DURING A WEEKLY AIRCOURSE EXAM A FALL WAS FOUND 1 X CUT INBY STATION 0917 INT HE #1 RETURN ENTRY OF NORTH MAINS. ALL ACCESSES TO FALL WERE TIMBERED OFF AND DANGER SIGN HUNG. THE FALL IS ABOUT 30' LONG, 20' WIDE AND 6"" HIGH. THE AREA WAS BOLTED WITH 60"" INSTALL B RESIN BOLTS WITH 6""X16"" PLATES AND CABLE BOLTS. NO MEN OR EQUIPMENT WERE INVOLVED.