What was found
(CAN) TAIL ROTOR HALF SHELL BEARINGS CONSIST OF 4 SEPARATE BEARINGS TO MAKE 1 SET. 2 OF THE 4 BEARINGS WERE FOUND WITH CRACKS THAT EXTENDED AROUND A CORNER OF THE RUBBER AND CONTINUED ALONG THE OTHER EDGE AND THE CRACKS WERE BEYOND ALLOWABLE LIMITS. THE HALF SHELLS ARE ON CONDITION ITEMS WITH MANDATORY INSPECTIONS AT "ALF/7 DAYS/10 HOURS" IAW AD 2012-0257. THEY HAVE BEEN FOUND TO LAST AN AVERAGE OF 500-700 HOURS BUT AS A PREVENTATIVE MAINTENANCE PROCEDURE, WE CHANGE THE SET OF HALF SHELL BEARINGS EVERY 500 HOURS WHILE PERFORMING THE MANDATORY AD 84-064-037(B) R3 "TAIL ROTOR BLADE SPAR INSPECTION". THIS IS THE FIRST TIME IN OUR FLEET WE HAVE HAD TO PREMATURELY REMOVE THESE BEARINGS.