What was found
DURING REPLACE OF THE RT ENGINE, AFT LOWER COWLING FWD BULKHEAD P/N 101-910038-3, CRACKS WERE DISCOVERED IN THE LT AND RT COWLING AFT DUCTS P/N 101-910049-11 AND 101-910049-12 UPPER MOUNTING FLANGES. THIS AREA IS ONLY ACCESSIBLE BY REMOVING THE PANEL (DOOR) PN 101-910049-47 LOCATED IN THE CTR OF THE AFT COWL DUCT ASSY AND USING A BRIGHT LIGHT AND A MIRROR OR BY USE OF A BORESCOPE. THIS PROBLEM WAS DISCOVERED ON A HIGH TIME ACFT WITH 9010 HOURS TT IN SERVICE, BUT THE CONDITION COULD BE PRESENT ON LOWER TIME ACFT. RECOMMEND THIS AREA BE INSPECTED DURING A 'DETAILED ENGINE INSP' SUCH AS A PHASE 4 OF THE ACFT RECOMMENDED INSP PROGRAM.