All Nippon Airways

Dear Sir or Madam: The purpose of this letter is to provide you with ANA’s comments and requested changes to the NPRM and proposed AD for the GE90-115B family HPC Stg.2-5 spool program, as communicated by NPRM docket #FAA-2011-0278. 1. The root cause of HPC 1-2 seal teeth for crack attributed to heavy eccentric rub early in life of spool. So when HPC forward case is removed from engine, ANA has inspected 1-2 seal teeth per Spot FPI or ECI and If no crack, installed the 1-2 seal with used HPC stator stage 1 inter-stage seal (used and already grooved due to rubs with seal teeth) or HPC stator stage 1 inter-stage seal that are pre-grooved (post SB 72-0320). According to this proposed AD, it indicates to use only post SB type seal, but SB 72-360 rev 02 accepted to use used seal and post SB type seal. ANA has started this program according to SB 72-360 rev 02 from last year. If we have to obey proposed AD, the shop TAT will be long for seal rework and the cost will be huge to modify seals. Most concerned point is to slow down our retrofit schedule. So, ANA would like to update Paragraph (i) of the proposal to include revision #3 of SB 72-0360, which was issued on May 3, 2011 because we can install any “seals ”of used pre SB 72-0320 type and post SB 72-0320 type per SB 72-0360 rev.3. In NPRM ‘Install Prohibition’ and ‘SUMMARY’ portion, FAA prohibits us to install “seals” except post SB 72-0320 (P/N: 351-109-503-0). Please allow us to install used any seals of pre SB 72-0320 type and post SB 72-0360 type. Thank you for your consideration of our submittal. Best Regards,