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 McDonnell Douglas Model DC-9 series airplanes and C-9 (military) series airplanes was published in the Federal Register on September 13, 1996 (61 FR 48433). That action proposed to require modification of the emergency internal release system of the tailcone and the accessory compartment. \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\tTwo commenters support the proposed rule. \n\nRequests to Revise the Compliance Times of the Proposed Modifications \n\n\tOne commenter requests that the compliance time for accomplishing the proposed modifications be extended from the proposed 36 months to 4 years. The commenter states that such an extension will allow the modifications to be accomplished during a regularly scheduled heavy maintenance check and will allow time for procurement of additional modification kits. The commenter also states that such an extension will allow time for revising the affected manual; training of inspection and maintenance personnel; drafting, checking, and approving engineering documents; and testing and debugging the proposed modifications. \n\n\tAnother commenter requests that the compliance times be shortened to 12 months. This commenter suggests that the proposed compliance times may be too long to fly with the potential of failure of the emergency internal release system of the tailcone. \n\n\tThe FAA does not concur with either of these commenters' request. In developing an appropriate compliance time for these modifications, the FAA considered not only the degree of urgency associated with addressing the unsafe condition, but the availability of required parts and the practical aspect of installing the required modifications within an interval of time that parallels normal scheduled maintenance for the majority of affected operators. The manufacturer has advised that an ample number of required parts will be available for modification of the U.S. fleet within the proposed compliance period. Further, the FAA estimates that the affected airplanes will undergo two heavy maintenance checks during the proposed compliance time. In addition, the FAA finds that the 36-month compliance time is sufficient for operators to train their personnel and to incorporate the modifications into various documents. 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 presented to justify such an adjustment. \n\nRequest to Remove Modification Requirement \n\n\tTwo commenters state that the modification specified in McDonnell Douglas DC-9 Service Bulletin 53-257, Revision 1, dated February 9, 1996 (which is referenced in paragraph (a) of the proposal as the appropriate source of service information) is difficult to accomplish and only adds more problems to the existing tailcone release system. One of these commenters contends that the tailcone release system described in the referenced service bulletin is unacceptable for an emergency exit system. This commenter also contends that the subject modification cannot be accomplished on airplanes equipped with aft ventral airstairs. \n\n\tFrom these comments, the FAA infers that the commenters are requesting that the proposed modification in paragraph (a) of the AD be removed from the final rule. The FAA does not concur. The FAA acknowledges that there were some problems associated with accomplishing the modification in accordance with the original issue of McDonnell Douglas DC-9 Service Bulletin 53-257, dated May 18, 1994. However, the FAA finds that these problems were addressed and corrected in Revision 1 of this service bulletin. The FAA recognizes that Revision 1 of the service bulletin does not address airplanes on which the aft ventral airstair handle has not been deactivated. However, based on a survey conducted by McDonnell Douglas, the FAA finds that affected operators are willing to deactivate the aft ventral airstair handle to accommodate the modification required by this AD. In addition, paragraph (c) of the AD contains a provision for requesting approval of an alternative method of compliance to address these types of unique circumstances. \n\nRequest to Add a New Requirement \n\n\tOne commenter requests that paragraph (b) of the proposed AD be revised to include procedures for adding protective padding between the added ceiling panel and beams, and on all other beams in the path of exiting passengers. The commenter contends that installation of ceiling panels (as required by paragraph (b) of the AD) provides a false sense of security and guidance to the flight attendants and evacuees. The commenter states that the ceiling panels could be damaged easily by tall and/or unruly passengers during emergency egress, which could expose the beams and supporting structure. Thus other passengers could strike their heads against the overhead beams. The commenter also states that the ceiling panels could detach from its support structure during an actual emergency, and consequently, also allow exposure of the beams and supporting structure. Further, the commenter states that the ceiling panels could fall in the path of the passengers that are exiting from the airplane. The FAA does not concur. The FAA has determined that installation of ceiling panels on the lower side of three frames and installation of a protective pad on the last frame in the aft accessory compartment provides an acceptable level of safety. In addition, the FAA finds that such an installation is comparable to other panel installations throughout the airplane. However, under provisions of paragraph (c) of the final rule, operators may apply for approval of analternative methods of compliance if sufficient justification is presented to the FAA. \n\nRequest to Address Deficiencies with Existing Tailcone Release System \n\n\tOne commenter states that the existing tailcone release system contains many design and reliability deficiencies. The commenter points out that the proposed AD does not specify any requirements to replace or repair the existing tailcone release system. The commenter also contends that, due to such deficiencies, the new interior release handle (installed in accordance with the requirements of paragraph (b) of the proposed AD) will fail to perform its intended function. From this comment, the FAA infers that the commenter is requesting that the FAA address the problems associated with the existing tailcone release system in the proposed AD. The FAA does not concur. The FAA has previously issued several other AD's that concern the tailcone deployment system on Model DC-9 series airplanes, which was discussed previously inthe Other Relevant Rulemaking Section in the preamble to the NPRM. Therefore, the FAA finds no change to the final rule is necessary. \n\nRequest to Revise the Proposed Modification of the Emergency Internal Release System \n\n\tOne commenter requests that the existing tailcone release system be replaced with an electro-mechanical system, which can be actuated from inside the airplane. The commenter states that it is more cost effective to install a modern and efficient system (i.e., electro-mechanical system), rather than a system with design technology standards that are 25 to 30 years old. The commenter also states that the existing system does not meet industry expectations. The FAA does not concur. The modification required by paragraph (b) of this AD was developed with operator, manufacturer, and FAA concurrence based on cost and technical feasibility. However, under the provisions of paragraph (c) of this AD, operators may apply for the approval of an alternative method ofcompliance, if sufficient justification is presented to the FAA. \n\nRequest to Revise Various Manufacturer Manuals \n\n\tOne commenter requests that the FAA require the manufacturer, rather than the affected operator(s), to update the affected Illustrated Parts Catalog, Airplane Maintenance Manual, Structural Repair Manual, and Wiring Diagram Manual to ensure continued airworthiness of the tailcone release system. The commenter states that an operator, who does not have "experience" with the modification required by the proposed AD, could enter erroneous information into these manuals. The FAA does not concur. The FAA finds that the subject service documents are not necessary to accomplish the modifications required by this AD. The FAA has been informed that the manufacturer is in the process of revising the DC-9 Airplane Maintenance Manual (AMM) to comply with the continued airworthiness requirements and will make the AMM available to operators. \n\nFAA's Conclusion \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 as proposed. Cost Impact \n\n\tThere are approximately 878 McDonnell Douglas Model DC-9 series airplanes and C-9 (military) series airplanes of the affected design in the worldwide fleet. The FAA estimates that 590 airplanes of U.S. registry will be affected by this AD. \n\n\tThe modification of the emergency internal release system will take approximately 7 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Required parts will cost approximately $6,660 per airplane. Based on these figures, the cost impact of this modification required by this AD on U.S. operators is estimated to be $4,177,200, or $7,080 per airplane. \n\n\tThe modification of the accessory compartment will take approximately 10 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. For the 395 airplanes identified as "Group I" in the referenced service bulletin, required parts will cost approximately $1,777 per airplane. For the 195 airplanes identified as "Group 2" in the referenced service bulletin, required parts will cost $5,369 per airplane. Based on these figures, the cost impact of \nthis modification required by this AD on U.S. operators of Group 1 airplanes is estimated to be $938,915, or $2,377 per airplane; and on U.S. operators of Group 2 airplanes is estimated to be $1,163,955, or $5,969 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 powerand 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: \n\nAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\n§ 39.13 - (Amended) \n\n\t2. Section 39.13 is amended by adding the following new airworthiness directive: