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 767 series airplanes was published in the Federal Register on August 5, 1998 (63 FR 41739). That action proposed to require a detailed visual inspection to detect corrosion inside the forward trunnion joint of the main landing gear (MLG); follow-on actions; and repair, if necessary. That action also proposed to provide for optional terminating action for the repetitive inspections. \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\nSupport for the Proposal \n\n\tTwo commenters support the proposal. Request to Clarify Certain Requirements \n\n\tOne commenter, the manufacturer, requests that paragraph (b) of the proposal be revised to clarify that the addition of corrosion-inhibiting compound to the trunnion joint is also needed to terminate the proposed inspections. \n\n\tThe FAA concurs. Although the appropriate service information for this AD provides procedures to apply corrosion-inhibiting compound to the trunnion joint whenever the chrome plate is applied to the trunnion, this was not explicitly stated in the wording of the AD. Therefore, the FAA has revised paragraphs (a)(1), (a)(2), and (b) of the final rule (where discussion of terminating actions occurs) to clarify that the terminating action will consist of applying chrome plate to the trunnion tabs and applying corrosion-inhibiting compound to the trunnion joint. \n\nRequest to Withdraw the NPRM or Require the Latest Modification \n\n\tOne commenter requests that the FAA withdraw the proposal, or at least revise the requirements to mandate the latest modification as the terminating action. The commenter states that the terminating action specified in the proposed rule will not prevent corrosion.The commenter states that its own inspections of other trunnions on which the terminating modification has been accomplished indicate that the terminating modification is inadequate to prevent corrosion. The commenter further notes that the proposed modification (which consists of applying chrome plate) does not address the areas of the joint that have proved to be the most susceptible to corrosion, e.g., the threads on the internal diameter of the trunnion and the aft surface of the joint. The commenter concludes that, in light of the fact that Boeing has recently abandoned its design philosophy for this joint, the proposed terminating modification is "dated." \n\nSpecifically, the commenter notes that the latest Boeing design entails removing the threads of the joint altogether. Further, the commenter states that mandating the proposal would impose costly and disruptive maintenance requirements if the proposal requires incorporating an ineffective modification when better solutions exist. \n\n\tThe FAA does not concur with the commenter's request to withdraw the proposal or to revise the terminating action specified in the AD. The FAA considers that, in this case, there are three factors that make stress corrosion cracking of the forward trunnion a safety concern. First, the material (i.e., 4340M high strength steel) is known to be highly susceptible to stress corrosion cracking; second, the material is in an environment that allows corrosion to form (as has been demonstrated numerous times); and third, the material is at times exposed to sustained tensile stresses. Since an unsafe condition has been identified, the FAA considers it appropriate and necessary to issue the final rule. \n\n\tAlthough the commenter's position is that the terminating modification is inadequate in preventing corrosion, the FAA has received no reports of corroded trunnions being identified after the terminating modification has been accomplished. The FAA has determined that since the release of Boeing Alert Service Bulletin 767-32A0127, dated January 29, 1996 (the appropriate service information for this final rule), an insufficient amount of time has passed that would allow corrosion to re-initiate on a MLG forward trunnion that has been removed from an airplane, then disassembled, inspected, cleaned, chrome-plated, and re-installed with corrosion inhibiting compound. Therefore, no change is necessary to this final rule in that regard. \n\n\tThe FAA acknowledges that the internal diameter of the trunnion and the aft surface of the joint are susceptible to corrosion, and that the modification specified in this final rule does not specifically address applying chrome plating to those areas. However, the FAA has determined that the required inspections for corrosion and the modification specified by this final rule are adequate to detect or prevent corrosion of the forward trunnion joint. If information becomes available that indicates that the terminating action may be inadequate, the FAA may initiate further rulemaking. \n\n\tThe commenter also asserts that the proposal would impose costly and disruptive maintenance requirements if it requires incorporating an ineffective modification when better solutions already exist. As explained previously, the FAA has received no information indicating that the modification is ineffective. Additionally, the FAA is aware that Boeing has developed a new design for the forward trunnion joint, which entails, among other things, the removal of the internal threads. The FAA also notes that the service information relating to the new design is not available for FAA review and approval at the current time. However, under the provisions of paragraph (c) of the final rule, the FAA will consider requests for approval of an alternative method of compliance if sufficient data are submitted to substantiate that such a design change would provide an acceptable level of safety. \n\nRequest to Withdraw the Proposalor Add Further Requirements \n\n\tThis same commenter requests that if the proposal is not withdrawn, it should simply require operators to remove and report any corrosion at overhaul (not to exceed 10 years), with aggressive lubrication intervals of 250 flight cycles or less. The FAA infers that the commenter is basing its request on a statement (of the commenter's) that contends that the stress levels in the forward trunnion area are below the stress corrosion cracking threshold for crack formation. Therefore, the commenter concludes that no risk exists for stress corrosion cracking to start. \n\n\tThe FAA does not concur with the commenter's request to withdraw the NPRM. For reasons specified in the discussion of the previous comment, the FAA finds that this rule is appropriate and necessary. Further, the FAA does not concur with the request to require removal of corrosion during overhaul. The FAA finds that the concept of stress corrosion threshold is not applicable to this situation because the affected structure is already corroded. The use of a stress corrosion threshold is only applicable during the material selection phase of a new design; it is not useful for predicting the behavior of corroded structure. Therefore, the FAA has determined that no change to the final rule is necessary. \n\nRequest to Revise the Compliance Time \n\n\tOne commenter states that the 18-month initial compliance time is too aggressive and will cause unnecessary costs and scheduling problems. \n\n\tThe FAA infers that the commenter would like the compliance time to be extended to correlate with the airplane's next scheduled overhaul. The FAA does not concur that the compliance time should be revised. In developing an appropriate compliance time, the FAA considered the safety implications, and normal maintenance schedules for timely accomplishment of the inspection and follow-on actions. In consideration of these items, as well as the reports of corrosion at the forward trunnion thrust face, tabs, and internal threads of the forward trunnion of the MLG, the FAA finds that a period of 18 months represents an appropriate compliance threshold wherein the inspection and follow-on actions can be accomplished during scheduled maintenance for the majority of affected operators and an acceptable level of safety can be maintained. However, under the provisions of paragraph (c) of the final rule, the FAA may approve requests for adjustments to the compliance time if data are submitted to substantiate that such adjustments would provide an acceptable level of safety. \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 455 Boeing Model 767 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 151 airplanes of U.S. registry will be affected by this AD. \n\n\tIt will take approximately 8 work hours per airplane to accomplish the visual inspection, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the required inspection on U.S. operators is estimated to be $72,480, or $480 per airplane, per inspection cycle. \n\n\tThe cost impact figures above do not account for the time to gain access to the forward trunnion joint or to return a main landing gear to service. In this case, however, the access and close-up work hours may account for the predominant portion of the total cost impact of this AD. It is estimated that it will take approximately 65 work hours to gain access to both forward trunnion joints, and 89 work hours to return the airplane to service. If these costs are included, the cost impact for the required inspections will be approximately $1,467,720, or $9,720 per airplane, per inspection cycle. \n\n\tRepair of the forward trunnions (two per airplane), if accomplished (which may include both corrosion blend-out repairs as well as the application of chrome plate to certain portions of the forward trunnion), will take approximately 72 work hours to accomplish, at an average labor rate of $60 per work hour. The cost of the repair kits will be approximately $16,000 per airplane. Based on these figures, the cost impact of the repair on U.S. operators is estimated to be $3,068,320, or $20,320 per airplane. \n\n\tThe cost impact figures discussed 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. \n\nRegulatory Impact \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\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: Authority: 49 U.S.C. 106(g), 40113, 44701. § 39.13 (Amended) \n\t2. Section 39.13 is amended by adding the following new airworthiness directive: