A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) by superseding AD 94-03-01, amendment 39-8807 (59 FR 6538, February 11, 1994), which is applicable to certain McDonnell Douglas Model DC-9 and C-9 (military) series airplanes, was published as a supplemental notice of proposed rulemaking (NPRM) in the Federal Register on January 9, 1996 (61 FR 637). The action proposed to require additional visual inspections of certain Principal Structural Elements (PSE's) on certain airplanes listed in the Structural Inspection Document (SID) planning data; a revision of the reporting requirements; an increase in the sample size for one PSE; and deletion of the requirement to perform certain visual inspections of the Fleet Leader Operator Sampling (FLOS) Principal Structural Elements (PSE). \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\tOne commenter supports the proposed rule. \n\nRequest to Extend the Compliance Time \n\n\tOne commenter requests that the compliance time for incorporating the SID revision into the FAA-approved maintenance inspection program be extended from the proposed 6 months to 1 year. This commenter also requests a corresponding increase in the completion end dates for each PSE inspection. The commenter states that it would have to special schedule its fleet of airplanes to accomplish this program within the proposed compliance time; this would entail considerable additional expenses and schedule disruptions. Further, this commenter points out that the SID program is becoming a larger and larger burden to airlines. \n\n\tThe FAA does not concur with the commenter's request to extend the compliance time. The FAA finds that changes in the program that are described in Volume III-92 and Volume III-95 of McDonnell Douglas Report No. L26-008, and required by this AD, introduce relatively minor changes to the overall scope of the DC-9 SID program. In addition, the FAA points out that Volume III-95 deletes the FLOS visual inspections that were previously required by AD 94-03-01 and, thereby, reduces the number of inspections required to be performed under the program. With regard to these changes, the FAA cannot agree with the commenter's assertion the SID and, thus, this AD are becoming a "larger burden" for operators. \n\n\tFurther, the proposed compliance time of 6 months was arrived at with the previous concurrence of affected operators, manufacturers, and the FAA. In light of these items, and in consideration of the amount of time that has already elapsed since issuance of the original notice, the FAA has determined that further delay of the implementation of the requirements of this final rule action is not appropriate. However, paragraph (d) of the final rule does provide affected operators the opportunity to apply for an adjustment of the compliance time if adequate data are presented to the FAA to justify such an adjustment. \n\nRequest to Revise Inspections to 100 Percent \n\n\tOne commenter requests that the PSE inspections be changed from sampling to 100 percent inspections. The commenter considers that this would eliminate the continual changes every year; thus, the program would be more manageable and straightforward. In addition, the commenter states that this would simplify scheduling of the SID inspections, which would streamline the program by reducing the workload for all parties concerned. \n\n\tThe FAA does not concur that a revision to the AD is necessary. The inspections in the McDonnell Douglas SID programs were established using specific criteria for determining whether a PSE should be defined as FLOS, Fleet Leader Sample (FLS), or 100 percent. The manufacturer established these criteria only after extensive and detailed consultations with large numbers of operators and with the FAA. The FAA finds that the 100 percent inspections are only necessary if an insufficient number of samples exists in the operator's sample size to use sampling concepts. However, if an operator has a sufficient number of samples and elects to accomplish 100 percent inspections, it is the operator's prerogative to do so. \n\nRequest to Permit Repairs in Accordance with SRM or DER Approval \n\n\tTwo commenters request that proposed paragraph (c) be revised to permit repair of any cracked structure in a PSE found during any inspection (i.e., a non-mandated or unscheduled inspection) to be accomplished in accordance with the FAA-approved Structural Repair Manual (SRM) or the Designated Engineering Representatives (DER) of the McDonnell Douglas Corporation. One of these commenters states that the current procedure for accomplishing the repair in accordance with a method "approved by the FAA" takes too long, adversely impacts work scheduling, and delays scheduled departure of airplanes. \n\n\tThe FAA does not concur with the commenters' request to revise paragraph (c) of this AD. While DER's are authorized to determine whether a design or repair method complies with a specific requirement, they are not authorized to make the discretionary determination as to what the applicable requirement is. Further, the SID program is based upon cooperation between aircraft operators, the FAA, and the manufacturer. The SID program functions most effectively in detecting fatigue cracks if all findings of fatigue cracking are reported to McDonnell Douglas as required by this AD. It is crucial that the FAA, as well as McDonnell Douglas, be aware of all repairs made to PSE's. \n\n\tFurther, every repair of PSE structure requires a damage tolerance assessment (DTA) to be performed (of the repair) in order to establish its effect on the fatigue life of the affected structure. The DTA process involves the review and use of type design data that are proprietary and may not be available to those persons (such as a DER) who are generally authorized to approve routine repairs. For this reason, it is appropriate that the Manager of the Los Angeles Aircraft Certification Office (ACO) be the focal point in the DTA approval process. \n\n\tIn some cases, repairs are made to PSE structure as a result of cracking that was found during an opportunity inspection (i.e., non-mandated or unscheduled inspection), and the approval of the repair is made without the coordination of the manufacturer or the Los Angeles ACO. When the time arrives for that PSE to be inspected in accordance with the AD, the PSE becomes a "discrepant PSE." If a DTA were not accomplished on the "discrepant PSE" at the time of the repair, compliance with the AD could require that the repair be removed or reworked at a later time. In either case, the Manager of the Los Angeles ACO is tasked to ensure that all repairs to cracked PSE's comply with the AD. \n\n\tThe FAA considers that any repair to cracked PSE's without therequired DTA can only be classified as "interim" or "temporary," and will eventually require coordination with the Manager of the Los Angeles ACO. Most methods of repair specified in the DC-9 Structural Repair Manual, the relevant service bulletins, or DER-designed repairs do not include a continuing inspection program to ensure that the repair is inspected at an acceptable level of safety. A DTA can be done most easily at the time of repair, rather than at a later date when the details of the repair may be hard to obtain and, undoubtedly, would be more costly. Currently, the Manager and staff of the Los Angeles ACO are working very closely with the manufacturer to expedite interim repair approval requests. Such requests may be made under the provisions of paragraph (d) of the final rule. \n\nRequest for Clarification of Repair Requirements \n\n\tOne commenter requests clarification as to what area of the subject structure is required to be repaired in accordance with a method approved by the FAA. The commenter notes that McDonnell Douglas maintains that the secondary structure in the general area of the PSE is not part of the PSE inspection; therefore, repair of this area does not require FAA approval if the area is found cracked during a SID inspection. McDonnell Douglas also indicates that its DER's have been given authority by the FAA to approve repairs for longerons 16 and 17 over the forward and aft cargo doors (PSE 53.09.001 and 53.09.035). \n\n\tThe FAA finds that clarification of this point is necessary. The FAA points out that the SID program and this AD do not use the term "secondary" structure when referring to the PSE's. Volume 1, Section 1, of MDC Report No. L26-008 defines a PSE as structure whose failure, if it remained undetected, could lead to the loss of the airplane. The physical boundaries of PSE's are clearly defined in Volume 1, Sections 2 and 3, of the SID, MDC Report No. L26-008. Accordingly, the FAA considers that the repair requirements of paragraph (c) of the AD are not limited only to certain parts of the PSE's, as implied by the commenter, but rather to any crack that is found within the physical boundaries of any PSE. Therefore, the FAA finds that any cracked structure, including the following cracks, must be repaired in accordance with a method approved by the Manager, Los Angeles ACO. \n\nAny crack that is found in longerons 16 and 17 within the shaded area between STA. 362.500 and STA. 434.500 of PSE 53.09.001 (for Model DC-9-30, -40, and -50 series airplanes) \n\nAny crack that is found in longerons 16 and 17 within the shaded area between STA. 710.500 and STA. 766.000 of PSE 53.09.035 (for Model DC-9-10, and -20 series airplanes) \n\nRequest to Eliminate Duplication of Reporting of Existing Repairs \n\n\tThis same commenter requests that the proposed rule be revised to eliminate the duplication of reporting of existing repairs from one inspection interval to the next. The commenter points out that theproposed rule would require that all existing repairs in the PSE area must be reported to McDonnell Douglas, along with details of each repair. \n\n\tThe FAA does not consider that any action is necessary since the rule does not require \nreporting relevant to existing repairs. However, paragraphs (a)(3) and (b)(3) of the AD do require that all inspection results (negative or positive) be reported to McDonnell Douglas. \n\nRequest to refer to "or Later FAA-Approved Revisions" of the SID \n\n\tOne commenter requests that the proposed rule be revised to include the phrase, "or later FAA-approved revisions," when referring to the SID document. The commenter states that this would allow operators to revise their programs whenever a new revision to the SID is released, and would eliminate the FAA's need to supersede the existing AD time and again as new revisions of the SID are issued. \n\n\tThe FAA does not concur. To use the phrase, "or later FAA-approved revisions," in an AD when referring to the service document, violates Office of the Federal Register (OFR) regulations regarding approval of materials "incorporated by reference" in rules. In general terms, these OFR regulations require that either the service document contents be published as part of the actual AD language; or that the service document be submitted for approval by the OFR as "referenced" material, in which case it may be only referred to in the text of an AD. The AD may only refer to the service document that was submitted and approved by the OFR for "incorporation by reference." In order for operators to use later revisions of the referenced document (issued after the publication of the AD), either the AD must be revised to reference the specific later revisions, or operators must request the approval to use them as an alternative method of compliance with this AD (under the provisions of paragraph (d)). \n\nConclusion \n\n\tAfter careful review of the available data, including the comments notedabove, the FAA has determined that air safety and the public interest require the adoption of the rule as proposed. \n\nCost Impact \n\n\tThere are approximately 889 Model DC-9 and C-9 (military) series airplanes of the affected design in the worldwide fleet. The FAA estimates that 568 airplanes of U.S. registry and 38 U.S. operators will be affected by this AD. \n\n\tIncorporation of the SID program into an operator's maintenance program, as required by AD 94-03-01, takes approximately 1,062 work hours (per operator) to accomplish, at an average labor rate of $60 per work hour. Based on these figures, the cost to the 38 affected U.S. operators of incorporating the revised procedures into the maintenance program is estimated to be $2,421,360, or $63,720 per operator. \n\n\tThe incorporation of the revised procedures in this AD action will require approximately 20 additional work hours per operator to accomplish, at an average labor rate of $60 per work hour. Based on these figures, thecost to the 38 affected U.S. operators to incorporate these revised procedures into the SID program is estimated to be $45,600, or $1,200 per operator. \n\n\tThe recurring inspection costs, as required by AD 94-03-01, take 362 work hours per airplane per year to accomplish, at an average labor rate of $60 per work hour. Based on these figures, the recurring inspection costs required by AD 94-01-03 are estimated to be $12,336,960, or $21,720 per airplane. \n\n\tThe recurring inspection procedures added to the program by this AD action will not add any new economic burden on affected operators, since certain inspections are added while others are deleted. \n\n\tBased on the figures discussed above, the cost impact of this AD is estimated to be $12,382,560 for the first year, and $12,336,960 for each year thereafter. These cost impact figures discussed above are based on assumptions that no operator has yet accomplished any of the requirements of this AD action. However, it can be reasonably be assumed that the majority of the affected operators have already initiated the SID program (as required by AD 94-03-01). \n\n\tAdditionally, the number of required work hours for each required inspection (and for the SID program revision), as indicated above, is presented as if the accomplishment of those actions were to be conducted as "stand alone" actions. However, in actual practice, these actions for the most part will be accomplished coincidentally or in combination with normally schedule airplane inspections and other maintenance program tasks. Therefore, the actual number of necessary additional work hours will be minimal in many instances. Further, any cost associated with special airplane scheduling can be expected to be minimal. \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 amongthe 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 theAmendment \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: \n\nAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\n§ 39.13 - (Amended) \n\n\t2. Section 39.13 is amended by removing amendment 39-8807 (59 FR 6538, February 11, 1994), and by adding a new airworthiness directive (AD), amendment 39-9671, to read as follows: