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 737-300, -400, and -500 series airplanes was published in the Federal Register on October 13, 1995 (60 FR 53307). That action proposed to require a visual inspection to detect damage of the wire bundle and clamp in the electronic/electrical (E/E) equipment bay, and repair, if necessary. Additionally, that action proposed to require replacement of the rubber cushioned steel clamp with a nylon clamp, and the installation of additional clamps to prevent contact between wire bundle W2132 (or W0132) and power feeder wire bundle W0142. \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. Request to Withdraw theRule: \n\n Basis May be an Isolated Incident \n\n\tOne commenter requests that the FAA first review the findings on airplanes inspected thus far and, if no incorrect routing exists on other airplanes, the proposed rule should be withdrawn. This commenter states that the Supplementary Information section of the preamble to the proposal only states that an unsafe condition is "likely to exist" on other airplanes, and asks that further explanation be given as to why the FAA believes other airplanes may be affected. This commenter has received no reports of similar conditions on other airplanes. \n\n\tThe FAA agrees that fleetwide corrective actions should not be mandated in response to incidents determined to be truly "isolated." In this case, however, AD action is warranted since the FAA has confirmed that the incident described in the notice was the result of a manufacturing error, and that this error was repeated on numerous airplanes. As part of its investigation, the FAA conductedinspections of 10 airplanes in the manufacturer's production facility. These inspections revealed that incorrect wire bundle clamps were installed in each of these airplanes. Furthermore, a review of manufacturing records indicates that this condition exists in approximately 620 previously delivered airplanes. In light of this evidence, the FAA has determined that the condition addressed by this AD is not the result of a single isolated incident, as the commenter suggests. Request to Withdraw the Rule:\n\n No Essential Flight Circuits are Involved \n\n\tOne commenter requests that the AD be withdrawn because of the fact that no essential flight circuits were affected as a result of the damage to the wiring. The wire bundle involved in the damage is not associated with flight-critical systems .\n\n\tThe FAA agrees that loss of the systems associated with the damaged wire bundle would not significantly affect safe flight and landing of the airplane. The FAA's primary concern, however, is not the loss of system function, but the possibility of chafing of a wire bundle that could cause short circuiting of the wire bundles. Such short circuiting of the wire bundles could result in an undetected in-flight fire, since Electrical Equipment (E/E) bays of Model 737 airplanes are not equipped with fire detection systems.\n\n Request to Withdraw the Proposal: No "Formal" Service Document Exists \n\n\tOne commenter contends that the FAA should not issue an AD that cites an "informal" service letter (Boeing Service Letter 737-SL-24-106, dated March 10, 1995) as the appropriate source of instructions for accomplishing the proposed actions. The commenter maintains that a "formal" service bulletin should be issued if the manufacturer finds the chafing problem to be more than an isolated incident. \n\n\tThe FAA does not concur with the commenter. The fact that the manufacturer chose to publish the service information in a form other than a "formal" service bulletin, is not a justifiable reason to withdraw the proposed AD. It is appropriate for the FAA to reference in AD's any document that is available to affected operators and contains procedural instructions necessary for conducting required actions. Further, the decision to mandate corrective actions via the AD process is based on the FAA's assessment of the potential hazardous condition, not the assessment by the manufacturer. \n\nRequest to Withdraw the Rule: Service Information Incomplete \n\n\tTwo commenters state that the service letter, cited in the proposed rule as the appropriate service information, contains an incomplete list of parts. The commenters assert that the service letter only indicates a "family" of hardware, and leaves the determination of the appropriate clamp diameters and screw lengths up to the operators. The commenters request that an AD not be issued unless the manufacturer finds it advisable to publish a formal service bulletin containing a complete and accurate list of parts. \n\n\tThe FAA acknowledges the commenters' observation that the service letter contains an incomplete list of parts; however, that list is not incomplete to the extent that the AD should be withdrawn. The FAA finds that clarification of these parts is necessary so that operators will have no difficulty performing the requirements of this AD. In those situations where part numbers are incomplete, the undefined parameters are limited to non-critical part dimensions or, in the case of the NAS42DD-6 spacer, a dimension and finish. The function of the subject parts is to establish a reasonable amount of separation from surrounding structure by providing positive mechanical support for the wire bundles. In these applications, a high degree of precision in the unspecified dimensions is not essential. It also is reasonable to assume that the modification will be accomplished by trained personnel, whose discretion in the selection of part sizes is appropriate. Such discretion will giveoperators the flexibility needed to deal with slight manufacturing variations in the wire bundle installation of the affected area. The FAA agrees that some guidance may prove useful to operators unfamiliar with the parts identified in the service letter; therefore, the FAA has revised paragraph (a) of the final rule to include descriptions for the installation of the screw size, spacer clearance, and specific finish requirements for the spacers. \n\nRequest to Extend Compliance Time \n\n\tTwo commenters request that the compliance time of the proposed rule be increased from the proposed 12 months to 18 months. The commenters state that extending the compliance period will allow operators to accomplish the inspection during a scheduled "C" check, when airplanes are brought to the main maintenance base for an extended hold. Adoption of a 12-month compliance time would require affected operators to special schedule airplanes so that the requirements of the rule can be accomplished; this would entail additional expenses over what the FAA estimated in its cost impact information. \n\n\tThe FAA concurs that the compliance time can be extended somewhat. The FAA's intent was that the inspections be conducted during a regularly scheduled maintenance visit for the majority of the affected fleet. The FAA now recognizes that 15 months corresponds more closely to the interval representative of the majority of affected operators' normal maintenance schedules. Extending the compliance time by three additional months will not adversely affect safety, and will allow the modification to be performed at a base during regularly scheduled maintenance. Paragraph (a) of the final rule has been revised to reflect a compliance time of 15 months.\n\n Request to Revise Cost Impact Information\n \n\tOne commenter requests that the FAA's cost impact estimation be revised to specify that two work hours are required to accomplish the proposed modification, instead of one work hour. The commenter explains that the access to the work area is from under the cabin floor, and the personnel performing the modification are in an awkward position and are unable to fully view the work area. Because of these factors, the modification would take a longer time that the FAA's estimated one work hour. \n\n\tThe FAA does not concur. The cost impact information, below, describes only the "direct" costs of the specific actions required by this AD. The FAA's estimate of 1 work hours necessary to accomplish the required actions is based on the best data available to date, and represents the time necessary to perform only the actions actually required by this AD. The FAA recognizes, that in accomplishing the requirements of any AD, operators may incur "incidental" costs in addition to the "direct" costs. The cost analysis in AD rulemaking actions, however, typically does not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions. Because incidental costs may vary significantly from operator to operator, they are almost impossible to calculate.\n\n 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 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 Cost Impact \n\n\tThere are approximately 620 Model 737-300, -400, and -500 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 195 airplanes of U.S. registry will be affected by this AD, that it will take approximately 1 work hour per airplane to accomplish the required actions, and that the average labor rate is $60 per work hour. Required parts will cost approximately $25 per airplane. Based on these figures, the cost impact of the AD on U.S. operators is estimated to be $16,575, or $85 per airplane. \n\n\tThe 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. \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 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 \nPART 39 - AIRWORTHINESS DIRECTIVES \n\n\t1. The authority citation for part 39 continues to read as follows: Authority: 49 USC 106(g), 40113, 44701. § 39.13 - (Amended) \n\t2. Section 39.13 is amended by adding the following newairworthiness directive: