A proposal to amend part 39 of the Federal Aviation Regulations to include an airworthiness directive (AD) that is applicable to certain Boeing Model 747-200B, -200C, -300, -400, and -400D series airplanes was published in the Federal Register on August 23, 1993 (58 FR 44468). That action proposed to revise the FAA-approved maintenance program to require unrestricted opening of the passenger service unit (PSU) door during functional testing of the passenger oxygen system; and to require an inspection to detect leaks in certain passenger oxygen system reservoir bags, and marking and replacement of damaged mask assemblies. \n\nInterested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received. \n\nTwo commenters support the proposed rule. \n\nOne commenter notes that an unsafe condition does not exist since its airplanes are equipped with approximately 20 percent more oxygen masks than the maximum number of passengers, and the projected failure rate for these masks is estimated to be only 10 to 15 percent. From this comment, the FAA infers that the commenter is requesting that the rule be withdrawn. The FAA does not concur. Although the projected failure rate is lower than the number of available masks, the FAA has determined that passengers using defective masks may not realize that the masks are supplying an insufficient quantity of oxygen; and thus, passengers would not seek out spare oxygen masks. Therefore, the potential would still exist for passengers to be unable to obtain unrestricted delivery of emergency oxygen through the passenger oxygen system reservoir mask assembly. This AD action addresses that potential unsafe condition. \n\nBoeing Commercial Airplane Group requests that the applicability of the proposal be revised to exclude airplanes that were delivered prior to August 1991. Boeing indicates that data have demonstrated that the masks installed on those airplanes have had significantly fewer leaks/failures than masks installed on airplanes that were delivered after August 1991; therefore, those earlier airplanes would not necessarily be subject to the same unsafe condition addressed by the proposed AD action. The FAA does not concur with the commenter's request to exclude certain airplanes from the applicability. The FAA has reviewed the new data concerning the failure rate of the subject masks, which indicate that the masks' failure rate is lower than previously anticipated.. While the data do demonstrate that airplanes delivered prior to August 1991 have had significantly fewer leaking masks that fail to provide oxygen at or above FAA-required levels than those airplanes delivered in August 1991 and later, the FAA does not consider that this lower failure rate warrants the exclusion of any airplanes from the requirements of the rule. However, in light of the lower than originally anticipated failure rates for all of these masks, coupled with the unlikely event of decompression of the airplane, the FAA has reconsidered the proposed compliance time for inspection and replacement of the masks, and has determined that the compliance time can be extended for all airplanes without adversely affecting safety. Accordingly, the final rule has been revised to require a 15-month compliance time for Model 747-200B, -200C, and -300 series airplanes (the earlier-delivered airplanes), and a 180-day compliance time for Model 747-400 and -400D series airplanes. \n\nSeveral other commenters request that the proposed compliance time of 45 days to inspect and replace the masks be extended for a variety of reasons: Two of these commenters request that the proposed compliance time be revised to coincide with operators' regularly scheduled maintenance periods. One of these commenters suggests an alternative compliance time of "the next 3C check" for Model 747-200 series airplanes, and "the next 2C check" for Model 747-400 series airplanes. One of these commenters did not offer an alternative suggestion to the proposed compliance time; however, the commenter asserts that the supplier of these replacement oxygen masks cannot deliver an adequate quantity of original or modified oxygen masks within the proposed compliance time, therefore an extension is necessary. Another commenter requests that the proposed compliance time be revised to coincide with the time at which a newly-designed mask is anticipated to become available. As discussed above, the FAA has extended the compliance time for the required actions, although not for the reasons requested by these commenters. The extended compliance time, however, should be sufficient to allow the inspection and replacement actions to be accomplished during normally scheduled maintenance, and to allow for any anticipated new mask design to become available. \n\nSeveral commenters request that the proposal be revised to include an option to replace the currently installed passenger oxygen masks with improved oxygen masks. These commenters request that installation of these improved oxygen masks eliminate the need to perform a one-time visual inspection to detect leaks in the passenger oxygen system reservoir bags. The FAA does not concur. The FAA acknowledges that Boeing is currently developing new passenger oxygen masks; however, those masks are not yet available. The FAA considers that delaying this action until the masks are available would be inappropriate. Since an unsafe condition exists, the FAA finds that defective masks must be replaced to ensure continued safety. Therefore, when the improved masks are developed, approved, and available, affected operators may request approval to install these improved masks as an alternative method of compliance, under the provisions of paragraph (e) of the final rule. \n\nTwo commenters note that the cost estimate presented in the preamble to the Notice was too low and did not take into account the time to clean, sanitize, repack, and stow the passenger oxygen masks following the proposed inspection. The commenters state that the required inspection, and the consequent cleaning, sanitizing, repacking, and stowing of the oxygen masks would necessitate approximately 90 work hours. After considering the data presented by commenters, the FAA concurs that the number of work hours required to accomplish the required actions is higher than previously approximated; the economic impact information, below, has been revised to indicate this higher amount. The economic analysis, however, is limited only to the cost of actions actually required by the rule. It does not consider the costs of "on condition" actions, e.g., "repair, if necessary," since those actions would be required to be accomplished, regardless of AD direction, in order to correct an unsafe condition identified in an airplane and to ensure operation of that airplane in an airworthy condition, as required by the Federal Aviation Regulations. \n\nAfter 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\nThere are approximately 160 Boeing Model 747-200B, -200C, -300, -400, and -400D series airplanes of the affected design in the worldwide fleet. The FAA estimates that 25 airplanes of U.S. registry will be affected by this AD, that it will take approximately 90 work hours per airplane to accomplish the required actions, and that the average labor rate is $55 per work hour. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $123,750, or $4,950 per airplane. This total cost figure assumes that no operator has yet accomplished the requirements of this AD. \n\nThe 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\nFor 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 beobtained from the Rules Docket at the location provided under the caption "ADDRESSES." \n\nList of Subjects in 14 CFR Part 39 \n\nAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \n\nAccordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends 14 CFR part 39 of the Federal Aviation Regulations as follows: \n\nPART 39 - AIRWORTHINESS DIRECTIVES \n\n1.\tThe authority citation for part 39 continues to read as follows: Authority: 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) \n2.\tSection 39.13 is amended by adding the following new airworthiness directive: