TM 55-1510220-10 NOTE To   achieve   best   accuracy,   engine   start   and heavy  loading  activity  should  be  delayed  until entry into NAV mode. (2) Verify  UTM  grid  coefficients  (if  UTM  coordinates are to be used). (a) Data selector (CDU) UTM WY PT. (b) Keys"5" and "9" Press simultaneously. Observe  TO-FROM  display  is  blank.    Earth flatness   coefficient   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. (c) Verify     that     values     correspond     to     those required for spheroid being used. NOTE Values for various spheroids are listed in table 3-1. (d)     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 the following steps: NOTE The INS geographic position, as read in  L/L  displays,  will  not  be  affected by any changes in these coefficients. (e)     Keys"2"  or  "8"  Press  to  indicate  following  is the   flatness   coefficient.      Observe   INSERT/ ADVANCE pushbutton annunciator illuminates. (f)     Load   earth   flatness   coefficient   by   pressing keyboard  keys  in  sequence.  Example: 2 9 4 9 8 = 29498.  Observe numbers appear in left display as keys are pressed. (g)     INSER/ADVANCE     pushbutton               Press. Observe INSERT/ ADVANCE pushbutton annunciator extinguishes. (h)     Keys"4"   or   "6"   Press,   to   indicate   that   the following     load     is     relative     earth     radius. Observe INSERT/ADVANCE pushbutton annunciator illuminates. (i)     Load   relative      earth      radius      by   pressing keyboard keys in sequence.  Example: 8 2 0 6 m  =  8206.    Observe  numbers  appear  in  the right display as keys are pressed. NOTE Zone symbol is to be ignored. (j) INSERT/ADVANCE    pushbutton            Press. Observe        INSERT/  ADVANCE  pushbutton annunciator extinguishes. (k)     Data   selector   (CDU)   UTM   POS.      Observe coordinate will reflect values of new spheroid. (3) Abbreviated INS interface test As required: NOTE Assuming a level aircraft, attitude indicators     will     become     level     during alignment  state  "8"  and  remain  level  in all    modes    until    INS    is    shut    down. Warning    indicators    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  displays  to  indicate  "8's"  and  the HSI and the ALERT annunciators illuminate.    Additional  HSI  test  signals are provided 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 indicate  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. Change 2        3-51