What was found
THE SUBSEQUENT INVESTIGATION AT PWA HAS REVEALED THAT THE CRACKING OF THE TURBINE SUPPORT CASE OUTER SKIRT WAS DUE TO MULTI-ORIGIN LOW CYCLE FATIGUE ALONG THE WELD HEAT AFFECTED ZONE. THE MODIFIED MICRO-STRUCTURE OBSERVED IN THE WELD HEAT AFFECTED ZONE CLOSE TO THE FRACTURE SURFACE WAS A CONTRIBUTING FACTOR AND MAY HAVE BEEN CAUSED BY HEAT TREATMENT OR ENGINE OPERATION. REFERENCE HNAA9792609. (M)