The FAA proposed to amend 14 CFR Part 39 with an AD for all Boeing Model 777-200, -200ER, and -300 series airplanes. That action, published in the Federal Register on November 4, 2004 (69 FR 64263), proposed to require inspection of the outer cylinder of the main landing gear (MLG) to determine the serial number; an ultrasonic inspection of the outer cylinder of the MLG for cracks if necessary; and applicable specified and corrective actions if necessary. \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 for Alternate Inspection or Extension of Compliance Time \n\n\tOne commenter asks that an "on-aircraft" inspection be allowed as an alternate means of accomplishing the inspection for cracking of the main landing gear (MLG) in order to avoid unnecessary removal and disassembly of the MLG. Additionally, the removal and disassembly costs would be saved if an on-wing (on-aircraft) inspection were available. The commenter also asks that, if an "on-aircraft" inspection is not possible, the compliance time for accomplishing the inspection of the outer cylinder of the MLG be extended until removal of the MLG can be done at a normal maintenance time for overhaul. The commenter states that it has airplanes that have been in-service for 4 years without any problems, and notes that the cracking of the MLG was found before it was installed on the airplane. The FAA would allow 6 years for compliance, as specified in the proposed AD. The commenter adds that the manufacturer states that 6 years is the time allowed for overhaul, but the overhaul limit is actually 10 years. \n\n\tWe do not agree with the commenter's request for an "on-aircraft" inspection in place of the inspection of the outer cylinder of the MLG. There are no procedures for accomplishing an "on-aircraft" inspection specified in the referenced serviceinformation. Nor do we agree to extend the compliance time for accomplishing the inspection of the outer cylinder of the MLG until the removal of the MLG can be done at a normal maintenance time for overhaul. In developing an appropriate compliance time for this action, we considered the recommendation of the manufacturer, the urgency associated with the subject unsafe condition, and the practical aspect of accomplishing the required inspection within a period of time that corresponds to normal scheduled maintenance for most affected operators. The compliance time specified in this final rule represents an acceptable interval of time wherein affected airplanes may be allowed to operate without jeopardizing safety. In addition, no technical justification was provided to substantiate this request. Paragraph (k)(1) of this AD provides affected operators the opportunity to apply for an alternative method of compliance (AMOC) and to present data to justify the adjustment of the compliancetime. We have made no change to the final rule in this regard. \n\nRequest for Part Number or Serial Number Identification on Affected Parts \n\n\tOne commenter asks that part number (P/N) or serial number (S/N) re-identification be done after accomplishing the required inspection. The commenter states that the referenced service bulletin does not require P/N or S/N re-identification of affected parts after accomplishing the inspection: the procedures only specify engraving the service bulletin number on the part. The commenter adds that the outer cylinder of the MLG is a life-limited part that must be tracked for the life of the part; therefore, P/N or S/N re-identification is necessary to track incorporation of the referenced service bulletin and the proposed AD. The commenter notes that life-limited parts are tracked for the life of the part, and operators must know on which airplanes the S/N identified in the referenced service bulletin is installed. \n\n\tWe do not agree with the commenter. The referenced service bulletin specifies vibro-engraving or electro-chemically etching the service bulletin number next to the existing P/N on the outer cylinder assembly. We have determined that this action sufficiently differentiates between pre- and post-modification of the part and allows tracking for the life of the part. We have made no change to the final rule in this regard. \n\nRequests To Change Applicability or Allow Alternate Method for Confirming the Serial Numbers \n\n\tOne commenter asks that the applicability specified in the proposed AD be changed to an appliance AD, which would be applicable only to airplanes with parts having the P/N and S/N identified in the referenced service bulletin, not all Model 777-200, -200ER, and -300 series airplanes. The commenter does not provide a reason for this request. \n\n\tWe do not agree with the commenter. Our general policy, when an unsafe condition results from an appliance or other item that is, or could be, installed on multiple airplane models, is that the AD is issued so that it is applicable to those airplane models, rather than to the item. The reason for this is simple: Making the AD applicable to the airplane models on which the appliance or other item is installed ensures that operators of those airplanes will be notified directly of the unsafe condition and the action required to correct it. While it is assumed that an operator will know the models of airplanes that it operates, there is a potential that the operator will not know or be aware of specific items that are installed on its airplanes. Therefore, calling out the airplane model as the subject of the AD prevents "unknowing non-compliance" on the part of the operator. We have made no change to the final rule in this regard. \n\n\tAnother commenter asks that the applicability specified in the proposed AD be changed to match the effectivity identified in the referenced service bulletin, which applies to Model 777-200 series airplanes only. If the applicability is not changed, the commenter asks that an alternate method of confirming the S/N of the outer cylinder of the MLG be allowed. The commenter notes that one method is using digital records provided by the manufacturer. The commenter does not provide a reason for this request. \n\n\tWe partially agree with the commenter. We agree to change the applicability specified in the proposed AD somewhat. As specified in the "Differences" section of the proposed AD, Model 777-300 series airplanes are included in the applicability since we determined that, because of the potential for the affected outer cylinders to be installed on Model 777-300 series airplanes, the proposed actions must be done on those airplanes. As discussed below in "Explanation of Changes to Proposed AD," we inadvertently included Model 777-200ER series airplanes; we have removed that model from the applicability specified in this final rule. \n\n\tWe agree to allow the use of digital records provided by the manufacturer for confirming the serial number of the outer cylinder of the MLG, provided that precise tracking of which outer cylinder serial number is on which airplane since delivery can be determined from the airplane maintenance records. The final rule already provides for this by the maintenance records review specified in paragraph (h) of this AD. We have made no change to the final rule in this regard. \n\nRequest for Preliminary Inspection \n\n\tOne commenter asks that the requirements specified in paragraph (h)(2) of the proposed AD be changed to allow for a preliminary inspection of serial numbers to determine which airplanes are affected by the proposed AD. The commenter also asks to be allowed to accomplish any necessary inspections and corrective action at a later time, as long as those actions are accomplished within the compliance time required by paragraph (g) of the proposed AD. The commenter states that paragraph (h)(2) of the proposed AD specifies that if any serial number identified in the referenced service bulletin is installed, the ultrasonic inspection must be accomplished before further flight, in addition to accomplishing all applicable specified actions and any corrective action. \n\n\tWe agree that a preliminary inspection to determine the serial numbers of affected airplanes may be accomplished before accomplishing the requirements specified in paragraph (h)(2) of this AD. Operators are always permitted to perform actions earlier than the compliance time specified in an AD. In this case, it is at the operator's discretion to accomplish a preliminary inspection of the serial numbers to determine which airplanes are affected by the AD at any time before the required compliance time, if that time more closely fits the operator's maintenance schedule. We also agree that the inspection for cracking and any applicable specified actions, as required by paragraph (h)(2), may be accomplished at a later time as long as the inspection for cracking is done within the compliance time required by paragraph (g) of this AD. Paragraph (h)(2) of this AD has been changed accordingly. \n\n\tWe do not agree that any applicable corrective action resulting from inspection findings may be accomplished at a later time; the corrective action must always be accomplished before further flight after accomplishing the required inspection to maintain safety of flight. We have made no change to the final rule in this regard. \n\nExplanation of Changes to Proposed AD \n\n\tThe applicability in the proposed AD addresses "All 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 all Model 777-200 and -300 series airplanes; therefore, we have changed the applicability in this final rule accordingly. \n\n\tBoeing has received a Delegation OptionAuthorization (DOA). We have revised this final rule to delegate the authority to approve an AMOC for any repair required by this AD to the Authorized Representative for the Boeing DOA Organization rather than the Designated Engineering Representative. \n\nConclusion \n\n\tWe have carefully reviewed the available data, including the comments that have been submitted, and determined that air safety and the public interest require adopting the AD with the changes described previously. These changes will neither increase the economic burden on any operator nor increase the scope of the AD. \n\nCosts of Compliance \n\n\tThis AD affects about 463 Model 777 series airplanes worldwide. The following table provides the estimated costs for U.S. operators to comply with this AD. \n\n\tEstimated Costs \n\n\nAction \nWork hours \nAverage labor rate per hour \nParts \nCost per airplane \nNumber of U.S.-registered airplanes \nFleet cost \n\n\n\n\n\n\n\n\n\n\n\n\n\n\nPart Number Inspection \n1 to 229 (depending \non which inspection \nmethod is used). \n$65 \nNone \n$65 to $14,885\n133 \n..$8,645 to \n$1,979,705 \n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\nUltrasonic Inspection (if \nnecessary). \n6 \n$65 \nNone \n$390 per outer cylinder, $780 for both outer cylinders on \nthe airplane. \n\nunknown, but there may be up to 26 affected outer cylinders in fleet.\n$10,140\n\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 theAdministrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that 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):