TM 55-1560-307-13&P Code Explanation AO-(Assembled by Items with these codes are not to be requested/ org/AVUM Level) requisitioned individually.  The parts that make AF-(Assembled by up the assembled item must be requisitioned or DS/AVIM Level) fabricated and assembled at the level of maint- AH-(Assembled by enance indicated by the source code.  If the 3rd GS Category) position code of the SMR code authorizes you to AL-(Assembled by replace the item, but the source code indicates SRA) the items are assembled at a higher level, order AD-(Assembled by the item from the higher level of maintenance. Depot) XA Do not requisition an "XA"-coded item.  Order its next higher assembly.  (Also, refer to the NOTE below.  ) XB If an "XB" item is not available from salvage, order it using the CAGE and part number given. XC  Installation  drawing,  diagram,  instruction  sheet,  field service  drawing,  that  is  identified  by  manufacturer's  part number. XD   Item   is   not   stocked.      Order   an   "XD"-coded   item through normal supply channels using the CAGE and part number given, if no NSN is available. NOTE Cannibalization or controlled exchange,   when   authorized,   may   be used  as  a  source  of  supply  for  items with  the  above  source  codes,  except for  those  source  coded  "XA"  or  those aircraft   support   items   restricted   by requirements of AR 750-1. (2)  Maintenance Code.  Maintenance code tells you  the  level(s)  of  maintenance  authorized  to  USE  and REPAIR   support   items.      The   maintenance   codes   are entered in the third and fourth positions of the SMR Code as follows: (a)    The  maintenance  code  entered  in  the third   position   tells   you   the   lowest   maintenance   level authorized  to  remove,  replace,  and  use  an  item.    The maintenance    code    entered    in    the    third    position    will indicate  authorization  to  one  of  the  following  levels  of maintenance. Code Application/Explanation C -Crew    or    operator    maintenance    done    within organizational or aviation unit maintenance. O -Organizational    or    aviation    unit    category    can remove, replace, and use the item. F -Direct support or aviation intermediate level can remove, replace, and use the item. H -General  support  level  can  remove,  replace,  and use the item. L -Specialized  repair  activity  can  remove,  replace, and use the item. D -Depot  level  can  remove,  replace,  and  use  the item. (b)    The  maintenance  code  entered  in  the fourth   position   tells   whether   or   not   the   item   is   to   be repaired and identifies the lowest maintenance level with the   capability   to   do   complete   repair   (i.e.,   perform   all authorized repair functions.) (NOTE:  Some limited repair may be done on the item at a lower level of maintenance, if authorized by the Maintenance Allocation Chart (MAC) and  SMR  codes.)  This  position  will  contain  one  of  the following maintenance codes. C-3