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 PTC Aerospace Model 91700 passenger oxygen system, installed in PTC Aerospace Model 881, 940, and 950 seats found on McDonnell Douglas DC-10 series aircraft, was published in the Federal Register on September 21, 1993 (58 FR 48486). That action proposed to require a one-time inspection to verify the proper configuration and functioning of the passenger oxygen system, and replacement, if necessary, with serviceable parts. The actions would be required to be accomplished in accordance with PTC Service Bulletin (SB) No. 25-1233, Revision D, dated February 2, 1993, that describes procedures for a one-time inspection to verify the proper configuration and functioning of the passenger oxygen system, and replacement, if necessary, with serviceable parts.\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\tOne commenter supports the rule as proposed.\n\n\tTwo commenters state that the compliance time should be reduced, one to six months after the effective date of the AD, the other to 30 days. The Federal Aviation Administration (FAA) does not concur. Neither comment offered engineering or technical data to support a reduction in the compliance interval from the 15-month compliance time contained in the proposed rule. The proposed compliance time was determined to provide an acceptable level of safety considering the maintenance schedules of the operators. Therefore, the FAA has retained the 15-month compliance time in the final rule.\n\n\tOne commenter states that the lanyard length check should be deleted due to difficulty in performing that check. The FAA concurs that the check was difficult to perform but does not concur in deleting the check. The check is needed to verify the correct lanyard length. Since publication of the NPRM, the manufacturer has advised the FAA that the lanyard length tolerance has been increased to plus or minus .25 inch, which will allow that check to be more easily accomplished. This tolerance factor has been added to paragraph (a)(3) of this Final rule.\n\n\tOne commenter states that the AD should require repetitive inspections. The FAA does not concur. The one-time inspection, and replacement, if necessary, with serviceable parts, required by this AD will obviate the need for repetitive inspections other than those performed during routine scheduled maintenance.\n\n\tThe commenter further states that the AD should contain a requirement for reporting malfunctions. The FAA does not concur. The one-time inspection, and replacement, if necessary, with serviceable parts, required by this AD will preclude the need for reporting malfunctions.\n\n\tThe commenter further states that the SB does not provide adequate work step instructions. The FAA concurs. Since issuance of the NPRM, PTC Aerospace has issued SB No. 25-1233, Revision E, dated April 15, 1994, which contains clarified work step instructions. The FAA has added this new service bulletin to the AD.\n\n\tThe commenter further states that the SB should specify a different oxygen canister safety cap. The revised SB specifies two safety caps.\n\n\tThe commenter further states that a functional test should be required prior to disassembly. The FAA does not concur. The FAA has determined that a functional test prior to disassembly would not provide any benefit in evaluating the passenger oxygen system.\n\n\tThe commenter further states that there should be a snag test on the release pin for grooves and burrs. The FAA does not concur. The FAA believes that the instructions for testing as stated in the revised SB are adequate.\n\n\tSince publication of the NPRM, the manufacturer has advised the FAA that an additional safety cap, Scott Part Number (P/N) 36425-00,is available. Also, the manufacturer has added a black plastic grommet, P/N 91880-2, on the pin release bracket, and a bushing, P/N 121836-1, on the activator assembly spring, P/N H13341. Finally, the manufacturer has included instructions for verifying the gap between the cable actuating lever and the cable activating lever stop in PTC Aerospace SB No. 25-1233, Revision E, dated April 15, 1994. These revised instructions have been added to the compliance section of this final rule.\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 described previously. The FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD.\n\n\tThe initial estimate in the NPRM of approximately 3,000 passenger oxygen systems of the affected design in the worldwide fleet was incorrect. The manufacturer has advised the FAA that the revised number is 4,800 passenger oxygen systems in the worldwide fleet. The FAA estimates that 4,000 passenger oxygen systems are installed on aircraft of U.S. registry, of which 2,500 have already been modified, leaving approximately 1,500 passenger oxygen systems that have not yet been modified in accordance with this AD. The FAA estimates that it will take approximately 1 work hour per passenger oxygen system to accomplish the required actions, and that the average labor rate is $55 per work hour. Required parts will cost approximately $20 per passenger oxygen system. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $112,500.\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\tAir Transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.\n\nAdoption of the Amendment \n\tAccordingly, pursuant to the authority delegatedto 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\t1.\tThe authority citation for part 39 continues to read as follows:\n\tAuthority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89.\n\n§39.13 - (AMENDED)\n\t2.\tSection 39.13 is amended by adding the following new airworthiness directive: