AD 99-26-21

The FAA has received one report from an operator of a Boeing Model 737-700 series airplane describing how one of the three electrical wires in the wire bundle to the electric motor driven pump (EMDP) had chafed the pressure hose for hydraulic system "B." The FAA also has received several reports of failed or damaged case drain or pressure hoses on the EMDP for hydraulic system "B" for Boeing Model 737-300, -400, and -500 series airplanes. Chafing between the hydraulic case drain and pressure hoses could damage the hoses, and cause a hydraulic leak and failure of the pressure hose. Chafing between the wire bundle and hydraulic hoses could damage those components, and lead to electrical arcing between the components and a consequent hydraulic leak, which could result in an increased risk of fire. Explanation of Relevant Service Information The FAA has reviewed and approved Boeing Alert Service Bulletin 737-29A1076, Revision 1 (for Model 737-300, -400, and -500 series airplanes), and Boeing Alert Service Bulletin 737-29A1077, Revision 1 (for Model 737-600, -700, and -800 series airplanes); both dated October 21, 1999; which describe procedures for an inspection of wire bundles W0334 and W5230, and the hydraulic case drain and pressure hoses for the EMDP for hydraulic system "B" to detect any discrepancies; and corrective actions, if necessary. Corrective actions include repair of the wire bundles if any damage is found; replacement of any hose that is damaged outside specified limits, and any incorrectly sized or loose components; and certain modifications. Modifications include adjusting or changing certain support clamps, fittings, and check valves; and installing additional clamps and spacers in the hydraulic hoses to obtain specified separation between the wire bundle and the hoses. For certain EMDP's, modifications also include ensuring that certain components are attached correctly. The alert service bulletins also specify a test of the EMDP if wire bundles W0334 or W5230 were repaired, or a leak test if the hydraulic case drain or pressure hoses were replaced in accordance with either Part 1 or Part 2 of the Accomplishment Instructions of the Boeing alert service bulletins, as applicable. Explanation of Requirements of the Rule Since an unsafe condition has been identified that is likely to exist or develop on other Boeing Model 737-300, -400, -500, -600, -700, and -800 series airplanes of the same type design, this AD is being issued to prevent electrical arcing due to chafing between certain hydraulic hoses and adjacent wire bundles, which could result in a consequent increased risk of fire. This AD requires a one-time detailed visual inspection of wire bundles W0334 and W5230 and the hydraulic case drain and pressure hoses for the EMDP for hydraulic system "B" located in the right main wheel well to detect discrepancies; and corrective actions, if necessary. The actions are required to be accomplished in accordance with the alert service bulletins described previously, except as described below. Differences Between This AD and the Alert Service Bulletins Operators should note that the alert service bulletins recommend accomplishment of the inspection and corrective actions as soon as manpower and equipment are available. However, the FAA has determined that the compliance time proposed by the manufacturer would not address the identified unsafe condition in a timely manner. In developing an appropriate compliance time for this AD, the FAA considered not only the manufacturer's recommendation, but the degree of urgency associated with addressing the subject unsafe condition, the average utilization of the affected fleet, and the time necessary to perform the inspection (less than two hours). In light of all these factors, the FAA finds a 90-day compliance time for accomplishing the required actions to be warranted, in that it represents an appropriate interval of timeallowable for affected airplanes to continue to operate without compromising safety. Determination of Rule's Effective Date Since a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days. Comments Invited Although this action is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this rule by submitting such written data, views, or arguments as they may desire. Communications shall identify the Rules Docket number and be submitted in triplicate to the address specified under the caption "ADDRESSES." All communications received on or before the closing date for comments will be considered, and this rulemay be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed. Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket. Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket Number 99-NM-342-AD." The postcard will be date stamped and returned to the commenter. Regulatory Impact The 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. The FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and that it is not a "significant regulatory action" under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures,a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES." List of Subjects in 14 CFR Part 39 Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. Adoption of the Amendment Accordingly, 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: PART 39 - AIRWORTHINESS DIRECTIVES 1. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. 106(g), 40113, 44701. § 39.13 (Amended) 2. Section 39.13 is amended by adding the following new airworthiness directive: