TM 10-1670-287-23&P 0064 00 NOTE Cannibalization or controlled exchanged, 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 item  restricted by requirements of AR 750-1.  Maintenance Code. Maintenance codes tell 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 follow:  Third position. 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.  Fourth position. 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.) 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  code. This position will contain one of the following maintenance codes.  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. MAINTENANCE CODE  APPLICATION/EXPLANATION  O -  Organizational (or aviation unit) is the lowest level  that can do complete repair of the item.  F -  Direct support (or aviation intermediate) is the  lowest level that can do complete repair of the  item. 0064 00-3 