The FAA proposed to amend 14 CFR part 39 with an AD for certain Boeing Model 777-200, -200ER, and -300 series airplanes. That action, published in the Federal Register on March 3, 2005 (70 FR 10337), proposed to require modification of the splice plate assemblies installed under the floor panels at the forward and aft edges of the cabin aisle. \n\nComments \n\n\tWe provided the public the opportunity to participate in the development of this AD. We have considered the comments that have been submitted on the proposed AD. \n\nRequest To Add Optional Inspection Program \n\n\tOne commenter asks that, in addition to the terminating action specified in the proposed AD, an optional inspection program be implemented to do inspections of the most affected areas, with replacement or repair of affected parts on attrition. The commenter states that such an inspection should be added as a compliance option, in lieu of a full modification, or in conjunction with a longer compliance time. The commenter adds that, in order to accomplish the modification, access to some locations will be difficult; therefore, consideration should be given to adding inspections to extend the compliance time. The commenter suggests adding to the proposed AD an internal general visual inspection of the floor splice plates that are visible from the forward and aft pit. In addition, the commenter recommends inspecting from above for flexing and "clicking" noises commonly associated with splice plate cracking of the remaining areas located in the overwing section and not viewable from the pits. The commenter suggests that the inspections be done at intervals no longer than 48 months apart, and that a full general visual inspection of all affected splice plates be done within a 72-month period to allow for normal maintenance cycles that facilitate the inspection. \n\n\tThe commenter states that it was instrumental in identifying and reporting cracked splice plate discrepancies to the airplane manufacturer in December 1999. The reports brought about changes addressing the subject issue that were \nadded to both the structural repair and airplane maintenance manuals for Boeing Model 777 airplanes. The commenter adds that its findings were significant enough to justify creating a specific maintenance program that contained procedures for finding and addressing the cracking in most affected areas. The inspections revealed an overwhelming propensity for cracking in the aisle nearest the passenger entry doors 1L and 2L. The commenter concludes that the approach of inspecting aisle and entry floor panels at 3C intervals has been highly effective in managing this issue. \n\n\tWe do not agree with the commenter's request. We understand that there are splice plates in some areas that can be inspected from below, but there are several inaccessible areas where difficulty gaining access would not allow for an inspection. The inspection methods suggested by the commenter are not reliable for those inaccessible areas. Further, inspection of other splice plates from below is of questionable reliability in determining the onset of cracking. Also, partially cracked splice plates and splice plates with repairs of unknown reliability are not acceptable for addressing the unsafe condition. For these reasons, we have determined that the modification required by the AD is the most effective method of addressing the identified unsafe condition. We note that the 60-month compliance time should allow for modification during normal maintenance cycles for most affected operators. However, under the provisions of paragraph (h) of this AD, if adequate technical justification is provided, affected operators may request approval of an alternative method of compliance (AMOC). \n\nRequest To Consider Alternative Action \n\n\tOne commenter states that it has paperwork in place to accomplish the proposed AD, but has some concerns about the methods proposed for solution to the described problem. The commenter notes that it appears that the unsafe condition specified in the proposed AD is a design flaw, though the airplane manufacturer has not accepted the responsibility for a resolution. The commenter concludes that, because of that fact, the manufacturer should re-address the problem and come up with a secondary solution that would not require replacement of the splice straps. \n\n\tWe do not agree with the commenter. The airplane manufacturer has developed an improved splice plate to correct the unsafe condition. The FAA has determined that the proposed modification (replacement of the splice straps) is necessary to address the unsafe condition specified in the proposed AD, which is due to cracking of the aluminum splice plates. We did not include the option of accomplishing inspections because access to many of the affected areas is limited, so an inspection would not provide reliable results. Therefore, replacing the splice straps with new, improved splice straps is the most effective way to address the unsafe condition. Additionally, the proposed AD allows a 60-month compliance time to allow for accomplishing the modification during regular maintenance visits. However, under the provisions of paragraph (h) of this AD, if adequate technical justification is provided, affected operators may request approval of AMOC. \n\nRequest To Change Costs of Compliance Section \n\n\tOne commenter states that, because the cause of the unsafe condition specified in the proposed AD is a design flaw that has not been resolved, the commenter must bear the cost of 48 work hours per airplane to accomplish the proposed modification. The commenter adds that gaining access to some locations to accomplish the modification will be difficult, and estimates that this modification would cost approximately $200,000 for labor and $308,000 for material for its entire fleet. The commenter does not provide a specific request. \n\n\tWe infer that the commenter is asking usto change the "Costs of Compliance" section of this AD. We do not agree. The estimate of 28 work hours per airplane is based on the best data available to date, and is consistent with the manufacturer's estimate contained in the service bulletin. The cost impact figures discussed in AD rulemaking actions represent only the time necessary to perform the specific actions actually required by the AD. We recognize that in accomplishing the requirements of any AD, operators may incur incidental costs in addition to the direct costs. However, the cost analysis in AD rulemaking actions 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. We have not changed the AD in this regard. \n\nExplanation of Change to Proposed AD \n\n\tThe applicability in the proposed AD addresses "Boeing Model 777- 200, -200ER, and -300 series airplanes." We inadvertently included Model 777-200ER series airplanes, which are not specified on the type certificate data sheet and are encompassed within the Model 777-200 series. Our intent is that the AD apply to certain Boeing Model 777-200 and -300 series airplanes; therefore, we have changed the applicability in this AD accordingly. \n\nConclusion \n\n\tWe have carefully reviewed the available data, including the comments that have been received, and determined that air safety and the public interest require adopting the AD with the change described previously. This change will neither increase the economic burden on any operator nor increase the scope of the AD. \n\nCosts of Compliance \n\n\tThere are about 330 airplanes of the affected design in the worldwide fleet. This AD affects about 131 airplanes of U.S. registry. The modification will take about 28 work hours per airplane, at an average labor rate of $65 per work hour. Required parts will cost between $4,717 and $9,099 per airplane. Based on these figures, the estimated cost of the AD for U.S. operators is between $856,347 and $1,430,389, or between $6,537 and $10,919 per airplane. \n\nAuthority for this Rulemaking \n\n\tTitle 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, Section 106, describes the authority of the FAA Administrator. Subtitle VII, Aviation Programs, describes in more detail the scope of the Agency's authority. \n\n\tWe are issuing this rulemaking under the authority described in Subtitle VII, Part A, Subpart III, Section 44701, "General requirements." Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe conditionthat is likely to exist or develop on products identified in this rulemaking action. \n\nRegulatory Findings \n\n\tWe have determined that this AD will not have federalism implications under Executive Order 13132. This AD 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. \n\n\tFor the reasons discussed above, I certify that this AD: \n\n\t(1) Is not a "significant regulatory action" under Executive Order 12866; \n\n\t(2) Is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and\n \n\t(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. \n\n\tWe prepared a regulatory evaluation of the estimated costs to comply with this AD. See the ADDRESSES section for a location to examine the regulatory evaluation. \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\nAccordingly, under the authority delegated to me by the Administrator, the FAA amends 14 CFR part 39 as follows: \n\nPART 39--AIRWORTHINESS DIRECTIVES \n\n1. 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\n2. The FAA amends Sec. 39.13 by adding the following new airworthiness directive (AD):