MECHANIC REPORTS AN ANNUAL INSPECTION OF THEIR CESSNA-172 NOTED THE AIRWORTHINESS DIRECTIVE (AD) TO INSPECT THE PILOT AND CO-PILOT'S SEAT BACK SUPPORT BRACKETS FOR CRACKS HAD BEEN MISSED ON TWO PREVIOUS; 100 HOUR INSPECTIONS.

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AIRWORTHINESS DIRECTIVE 2008-05-09 SEAT BACK SUPPORT BRACKET COULD CRACK; CAUSING SEAT BACK TO FAIL. IT WAS MISSED ON 2 PREVIOUS 100 HR INSPECTIONS (FIRST ON MAY/XA/08; SECOND ON JUL/XA/08) CAUSING PLANE TO FLY OVER AIRWORTHINESS DIRECTIVE BY ABOUT 170 HRS. IT WAS CAUGHT ON ANNUAL INSPECTION ON OCT/XA/08 CAUSING PLANE TO BE GNDED UNTIL PARTS CAME IN NOV/08. NO CRACKS WERE NOTED AT THIS TIME. TO PREVENT THIS PROB FROM HAPPENING AGAIN; I WILL BE DOING AIRWORTHINESS DIRECTIVE CHKS AT EVERY 100 HR INSPECTION; AND NOT JUST WAITING FOR ANNUAL INSPECTION. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THE AIRWORTHINESS DIRECTIVE (AD) 2008-05-09 INVOLVED INSPECTING THE PILOT AND CO-PILOT'S SEAT BACK SUPPORT BRACKET FOR CRACKS THAT COULD CAUSE THE SEAT BACK TO FALL BACKWARDS (AFT). REPORTER STATED THIS AD ONLY APPLIES TO CERTAIN SEAT BACKS WITH SPECIFIC SERIAL NUMBERS ON CESSNA 172 AIRCRAFT AND POSSIBLY OTHER CESSNA MODEL AIRCRAFT. NO CRACKS WERE FOUND ON THEIR CESSNA. REPORTER STATED SINCE THE MISSED INSPECTIONS; THEY HAVE CONTRACTED WITH A MAINTENANCE TRACKING SOFTWARE COMPANY THAT WILL PROVIDE AN UPDATE OF ALL AIRWORTHINESS DIRECTIVES IN A CD FORMAT EVERY TWO WEEKS.