TM 1-1510-223-10 Change 3          3-75 was depressed. This difference is displayed in nautical miles and tenths if LAT/LONG is selected, and in kilome- ters and tenths if UTM is selected. 3.   To accept the INS update - Depress L1 (UPDATE ACCEPT). 4.   To reject the INS update - Depress L2 (UPDATE REJECT). (9)    INS  stored  heading  procedure.  An  accurate INS  heading  and  the  local  magnetic  variation  will  be stored in the computer memory by performing the stored heading shutdown procedure. This will allow the INS to be ready for the next flight in a shorter period of time. NOTE Once a stored heading alignment has been per- formed, the next alignment must be a full align- ment. (a)   Stored heading shut down.   1.   Come  to  a  complete  stop  in  desired parking position. 2.   Wait  for  STORED  HEADING  to  ap- pear in the advisory box on the MFD. This  will  take  approximately  5  min- utes. 3.   INS mode selector - OFF. NOTE After completion of the stored heading shutdown the aircraft must not be moved until the stored heading alignment is complete. If more than one week elapses prior to the next alignment,  a  stored  heading  alignment  should not be attempted. (b)   Stored heading alignment.  This procedure may be done before or after starting the engines. If prior to engine start (GPU), the complete procedure must be done before engaging the starter switch to ensure the data is not dropped from the INS due to power drop. 1.   INS mode selector - STBY. 2.   B mode selector switch - Depress to call up FPLN page. 3.   R5  line  selector  switch  -  Depress  to call up NAV SETUP page. 4.   R5  line  selector  switch  -  Depress  to call up INS SETUP page. 5.   Valid   alignment   data   -   Enter   into scratchpad. “2” for LAST KNOWN as long as this reflects the correct present position coordinates, or scratchpad in correct coordinates. 6.   L1 - Depress to enter position. 7.   INS mode selector - NAV. 8.   Wait for completion of alignment. This will take 7 to 8 minutes. This can be confirmed  by  noting  that  the  ALIGN STATE legend at L1 of the INS SETUP page has disappeared. NOTE Do not move the aircraft until the alignment is complete. 3-28.   GLOBAL POSITIONING SYSTEM (AN/ ASN-149 ((B)3)). a.   Description. The GPS is used to provide updated position information to the inertial navigation system and to  mission  equipment.  The  GPS  system  consists  of  a receiver-processor, an antenna electronics unit, and an antenna. The GPS is controlled by the aircraft survivabil- ity equipment/avionics control system (ASE/ACS). b.   GPS Normal Operation. (1)    Turn-On Procedure. 1.   BATTERY  switch  (overhead  control panel, fig. 2-13) - ON. 2.   AVIONICS MASTER POWER SWITCH (overhead control panel, fig. 2-13) - ON. 3.   #1 3 AC inverter control switch (mis- sion control panel, fig. 4-1) - RESET, then ON. 4.   A mode selection switch (multifunction display,  fig.  4-2)  -  Depress  to  select UTILITY  page. 5.   B mode selection switch (multifunction display,  fig.  4-2)  -  Depress  to  select FLIGHT PLAN page. 6.   R5 line selection switch - Depress to select NAV SETUP page. 7.   R4 line selection switch - Depress to select GPS SETUP page. NOTE On the GPS SETUP page, data fields are filled with dashes if data is unavailable from the GPS or if the data is invalid.