AD 99-08-03

This amendment adopts a new airworthiness directive (AD) that is applicable to all Boeing Model 737-600, -700, and -800 series airplanes. This action requires an inspection of the power distribution panels (PDP) to verify proper installation of the power feeder terminals and associated hardware, and corrective actions, if necessary. This action also requires repetitive torque checks of the terminal attachment screws. This amendment is prompted by reports indicating the loss of electrical power from the engine-driven generators or the auxiliary power unit due to overheating, melting, and subsequent failure of the power feeder terminals. The actions specified in this AD are intended to prevent such conditions, which could result in increased risk of fire and the loss of electrical power from the associated alternating current power source.

Final rule; request for comments

99-08-03 BOEING: Amendment 39-11107. Docket 99-NM-38-AD. \n\n\tApplicability: All Boeing Model 737-600, -700, and -800 series airplanes; certificated in any category.\n \n\tNOTE 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (c) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo preventoverheating, melting, and subsequent failure of the power feeder terminals, which could result in increased risk of fire and the loss of electrical power from the associated alternating current (AC) power source, accomplish the following: \n\nInitial Inspection \n\n\t(a)\tWithin 90 days after the effective date of this AD: Perform a one-time general visual inspection to verify proper installation of the power feeder terminals and associated hardware located in power distribution panels (PDP) P91 and P92, in accordance with the following procedures. \n\n\tUsing a flashlight, inspect each of the six power feeder terminals by looking into the access holes located in the plastic cover of the rigid bus assembly. The holes are located on the aft face of PDP's P91 and P92. (Refer to the Boeing 737-600, -700, -800, -900 Airplane Maintenance Manual (AMM), Section 24-21-71/401, Figure 401 (Sheet 1), for the location of PDP P91 and P92.) On PDP P91, the holes are adjacent to terminal blocks TB5001 and TB5002. On PDP P92, the holes are adjacent to terminal blocks TB5005 and TB5006. There are a total of six holes per PDP. (Refer to the Boeing 737-600, -700, -800, -900 AMM, Section 24-21-71/401, Figure 401 (Sheet 2), for the location of the access holes on the PDP's.) Note that although each PDP has nine power feeder terminals, only the six terminals adjacent to the access holes require inspection. Verify that the power feeder terminal is properly installed and held in place on the busbar by the No. 8 socket head cap screw, and verify that the cap screw is inserted into the hole in the terminal. For the proper power feeder terminal and screw buildup, refer to the Boeing 737-600, -700, -800, -900 AMM, Chapter 24-21-71/401, Figure 401 (Sheet 4). The subject power feeder terminal is identified as item (7) and the cap screw as item (12). This visual inspection does not require loosening or removing any fasteners. The inspection may require looking through the access hole ata slight angle to see the terminal clearly. The terminal can be identified by its shiny metal finish; the current transformer behind the terminal block is made of plastic with a flat black finish. If the power feeder terminal and No. 8 socket head cap screw are not assembled as shown in Boeing 737-600, -700, -800, -900 AMM, Section 24-21-71/401, Figure 401 (Sheet 4): Prior to further flight, replace the rigid bus assembly with a new assembly, in accordance with the procedures specified in Boeing 737-600, -700, -800, -900 AMM, Section 24-21-22. \n\nRepetitive Torque Check\n \n\t(b)\tConcurrent with the accomplishment of the requirements of paragraph (a) of this AD: Perform a torque check of the attachment screws of the power feeder terminals in accordance with the procedures specified in Boeing Maintenance Tip 737 MT 24-003, dated May 14, 1998. Repeat the torque check thereafter at intervals not to exceed 1,000 flight hours, in accordance with the maintenance tip. \n\nAlternative Methods of Compliance \n\n\t(c)\tAn alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Seattle ACO.\n \n\tNOTE 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO. \n\nSpecial Flight Permits\n \n\t(d)\tSpecial flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished. \n\n\t(e)\tThis amendment becomes effective on April 19, 1999.

The FAA has recently received several reports indicating the loss of electrical power from the engine-driven generators or the auxiliary power unit on Boeing Model 737 series airplanes, due to failure of the power feeder terminals located in power distribution panels (PDP) P91 and P92. This failure is attributed to an overheat condition caused by loosening of the screws that fasten the power feeder terminals to the PDP rigid bus assembly. Investigation revealed that inadequate support of the power feeder terminal allows movement of the terminal during the power feeder wire installation and removal procedures. The consequent loosening of the screws may result in increased electrical resistance and the generation of heat between the power feeder terminal and the rigid busbar at the terminal-to-busbar interface. This condition, if not corrected, may cause overheating and melting of the power feeder terminals, which could result in increased risk of fire and the loss of electrical power from the associated alternating current (AC) power source. \n\nExplanation of the Requirements of the Rule \n\n\tSince an unsafe condition has been identified that is likely to exist or develop on other Boeing Model 737-600, -700, and -800 series airplanes of the same type design, this AD is being issued to prevent overheating, melting, and subsequent failure of the power feeder terminals, which could result in increased risk of fire and the loss of electrical power from the associated AC power source. This AD requires an inspection of the PDP's to verify proper installation of the power feeder terminals and associated hardware, and corrective actions, if necessary. This action also requires repetitive torque checks of the terminal attachment screws. \n\nInterim Action \n\n\tThis is considered to be interim action. The FAA is currently considering further rulemaking action to supersede this AD to require repetitive replacement of the PDP rigid bus assembly for all Boeing Model 737-600, -700, and -800 series airplanes. However, the planned compliance time for the repetitive replacement is sufficiently long so that notice and opportunity for prior public comment will be practicable. \n\nDetermination of Rule's Effective Date \n\n\tSince 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. \n\nComments Invited \n\n\tAlthough 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 rule may 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. \n\n\tComments 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. \n\n\tCommenters 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-38-AD." The postcard will be date stamped and returned to the commenter.\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\tThe 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." \n\nList of Subjects in 14 CFR Part 39 \n\n\tAir transportation, Aircraft, Aviation 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 U.S.C. 106(g), 40113, 44701. § 39.13 (Amended) \n\t2. Section 39.13 is amended by adding the following new airworthiness directive: