A proposal to amend part 39 of the Federal Aviation Regulations to include an airworthiness directive (AD) that is applicable to Pratt & Whitney (PW) JT9D-7R4 series turbofan engines was published in the Federal Register on June 2, 1993 (58 FR 31356). That action proposed to require initial and repetitive on-wing or shop fan blade leading edge inspections to check for leading edge damage in accordance with PW Service Bulletin (SB) No. 72- 255, Revision 5, dated January 8, 1990; and to require fan blade set replacement or optional rework of the fan blade shrouds in accordance with PW SB No. 72-309, Revision 9, dated June 12, 1991. Though the NPRM referenced PW SB No. 72-309, Revision 9, dated June 12, 1991, this final rule incorporates the later Revision 10, dated September 2, 1993, which is substantially unchanged from Revision 9. Rework of the fan blade shrouds in accordance with PW SB No. 72-309, Revision 9, dated June 12, 1991, is an acceptable alternate means of compliance for paragraphs (c) and (d) of this AD.
Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.
One comment states that the proposed 90-day requirement for initializing the inspection program poses a significant hardship and economic impact due to difficulty in scheduling engine maintenance. This comment requests extending the initializing period to 180 days. The Federal Aviation Administration (FAA) agrees that the proposed initial 90-day eddy current inspection requirement may be burdensome to some operators. The FAA has therefore added a visual inspection as an option to the eddy current inspection in this final rule. This visual inspection offers greater flexibility in scheduling as it can easily be performed in the field. The FAA does not concur, however, in extending the initializing period to 180 days, as this time period does not offer an adequate level of safety based on risk analysis results. This final rule establishes an interval of 200 cycles in service (CIS) before visual or eddy current inspection that should enable operators to initialize the inspection program with minimum disruption to scheduling without reducing flight safety. Also, the FAA has added guidance emphasizing the manner in which the visual inspection should be performed.
One comment requests eliminating the reference in paragraphs (a) and (b) of the proposed rule to the leading edge refurbishment described in PW Service Bulletin (SB) No. 72-117, as the determining factor for beginning the inspection program. The comment further states that a previous AD, 90-14-08, already requires the leading edge refurbishment described in PW SB No. 72- 117, and therefore meets the intent of paragraphs (a) and (b) of the proposed rule. The FAA concurs. Repetitive leading edge refurbishment as described in PW SB No. 72-117 is already required by AD90-14-08. The compliance section of this AD has been changed from the wording in the NPRM to eliminate reference to leading edge refurbishment, and combines paragraphs (a) and (b) of the proposed rule into a new paragraph (a) which has the same inspection requirements and interval of 200 CIS as the repetitive inspections of paragraph (c) of the proposed rule.
One comment states that the mandatory incorporation of the fan blade shroud angle rework to 52 degrees as described in PW SB No. 72-309 should be relaxed from within two years after the effective date of this AD to the next engine shop visit, thereby reducing the potential for on-wing maintenance induced error. The FAA does not concur. The FAA has determined that it is necessary to expeditiously remove fan blades with the 62 degree shroud configuration, thereby reducing the potential for operating the fan blade in flutter. The FAA has reviewed a risk analysis study that indicates that a two-year time period for incorporating this modification is required to lower the risk sufficiently to avert future potential uncontained fan blade failures.
After careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of the rule with the changes described previously. The FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD.
There are approximately 730 PW JT9D-7R4 series engines of the affected design in the worldwide fleet. The FAA estimates that 220 engines installed on aircraft of U.S. registry would be affected by this AD, and that the average labor rate is $55 per work hour. The inspections required by this AD will take approximately 1.6 work hours per engine. The blade rework will cost approximately $15,600 per engine. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $3,451,360.The regulations adopted herein will not have substantial direct effects on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government. Therefore, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment.
For the reasons discussed above, I certify that this action (1) is not a "significant regulatory action" under Executive Order 12866; (2) is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. A final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it may be obtained fromthe Rules Docket at the location provided under the caption "ADDRESSES."
List of Subjects in 14 CFR Part 39
Air Transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.
Adoption of the Amendment
Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends 14 CFR part 39 of the Federal Aviation Regulations as follows:
PART 39 - AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89.
39.13 - [AMENDED]
2. Section 39.13 is amended by adding the following new airworthiness directive: