3 PA28 ACFT WERE OPERATED IN NON COMPLIANCE OF AN AIRWORTHINESS DIRECTIVE WHEN NON CONFORMING OIL COOLER HOSES WERE INSTALLED.

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DISCOVERED OVERSIGHT DURING ROUTINE PHASE INSPECTION OF COMPANY ACFT THAT AIRWORTHINESS DIRECTIVE 95-26-13; OIL COOLER HOSE INSPECTION/REPLACEMENT WAS OVERDUE. FURTHER INVESTIGATION REVEALED THAT 2 OTHER COMPANY ACFT WERE ALSO OVERDUE. ALL 3 ACFT ARE CURRENTLY GNDED AND ARE AWAITING REPLACEMENT OF OIL COOLER HOSE ASSEMBLIES CONFORMING TO TSO-C53A; TYPE D; WHICH WHEN INSTALLED; TERMINATES THE REPETITIVE INSPECTION/REPLACEMENT REQUIREMENTS OF THE AIRWORTHINESS DIRECTIVE. DURING THE MOST RECENT ENG CHANGE ON EACH OF THE AFFECTED ACFT; THE OIL COOLER HOSE ASSEMBLIES WERE REPLACED WITH TSO-C53A; TYPE C HOSES; WHICH REQUIRES REPETITIVE INSPECTIONS AT 100 HR INTERVALS AND REPLACEMENT AT EACH 1000 HR INTERVAL OR 8 YRS; WHICHEVER IS FIRST. RECORDS SHOW THAT NO INSPECTIONS OR REPLACEMENTS TOOK PLACE AFTER THE HOSE ASSEMBLIES WERE INSTALLED AND THAT EACH ACFT ARE OVERDUE FOR HOSE REPLACEMENT. 1) AIRWORTHINESS DIRECTIVE 95-26-13 WAS PREVIOUSLY COMPLIED WITH BY INSTALLATION TO TSO-C53A; TYPE D HOSE ASSEMBLIES AND WERE SIGNED OFF IN ALL 3 AFFECTED ACFT LOGBOOKS AS 'NO FURTHER ACTION REQUIRED' AND THE AIRWORTHINESS DIRECTIVE THEN LISTED AS A NON-RECURRING AIRWORTHINESS DIRECTIVE. 2) DURING THE MOST RECENT ENG CHANGE; THE TYPE D HOSES WERE SENT OUT AS SAMPLES FOR FABRICATION BY AN OUTSIDE HOSE SHOP AND TYPE C HOSES WERE SUBSTITUTED AND RETURNED. 3) FAILURE TO RECOGNIZE SUBSTITUTION OF HOSE TYPE PRIOR TO INSTALLATION OF HOSE ASSEMBLIES AND THAT REPETITIVE INSPECTION/REPLACEMENT OF THE TYPE C HOSES WERE NOW REQUIRED.