A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to certain Boeing Model 757 series airplanes was published in the Federal Register on August 4, 1999 (64 FR 42050). That action proposed to require repetitive inspections to detect wire chafing of the left and right engine fuel shutoff valve wire bundles at Power Plant Station 278 on each engine strut, and repair if necessary. That action also proposed to require repetitive replacement of three wire support brackets with improved wire support brackets. \n\nComments \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. \n\nAddition of Service Bulletin Information Notice \n\n\tOne commenter, the airplane manufacturer, indicates that during its investigation of the wire support bracket failure it established thatBoeing Service Bulletin 757-54-0013, Revision 3, dated October 23, 1997 (cited in the proposal as the source of service information for doing the specified actions) contained an incorrect part number for an attachment fastener. The commenter adds that the part number was corrected in Boeing Information Notice 757-54-0013 IN 01, dated October 22, 1998. \n\n\tThe FAA infers that the commenter wants to add IN 01 to the service information cited in the final rule. Subsequent to receipt of this comment, we reviewed and approved Boeing Information Notice 757-54-0013 IN 02, dated April 8, 1999, which supersedes IN 01. IN 02 contains additional information for proper accomplishment of the modifications described in the service bulletin, as well as the corrected part number specified by the commenter. We concur with the commenter's request, but will add IN 02 to the service information cited in the final rule. \n\nRevise Paragraph (a) \n\n\tOne commenter, the airplane manufacturer, states that itdid an analysis of the new, improved wire support brackets to determine the fatigue level allowable. The analysis showed that the two lower aluminum brackets were undersized for the vibration environment in the aft strut area, and that the nickel alloy brackets were capable of withstanding the vibration environment, with fatigue allowables that exceed the stress levels by 80 percent. Analysis done on the third bracket showed that the aluminum brackets are also satisfactory. This analysis was conducted per standard Boeing practice for equipment in the nacelle and strut areas, using well-established stress values. \n\n\tBased on the above information, the commenter states that replacing all 6 brackets every 12 months is unnecessary and will impose a considerable economic burden on affected operators. The commenter proposes revising paragraph (a) of the proposed rule as follows: \n\nIncorporate Boeing Service Bulletin 757-54-0013, Revision 3, dated October 23, 1997, within 12 months afterthe effective date of the AD. This would constitute terminating action for the proposed rule. Or \n\nFor operators that do not incorporate the Revision 3 of the service bulletin, repetitively inspect the installation for chafing or damage of the wire bundle, and for cracked or fractured brackets. The repetitive inspection should be accomplished at intervals not to exceed 18 months, with bracket replacement if any evidence of cracking or damage is found. \n\n\tThe FAA partially agrees with the commenter's proposal, as follows: \n\n\tWe agree with the assessment that the replacement brackets specified in Revision 3 of the service bulletin are adequate to meet the strut vibration environment, and that incorporation of such replacement brackets would eliminate the need for the repetitive inspections and repetitive replacements of the wire support brackets specified in the proposed rule. Therefore, paragraphs (a) and (b) have been combined into paragraph (a) with the repetitive inspections and replacements omitted, and subsequent paragraphs have been re-numbered accordingly. Additionally, the preamble and the cost impact sections of the final rule have been changed. \n\n\tWe do not agree with the commenter's proposal to allow continued use of the existing brackets with repetitive inspections beyond the initial 12-month compliance time. The commenter did not submit adequate justification for allowing the continued use of these brackets, or extending the compliance time for the repetitive inspections from 12 to 18 months. The existing brackets can fail in service, and such failures could result in damage to wiring, ignition of fuel vapors in a flammable leakage zone, or loss of the fuel shutoff valve function. Considering these safety concerns, repetitive inspections without replacement of the wire support brackets after the doing the inspection would not adequately address the identified unsafe condition. \n\nWithdraw Proposed Rule \n\n\tOne commenter asks that the FAA withdraw the proposed rule. The commenter provided in service data showing that airplanes which have replaced the wire support brackets per Boeing Service Bulletin 757-54-0013, Revision 3, have experienced no problems with the brackets. The commenter states that the annual bracket replacement (every 12 months) is not possible or practical because the repetitive bracket replacements would involve repetitive replacement of close tolerance fasteners, and would require repeated oversizing of the existing airplane mounting holes. This could result in the holes being too large for proper installation of the brackets. The commenter adds that a deviation to the proposed rule would be necessary each time the fasteners are replaced. \n\n\tThe FAA concurs with the commenter's assessment that the brackets that were replaced per Revision 3 of the service bulletin are adequate; however, we do not agree with the request to withdraw the proposed rule. Failure to install the replacement brackets per the referenced service bulletin could result in the unsafe conditions stated under the previous section titled "Revise Paragraph (a)." Also stated in that section is our intent to omit the repetitive inspections and repetitive bracket replacements specified in paragraph (a) of the proposed rule. Paragraph (a) of the final rule has been revised to require a one-time inspection and one-time replacement of the wire support brackets. \n\nReduce Compliance Time \n\n\tOne commenter asks that the FAA reduce the proposed compliance time for the initial inspection specified in paragraph (a) of the proposed rule from 12 months to 6 months after the effective date of the AD. The commenter states that 12 months is too long and notes that, based on previous administrative procedures and industry practices, it could be almost 18 months before an airplane is inspected. The commenter adds that this places the traveling public at an elevated risk and greatly reduces the margin of safety on the airplane. \n\n\tThe FAA does not agree. As discussed in the section "Differences Between Proposed Rule and Service Bulletin" in the preamble of the proposed rule, we find that a 12-month compliance time for the initial inspection would address the unsafe condition in a timely manner. In developing an appropriate compliance time for the proposed AD, we considered not only the manufacturer's recommendation, but the degree of urgency associated with addressing the subject unsafe condition, the average utilization of the affected fleet, and the time necessary to do the initial inspection/modification. \n\n\tOperators are always permitted to accomplish the requirements of an AD at a time earlier than that specified as the compliance time; therefore, if an operator wants to do the initial inspection required by paragraph (a) of this AD earlier than 12 months after the effective date of the AD, the operator can do so. Therefore, no change to the compliance time for the initial inspection required by paragraph (a) of the final rule is necessary. \n\nExtend Compliance Time \n\n\tOne commenter states that the proposed 12-month compliance timetable for the bracket replacement is unrealistic and asks that the compliance time be extended to 18 months. The commenter notes that it is currently implementing the modification at its C-check, and requires 18 months to modify its entire fleet. The commenter also states that the manufacturer has quoted a 22-month lead time for obtaining the necessary kits, which is not compatible with the timetable specified in the proposed rule. \n\n\tThe FAA does not agree. As stated above, we find that a 12-month compliance time for the initial inspection/modification is appropriate. \n\nFuel Shutoff Valve (FSOV) \n\n\tOne commenter notes that the FSOV can be closed using the redundant circuit routed on the front spar, as long as power is available to that circuit. The FAA agrees with the statement and infers that the commenter wants further explanation of the proceduresavailable should this situation occur. This can occur only if the engine fuel cutoff switch is placed in the "cutoff" position before the engine fire handle is pulled. The procedural information is described in the Emergency Procedures section of the 757 Airplane Flight Manual. \n\nConclusion \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. \n\nCost Impact \n\n\tThere are approximately 501 airplanes of the affected design in the worldwide fleet. The FAA estimates that 249 airplanes of U.S. registry will be affected by this AD. \n\n\tIt will take approximately 2 work hours to accomplish the required inspection and approximately 6 work hours per airplane to accomplish the required replacement. The average labor rate is estimated to be $60 per work hour. Required parts will cost approximately $525 per airplane. Based on these figures, the cost impact of the AD on U.S. operators is estimated to be $250,245, or $1,005 per airplane. \n\n\tThe cost impact figures discussed above are based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted. The cost impact figures discussed in AD rulemaking actions represent only the time necessary to perform the specific actions actually required by the AD. These figures typically do not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions. \n\nRegulatory 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 theStates, 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\n\tAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\nSec. 39.13 (Amended) \n\n\t2. Section 39.13 is amended by adding the following new airworthiness directive: