)  Abbreviated  INS  Interface  Test  -  As required. NOTE Assuming  a  level  aircraft,  attitude  indica- tors   will   become   level   during   alignment state  “8“  and  remain  level  in  all  modes until  INS  is  shut  down.  Warning  indica- tors  for  INS  attitude  signals  from  the  INS are  valid  while  attitude  sphere  display  is level. NOTE The  INS  can  provide  test  signals  to  the Horizontal   Situation   Indicator   (HSI)   and connected  displays.  Pressing  TEST  switch during  STBY,  ALIGN,  or  NAV  mode causes  all  digits  on  connected  digital  dis- plays   to   indicate   “8’s,”   and   lights   the WYPT on the pilot’s HSI and the ALERT light.  Additional  HSI  test  signals  are  pro- vided  when  INS  is  in  ALIGN  and  data selector  is  at  any  position  other  than DSRTK/STS.   Under   those   conditions, pressing  TEST  switch  causes  HSI  to  indi- cate  heading,  drift  angle,  and  track  angle error  -  all  at  “0°"  or  “30°.“  At  the  same time,  cross  track  deviation  is  indicated  at “3.75“   nautical   miles   (one   dot)   right   or left   and   INS-controlled   HSI   flags   are retracted  from  view. NOTE Output  test  signals  are  supplied  to  the autopilot   when   INS   steering   is   selected. Rotating  AUTO/MAN  switch  to  AUTO and  pressing  TEST  during  alignment  fur- nishes  a  15°  left  bank  steering  command. A 15° right bank steering command is fur- nished  when  AUTO/MAN  switch  is  set  to MAN. 3-53