AD 99-05-15 SUPERSEDED

This amendment adopts a new airworthiness directive (AD) that is applicable to certain Boeing Model 737-100, -200, -200C, -300, -400, and -500 series airplanes. This action requires a one-time inspection of the attachment nuts at each end attachment of the elevator tab push rods to measure run-on torque values, and corrective actions, if necessary. This amendment is prompted by reports of excessive high-frequency airframe vibration during flight, with consequent structural damage to the elevator tab, elevator, and stabilizer. The actions specified in this AD are intended to prevent detachment of an elevator tab push rod due to a detached nut at either end attachment of a push rod, which could result in excessive high-frequency airframe vibration during flight; consequent structural damage to the elevator tab, elevator, and horizontal stabilizer; and reduced controllability of the airplane.

Final rule; request for comments.

99-05-15 BOEING: Amendment 39-11063. Docket 99-NM-09-AD. \n\n\tApplicability: Model 737-100, -200, -200C, -300, -400, and -500 series airplanes; line numbers 1 through 2939 inclusive; 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 (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 detachment of an elevator tab push rod due to a detached nut at either end attachment of a push rod, which could result in excessive high-frequency airframe vibration during flight; consequent structural damage to the elevator tab, elevator, and horizontal stabilizer; and reduced controllability of the airplane; accomplish the following: \n\n\t(a)\tWithin 90 days after the effective date of this AD, perform a one-time inspection of all attachment nuts at each end of each elevator tab push rod to measure the run-on torque values of the nuts, in accordance with Boeing Alert Service Bulletin 737-27A1205, dated August 28, 1997. \n\n\t\t(1)\tIf the run-on torque value of any end attachment nut is within the limits specified in the alert service bulletin, prior to further flight, ensure that the final seating torque of the attachment nuts is within the torque values specified in the alert service bulletin. \n\n\t\t(2)\tIf the run-on torque value of anyend attachment nut is outside the limits specified in the alert service bulletin, prior to further flight, replace all existing bolts and attachment nuts at each end of each elevator tab push rod with new bolts and self-locking castellated nuts that have cotter pins installed as a secondary locking feature in accordance with Boeing Service Letter 737-SL-27-118-A, dated November 14, 1997, and ensure that the final seating torque of the nuts is within the torque values specified in the service letter. \n\n\tNOTE 2: Accomplishment of the inspection and ensuring adequate final seating torque values, prior to the effective date of this AD, in accordance with Boeing All-Base Telex M-7272-97-0897, dated February 13, 1997, are considered acceptable for compliance with the actions specified in paragraphs (a) and (a)(1) of this AD for only the forward attachment nuts. \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)\tThe actions shall be done in accordance with Boeing Alert Service Bulletin 737-27A1205, dated August 28, 1997, and Boeing Service Letter 737-SL-27-118-A, dated November 14, 1997. 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 March 23, 1999.

The FAA has received two reports indicating that excessive high-frequency airframe vibration occurred during flight on Boeing Model 737-200 and 737-300 series airplanes, which resulted in severe damage to the elevator, elevator tab, and elevator tab control mechanism. One report indicated that the source of the vibration was due to a detached elevator tab push rod that resulted from a missing or detached end attachment nut. The other report indicated that the initial source of vibration was a missing end bearing on an elevator tab push rod. \n\n\tThe FAA also has reviewed the results of inspections that were accomplished in accordance with Boeing Alert Service Bulletin 737-27A1205, dated August 28, 1997, and Boeing All-Base Telex M-7272-97-0897, dated February 13, 1997. Findings revealed that after 478 airplanes were inspected, 3 loose end attachment nuts and 7.9 per cent of all end attachment nuts inspected (a total of 2,278 nuts) did not have adequate run-on torque. These findings indicate that the occurrence of inadequate run-on and seating torque values of the end attachment nuts of the elevator tab push rods is not an isolated event. \n\n\tThe FAA has determined from these reports that, if an end attachment nut of an elevator tab push rod is removed and reinstalled during routine or non-routine maintenance, the self-locking capability (run-on torque) of the nut may become degraded. If an end attachment nut having inadequate run-on torque has been installed on an airplane, the likelihood of the nut becoming loose is increased significantly. The same is true for a nut having a seating torque with less than the minimum value specified in the alert service bulletin. \n\n\tInadequate run-on and/or seating torque values of an attachment nut at either end of an elevator tab push rod, if not corrected, could result in a nut becoming detached from an end attachment bolt of a push rod, which could cause excessive high-frequency vibration during flight. Such vibration could result in structural damage to the elevator tab, elevator, and horizontal stabilizer; and result in reduced controllability of the airplane.\n \nExplanation of Relevant Service Information \n\n\tThe FAA has reviewed and approved the previously referenced alert service bulletin, which describes procedures for a one-time inspection of the attachment nuts at each end of each elevator tab push rod to measure run-on torque values, and corrective actions, if necessary. Corrective actions include the replacement of any end attachment nut that is outside the run-on torque values specified in the alert service bulletin with a new nut, and ensuring that the final seating torque of the nuts is within the limits specified in the alert service bulletin. \n\n\tThe FAA also has reviewed and approved Boeing Service Letter 737-SL-27-118-A, dated November 14, 1997, which describes procedures for the replacement of the existing bolts and nuts at each end of the push rods with new bolts and nuts that incorporate the installation of cotter pins as a secondary locking feature. This new bolt, nut, and cotter pin design provides an additional level of safety in preventing detachment of an end attachment nut, which could result in detachment of an elevator tab push rod. \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 737-100, -200, -200C, -300, -400, and -500 series airplanes of the same type design, this AD is being issued to prevent detachment of the elevator tab push rod due to a detached nut at either end attachment of a push rod, which could result in excessive high-frequency airframe vibration during flight; consequent structural damage to the elevator tab, elevator, and horizontal stabilizer; and reduced controllability of the airplane. This AD requires accomplishment of actions specified in the alert service bulletin and the service letterdescribed previously, except as discussed below. \n\nDifferences Between the Alert Service Bulletin and This AD \n\n\tOperators should note that, although the effectivity listing in the Summary of the alert service bulletin specifies "all 737 airplanes line positions 1 through 2892," the applicability statement of this AD specifies "Model 737-100, -200, -200C, -300, -400, and -500 series airplanes, line numbers 1 through 2939 inclusive." The FAA points out that, at the time of issuance of the alert service bulletin, "all 737 airplanes" only included Model 737-100 through -500 series airplanes. The FAA has determined that the use of "line numbers" rather than "line positions" is the more appropriate term. The FAA also has determined that it is necessary to include the line numbers 2893 through 2939 in the applicability of this AD because those additional airplanes are subject to the same unsafe condition as the airplanes specified in the alert service bulletin. \n\n\tOperators also should note that the alert service bulletin specifies replacement of any end attachment nut that is outside the run-on torque values specified in the alert service bulletin with a new nut. However, if the run-on torque value of any end attachment nut is outside the limits specified in the alert service bulletin, paragraph (a)(2) of this AD requires replacement of all existing attachment nuts at each end of each elevator tab push rod with new bolts and self-locking castellated nuts that have cotter pins installed as a secondary locking feature. The FAA has determined that such a replacement provides an additional level of safety in preventing detachment of an end attachment nut, which could result in detachment of an elevator tab push rod. \n\n\tOperators also should note that the alert service bulletin recommends that the one-time inspection to measure run-on torque values of the attachment nuts at each end attachment of the elevator tab push rods be accomplished at the next scheduled elevator tab maintenance work. However, this AD requires that the inspection be accomplished within 90 days after the effective date of this AD. In developing an appropriate compliance time for this AD, the FAA considered not only the degree of urgency associated with addressing the subject unsafe condition, but the average utilization of the affected fleet and the time necessary to perform the inspection (4 hours). In light of all of these factors, the FAA finds that a 90-day compliance time for initiating the required actions is warranted, in that it represents an appropriate interval of time allowable for affected airplanes to continue to operate without compromising safety. \n\nInterim Action \n\n\tThis AD is considered to be interim action until final action is identified, at which time the FAA may consider further rulemaking, which could include replacement of the existing bolts and nuts at each end of the push rods with new bolts and self-locking castellated nuts that have cotter pins installed. \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. Factualinformation 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-09-AD." The postcard will be date stamped and returned to the commenter. \n\nRegulatory Impact \n\n\tThe regulationsadopted 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, Incorporation by reference, Safety.\n Adoption 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:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 99-NM-09-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.\n\n\tThe service information referenced in this AD may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. This information may be examined 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.

Greg Schneider, Aerospace Engineer, Airframe Branch, ANM-120S; FAA, Transport Airplane Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-2028; fax (425) 227-1181.