A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) by superseding AD 99-05-15, amendment 39-11063 (64 FR 10935, March 8, 1999); applicable to certain Boeing Model 737-100, -200, -200C, -300, -400, and -500 series airplanes; was published in the Federal Register on December 3, 1999 (64 FR 67807). The action proposed to continue to require a one-time inspection of the attachment nuts at each end attachment of the elevator tab push rods to measure run-on torque values, and corrective actions, if necessary. The action also proposed to add a requirement to replace all existing bolts and attachment nuts at the forward and aft end attachment of each elevator tab push rod with new bolts and self-locking castellated nuts with cotter pins. Comments \n\n\tInterested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received. Supportive CommentOne commenter supports the proposed rule. Request to Extend Compliance Time in Paragraph (b) \n\n\tSeveral commenters request that the FAA extend the proposed compliance time for the replacement of the existing bolts and attachment nuts specified in paragraph (b) of the proposal. One commenter requests that the proposed compliance time be extended from 12 months to 18 months after the effective date of this AD. The commenter indicates that an 18-month compliance time will allow the work to be incorporated into its regularly scheduled maintenance visits when sufficient time and resources are available. \n\n\tA second commenter requests that the proposed compliance time be extended to within 24 months after the effective date of the this AD, not to exceed 4,000 flight cycles. The commenter states that this change will enable the tab freeplay inspections and tab push rod bolt and nut replacement to be made concurrently during a regularly scheduled major maintenance check (a "C" check).The commenter adds that this change also will reduce the impact on fleet operations, a concern operators expressed during the lead airline reviews for Boeing Service Bulletin 737-55A1070, dated January 13, 2000. According to the commenter, 737-55A1070 specifies that tab installation inspections and tab hinge and tab trailing edge freeplay checks be made within 4,000 flight cycles or 24 months after release of the service bulletin. That service bulletin also has repeat inspections at 1,500 flight cycles or 2,000 flight hours. \n\n\tA third commenter requests an extension of the proposed compliance time to 24 months after the effective date of this AD. The commenter states that the extension would allow accomplishment of the replacement during its heavy maintenance checks. \n\n\tA fourth commenter requests an extension of the proposed compliance time to 4 years after the effective date of this AD. The commenter states that replacement of the hardware cannot be done in a short (overnight) maintenance visit. The commenter proposes that the compliance time be extended in order to allow the work to be accomplished during a major maintenance visit. The commenter currently is working on replacing the subject hardware per the accomplishment schedule in the proposed rule. The commenter indicates that the inspection of the bolts for current run-on torque values specified in the proposal has been accomplished on its fleet, and the attachment hardware has been replaced if its condition was beyond allowable limits. In light of this fact, the commenter notes that an extension of the compliance time for the remaining attachments should not pose a significant decrease in safety. \n\n\tThe FAA concurs with the commenters' requests to extend the compliance time required by paragraph (b) of the final rule. Following careful consideration of the comments, and in light of the fact that AD 99-05-15, amendment 39-11063, mandated the one-time inspection and corrective actions, the FAA has determined that it will not compromise safety to extend the compliance time for the replacement required by paragraph (b) of this AD. Therefore, the compliance time in paragraph (b) of this final rule has been extended to within 24 months or 4,000 flight cycles after the effective date of this AD, whichever occurs first. \n\nRequest to Revise Cost Impact Information \n\n\tOne commenter states that the actual time required to modify an airplane (replace the existing bolts and nuts) is 12 work hours and will exceed the 4 work hours estimated in the proposed rule. The commenter adds that the modification cannot be done during an overnight maintenance visit without disrupting service, and special routing would be required. \n\n\tThe FAA acknowledges that the cost impact information, below, describes only the "direct" costs of the specific actions required by this AD. The estimate of 12 work hours submitted by the commenter includes time for gaining access and closing up. The cost analysis in AD rulemaking actions, however, typically does not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions. Because incidental costs may vary significantly from operator to operator, they are almost impossible to calculate. The number of work hours necessary to accomplish the required actions, specified as 4 in the cost impact information in the proposal and restated below, represents the time necessary to perform only the actions actually required by this AD (that is, the replacement). No change to the final rule is necessary in this regard. Later Revision of Service Letter \n\n\tTwo commenters state that the most current revision level of the service letter should be used in the proposed rule. The FAA agrees with the commenters statement. The FAA has reviewed and approved Boeing Service Letters 737-SL-27-118-B, dated April 14, 1999; 737-SL-27-118-C, dated May 19, 1999; and 737-SL-27-118-D, dated December 17, 1999; and finds that they are essentially similar to the service letter referenced in paragraphs (a)(2) and (b) of the proposed rule. Accordingly, Revision 'D' has replaced the reference to Revision 'A' in paragraphs (a)(2) and (b) of this AD. In addition, a new note (Note 3) has been added to this final rule to give credit for accomplishment of the actions in paragraphs (a)(2) and (b) of this AD in accordance with Revisions 'A,' 'B,' or 'C' of the service letter prior to the effective date of this AD. Explanation of Change to Proposal \n\n\tSince the issuance of the notice of proposed rulemaking (NPRM), the FAA has concluded that paragraph (c)(2) of the proposal is incorrect. That paragraph reads, "Alternative methods of compliance (AMOC), approved previously in accordance with AD 99-05-15, amendment 39-11063, are NOT considered to be approved as alternative methods of compliance with this AD." The FAA has determined that the AMOC's specified are indeed approved. Therefore, paragraph (c)(2) of this final rule has been revised accordingly. Conclusion \n\n\tAfter 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 previously described. The FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD. Cost Impact \n\n\tThere are approximately 2,742 airplanes of the affected design in the worldwide fleet. The FAA estimates that 1,106 airplanes of U.S. registry will be affected by this AD. \n\n\tThe new replacement that is required in this AD action takes approximately 4 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Required parts will cost approximately $560 per airplane. Based on these figures, the cost impact of the replacement required by this AD on U.S. operators is estimated to be $884,800,or $800 per airplane. \n\n\tThe cost impact figure discussed above is based on assumptions that no operator has yet accomplished any of the current or new requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted. \n\n\tThe one-time inspection required by AD 99-05-15 was required to be accomplished within 90 days after the effective date of that AD (March 23, 1999). Since the 90-day compliance time has passed, the FAA assumes that all airplanes currently on the U.S. Register have been inspected. Therefore, there is no future cost impact of this requirement on current U.S. operators of these airplanes. \n\n\tHowever, should an affected airplane be imported and placed on the U.S. Register in the future, it would take approximately 4 work hours per airplane to accomplish the one-time inspection, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the inspection required by this AD onU.S. operators is estimated to be $240 per airplane. Regulatory Impact \n\n\tThe regulations adopted herein will 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 responsibilities among the various levels of government. Therefore, it is determined that this final rule does not have federalism implications under Executive Order 13132. \n\n\tFor 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 from the Rules Docket at the location provided under the caption "ADDRESSES." \n\nList of Subjects in 14 CFR Part 39 \n\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \n\n\tAccordingly, 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: \n\nPART 39 - AIRWORTHINESS DIRECTIVES \n\n\t1. The authority citation for part 39 continues to read as follows: \n\tAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\n§ 39.13 (Amended) \n\n\t2. Section 39.13 is amended by removing amendment 39-11063 (64 FR 10935, March 8, 1999), and by adding a new airworthiness directive (AD), amendment 39-11906, to read as follows: