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 Boeing Model 757 and 767 series airplanes was published in the Federal Register on March 8, 1994 (59 FR 10759). That action proposed to require modification of the latch hook installation for the number two cockpit window frame. \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 proposal. \n\n\tSeveral commenters question the need for the rule and consider that the proposal should be withdrawn for various reasons: \n\n\tOne of these commenters contends that the nature of the addressed problem does not constitute an unsafe condition. This commenter states that, if the window is not completely closed, it is not possible for the latch cams to engage with the latchposts; thus, improperly closed windows are readily identified by physically trying to open the window. The FAA does not concur. If the window latch cams do not engage with the latch posts, it is still possible to rotate the latch handle. Whenever the latch handle is rotated, a "closed" indicator appears above the window. This makes it possible for the window actually to be open, but to appear to be closed and to have a "closed" indicator as well. The modification required by this AD addresses that situation, since it will prevent the possibility of rotating the latch handle into the forward, latched position unless the window is fully closed. Because of the consequences associated with an open window, the FAA considers this modification to be warranted and appropriate. \n\n\tSome of these commenters consider that current flight crew procedures are adequate to address the problem that is the subject of the proposed AD. These commenters point out that current procedures provide fora check of these windows to ensure that they are closed and locked; some operators' procedures require that the flight crew check the windows twice. The FAA does not concur. As described above, the current configuration of the window latching mechanism and associated indicator make it possible for the window to appear to be closed and to have a "closed" indicator, even though the window is not actually closed and latched. Service experience has shown that the flight crew will not always verify that the window is closed if they have a "closed" indication. For these reasons, the FAA finds that flight crew procedures alone are not effective in addressing the identified unsafe condition. \n\n\tAnother of these commenters states that there has been only a limited number of operators that have experienced difficulty with the subject windows; this commenter does not consider that it is reasonable for the FAA to burden all operators with the requirements of the rule because of the service experience of only a few operators. The FAA acknowledges that only a few operators have experienced in service the problems addressed by this AD action. However, since the configuration of the windows, the window latching mechanism, and the associated indicating system is similar on all of the affected Model 757 and 767 series airplanes, the FAA has determined that the potential exists for this problem to occur on any of these airplanes. \n\n\tAnother of these commenters states that the referenced service bulletin describes the modification as desirable only to "reduce noise in the cockpit" should the subject windows not be latched. This commenter states that at no time have there been reports of an uncommanded window opening; instead, there have been reports only of false window latching, which resulted in air leakage and noise. Therefore, the commenter considers the proposed modification to be merely a "product improvement" and not necessarily meant to correct an unsafe condition.The FAA does not concur. The modifications described in the referenced service bulletins eliminate the possibility of the "closed" indicator being visible when the window is not actually fully closed. The air leakage and noise that have resulted from open windows have led to rejected takeoffs (RTO) and air turnbacks (ATB); some of the RTO's have resulted in considerable damage to the airplane. To address this unsafe condition, the FAA has determined that the need for the proposed modification is warranted. \n\n\tFinally, one of these commenter states that there have been reports of RTO's and ATB's involving airplanes that have incorporated the modification; therefore, the modification will not eliminate these occurrences. The FAA acknowledges that RTO's and ATB's have taken place after modification, and points out that the subject modification is not intended to prevent all future occurrences of these incidents. Conversely, it is not intended that the modification terminate any requirements for crew preparation of the flight deck for flight. The modification does address a design problem that can lead the crew to believe that the window is closed when, in fact, it is not. \n\n\tOne commenter requests that the proposed rule be revised to provide "credit" to operators with Model 767 series airplanes that have been previously modified only in accordance with Boeing Service Bulletin 767-56-0002, dated August 30, 1985, and not in accordance with that service bulletin as amended by Notice of Status Change (NSC) 1, dated July 3, 1986, as specified in the notice. This commenter points out that NSC 1 simply added data concerning existing part accountability; additionally, NSC 1 contains a statement indicating that "no more work is necessary on airplanes changed by the initial release of this service bulletin." The FAA concurs, and has revised the final rule accordingly. \n\n\tThis same commenter requests that the comment period be extended by an additional 60 days in order to obtain information as to whether or not all affected Model 767 series airplanes have already been modified in accordance with the proposed requirements of the rule. The commenter considers that, by obtaining such affirmative data, the Model 767 could be eliminated from the applicability of the rule. The FAA does not concur, and considers that such a delay in this rulemaking action is inappropriate. Regardless, as specified in the "Compliance" statement of the final rule, airplanes that have been modified previously in accordance with the requirements of the rule are considered in compliance and require no additional work relative to this rule. \n\n\tOne commenter requests that the proposed compliance time of 18 months be extended to 30 months in order to accommodate parts delivery time and orderly modification of the fleet. This commenter states that the lead time necessary for obtaining the modification parts is extensive (44 weeks), and an 18-month compliance time is unreasonably short to expect operators of large fleets to modify all of the affected airplanes. The FAA concurs. In developing an appropriate compliance time for this AD action, the FAA intended that it fall during a time of regularly scheduled maintenance in order to allow the modification to be performed at a base where special equipment and trained maintenance personnel will be available if necessary. The FAA considers that extending the compliance time to 30 months will not adversely affect safety and will allow timely and orderly modification of the affected fleet. \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 increase the economic burden on any operator nor increase the scope of the AD. \n\n\tThere are approximately 640 Model 757 and 767 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 409 airplanes of U.S. registry will be affected by this AD, that it will take approximately 8 work hours per airplane to accomplish the required actions, and that the average labor rate is $55 per work hour. Required parts will cost approximately $2,000 per airplane. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $997,960, or $2,440 per airplane. \n\n\tThe total cost impact figure discussed above is 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. However, the FAA has been advised that at least 44 of the affected airplanes have already been modified in accordance with the requirements of this AD, and that numerous others are either currently undergoing or will have undergone modification by the date that this AD is effective.Therefore, the future economic cost impact of this rule on U.S. operators is now only $890,600 (and, most likely, considerably less than that amount as of the effective date of this AD). \n\n\tThe FAA recognizes that the obligation to maintain aircraft in an airworthy condition is vital, but sometimes expensive. Because AD's require specific actions to address specific unsafe conditions, they appear to impose costs that would not otherwise be borne by operators. However, because of the general obligation of operators to maintain aircraft in an airworthy condition, this appearance is deceptive. Attributing those costs solely to the issuance of this AD is unrealistic because, in the interest of maintaining safe aircraft, most prudent operators would accomplish the required actions even if they were not required to do so by the AD. \n\n\tA full cost-benefit analysis has not been accomplished for this AD. As a matter of law, in order to be airworthy, an aircraft must conform to its typedesign and be in a condition for safe operation. The type design is approved only after the FAA makes a determination that it complies with all applicable airworthiness requirements. In adopting and maintaining those requirements, the FAA has already made the determination that they establish a level of safety that is cost- beneficial. When the FAA, as in this AD, makes a finding of an unsafe condition, this means that the original cost-beneficial level of safety is no longer being achieved and that the required actions are necessary to restore that level of safety. Because this level of safety has already been determined to be cost-beneficial, a full cost-benefit analysis for this AD would be redundant and unnecessary. \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\n List 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\n PART 39 - AIRWORTHINESS DIRECTIVES \n\n\t1.\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. § 39.13 - (Amended) \n\n\t2.\tSection 39.13 is amended by adding the following new airworthiness directive: