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 all McDonnell Douglas Model DC-9 and C-9 (military) series airplanes was published in the Federal Register on May 24, 1995 (60 FR 27449). That action proposed to require replacement, inspection, and modification of the attach fittings of the main landing gear (MLG). \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\n\tSeveral commenters support the proposed rule. \n\nRequests for Extension of the Compliance Time\n\n\tSeveral commenters request that the proposed compliance time of 12 months be extended by as much as 12 additional months. Two commenters indicate that a parts availability problem was encountered when accomplishing one of the service bulletins cited in the proposed rule, McDonnell Douglas DC-9 Service Bulletin 57-148. One of these commenters indicates that the manufacturer requires a lead time in excess of 6 months to provide required parts. Another commenter states that, in light of the proposed time frame for compliance with the proposal, the number of work hours specified in the AD is too low because operators would need to schedule special maintenance visits to modify their aircraft. Similarly, other commenters request an extended compliance time that would align with regularly scheduled maintenance visits, thereby reducing lost revenue service. One commenter contends that inspection of MLG attach fittings in accordance with Revision 5 of McDonnell Douglas DC-9 Service Bulletin 57-148 will provide an adequate level of safety until modification of those fittings is accomplished. \n\n\tIn light of these considerations, the FAA concurs with the commenters' requests to extend the compliance time. The FAA finds that extending the compliance time by 12 additionalmonths will not adversely affect safety significantly, and will allow operators to accomplish the requirements of this AD at a base during regularly scheduled maintenance where special equipment and trained maintenance personnel will be available if necessary. Accordingly, paragraphs (a) and (b) of the final rule have been revised to specify a compliance time of 24 months. \n\nRequest to Clarify the Applicability of the AD \n\n\tOne commenter requests that the applicability of the proposal be revised to reference the specific series of Model DC-9 airplanes affected, rather than simply specifying that the proposed AD applies to "All Model DC-9 and C-9 (military) series airplanes." The commenter justifies its request by stating that McDonnell Douglas considers Model MD-80 airplanes to be "Series 80 DC-9" airplanes. Therefore, since the service bulletins cited in the proposed AD only apply to Model DC-9 series 10 through 50 and C-9 (military) series airplanes, the commenter suggests that those airplanes specifically be identified in the applicability of the AD to avoid any confusion and misinterpretation on the part of operators. The FAA concurs with the commenter's request, and has revised the applicability of the final rule accordingly. \n\nRequest to Include Actions Already Required by Other AD's \n\n\tOne commenter requests that the actions currently required by three existing AD's be included in the proposed rule. Those AD's are: \n\n\tAD 80-06-04 R1, amendment 39-4909 (49 FR 35617, September 11, 1984); \n\n\tAD 84-26-01, amendment 39-4971 (50 FR 448, January 4, 1985); and \n\n\tAD 90-18-03, amendment 39-6701 (55 FR 34704, August 24, 1990). The commenter provides the following justification for this request: \n\n\t1. The three existing AD's address the same subject as that specified in the proposed AD. \n\n\t2. One of the existing AD's, AD 90-18-03, specifies a compliance time for accomplishment of McDonnell Douglas DC-9 Service Bulletin 57-125 that is different from the compliance time specified in the proposal for accomplishment of the same action. \n\n\t3. McDonnell Douglas DC-9 Service Bulletin 57-148, which is cited in paragraph (b) of the proposed rule, also is listed in Table 2.3 of Report No. MDC K1572, "DC-9/MD80 Aging Aircraft Service Action Requirements Document (SARD)," Revision B, dated January 15, 1993 (hereinafter referred to as the "SARD"). The compliance time specified in Table 2.3 of the SARD for accomplishment of McDonnell Douglas DC-9 Service Bulletin 57-148 differs from that specified in paragraph (b) of this proposed rule for accomplishment of the same action. Therefore, if a new AD is issued to mandate accomplishment of Table 2.3 of the SARD, the compliance time specified in this proposed AD may conflict with the compliance time specified in the new AD that addresses the SARD. \n\n\tThe FAA acknowledges that certain actions specified in earlier versions of the service bulletins addressed in this AD (McDonnell Douglas DC-9 Service Bulletins 57-125 and 57-148) are mandated currently in the three existing AD's cited by the commenter and that the compliance times between certain documents vary. However, the FAA does not concur with the commenter's request to include the requirements of those AD's in this final rule for several reasons: \n\n\tOn November 4, 1994, the FAA issued a notice of proposed rulemaking (NPRM), Docket 94- NM-92-AD (59 FR 56011, November 11, 1994), which proposes to supersede AD 90-18-03. That NPRM proposes to require, in part, the accomplishment of certain inspections and structural modifications specified in Table 2.3 of the SARD. The FAA acknowledges that the SARD references the two service bulletins cited in this final rule (McDonnell Douglas DC-9 Service Bulletins 57-125 and 57-148). However, in the final rule for Docket 94-NM-92-AD, the FAA intends to exclude the actions specified in the two service bulletins from the requirements of that AD. Therefore, the actions describedin those service bulletins would be required by this AD only at the times specified herein. \n\n\tFurther, the FAA finds that the accomplishment of the requirements of this final rule will terminate the requirements of AD 80-06-04 R1 and AD 84-26-01. The FAA has added a new paragraph (c) in the final rule to specify this information.\n\nRequests to Limit the Applicability of the AD \n\n\tOne commenter requests that only airplanes equipped with certain gear fitting installations be applicable to the proposed AD. The commenter indicates that replacement of the attach fittings, as described in McDonnell Douglas DC-9 Service Bulletin 57-125, is addressed in AD 90-18-03, and that there are various configurations of fitting installations for which installation of smaller (7/8-inch diameter) lower tension bolts is not required. The commenter also indicates that, since the intent of the proposed AD is to improve the breakaway feature of the MLG (which is affected by the diameter of the lowertension bolts), only airplanes equipped with certain gear fittings would be affected by the proposed AD. \n\n\tThe same commenter states that airplanes equipped with fittings having large counterbore radii (7075-T73 fittings) that were installed with clearance fit NAS bolts should be excluded from the applicability of the proposal. The commenter indicates that it operates such airplanes and, at one time, this type of installation was permissible. The commenter explains that, although the complete intent of McDonnell Douglas DC-9 Service Bulletin 57-148 has not been accomplished, the portion of the service bulletin that has not been accomplished does not affect the breakaway function of the fitting. \n\n\tAdditionally, one commenter states that the proposed AD should require only the installation of a reduced diameter lower tension bolt (7/8-inch) and bushing portion of McDonnell Douglas DC-9 Service Bulletin 57-148 at an accelerated rate. The commenter adds that operators of large fleets should be allowed to accomplish the remainder of the actions specified in the service bulletin (including the enlargement of the counterbore, the replacement of the lower flange attachments with interference fit fasteners, and glass bead shotpeening of the fitting) on schedule in accordance with the SARD, which is being addressed in the final rule for Docket 94-NM-92-AD. The commenter contends that the actions required by the proposed AD would impose a severe hardship on operators. The commenter adds that only the reduction in size of the lower tension bolt improves the breakaway function of the gear fitting, which is the immediate concern addressed in the proposed AD. \n\n\tThe FAA does not concur with these commenters' requests. The FAA acknowledges that the key to breakaway capability of the MLG is the installation of smaller (7/8-inch) diameter tension bolts that attach the MLG fittings to the airframe. However, the FAA finds that accomplishment of the corrective actions necessary to address stress corrosion cracking of these fittings is equally as critical as incorporation of the breakaway feature. Therefore, the FAA has determined that the two objectives must be accomplished concurrently to address these safety issues in a timely manner. The FAA finds that accomplishment of the actions specified in both service bulletins cited in this AD (McDonnell Douglas DC-9 Service Bulletins 57-125 and 57-148) within 24 months after the effective date of this AD will adequately address these safety concerns. \n\nRequest to Clarify Shotpeening Requirements \n\n\tOne commenter questions the effectiveness of on-wing, glass bead shotpeening of the MLG fittings, as described in McDonnell Douglas DC-9 Service Bulletins 57-125 and 57-148. The commenter states that, in order to be effective, shotpeening must be controlled precisely to attain the required Almen Intensity. The commenter remarks that on-wing shotpeening of the gear fittings cannot be controlled to obtain therequired Almen Intensity and fatigue life improvement. The commenter specifies that the use of glass particles in the landing gear area, which includes many moveable components, raises a serious issue of system contamination and premature failure of components (i.e., bearings, due to glass particle contamination). The commenter makes no specific request for a change to the final rule, and provides no engineering data to substantiate that the fatigue life improvement is reduced or that premature failure of components occurs due to system contamination from glass particles. \n\n\tThe FAA finds that some clarification is necessary. Although the shotpeening process described in the service bulletins has been used in service for a substantial period of time, neither the FAA nor the airplane manufacturer have received any reports concerning system contamination or premature failure of components. Therefore, the FAA finds that no change to the final rule is necessary in this regard. However, the FAA would consider a request for approval of an alternative method of compliance, in accordance with the provisions of paragraph (d) of this AD, provided that adequate justification is presented to support such a request. \n\nRequest to Clarify Number of Necessary Work Hours \n\n\tOne commenter states that the actual work hours and elapsed times required to accomplish the actions specified in McDonnell Douglas DC-9 Service Bulletin 57-148 differ substantially from the figures reflected in the service bulletin. The commenter remarks that the actual work hours are approximately 400 more than the number specified in the service bulletin, and that the actual elapsed time is 100 hours more. \n\n\tThe FAA infers from these remarks that the commenter requests that the FAA revise the economic impact information, below, to increase the number of work hours required for accomplishment of the actions specified in this AD. The FAA concurs with the commenter's request. The FAA has revisedthe number of work hours estimated for accomplishment of the inspection and modification specified as Phase 2 in McDonnell Douglas DC-9 Service Bulletin 57-148 from 36 to 436 work hours. Estimated hours for elapsed time are not reflected specifically in AD actions. \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 significantly increase the economic burden on any operator nor increase the scope of the AD. \n\nEconomic Impact \n\n\tThere are approximately 906 Model DC-9 and C-9 (military) series airplanes of the affected design in the worldwide fleet. The FAA estimates that 549 airplanes of U.S. registry will be affected by this AD. \n\n\tThe FAA estimates that the replacement specified as Option 1 in McDonnell Douglas DC-9 Service Bulletin 57-125 has been accomplished on all 549 airplanes of U.S. registry that will be affected by this AD. (As discussed previously, accomplishment of Option 1 was required by AD 90-18-03.) Accordingly, the FAA finds that the replacement required by this AD will impose no additional economic burden on any U.S. operator. \n\n\tHowever, should an affected airplane be imported and placed on the U.S. Register in the future, it will require approximately 425 work hours to accomplish Option 1, at an average labor rate of $60 per work hour. The cost of required parts will be $58,853 per airplane. Based on these figures, the cost impact for accomplishing Option 1 will be $84,353 per airplane. \n\n\tThe FAA estimates that all 549 airplanes of U.S. registry will be required to accomplish the inspection and modification specified as Phase 2 in McDonnell Douglas DC-9 Service Bulletin 57-148. It will take approximately 436 work hours per airplane to accomplish Phase 2, at an average labor rate of $60 per work hour. Requiredparts will cost approximately $4,338 per airplane. Based on these figures, the cost impact on U.S. operators for accomplishing Phase 2 is estimated to be $16,743,402, or $30,498 per airplane. \n\n\tThe cost impact figure discussed above is based on assumptions that no operator has yet accomplished the requirement (Phase 2) of this AD action, and that no operator would accomplish that action 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 "significantregulatory 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 USC 106(g), 40101, 40113, 44701. § 39.13 - (Amended) \n\n\t2. Section 39.13 is amended by adding the following new airworthiness directive: