AD 96-23-04 ACTIVE

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 737-100 and -200 series airplanes, that requires replacement of the 250 volt-ampere (VA) rated static inverters with 410 VA or 500 VA rated static inverters, and an operational test of the standby electrical power system. This amendment is prompted by a report that accomplishment of a certain modification could result in overload of the static inverter on these airplanes. The actions specified by this AD are intended to prevent overload of the static inverter, which could result in the loss of the 115 volt alternating current (VAC) standby bus and the associated flight instruments when the airplane is operating on standby electrical power.

Final rule

96-23-04 BOEING: Amendment 39-9809. Docket 96-NM-06-AD. \n\n\tApplicability: Model 737-100 and -200 series airplanes; as listed in Boeing Alert Service Bulletin 737-24A1113, dated February 29, 1996; 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 otherwise 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 (b) 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 prevent overload of the static inverter, which could result in the loss of the 115 VAC standby power and the associated flight instruments, accomplish the following: \n\n\t(a)\tWithin 10 months after the effective date of this AD, replace the 250 VA rated static inverters either with 500 VA-rated static inverters having Boeing part number (P/N) 60B40023-2, or with 410 VA-rated static inverters having Jet Electronics and Technology P/N 3S2060DV109B1, in accordance with Boeing Alert Service Bulletin 737-24A1113, dated February 29, 1996; or in accordance with Section 20-10-111 of the Boeing 737 Airplane Maintenance Manual. Prior to further flight following the replacement, perform an operational test of the standby electrical power system in accordance with the service bulletin; or in accordance with Section 24-54-0 or 24-54-2 of the maintenance manual. \n\n\t(b)\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 3: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO. \n\n\t(c)\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(d)\tExcept as provided by paragraph (a) of this AD, the replacement and operational test shall be done in accordance with Boeing Alert Service Bulletin 737-24A1113, dated February 29, 1996. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC. \n\n\t(e)\tThis amendment becomes effective on December 19, 1996.

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 737-100 and -200 series airplanes was published in the Federal Register on June 7, 1996 (61 FR 29038). That action proposed to require replacement of the 250 VA rated static inverters with certain 410 VA or 500 VA-rated static inverters. \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. \n\nRequest to Revise the Applicability of the Proposed Rule \n\n\tThe manufacturer requests that the applicability of the proposed rule be revised to specify that the only Model 737-100 and -200 series airplanes affected by the AD are those that are listed in Boeing Alert Service Bulletin 737-24A1113, dated February 29, 1996. The manufacturer indicates that it has reviewed the loading of the 115 VAC standby electrical power bus of the Model 737-100 and -200 series airplanes that were delivered with 250 VA static inverters and modified in accordance with Boeing Service Bulletin 737-24-1051. This review verified that the 115 VAC standby bus of some of the 250VA static inverters installed on airplanes that had been modified in accordance with Boeing Service Bulletin 737-24-1051 are less heavily loaded than others and, therefore, are not susceptible to the addressed unsafe condition. The commenter states that, for 21 of the airplanes specified in the applicability of the proposal, the currently-installed 250 VA static inverter is adequate and need not be replaced.\n\n\tThe FAA concurs. The FAA's initial assessment of the unsafe condition concluded that all Model 737-100 and -200 series airplanes equipped with 250 VA static inverters and modified in accordance with Boeing Service Bulletin 737-24-1051 were susceptible to overloading of the static inverters. Since issuance of the proposal, however, the FAA has reviewed the electrical load analysis conducted by the manufacturer and agrees that, for the 21 identified airplanes, the 250 VA static inverter does possess sufficient capacity to preclude the unsafe condition. The FAA finds that the airplanes listed in the effectivity listing of Boeing Alert Service Bulletin 737-24A1113, dated February 29, 1996, are the only ones subject to the unsafe condition addressed by this AD action. Accordingly, the applicability of this final rule has been revised to indicate this. Additionally, the cost impact information, discussed below, has been revised to clarify the number of affected airplanes.\n \nRequest to Allow Replacement with Any FAA-Approved Static Inverter \n\n\tOne commenter requests that paragraph (a) of the proposal be revised to allow any FAA- approved 410 VA-rated or 500 VA-rated static inverter to be used as a replacement part, instead of requiring the installation of specific static inverters by part number. This commenter considers that such a change to the proposes rule would alleviate the need for operators to obtain approvals for use of alternative methods of compliance in the event that a new static inverter with a new part number is developed in the future. \n\n\tThe FAA does not concur with the commenter's request. While other static inverters may be FAA-approved, the static inverters having the part numbers specified in this AD are the only 410 VA and 500 VA inverters that have been approved specifically for use in Boeing Model 737-100 and -200 series airplanes. These units have been demonstrated to be compatible with the electrical power system and the electromagnetic environment of those airplane models. The FAA must ensure that only these units, which have been tested for compatibility with the affected airplane models, be used to satisfy the requirements of this AD. \n\nRequest to Include Additional Maintenance Manual Reference \n\n\tOne commenter requests that paragraph (a) of the proposal be revised to indicate that the operational test of the standby electrical power system may be performed in accordance with Section 24-54-2, as well as Section 24-54-0, of the Model 737 Maintenance Manual. The commenter points out that, for some of the affected operators, the operational test is located in Section 24-54-2 instead of Section 24-54-0 (which was the only Section specified in the proposal). \n\n\tThe FAA concurs with the commenter's request and has revised paragraph (a) of this final rule accordingly. \n\n\tThe FAA also has revised paragraph (a) to include Boeing Alert Service Bulletin 737-24A1113 as an additional source of appropriate service instructions for accomplishing both the replacement of the static inverter and the operational test of the associated system. \n\nConclusion \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 52 Boeing Model 737-100 and -200 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 1 airplane of U.S. registry will be affected by this AD, that it will take approximately 2 work hours per airplane to accomplish the required actions, and that the average labor rate is $60 per work hour. Required parts will cost approximately $10,500 per airplane. Based on these figures, the cost impact of the AD on the single affected U.S. operator is estimated to be $10,620. \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 U.S.C. 106(g), 40113, 44701. § 39.13 - (Amended) \n\n\t2. Section 39.13 is amended by adding the following new airworthiness directive:

The service information referenced in this AD may be obtained from Boeing\nCommercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. This information may be examined at the Federal Aviation Administration (FAA), Transport Airplane Directorate, Rules Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

Stephen Oshiro, Aerospace Engineer, Systems and Equipment Branch, ANM-130S, FAA, Transport Airplane Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (206) 227-2793; fax (206) 227-1181.