AD 96-25-17

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 737-300, -400, and -500 series airplanes, that requires inspections to detect bent or damaged tie links and washers of the elevator feel and centering unit, and replacement of the centering unit with a new or serviceable unit, if necessary. This amendment also provides an optional replacement of the centering unit, which, if accomplished with the installation of supports and a stop bolt, constitutes terminating action for the repetitive inspections. This amendment is prompted by a report of high control column forces that occurred during takeoff and landing. The actions specified by this AD are intended to prevent such high forces, which could result in restriction of elevator control during takeoff, climbout, and landing.

Final rule

96-25-17 BOEING: Amendment 39-9860. Docket 96-NM-23-AD. \n\n\tApplicability: Model 737-300, -400 and -500 series airplanes through line position 2764, 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 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 (f) 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 restriction of elevator control during takeoff, climbout, and landing, due to higher than normal elevator control forces caused by damaged tie links in the elevator centering unit, accomplish the following: \n\n\t(a)\tWithin 6 months after the effective date of this AD: Perform a visual inspection to detect any bent or damaged tie links of the elevator feel and centering unit, in accordance with Boeing Alert Service Bulletin 737-27A1194, dated February 8, 1996, as revised by Boeing Notice of Status Change 737-27A1194 NSC 01, dated March 7, 1996, and Boeing Notice of Status Change 737-27A1194 NSC 02, dated April 4, 1996; or Boeing Alert Service Bulletin 737-27A1194, Revision 1, dated September 26, 1996.\n\n\t(b)\tIf no tie link is found to be broken, bent, or damaged during the inspection required by paragraph (a) of this AD: Accomplish either paragraph (b)(1) or (b)(2) of this AD, in accordance with Boeing Alert Service Bulletin 737-27A1194, dated February 8, 1996, as revised by Boeing Notice of Status Change 737-27A1194 NSC 01, dated March 7, 1996, and Boeing Notice of Status Change 737-27A1194 NSC 02, dated April 4, 1996; or Boeing Alert Service Bulletin 737-27A1194, Revision 1, dated September 26, 1996. \n\n\t\t(1)\tPrior to further flight, install supports and a stop-bolt on the elevator centering unit. Once this installation is accomplished, no further action is required by this AD. Or \n\n\t\t(2)\tRepeat the inspection required by paragraph (a) of this AD thereafter at intervals not to exceed 1,000 flight cycles. Installation of supports and a stop-bolt in accordance with the alert service bulletin, constitutes terminating action for the repetitive inspections required by this AD, provided that no damage is detected during any inspection required by paragraph (a) of this AD. \n\n\t(c)\tIf any tie link is found to be bent or damaged during the inspection required by paragraph (a) of this AD, and damage is within acceptable limits asspecified in Figure 1 of Boeing Alert Service Bulletin 737-27A1194, dated February 8, 1996, Boeing Notice of Status Change 737-27A1194 NSC 01, dated March 7, 1996, and Boeing Notice of Status Change 737-27A1194 NSC 02, dated April 4, 1996; or as specified in Boeing Alert Service Bulletin 737-27A1194, Revision 1, dated September 26, 1996: Accomplish paragraphs (c)(1) and (c)(2) of this AD in accordance with the alert service bulletin: \n\n\t\t(1)\tRepeat the inspection required by paragraph (a) of this AD thereafter at intervals not to exceed those specified in Figure 1 of the alert service bulletin. And \n\n\t\t(2)\tWithin 6 months after the effective date of this AD, install supports and a stop-bolt on the elevator centering unit. This installation does not terminate the repetitive inspection requirements of this paragraph. \n\n\t(d)\tIf any tie link is found to be bent or damaged during any inspection required by this AD, and the damage is beyond the acceptable limits as specified in Figure 1 of Boeing Alert Service Bulletin 737-27A1194, dated February 8, 1996, Boeing Notice of Status Change 737-27A1194 NSC 01, dated March 7, 1996, and Boeing Notice of Status Change 737-27A1194 NSC 02, dated April 4, 1996; or Boeing Alert Service Bulletin 737-27A1194, Revision 1, dated September 26, 1996: Prior to further flight, replace the elevator centering unit with a new or serviceable unit and accomplish either paragraph (d)(1) or (d)(2) of this AD in accordance with the alert service bulletin: \n\n\t\t(1)\tInstall supports and a stop-bolt on the elevator centering unit; or \n\t\t(2)\tRepeat the inspection required by paragraph (a) of this AD thereafter at intervals not to exceed 1,000 flight cycles until the installation specified in paragraph (d)(1) of this AD is accomplished.\n\n\t(e)\tReplacement of the elevator centering unit with a unit in which the tie links have been inspected and determined to be acceptable and in which supports and a stop-bolt have been installed, in accordance with Boeing Alert Service Bulletin 737-27A1194, dated February 8, 1996, as revised by Boeing Notice of Status Change 737-27A1194 NSC 01, dated March 7, 1996, and Boeing Notice of Status Change 737-27A1194 NSC 02, dated April 4, 1996; or Boeing Alert Service Bulletin 737-27A1194, Revision 1, dated September 26, 1996, constitutes terminating action for the requirements of this AD. \n\n\t(f)\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\n\t(g)\tSpecial flight permits may be issuedin 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(h)\tThe actions shall be done in accordance with Boeing Alert Service Bulletin 737-27A1194, dated February 8, 1996, as revised by Boeing Notice of Status Change 737-27A1194 NSC 01, dated March 7, 1996, and Boeing Notice of Status Change 737-27A1194 NSC 02, dated April 4, 1996; or in accordance with Boeing Alert Service Bulletin 737-27A1194, Revision 1, dated September 26, 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(i)\tThis amendment becomes effective on February 3, 1997.

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 737-300, -400, and -500 series airplanes was published in the Federal Register on June 26, 1996 (61 FR 33049). That action proposed to require repetitive visual inspections to detect bent or damaged tie links of the elevator centering unit, and replacement of the elevator centering unit with a new or serviceable unit, if necessary. \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 rule.\n\n Request to Extend the Initial Inspection Compliance Time \n\n\tSeveral commenters request that the proposed compliance time of 6 months for the initial inspection be extended to at least 12 or 15 months. The commenters express concern that there may be a shortage of available tie link units to use as replacement units since the proposed rule would require replacement of damaged tie links with new or serviceable parts prior to further flight. \n\n\tThe FAA does not concur with the commenters' request to extend the compliance time. Replacement of the elevator feel and centering unit prior to further flight is required only if the tie links have damage that exceeds the limits as specified in Boeing Alert Service Bulletin 737-27A1194. The manufacturer specifically devised the inspection plan described in the service bulletin to address the concern of the availability of an ample number of replacement tie link units. Damage found to be within the service bulletin's specified limits requires certain repetitive inspections until the elevator feel and centering unit can be serviced or replaced. This is intended to allow relief for the operators if a spare feel and centering unit is not readily available. In developingan appropriate compliance time for this proposal, the FAA considered the safety implications and the parts availability, and finds no basis to extend the 6-month compliance time. However, paragraph (f) of the final rule does provide affected operators the opportunity to request an adjustment of the compliance time if data are presented to justify such an extension. \n\nRequest to Revise Inspection Times and Mandate the Terminating Action \n\n\tAnother commenter requests that: \n\n\t1. the compliance time for the initial inspection be extended to 12 months, \n\t2. repetitive inspections be required every 12 months thereafter, and \n\t3. "the modification" specified in Boeing Alert Service Bulletin 737-27A1194 should be required to be installed within 2 years.\n\n\tThis commenter states that changing the elevator feel and centering unit is labor-intensive and would require at least 8 hours to accomplish. However, this commenter offered no data or technical basis for revising the compliance times or for mandating the terminating action provided in paragraph (e) of the proposed rule. \n\n\tAs for the commenter's request to extend the compliance time to extend the compliance time of the initial and repetitive inspections, the FAA does not concur. As previously explained, the FAA considered the safety implications, parts availability, and maintenance schedules when developing the compliance time. The commenter has offered no new technical data that would indicate a need to revise the compliance times. However, paragraph (f) of the final rule does provide affected operators the opportunity to request an adjustment of the compliance time if data are presented to justify such an extension. \n\n\tAs for the commenter's request to mandate "the modification," the FAA infers that the modification the commenter is referring to is that of the feel and centering unit. (The referenced Boeing alert service bulletin actually describes two different modifications: modification of the supports and stop-bolt, and modification of the feel and centering unit.) The FAA does not concur with this request. The commenter offered no data to justify a compliance time of 2 years for mandating the installation of this modification. The FAA considers that, by providing the modification as an optional terminating action for this AD, prudent operators may accomplish that action at a time of their own discretion. Additionally, the optional terminating action does not preclude any operator from installing the modification before an arbitrary 2-year period, as suggested by the commenter. Further, the FAA finds that the required inspections, and replacement action as necessary, are both adequate and appropriate in addressing the subject damage associated with the elevator feel and centering unit.\n\nRequest to Extend the Repetitive Inspection Interval \n\n\tTwo commenters state that, when the stop bolt and support are installed, they will prevent excessive travel of the elevatorfeel actuator and preclude further damage to the tie links. Therefore, one of these commenters requests that, once the stop bolt and support are installed, the repetitive inspection intervals be extended from those intervals specified in proposed paragraph (c) (and specified in Figure 1 of Boeing Alert Service Bulletin 737-27A1194). This commenter, an operator, proposes that the inspection intervals be increased to coincide with the current maintenance schedules established for its fleet of airplanes. \n\n\tThe FAA does not concur. The commenter provided no substantiating evidence to justify extending the repetitive inspection intervals; and the FAA does not consider it appropriate to revise provisions in an AD to accommodate a single operator's maintenance schedule. The FAA has determined that the repetitive inspection interval described in Boeing Alert Service Bulletin 737- 27A1194 (the appropriate service information for this AD) will ensure that any damage to the tie links is identified and corrected in a timely manner. However, paragraph (f) of the final rule does provide affected operators the opportunity to request an adjustment of the compliance time if data are presented to justify such an extension.\n\nRequest to Clarify Damage Limits \n\n\tOne commenter, the manufacturer, states that the phrase ". . . and damage is within limits specified in Figure 1 . . .", as used in paragraphs (c) and (d) of the proposal is confusing. The manufacturer notes that Figure 1 of Boeing Alert Service Bulletin 737-27A1194, which is referenced as the appropriate source of service information in the proposal, has two action paths: One path depicts actions to follow if damage is within acceptable limits (which starts an inspection program); the other path depicts actions to follow if damage is outside the acceptable limits (which specifies replacement of the unit). The manufacturer requests that the phrase be clarified to read ". . . and damage is within acceptable limitsas specified in Figure 1 . . .".\n\n\tThe FAA concurs and has revised paragraphs (c) and (d) of the AD accordingly. \n\nRequest to Clarify the Unsafe Condition \n\n\tThe manufacturer also suggests that the wording, "Since an unsafe condition has been identified that is likely to exist or develop . . .", which appeared in the preamble to the notice, be changed. The manufacturer requests that this language be revised to specify that a "possible unsafe condition" has been identified. The manufacturer states that this change of wording is warranted, since the worst scenario that has been identified is "high control column forces" and, even in that situation, an airplane still would be controllable. \n\n\tThe FAA does not concur with the commenter's suggestion. First, all unsafe conditions are "possible" events that "could occur." In fact, they are described in the regulations as conditions that are "likely to exist or develop" in aircraft. Second, as for this specific AD, in the event that the tie links were to become bent, it could lead to the elevator control forces being higher than normal, thus restricting the elevator control. This would be especially noticeable when larger elevator inputs are necessary, such as during takeoff, climb, and landing. The FAA considers this restriction of elevator control during these critical flight regimes to be an unsafe condition. (Further, since that language is not repeated in this final rule, no change is necessary.) \n\nRequest to Refer to Terminating Action \n\n\tThe manufacturer requests that reference to "see paragraph (e) for terminating action" be added to paragraph (c)(2) of the proposed rule. \n\n\tThe FAA does not concur. The FAA finds that it is unnecessary to reference paragraph (e) for operators who may be required to accomplish paragraph (c)(2) of the AD, since the terminating action specified in paragraph (e) of this AD is not a required terminating action.\n\n Request to Change the Date of the Referenced AlertService Bulletin \n\n\tAdditionally, the manufacturer requests that the release date of Boeing Alert Service Bulletin 737-27A1194 be changed from February 1, 1996, as specified in the proposed rule, to the actual release date of February 8, 1996. \n\n\tThe FAA concurs. The FAA notes that the subject alert service bulletin dated February 1, 1996, has been replaced with the February 8, 1996, version. The FAA has revised the final rule accordingly.\n\n Additional Sources of Service Information \n\n\tSince the issuance of the proposed rule, the FAA has reviewed and approved Boeing Notices of Status Change (NSC) 737-27A1194 NSC 01, dated March 7, 1996, and 737-27A1194 NSC 02, dated April 4, 1996; and Boeing Alert Service Bulletin 737-27A1194, Revision 1, dated September 26, 1996. The NSC's and service bulletin revision provide further clarification of the inspection and modification procedures required by this AD. Therefore, the FAA has revised the AD to cite those documents as additionalsources of service information. \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\nCost Impact \n\n\tThere are approximately 1,618 Boeing Model 737-300, -400, and -500 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 684 airplanes of U.S. registry will be affected by this AD, that it will take approximately 3 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 $140 per airplane. Based on these figures, the cost impact of the AD on U.S. operators is estimated to be $218,880, or $320 per airplane. \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\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: