The FAA has received reports of fractures of the outer cylinder of the aft trunnion of the main landing gear (MLG) on three Boeing Model 767 series airplanes. One of the three airplanes was six years old and had accumulated 28,887 total flight hours; another was six years old and had accumulated 25,841 total flight hours; and the third was eight years old and had accumulated 27,177 total flight hours. All of these airplanes were equipped with the original MLG, none of which had been overhauled at the time of the failure. Investigation revealed that in each case, moisture had entered the area between the outer cylinder of the MLG and a mating bushing. The effects of such moisture subsequently caused stress corrosion cracking. This condition, if not detected and corrected in a timely manner, could cause more fractures of the outer cylinder of the aft trunnion, which could result in the loss of the MLG. \n\n\tThe FAA has reviewed and approved Boeing Service Letter 767-SL-32-067, dated August 4, 1995, which describes the following procedures: \n\n\t1. Performing repetitive visual inspections to determine if the fillet seal of the outer cylinder aft trunnion is cracked or missing; \n\t2. Removing the fillet seal, solvent-cleaning the adjacent area, applying corrosion inhibiting compound (CIC), and visually inspecting to detect corrosion, if any fillet seal is found cracked or missing; and \n\t3. Re-applying CIC and greasing, if no corrosion is detected, or repairing the aft trunnion, if any corrosion is detected. Accomplishment of this repair eliminates the need for the repetitive inspections. \n\n\tSince an unsafe condition has been identified that is likely to exist or develop on other Boeing Model 767 series airplanes of the same type design, this AD is being issued to prevent stress corrosion cracking, which could result in fractures of the outer cylinder aft trunnion and the subsequent loss of the MLG. This AD requires visual inspections to determine if the fillet seal of the outer cylinder aft trunnion is cracked or missing, and the correction of any discrepancy or follow-on actions, if necessary. Repairing the aft trunnion constitutes terminating action for the repetitive inspection requirements. The actions are required to be accomplished in accordance with the service letter described previously. \n\n\tOperators should note that this AD requires repetitive application of CIC and grease every 500 flight hours, rather than at the 2A check interval (1,000 flight hours), as recommended in the service letter. In developing an appropriate compliance time for this action, the FAA considered not only the degree of urgency associated with addressing the subject unsafe condition, but the susceptibility of the subject area to a high velocity of water spray (such as, landing on wet runways, high pressure washing, etc.), which could lead to the accumulation of water and subsequent stress corrosion cracking of the outercylinder of the aft trunnion. \n\n\tThe FAA considers this AD to be interim action. The manufacturer has advised that it is developing a modification that will prevent future occurrences of this unsafe condition. Once this modification is developed, approved, and available, the FAA may consider additional rulemaking. \n\n\tAs a result of recent communications with the Air Transport Association (ATA) of America, the FAA has learned that, in general, some operators may misunderstand the legal effect of AD's on airplanes that are identified in the applicability provision of the AD, but that have been altered or repaired in the area addressed by the AD. The FAA points out that all airplanes identified in the applicability provision of an AD are legally subject to the AD. If an airplane has been altered or repaired in the affected area in such a way as to affect compliance with the AD, the owner or operator is required to obtain FAA approval for an alternative method of compliance with the AD, in accordance with the paragraph of each AD that provides for such approvals. A note has been included in this rule to clarify this long-standing requirement.\n \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\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 datefor 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\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 95-NM-149-AD."The postcard will be date- stamped and returned to the commenter. \n\n\tThe regulations adopted herein will not have substantial direct effects 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, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment. \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\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\n PART 39 - AIRWORTHINESS DIRECTIVES \n\n\t1. The authority citation for part 39 continues to read as follows: Authority: 49 USC 106(g), 40101, 40113, 44701. § 39.13 - (Amended) \n\n\t2. Section 39.13 is amended by adding the following new airworthiness directive: