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 777 series airplanes was published in the Federal Register on July 25, 2001 (66 FR 38588). That action proposed to require modification of the supports for the fuel quantity indicator system (FQIS) wire bundles. \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\nRequest To Withdraw Proposed Rule \n\n\tOne commenter states that the change proposed by the FAA has already been addressed by the manufacturer, per the release of the service bulletins referenced in the proposed rule that specify inspecting the in-tank wiring and revising the installation to enhance the wire separation from the in-tank structure. The commenter adds that, in testing where there was the potential for wire chafing from fuel sloshing and vibration, and during inspections, wire chafing was not found. The commenter states that chafed fuel quantity indicator system (FQIS) wiring, in combination with certain wiring or component failures, resulting in a potential ignition source, is improbable because of the safety design features that preclude such an occurrence. The commenter notes several reasons that the actions in the proposed rule are not necessary. First, the FQIS processor on Model 777 series airplanes is designed to meet electrical unit intrinsic safety levels, per the manufacturer's requirements. Second, the FQIS wiring has an outer insulation jacket, then a double-braided shield for protection, and each wire has its own insulation jacket. Third, for 70 percent of the distance from the processor to the wing spar, the FQIS wiring has a spatial separation from other airplane wiring. Fourth, the in-tank wiring conductor is nickel-plated, which, per in-service data, is provento be resistant to fuel tank corrosion. \n\n\tThe FAA infers that the commenter wants the proposed rule withdrawn. We do not agree. We have conducted many inspections of the fuel tanks on Model 777 series airplanes, and have found that the current wiring installation design is highly sensitive to wiring installation quality, such that the level of installation quality control necessary to prevent chafing is unrealistic. In addition, other factors such as fuel sloshing, airplane flexure, inertial loads, and fuel tank maintenance can cause the wiring to move into positions where chafing can occur. The modifications specified in the referenced service bulletins provide the necessary improvements to prevent chafing of the FQIS wiring. Additionally, although the commenter stated that chafed wiring, in combination with certain wiring or component failures, would not result in a potential ignition source, we do not agree. The design features of the FQIS cannot ensure that, over the lifetime of the airplane, sufficient energy will not cause electrical arcing from entering the fuel tank. \n\n\tThe same commenter asks that, if the proposed rule is adopted as final, it be changed to reference subsequent revisions of the referenced service bulletins for accomplishment of the specified actions. \n\n\tWe do not agree with the commenter. An AD may only refer to service documents that are submitted and approved by the Office of the Federal Register for "incorporation by reference." In order for operators to use later revisions of the referenced document (issued after the publication of the AD), either the AD must be revised to refer to the specific later revisions, or operators must request approval for the use of them as an alternative method of compliance with this AD under the provisions of paragraph (c) of this AD. No change to the final rule is necessary in regard to the previous comments. \n\nExtend Compliance Time \n\n\tOne commenter asks that the compliance time specified in the proposed rule be extended from 24 to 48 months. The commenter states that the airlines should be allowed to schedule incorporation of the modifications at a convenient heavy maintenance check if the specified safety procedures are in place and no evidence of chafing is found during testing or incorporation of the modifications. \n\n\tWe do not agree with the commenter. The commenter provides no technical justification for increasing the compliance time as requested. Further, the areas where the wiring concerns being remedied by this AD are regularly exposed to flammable fuel vapors. Arcing in the tank can cause ignition of these flammable fuel vapors. In light of this, and since the unsafe condition addressed by this AD is a significant safety issue, we have determined that the compliance time of 24 months, as proposed, is warranted. \n\n\tIn developing an appropriate compliance time for the actions required by this AD, we considered not only those safety issues, but the manufacturer's recommendations, parts availability, and the practical aspect of accomplishing the modifications within an interval paralleling normal scheduled maintenance for the majority of affected operators. In light of all of these factors described previously, we consider 24 months to be an appropriate compliance time wherein safety will not be adversely affected. No change to the final rule is necessary in this regard. \n\nEliminate Reporting Requirement \n\n\tOne commenter asks that the reporting requirement included in paragraph (b) of the proposed rule be eliminated. The commenter states that at the time it accomplished the specified modifications, the referenced service bulletins did not include formal procedures or steps for inspection of the damaged wire. Therefore, the commenter did not include those steps in its internal documentation and cannot compile the information for the reporting requirement. The commenter notes that to comply it would have to re-inspect the wiring that has already been modified on all affected airplanes. This would include unscheduled fuel tank entries, which would not take place during a normal maintenance visit and would have a significant financial impact on the airlines. \n\n\tWe partially agree with the commenter, but we do not agree to eliminate paragraph (b) of the final rule. However, we agree that if operators have accomplished the modifications required by paragraph (a) of the final rule, they should not have to re-enter the fuel tank to obtain the information necessary for the reporting requirement submission. Therefore, we have revised paragraph (b)(2) of the final rule to require submission of a report of findings from the previously completed fuel tank modification within 60 days after the effective date of this final rule. \n\nExplanation of Change to Final Rule \n\n\tThe FAA finds that the follow-on actions (Replacement and Reporting of Damaged Wiring), as specified in paragraph (b) of this AD, were inadvertently omitted fromthe Summary section of the proposed rule. Those actions have been included in the Summary section of this final rule for clarification. We also have changed the heading for paragraph (b) of the final rule to specify "Follow-On Actions," in lieu of "Replacement and Reporting of Damaged Wiring," to better define the actions specified in paragraph (b) of this final rule. \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 266 airplanes of the affected design in the worldwide fleet. The FAA estimates that 75 airplanes of U.S. registry will be affected by this AD, that it will take approximately the number of work hours per airplane displayed in the table below to accomplish the required modifications, and that the average labor rate is $60 per work hour. Required parts costs are also listed in the table below: \n\n\nESTIMATED COST IMPACT\n\n\nBoeing service bulletin\nNumber of work hours per airplane\nParts cost per airplane\nEstimated cost per airplane\nNumber of U.S. airplanes affected\nEstimated cost to U.S. fleet\n777-28-0012\n38\n$628\n$2,908\n23\n$66,884\n777-28-0016 (Group 1)\n43\n490\n3,070\n18\n55,260\n777-28-0016 (Group 2)\n48\n839\n3,719\n57\n211,983\n777-28-0021 (Work Package 1)\n30\n1,058\n2,858\n75\n214,350\n777-28-0021 (Work Package 2)\n32\n1,058\n2,978\n75\n223,350\n\n\tService Bulletins 777-28-0012 and 777-28-0016 both address center fuel tank (CFT) wiring improvements and require CFT entry. Operators should note that concurrent incorporation of these two service bulletins would minimize tank entries and would be a cost savings (33 work hours per airplane) to the operators because they would need tode-fuel, access, and close access to the CFT only once.\n \n\tThe cost impact figures discussed in the table 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\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\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: