The FAA has received a report indicating that, during fatigue testing of a Boeing Model 777-200 series airplane, a wearplate of the upper housing assembly of the forward trunnion of the main landing gear (MLG) was found to have migrated, and the attachment screws were fractured. The airplane had accumulated approximately 32,000 flight cycles. Subsequent to that report, one operator reported finding loose or fractured attachment screws of the wearplate on three Model 777-200 series airplanes. The wearplate had not migrated on any of those airplanes. The airplanes had accumulated approximately 4,300 to 4,500 flight cycles, and 20,700 to 22,690 flight hours. Loose or fractured attachment screws could lead to migration or loss of the upper housing wearplate, which could result in loss of the MLG during the takeoff roll; consequent damage to the airplane structure; and injury to flight crew, passengers, or ground personnel. \n\nExplanation of Relevant ServiceInformation \n\tThe FAA has reviewed and approved Boeing Alert Service Bulletin 777-57A0011, Revision 1, dated January 25, 2001, which describes procedures for repetitive inspections of the upper housing assembly of the forward trunnion of the MLG for discrepancies (migrated or missing wearplates, loose or fractured attachment screws), and corrective action (modification) if any discrepancies are found. The modification includes, but is not limited to, replacement of the lower housing fuse pins if the wearplates are fully migrated or missing; replacement of the upper and lower housing assemblies, and replacement of the wearplate if missing or damaged. Doing the modification eliminates the need for the repetitive inspections. The service bulletin references certain Boeing 777 Airplane Maintenance Manuals as the appropriate sources for accomplishment of the modification. Accomplishment of the actions specified in the service bulletin is intended to adequately address the identified unsafe condition. \n\nExplanation of the Requirements of the Rule \n\tSince an unsafe condition has been identified that is likely to exist or develop on other Model 777-200 series airplanes of the same type design, this AD is being issued to prevent migration or loss of the upper housing wearplate, which could result in loss of the MLG during takeoff roll; consequent damage to the airplane structure; and injury to flight crew, passengers, or ground personnel. This AD requires repetitive inspections of the upper housing assembly of the forward trunnion of the MLG for discrepancies (migrated or missing wearplates, loose or fractured attachment screws); and corrective action, if necessary. This AD also provides for an optional modification of the upper housing assembly for airplanes without discrepant wearplates, which would end the repetitive inspections. The actions are required to be accomplished per the service bulletin described previously, except as discussed below. \n\nDifference between Alert Service Bulletin and this AD \n\tAlthough the service bulletin specifies accomplishment of inspections, the FAA finds that "detailed visual inspection" is the appropriate terminology for the inspections described in the service bulletin. A definition of a detailed visual inspection is included in Note 2 of this AD. \n\nInterim Action \n\tThis is interim action. The service bulletin recommends doing the modification of the upper housing assembly of the forward trunnion within 6 years since date of delivery of the airplane or within 24 months after the date of the service bulletin, whichever is later. This AD provides for the modification as optional. The FAA is currently considering requiring the modification, which is described in the service bulletin and which would end the repetitive inspections required by this AD action. However, the planned compliance time for the replacement is sufficiently long so that notice and opportunity for prior public comment will be practicable. \n\nDetermination of Rule's Effective Date \n\tSince a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days. \n\nComments Invited \n\tAlthough this action is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this rule by submitting such written data, views, or arguments as they may desire. Communications shall identify the Rules Docket number and be submitted in triplicate to the address specified under the caption "ADDRESSES." All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed. \n\n\tSubmit comments using the following format: \n\nOrganize comments issue-by-issue. For example, discuss a request to change the compliance time and a request to change the service bulletin reference as two separate issues. \n\nFor each issue, state what specific change to the AD is being requested. \n\nInclude justification (e.g., reasons or data) for each request. \n\n\tComments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket. \n\n\tCommenters wishing the FAA to acknowledge receipt of their comments submitted in response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket Number 2001-NM-73-AD." The postcard will be date stamped and returned to the commenter. \n\nRegulatory Impact \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\tThe FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and that it is not a "significant regulatory action" under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES."\n\n List of Subjects in 14 CFR Part 39 \n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \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\t1. The authority citation for part 39 continues to read as follows: \nAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\n§ 39.13 (Amended) \n\t2. Section 39.13 is amended by adding the following new airworthiness directive: