AD 97-14-04

This amendment supersedes two existing airworthiness directives (AD), applicable to certain Boeing Model 737 series airplanes, that currently require tests of the main rudder power control unit (PCU) to detect excessive internal leakage of hydraulic fluid, stalling, or reversal, and to verify proper operation of the PCU; and replacement of the PCU with a unit having a different part number, if necessary. This amendment adds requirements for replacement of the PCU and the vernier control rod bolts with newly designed units. This amendment also adds a requirement for leak tests of the PCU, and replacement of the PCU with a serviceable or newly designed unit, if necessary. This amendment is prompted by reports of fracturing of the vernier control rod bolts as a result of the shank of the bolt running into the threads on the nutplate during installation of the rod. The actions specified by this AD are intended to prevent such fracturing, which could result in uncommanded movements of the rudder, and consequent reduced controllability of the airplane.

Final rule

97-14-04 BOEING: Amendment 39-10061. Docket 97-NM-29-AD. Supersedes AD 94-01-07, Amendment 39-8789, and AD 96-23-51, Amendment 39-9818.\n\n\tApplicability: All Model 737-100, -200, -300, -400, and -500 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 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 (i) 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 addressit. \n\n\tCompliance: Required as indicated, unless accomplished previously. \n\n\tTo prevent uncommanded movements of the rudder, and consequent reduced controllability of the airplane, accomplish the following: \n\nRESTATEMENT OF REQUIREMENTS OF AD 94-01-07: \n\n\t(a)\tWithin 750 flight hours after March 3, 1994 (the effective date of AD 94-01-07, amendment 39-8789), perform a test of the main rudder PCU, part number 65-44861-2/-3/-4/ -5/-6/-7/-8/-9, to detect internal leakage of hydraulic fluid, in accordance with Boeing Service Letter 737-SL-27-82-B, dated July 13, 1993. \n\n\t\t(1)\tIf no discrepancy, as described in paragraph 3.B. of the Service Letter, is detected, repeat the test at intervals not to exceed 750 flight hours. \n\n\t\t(2)\tIf any discrepancy, as described in paragraph 3.B. of the Service Letter, is detected during any check, prior to further flight, accomplish either paragraph (a)(2)(i) or (a)(2)(ii) of this AD: \n\n\t\t\t(i)\tReplace the main rudder PCU with a serviceable PCU in accordance with the Model 737 Overhaul Manual. After such replacement, repeat the test at intervals not to exceed 750 flight hours. \n\n\t\t\t(ii)\tReplace the main rudder PCU with a new main rudder PCU having part number 65-44861-11 or 65C37052-2/-3/-4/-5/-6/-7/-8/-9, in accordance with Boeing Service Bulletin 737-27-1185, dated April 15, 1993. Such replacement constitutes terminating action for the tests required by paragraph (a) of this AD. \n\n\t(b)\tReplacement of the main rudder PCU, part number 65-44861-( ), with a new main rudder PCU having part number 65-44861-11 or 65C37052-2/-3/-4/-5/-6/-7/-8/-9, in accordance with Boeing Service Bulletin 737-27-1185, dated April 15, 1993, constitutes terminating action for the tests required by paragraph (a) of this AD. \n\nRESTATEMENT OF REQUIREMENTS OF AD 96-23-51: \n\n\t(c)\tWithin 10 days after November 27, 1996 (the effective date of AD 96-23-51, amendment 39-9818), perform a test to verify proper operation of the rudder PCU, in accordance with Boeing Alert Service Bulletin 737-27A1202, dated November 1, 1996, or Revision 1, dated December 6, 1996. \n\n\t\t(1)\tIf the rudder PCU operates properly, repeat the test thereafter at intervals not to exceed 250 flight hours. \n\n\t\t(2)\tIf the rudder PCU operates improperly, prior to further flight, replace the rudder PCU with a new rudder PCU, in accordance with the alert service bulletin. Repeat the test thereafter at intervals not to exceed 250 flight hours. \n\nNEW REQUIREMENTS OF THIS AD: \n\n\t(d)\tWithin 2 years after the effective date of this AD, accomplish paragraphs (d)(1) and (d)(2) of this AD in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. Accomplishment of these actions terminates the requirements of paragraphs (a), (b), and (c) of this AD. \n\n\t\t(1)\tReplace any main rudder PCU having Boeing part number (P/N) 65-44861-( ) or P/N 65C37052-\n( ) with a new main rudder PCU that hasbeen approved by the Manager, Seattle ACO. \n\n\t\t(2)\tReplace the vernier control rod bolts having Boeing P/N 69-27229-( ) with new bolts that has been approved by the Manager, Seattle ACO. \n\n\t(e)\tPerform a leak test of the main rudder PCU in accordance with a method approved by the Manager, Seattle ACO, at the applicable times specified in paragraph (e)(1) or (e)(2) of this AD. If any discrepancy is found, prior to further flight, replace the PCU with a serviceable or newly designed unit in accordance with a method approved by the Manager, Seattle ACO. \n\n\tNOTE 2: If the PCU is replaced in accordance with the requirements of paragraph (e) prior to accomplishing the replacement required by paragraph (d) of this AD, "serviceable" includes the newly designed PCU referenced in paragraph (d)(1) of this AD and PCU's having part number 65-44861-11 and 65C37052-2, -3, -4, -5, -6, -7, -8, and -9. However, after the PCU has been replaced in accordance with paragraph (d)(1) of this AD, "serviceable" is limited to the newly designed PCU's referenced in that paragraph. \n\n\t\t(1)\tFor airplanes on which the replacement specified in paragraph (a)(2)(ii), (b), or (c)(2) of this AD has been accomplished prior to the effective date of this AD: Within 4,000 flight hours after the effective date of this AD, and thereafter at intervals not to exceed 6,400 flight hours. \n\n\t\t(2)\tFor airplanes other than those identified in paragraph (e)(1) of this AD: Within 6,400 flight hours after accomplishment of the replacement required by paragraph (d)(1) of this AD, and thereafter at intervals not to exceed 6,400 flight hours. \n\n\t(f)\tRevision of the FAA-approved maintenance program to require an FAA-approved leak test constitutes terminating action for the repetitive leak test requirements of paragraph (e) of this AD. \n\n\t(g)\tOnce a newly designed PCU specified in paragraph (d)(1) of this AD is installed on an airplane, no operator shall install on that airplane any PCU other than sucha newly designed unit. \n\n\t(h)\tOnce a newly designed vernier control rod bolt specified in paragraph (d)(2) of this AD is installed on an airplane, no operator shall install on that airplane any bolt other than such a newly designed bolt. \n\n\t(i)\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\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(j)\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(k)\tTheactions shall be done in accordance with Boeing Service Letter 737-SL-27-82-B, dated July 13, 1993; Boeing Alert Service Bulletin 737-27A1202, dated November 1, 1996; and Boeing Alert Service Bulletin 737-27A1202, Revision 1, dated December 6, 1996. The incorporation by reference of Boeing Service Letter 737-SL-27-82-B, dated July 13, 1993, as listed in the regulations, was approved previously by the Director of the Federal Register as of March 3, 1994 (59 FR 4570, February 1, 1994). The incorporation by reference of Boeing Alert Service 737-27A1202, dated November 1, 1996, as listed in the regulations, was approved previously by the Director of the Federal Register as of November 27, 1996 (61 FR 59317, November 22, 1996). The incorporation by reference of Boeing Alert Service Bulletin 737-27A1202, Revision 1, dated December 6, 1996, is 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(l)\tThis amendment becomes effective on August 4, 1997.

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) by superseding both AD 94-01-07, amendment 39-8789 (59 FR 4570, February 1, 1994), and AD 96-23-51, amendment 39-9818 (61 FR 59317, November 22, 1996), was published in the Federal Register on March 14, 1997 (62 FR 12126). Both of the existing AD's are applicable to various Boeing Model 737 series airplanes. \n\n\tThe NPRM proposed to continue to require tests of the main rudder power control unit (PCU) to detect excessive internal leakage of hydraulic fluid, stalling, or reversal, and to verify proper operation of the PCU; and replacement of the PCU with a unit having a different part number, if necessary. The NPRM also proposed to require replacement of the PCU and vernier control rod bolts with newly designed units; repetitive leak tests of the PCU; and replacement of the PCU with a serviceable or newly designed 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 proposed rule. \n\nRequest to Extend the Comment Period of the Proposal\n\n\tSeveral commenters request an extension of the public comment period for the proposed AD. These commenters state that such an extension will enable operators to better understand the issues surrounding the proposed actions and to review recent material presented by Boeing and comments submitted by the National Transportation Safety Board (NTSB) in response to Rules Docket No. 96-NM-266-AD. \n\n\tThe FAA does not concur. The FAA has considered the degree of urgency associated with addressing the identified unsafe condition of the rudder PCU, and the amount of time that has already elapsed since issuance of the original proposed rule. In light of these items, the FAA has determined that further delay of this final rule is not appropriate. \n\nRequest to Delay Issuance of Final Rule \n\n\tOne commenter requests that the FAA delay issuance of the final rule until Boeing can release the service bulletins containing procedures for replacement of the main rudder PCU and vernier control rod bolts with newly designed units. The commenter states that neither Boeing nor its suppliers have completed engineering the proposed design changes; therefore, the commenter is unable to provide meaningful or technically relevant comments regarding the actions specified in the proposed AD. \n\n\tThe FAA does not concur with the commenter's request. In light of the critical nature of the addressed unsafe condition, the FAA does not consider that delaying this action until after release of Boeing's planned service bulletins is warranted. Furthermore, the FAA disagrees with the commenter's assertion that it is unable to submit meaningful comments on this AD until Boeing's design changes are completed. On the contrary, the proposedAD provided extensive information on the nature of the unsafe condition, the proposed corrective actions, and the proposed compliance times for those actions. The only information not provided (because it was not available) was reference to a specific service document providing details on specific methods for accomplishing the proposed actions. \n\n\tThe FAA considers that this proposed AD has complied fully with the requirements of the Administrative Procedure Act to provide the public with a reasonable opportunity to comment by including in the proposal "either the terms or substance of the proposed rule or a description of the subjects and issues involved." \n\nRequest to Reference Latest Boeing Service Bulletin \n\n\tOne commenter requests that paragraph (c) of the proposed rule be revised to reference Revision 1 of Boeing Alert Service Bulletin 737-27A1020, dated December 6, 1996, and Revision 2 of that alert service bulletin (which has not been released yet). The commenter statesthat the terminating action for the requirements of paragraph (c) of the proposed AD will be included in Revision 2 of the alert service bulletin. \n\n\tThe FAA concurs partially. Regarding Revision 2 of the service bulletin, the FAA does not reference service bulletins that have not yet been released in an AD. Office of the Federal Register (OFR) regulations require that either the service document contents be published as part of the actual AD language; or that the service document be submitted for approval by the OFR as "referenced" material, in which case it may be only referred to in the text of an AD. An AD may only refer to a service document that was submitted and approved by the OFR for "incorporation by reference." In order for operators to use later revisions of a referenced document (issued after the publication of an AD), either the AD must be revised to reference the specific later revisions, or operators must request the approval of the use of them as an alternativemethod of compliance under the provisions of paragraph (i) of this AD. \n\n\tSince issuance of the NPRM, the FAA has reviewed and approved Boeing Alert Service Bulletin 737-27A1202, Revision 1, dated December 6, 1996, as an alternative method of compliance for the requirements of paragraph (c) of the AD. The FAA has revised paragraph (c) of this final rule to include Revision 1 of the alert service bulletin as an additional source of service information. \n\nRequests to Revise the Compliance Time for New Requirements \n\n\tSeveral commenters request a revision to the proposed compliance time of 2 years for accomplishment of the new requirements of this proposed AD: \n\n\tOne commenter requests that the new requirements proposed by the AD be accomplished by December 31, 1997. The commenter states that the NTSB and FAA have known about the problems with the rudder PCU since 1986 or earlier. The commenter asserts that further delays will only increase the possibility of another catastrophic accident. \n\n\tTwo commenters request that the compliance time for accomplishing the proposed replacement of the main rudder PCU and the vernier control rod bolts be extended from the proposed 2 years. One of these commenters requests a compliance time of 3 years. The other commenter requests a compliance time of 5 years. One of these commenters states that if the functional test of the main rudder PCU (as required by paragraph (e) of the proposed AD) requires the phase lag test of the yaw damper system to be performed, it will be forced to send all PCU's to Parker Hannifin for modification and testing. The same commenter suggests that Parker Hannifin does not have the capability to manufacture the replacement parts within the proposed compliance time. The other commenter points out that Parker Hannifin will be especially hard pressed to manufacture the required parts within the proposed compliance time. \n\n\tOne commenter questions, due to past difficulties with vendors and parts availability, whether the 2-year compliance time of the subject replacement of the proposed AD is feasible. \n\n\tThe FAA does not concur with any of the commenters' requests. In response to the commenter that states the FAA has known about the problems associated with the main rudder PCU since 1986 or earlier, the FAA finds this statement to be incorrect. The FAA learned of the design deficiencies in the main rudder PCU servo valve and control rod bolts in the last quarter of 1996. The FAA has determined that Parker Hannifin has the capability to manufacture the replacement parts for all affected airplanes within the proposed compliance time. In addition, the FAA finds that a compliance time of less than 2 years would significantly increase the possibility of new design or manufacturing errors. Further, the FAA points out that once Boeing has developed the design changes for the main rudder PCU servo valve and control rod bolts, time will be necessary to test the new design changes to ensure those changes meet certification requirements for FAA approval.\n \n\tIn developing an appropriate compliance time for the required replacements, the FAA considered not only the degree of urgency associated with addressing the unsafe condition, but the availability of required parts and the practical aspect of accomplishing the replacements within an interval of time that parallels normal scheduled maintenance for the majority of affected operators. In consideration of all of these factors, the FAA has determined that 2 years represents an appropriate interval of time allowable wherein the replacements can be accomplished during scheduled maintenance intervals for the majority of affected operators, and an acceptable level of safety can be maintained. \n\nRequest to Revise Part Numbers of PCU's \n\n\tOne commenter requests that part numbers (P/N) 65-44861-( ) and 65C37052-( ) of the PCU identified in paragraph (d)(1) of the proposal be revised to include P/N's 65-44861-10and 65C36052-10, respectively. The commenter states that -10 P/N's were addressed in Notice of Status Change 737-27-1185 NSC1, dated May 27, 1993, which was incorporated into Boeing Service Bulletin 737-27-1185, Revision 1, dated April 14, 1994. \n\n\tThe FAA does not concur. The symbol "( )" at the end of the subject P/N's indicates any dash number. Therefore, P/N's 65-44861-10 and 65C36052-10 are affected by the requirements of paragraph (d)(1) of the final rule. \n\nRequest to Add a New Requirement \n\n\tOne commenter states that the vernier control rod must be replaced or reworked at the same time the bolts are replaced in order to replace the two nutplates. The commenter notes that this action is not included in the proposed AD. From this comment, the FAA infers that the commenter is requesting that paragraph (d)(2) of the proposed AD be revised to include a requirement to replace or rework the vernier control rod. \n\n\tThe FAA does not concur. The FAA acknowledges that replacing the two nutplates could correct the bolt design deficiency; however, such a design change has not been submitted to the FAA for approval. However, under the provisions of paragraph (i) of the final rule, the FAA may consider requests for approval of an alternative method of compliance if sufficient data are submitted to substantiate that such a design change would provide an acceptable level of safety.\n\n Request to Revise Reference to Vernier Control Rod Bolt \n\n\tOne commenter requests that reference to a vernier control rod "bolt" (singular) be changed to "bolts" (plural) throughout the proposal. The commenter states that there are two bolts -- one on each end of the rod. The FAA concurs with this suggestion and has revised the final rule accordingly.\n\n Request to Incorporate the Leak Test into the Maintenance Program \n\n\tOne commenter requests that the leak test required by paragraph (e) of the proposed AD be incorporated into each operator's FAA-approved maintenance program as terminating action for the requirements of that paragraph. \n\n\tThe FAA concurs. The FAA finds that revising the FAA-approved maintenance program to require an FAA-approved leak test may be accomplished as an optional terminating action for the repetitive leak test requirements of paragraph (e) of the final rule. Therefore, the FAA has added a new paragraph (f) to this final rule to provide for this option. \n\nRequest to Extend Repetitive Interval for Leak Test\n\n\tOne commenter requests that the repetitive intervals for the leak test (specified in paragraphs (e)(1) and (e)(2) of the proposed AD) be extended from the proposed 6,000 flight hours to 6,400 flight hours. The commenter states that such an extension will coincide with the interval of the "2C" maintenance check for Boeing Model 737-300, -400, and -500 series airplanes. \n\n\tThe FAA concurs. The FAA's intent was that the specified intervals coincide with the "2C" maintenance check. Accordingly, the FAA has revised paragraphs (e)(1) and (e)(2) of the final rule to specify this revised repetitive interval. \n\nRequest to Accept Previously Approved Alternative Methods of Compliance \n\n\tOne commenter states that the leak test specified in Boeing Service Letter 737-SL-27-91 was considered acceptable as an alternative method of compliance (AMOC) in accordance with AD 94-01-07. The commenter questions whether the FAA will continue to accept that AMOC, or whether it will be necessary to apply for approval of a new AMOC.\n\n\tThe FAA has not approved a leak test as an AMOC for the requirements of this AD. However, the FAA may consider requests for approval of the subject leak test as an AMOC if sufficient data are submitted to substantiate that such a test would provide an acceptable level of safety. \n\nRequest to Add a Requirement for the Control Rod and Its Bolts \n\n\tOne commenter requests that an identical requirement to that of paragraph (f) of the proposed AD (designated as paragraph (g) in the final rule) be included in the final rule for the control rod and its bolts. \n\n\tThe FAA concurs. The FAA inadvertently omitted such a requirement for the control rod and its bolts from the proposal. The FAA's intent was to include a requirement that states, "Once a newly designed vernier control rod bolt specified in paragraph (d)(2) of this AD is installed on an airplane, no operator shall install on that airplane any bolt other than such a newly designed bolt." Therefore, the FAA has added a new paragraph (h) to the final rule to include such a requirement. \n\n\tThis new paragraph (h) simply states the effect of Section 39.3 of part 39 of the Federal Aviation Regulations (14 CFR 39.3), which provides, "No person may operate a product to which an airworthiness directive applies except in accordance with the requirements of that airworthiness directive." Thus, once an operator has complied with paragraph (d)(2) of this AD, it is required to continue to operate in compliance with that paragraph. As a result, this new paragraph (h) does not impose an additional burden on any operator.\n\n FAA's Conclusion \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 2,900 Boeing Model 737 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 1,350 airplanes of U.S. registry will be affected by this AD.\n \n\tThe tests that are currently required by AD 94-01-07 take approximately 8 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the currently required tests on U.S. operators is estimated to be $648,000, or $480 perairplane, per test.\n\n\tThe replacement that is currently required by AD 94-01-07 takes approximately 20 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Required parts will be supplied by the manufacturer at no cost to operators. Based on these figures, the cost impact of the currently required replacement on U.S. operators is estimated to be $1,620,000, or $1,200 per airplane. \n\n\tThe tests that are currently required by AD 96-23-51 take approximately 2 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the currently required tests on U.S. operators is estimated to be $162,000, or $120 per airplane, per test. \n\n\tThe replacement of the PCU that is required by this AD action takes approximately 9 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Required parts will be supplied by the manufacturer at no cost to operators. Based onthese figures, the cost impact of the required replacement of the PCU on U.S. operators is estimated to be $729,000, or $540 per airplane. \n\n\tThe replacement of the vernier control rod bolts that is required by this AD action takes approximately 1 work hour per airplane to accomplish, at an average labor rate of $60 per work hour. Required parts will be supplied by the manufacturer at no cost to operators. Based on these figures, the cost impact of the required replacement of the vernier control rod bolts on U.S. operators is estimated to be $81,000, or $60 per airplane. \n\n\tThe leak tests that are required in this AD action take approximately 8 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the required leak test on U.S. operators is estimated to be $648,000, or $480 per airplane, per leak test.\n\n\tThe cost impact figures discussed above are 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\nList 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: \n\nAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\n§ 39.13 - (Amended) \n\t2. Section 39.13 is amended by removing amendments 39-8789 (59 FR 4570, February 1, 1994) and 39-9818 (61 FR 59317, November 22, 1996), and by adding a new airworthiness directive (AD), amendment 39-10061, to read as follows: