TM  5-2815-240-34&P Change 3        B-3 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 items source coded “XA”. d. 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 follows: (1) 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 the following levels of maintenance: B-3.   EXPLANATION OF COLUMNS IN THE REPAIR PARTS LIST AND SPECIAL TOOLS LIST WORK PACKAGE (Continued). XA XB XC XD Do not requisition an “XA” coded item. Order the next higher assembly (refer to NOTE below). If an item is not available from salvage, order it using the CAGE Code and P/N. Installation  drawings,  diagrams, instruction sheets, field services drawings;  identified  by  manufacturer’s P/N. Item is not stocked.  Order an XD- coded item through normal supply channels using the CAGE Code and P/ N given, if no NSN is available. AO-Assembled by   unit/AVUM level AF-Assembled by   DS/AVUM level AH-Assembled by   GS level 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 level of maintenance indicated by the source code.  If the 3rd position of the SMR code authorizes you to replace the item, but the source code indicates the item is assembled at a higher level, order the item from the higher level of maintenance.