TM 5-1080-250-12&P C-3 Code Explanation AO - Assembled by org/   AF - Assembled by DS/   AH - Assembled by GS   category AL - Assembled by  SRA AD - Assembled by Depot Items with these codes are not to be requested/requisitioned individually.  The parts that make up the assembled item must be requisitioned or fabricated and assembled at the category of maintenance indicated by the source code.  If the 3rd position code of the SMR code authorizes you to replace the item, but the source code indicates the item is assembled at a higher category, order the item from the higher level of maintenance. Code       Explanation XA -   Do not requisition an "XA"-coded item.  Order its next higher assembly. (Refer to the NOTE below). XB -   If an "XB" item is not available from salvage, order it using the CAGEC and Part Number given. XC -   Installation drawing, diagram, instruction sheet, field service drawing, that is identified by manufacturer's part umber XD -   Item is not stocked. Order an "XD"-coded item through normal supply channels using the CAGEC 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 codes tell you the levels of maintenance authorized to USE and REPAIR support items.  The maintenance codes are entered in the third and fourth positions or the SMR code as follows: (a) The maintenance code entered in the third position tells you the lowest maintenance category authorized to remove, replace, and use an item.  The maintenance code entered in the third position will indicate authorization to one of the following categories of maintenance. Code Application/Explanation C - Crew or operator maintenance done within unit AVUM maintenance. O - Unit level /AVUM maintenance can remove, replace, and use the item. F - Direct support/AVIM maintenance can remove, replace, and use the item. H - General support maintenance can remove, replace, and use the item. L - Specialized repair activity can remove, replace, and use the item. D - Depot 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 category   of maintenance, if authorized by the Maintenance Allocation Chart (MAC) and SMR codes.)  This position will contain one of the following maintenance codes.