AD 2000-15-12

This amendment adopts a new airworthiness directive (AD) that is applicable to certain Boeing Model 737-100, -200, and -200C series airplanes. This action requires inspections of a certain component, and corrective action, if necessary. This action is necessary to detect and correct stress corrosion cracking in the front spar of the center section of the horizontal stabilizer, which could result in structural failure of the horizontal stabilizer and loss of control of the airplane. This action is intended to address the identified unsafe condition.

Final rule; request for comments

2000-15-12 BOEING: Amendment 39-11844. Docket 2000-NM-183-AD. \n\n\tApplicability: Model 737-100, -200, and -200C series airplanes; line numbers 1 through 315 inclusive, 323, and 324; 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 (d) 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 detect and correct stress corrosion cracking in the front spar of the center section of the horizontal stabilizer, which could result in structural failure of the horizontal stabilizer and loss of control of the airplane, accomplish the following: \n\nRepetitive Detailed Visual Inspections \n\n(a)\tWithin 90 days after the effective date of this AD, perform a detailed visual inspection to detect cracks in the front spar of the center section of the horizontal stabilizer, in accordance with Boeing Alert Service Bulletin 737-55A1071, dated February 24, 2000. Thereafter, repeat the inspection twice more at intervals not to exceed 200 days, and thereafter at intervals not to exceed 24 months or 4,000 flight cycles, whichever occurs first. \n\n\tNote 2: For the purposes of this AD, a detailed visual inspection is defined as: "An intensive visual examination of a specific structural area, system, installation, or assembly to detect damage, failure, orirregularity. Available lighting is normally supplemented with a direct source of good lighting at intensity deemed appropriate by the inspector. Inspection aids such as mirror, magnifying lenses, etc., may be used. Surface cleaning and elaborate access procedures may be required." \n\nRework \n\n\t(b)\tExcept as required by paragraph (c) of this AD, if any crack is detected during any inspection required by paragraph (a) of this AD, prior to further flight, accomplish rework of the front spar of the center section of the horizontal stabilizer (including removing damaged material, accomplishing a high frequency eddy current inspection to detect cracking, and shot peening the damaged area), in accordance with Boeing Alert Service Bulletin 737-55A1071, dated February 24, 2000. \n\nCracking Outside the Limits Specified in the Alert Service Bulletin\n \n\t(c)\tIf any crack that is outside the limits specified in the alert service bulletin is detected during any inspection required by paragraph (a) of this AD, prior to further flight, repair in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate; or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company Designated Engineering Representative who has been authorized by the Manager, Seattle ACO, to make such findings. For a repair method to be approved by the Manager, Seattle ACO, as required by this paragraph, the approval letter must specifically reference this AD. \n\nAlternative Methods of Compliance \n\n\t(d)\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 ACO. 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\nSpecial Flight Permits \n\n\t(e)\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\nIncorporation by Reference \n\n\t(f)\tExcept as provided by paragraph (c) of this AD, the actions shall be done in accordance with Boeing Alert Service Bulletin 737-55A1071, dated February 24, 2000. 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 CapitolStreet, NW., suite 700, Washington, DC. Effective Date \n\n\t(g)\tThis amendment becomes effective on August 23, 2000.

The FAA has received reports indicating that, during regular maintenance, operators found stress corrosion cracks in the front spar of the center section of the horizontal stabilizer on two Boeing Model 737-100 and -200 series airplanes. The subject airplanes had 42,700 and 67,100 flight cycles. The front spar is made from 7079-T6 aluminum, a material that was used for this component until the manufacturer determined that the material is susceptible to stress corrosion cracking. Cracks in the front spar will decrease the structural strength of the center section of the horizontal stabilizer. This condition, if not corrected, could result in structural failure of the horizontal stabilizer and loss of control of the airplane. \n\nExplanation of Relevant Service Information \n\n\tThe FAA has reviewed and approved Boeing Alert Service Bulletin 737-55A1071, dated February 24, 2000, which describes procedures for repetitive detailed visual inspections to detectcracking in the front spar of the center section of the horizontal stabilizer, and corrective actions, if necessary. If cracking is within certain limits, corrective actions involve rework of the front spar fitting that includes removing damaged material, performing a high frequency eddy current inspection to detect cracking, and shot peening the damaged area. If cracking is outside the limits, the alert service bulletin specifies to contact the manufacturer for repair instructions. Accomplishment of the actions specified in the service bulletin is intended to adequately address the identified unsafe condition. \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 airplanes of the same type design, this AD is being issued to detect and correct stress corrosion cracking in the front spar of the center section of the horizontal stabilizer, which could result in structural failure of the horizontalstabilizer and loss of control of the airplane. This AD requires accomplishment of the actions specified in the alert service bulletin described previously, except as discussed below. \n\nDifferences Between Alert Service Bulletin and This AD \n\n\tOperators should note that, although the alert service bulletin specifies that the manufacturer may be contacted for disposition of certain repair conditions, this AD requires the repair of those conditions to be accomplished in accordance with a method approved by the FAA, or in accordance with data meeting the type certification basis of the airplane approved by a Boeing Company Designated Engineering Representative who has been authorized by the FAA to make such findings. \n\n\tThe service bulletin also provides for a terminating action by replacing the front spar with a spar made from a 7050 or 7075 aluminum forging. However, this AD does not authorize the terminating action proposed in the service bulletin. \n\nDetermination of Rule'sEffective Date \n\t\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\nSubmit comments using the following format: \n\n Organize comments issue-by-issue. For example, discuss a request to change the compliance time and a request to change the service bulletin reference as two separate issues. \n For each issue, state what specific change to the AD is being requested. \n Include justification (e.g., reasons or data) for each request. \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 wishingthe 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 2000-NM-183-AD." The postcard will be date stamped and returned to the commenter. \n\nRegulatory Impact \n\n\tThe regulations adopted herein will not have a substantial direct effect 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, it is determined that this final rule does not have federalism implications under Executive Order 13132. \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 underDOT 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\nAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \n\nAccordingly, 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 \n1. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. 106(g), 40113, 44701. \n§ 39.13 (Amended) \n2. Section 39.13 is amended by adding the following new airworthiness directive: