What was found
NR 1 ENGINE N1 VIBRATIONS. 6TH STAGE TURBINE AIRSEAL FAILURE REF: PW4074/77 IPC (PN 51A346) 72-53-00 FIGURE 7, ITEM 70A. A 4-INCH AXIAL BY 6-INCH CIRCUMFERENTIAL PIECE OF THE SEAL HAD BROKEN OUT & WAS MISSING. THE REMAINDER OF THE LPT SUFFERED HEAVY DOWNSTREAM DAMAGE. THE SEAL WAS OF THE POST SERVICE BULLETIN PW4G-112-72-171 CONFIGURATION. THIS IS A NEW FAILURE MODE. THE 2ND SUCH FAILURE UA HAS SEEN. SEALS FROM BOTH FAILURES HAVE BEEN RETURNED TO PW & MTU FOR ROOT CAUSE ANALYSIS.