A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an AD that is applicable to PW JT9D-7R4 series turbofan engines was published in the Federal Register on August 30, 2001 (66 FR 45789). That action proposed to require a one-time inspection of low pressure turbine (LPT) 5th stage disks for evidence of blend repairs and mechanical damage, and replacement of the affected disks based on the extent of those repairs and damage, in accordance with PW service bulletin (SB) JT9D-7R4-72-574, Revision 1, dated June 26, 2001.
Comments
Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.
Clarification of Areas To Be Inspected
One commenter states that the areas of inspection are not defined for the requirement to remove disks with five or more blended or unblended areas of damage by any cause. By not defining the areas of inspection, blends or areas of damage anywhere on the disk could be counted. The commenter states that blends to remove part markings such as TT and TC marks or other blends on fir trees, for example, should not be counted toward the five or more rejection limit.
Another commenter requests clarification of whether a disk may be returned to service after five or more blended or unblended damage areas are found on the disk but all of the damage is identified as non-tiebolt damage. The clarification is requested because the blended areas or areas of damage called out in the NPRM are not specific. The commenter also asks if the determination of acceptance of a disk could be done on a case-by-case basis.
The FAA agrees that the proposal does not specify where on the disk to look for blended areas or areas of damage. Therefore the FAA has changed paragraph (a)(2) of this final rule to specify that the areas to be inspected are the forward and aft web and bore areas. The FAA disagrees, however, that disks with five or more areas of damage in the forward and aft web areas may be returned to service, even if the damage is known to be unrelated to a tiebolt failure during operation. Operators may request case-by-case review using the procedure to request an Alternative Methods of Compliance, paragraph (c).
Use the Same Wording as the Service Bulletin
One commenter requests that the FAA use the same wording in the compliance instructions for the AD as that which is contained in PW Service Bulletin (SB) JT9D-7R4-72-574. Paragraph (a)(1) of the proposal states: "remove from service those LPT 5th stage disks that were installed in engines that experienced a tiebolt fracture AND are found with blended or unblended damage in the web and bore areas, and replace with a serviceable disk." In place of the AND above, the SB uses the word OR. Using the word AND, implies that the final rule would require both tiebolt fracture history and damage to meetreplacement criteria.
The FAA disagrees that any change to Paragrap (a)(1) is necessary, but agrees that the final rule could be worded clearer. Paragraph (a)(1) of the proposal covered those disks for which the operator knew that the damage was due to tiebolt failure. Paragraph (a)(2) of the proposal covers those disks for which the tiebolt fracture history is unknown. The FAA has changed final rule paragraph (a)(1) to clarify that it applies to disks for which there is a known history of tiebolt failure in operation.
Exclude Damage Caused by Tierod Removal
One commenter states that many disks have tierod removal damage on the rear side of the disk, due to tierod fracture during disassembly. The commenter requests that damage found on the rear side of the disk, that is in line with the tierod holes should not be taken into account because it is due to tierod removal. The commenter requests that alternate inspection requirements be provided that identify the type of damage rather than the number of damaged areas.
The FAA partially agrees. The FAA agrees that the wording should include the specification that the tierod damage occurs during operation. Therefore, the FAA has changed the wording in final rule paragraph (a)(1) to specify that the damage must be due to tiebolt fracture during operation. This change is justified because high-energy damage to the disk caused by a tiebolt fracture occurs during operation rather than during LPT disassembly. However, the FAA does not agree that the type of damage, as a result of tiebolt failure during operation, should be specified differently than specified in PW SB JT9D-7R4-72-574. A tiebolt fracture during operation is capable of damaging the aft side of the disk in the web and bore areas. The FAA expects operators to use good maintenance practices to prevent damage to disks during LPT disassembly. If damage occurs during disassembly, the Engine Manual must be used to determine serviceability.
Concernfor Engine Manual Revision
One commenter expresses concern that neither the proposal nor PW SB JT9D-7R4-72-574 indicate that the Engine Manual-provided blend repair (Section 72-52-11, Repair-01 for JT9D-7R4G2 Engines) will be revised to effectively address the tiebolt failure mode and cause. The compliance in the proposal does not prevent future blending of the disk web and bore when the disk is routed for repair after the one-time mandated visual inspection has been completed. The commenter requests that the Engine Manual blend repair be referenced in the final rule.
The FAA agrees that the AD and the Engine Manual should address future situations where the one-time mandated visual inspections are completed. The manufacturer will include a requirement in the Engine Manual to remove from service any LPT 5th stage disk that experienced damage to the fore and aft web and bore areas from a fractured tiebolt during operation. The intent of the AD is to specify a one-time inspection of LPT 5th stage disks. In addition, the AD will more clearly state in paragraph (b) of the compliance section that any LPT 5th stage disk that experiences damage to the fore and aft web and bore areas from a fractured tiebolt during operation must be removed from service. The repair and serviceability requirements for LPT 5th stage disks are not part of the AD.
Revision to Manufacturer's Service Information
The manufacturer comments that since the publication of the proposal, Revision 2 of the SB has been published, which provides a revised Figure 2 and a consistent description of the one-time inspection rejection criteria.
The FAA agrees and has added this SB Revision to the incorporation by reference.
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.
Economic Analysis
There are approximately 647 Pratt & Whitney (PW) JT9D-7R4 series turbofan engines of the affected design in the worldwide fleet. The FAA estimates that 151 engines installed on airplanes of U.S. registry would be affected by this AD. The FAA also estimates that it would take approximately one work hour per engine to accomplish the proposed actions, and that the average labor rate is $60 per work hour. A replacement disk would cost approximately $145,260 per engine. Based on these figures, the total cost effect of the AD on U.S. operators is estimated to be $21,943,320.
Regulatory Analysis
This final rule does not have federalism implications, as defined in Executive Order 13132, because it would not have a substantial direct effect on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilitiesamong the various levels of government. Accordingly, the FAA has not consulted with state authorities prior to publication of this final rule.
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 the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) if promulgated, 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 by contacting the 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 part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows:
PART 39--AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701.
Sec. 39.13 [Amended]
2. Section 39.13 is amended by adding a new airworthiness directive to read as follows: