94-347. Airworthiness Directives; Boeing Model 737 Series Airplanes  

  • [Federal Register Volume 59, Number 21 (Tuesday, February 1, 1994)]
    [Unknown Section]
    [Page 0]
    From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
    [FR Doc No: 94-347]
    
    
    [[Page Unknown]]
    
    [Federal Register: February 1, 1994]
    
    
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    DEPARTMENT OF TRANSPORTATION
    14 CFR Part 39
    
    [Docket No. 93-NM-79-AD; Amendment 39-8789; AD 94-01-07]
    
     
    
    Airworthiness Directives; Boeing Model 737 Series Airplanes
    
    AGENCY: Federal Aviation Administration, DOT.
    
    ACTION: Final rule.
    
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    SUMMARY: This amendment adopts a new airworthiness directive (AD), 
    applicable to certain Boeing Model 737 series airplanes, that requires 
    repetitive tests of the main rudder power control unit (PCU) to detect 
    excessive internal leakage of hydraulic fluid, stalling, or reversal, 
    and the eventual replacement of the main rudder PCU with an improved 
    model. This amendment is prompted by results of an investigation which 
    revealed that the secondary slide in the servo valve of certain PCU's 
    can go past the intended maximum-travel position. The actions specified 
    by this AD are intended to prevent secondary slide overtravel from 
    occurring, which could cause the rudder actuator piston and the rudder 
    to operate with reduced force capability or to move in a direction 
    opposite to the intended direction; this could result in reduced 
    controllability of the airplane.
    
    DATES: Effective March 3, 1994.
        The incorporation by reference of certain publications listed in 
    the regulations is approved by the Director of the Federal Register as 
    of March 3, 1994.
    
    ADDRESSES: The 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 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.
    
    FOR FURTHER INFORMATION CONTACT: Kenneth W. Frey, Aerospace Engineer, 
    Seattle Aircraft Certification Office, Systems & Equipment Branch, ANM-
    130S, FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., 
    Renton, Washington 98055-4056; telephone (206) 227-2673; fax (206) 227-
    1181.
    
    SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal 
    Aviation Regulations to include an airworthiness directive (AD) that is 
    applicable to certain Boeing Model 737 series airplanes was published 
    in the Federal Register on August 16, 1993 (58 FR 43301). That action 
    proposed to require periodic tests of the main rudder PCU to detect 
    excessive internal leakage of hydraulic fluid, stalling, or reversal, 
    and the correction of discrepancies. That action also proposed to 
    require the eventual replacement of the main rudder PCU with an 
    improved model; such replacement would constitute terminating action 
    for the periodic tests.
        Interested persons have been afforded an opportunity to participate 
    in the making of this amendment. Due consideration has been given to 
    the comments received.
        Several commenters request that the proposed rule be revised to 
    require a one-time internal leakage test of the PCU, instead of the 
    proposed repetitive tests every 750 flight hours. These commenters 
    consider that the existing pre-flight controls check is adequate to 
    detect rudder control anomalies that would be due to dual servo valve 
    secondary slide overtravel; since this check is performed prior to each 
    flight, it will verify the function of the rudder control system on a 
    regular basis. These commenters believe that the proposed repetitive 
    test is not appropriate or reliable, since it is sensitive to variables 
    such as temperature and the inspecting technician's individual 
    technique and judgment. In addition, some of these commenters believe 
    that the secondary slide overtravel problems are attributable to either 
    adverse tolerance build-up or improper assembly of the PCU during 
    manufacture, and are not due to wear or deterioration of the valve over 
    time; therefore, these commenters consider that repetitive tests are 
    unnecessary. One commenter states that the proposed test has not proved 
    to be reliable in identifying rudder PCU anomalies, and that this test 
    could cause a rise in the number of removals of PCU's that would 
    typically be serviceable; this would have a severe economic impact on 
    affected operators.
        The FAA does not concur with the commenters' request. First, the 
    FAA notes that rapid rudder inputs are a factor in uncovering rudder 
    control anomalies. During a pre-flight check, the flight crew may not 
    cycle the rudder PCU at a rate fast enough to uncover secondary slide 
    overtravel. For this reason, the FAA does not agree that all rudder 
    control anomalies due to secondary slide overtravel can be detected 
    during pre-flight checks.
        Second, although the FAA agrees that the required repetitive test 
    is not completely repeatable and could be subject to the judgment of 
    the technician, the FAA recognizes it as a written procedure for 
    maintenance crews to follow, which emphasizes cycling of the rudder 
    pedals at a maximum rate. While this test cannot ensure that the 
    secondary slide overtravel anomaly does not exist, it can detect 
    certain conditions that contribute to secondary slide overtravel. For 
    example, the overtravel anomaly, combined with either (1) A secondary 
    summing arm missing its stop or (2) a primary slide jamming to the 
    secondary slide, would be detected during the repetitive test. During 
    bench testing on one PCU, the secondary summing arm was observed 
    hitting its stop on some occasions and missing it on others; this 
    intermittent condition, if combined with the secondary overtravel 
    anomaly and rapid rudder inputs, could cause rudder control problems. 
    For these reasons, the FAA has determined that the required repetitive 
    tests will contribute to flight safety because they exercise the rudder 
    pedals at a rapid rate and they can detect high internal leakage within 
    the servo valve.
        Several commenters request that the compliance time for replacing 
    the main rudder PCU be extended from the proposed 5 years to at least 7 
    years. These commenters state that such an extension is necessary to 
    avoid the economic burden to operators that would be caused by a 
    campaign of scheduled removals. A 7-year compliance time would 
    correspond to a typical overhaul period for the main rudder PCU, and 
    would avoid unscheduled removal of PCU's that exhibit no operational 
    anomalies. Some commenters note that the design feature that allows 
    secondary slide overtravel has existed for over 25 years and, over that 
    time period, has accumulated 55 million flight hours in the affected 
    fleet with no known in-flight control problems. These commenters state 
    that it would be extremely rare for the problem condition to exist in 
    combination with other factors so as to result in a reduction of rudder 
    control capability. For these reasons, these commenters consider that 
    extending the compliance time for completion of the replacement would 
    not appreciably affect the safety of the fleet.
        The FAA does not concur with the commenters' request to extend the 
    compliance time for replacement of the PCU. Although the FAA 
    acknowledges that no known in-flight control problems have been 
    documented on Model 737 airplanes with regard to the subject condition, 
    the FAA does recognize that two PCU's have been removed from Model 737 
    series airplanes after the pilot identified rudder control problems 
    during the pre-flight check. In developing an appropriate compliance 
    time for this action, the FAA considered the safety implications of 
    incidents such as these, the availability of required parts, and the 
    normal maintenance schedules for timely accomplishment of the 
    replacement. Further, only the original equipment manufacturer 
    possesses approved data allowing it to accomplish the rework of the 
    affected PCU's; therefore, the compliance time also was based on the 
    capability of this manufacturer to schedule and modify all of the 
    affected servo valves. In light of these items, the FAA has determined 
    that 5 years for compliance is appropriate. The FAA considers that a 5-
    year compliance time allows ample time for all affected PCU's to be 
    modified by the manufacturer, without creating a burden on either the 
    operators or the manufacturer. Five years also allows ample time for 
    the replacement to be accomplished coincidentally with scheduled major 
    airplane inspection and maintenance activities, thereby minimizing the 
    costs associated with special airplane scheduling. However, paragraph 
    (c) of the final rule does provide affected operators the opportunity 
    to apply for an adjustment of the compliance time if data is presented 
    to justify such an adjustment.
        One commenter strongly supports the proposed rule, but considers 
    that the 5-year compliance time for replacement of the PCU's is too 
    long. This commenter requests that replacement of all affected PCU's 
    should begin immediately as replacement parts become available, instead 
    of allowing operators to operate airplanes equipped with potentially 
    defective PCU's for up to 5 years. This commenter notes that the 
    addressed anomaly was first discovered in July 1992 and, by the time 
    the proposed rule becomes effective and the end of the 5-year 
    compliance period is reached, approximately 7 years will have elapsed 
    since then. This amount of time is too long, considering the 
    significance of the addressed unsafe condition.
        The FAA does not concur with the commenter's request to shorten the 
    compliance time for replacement of the PCU's. For the same reasons 
    explained previously, the FAA has determined that a 5-year compliance 
    time is appropriate. The repetitive tests of the PCU required by this 
    AD will provide an acceptable level of safety in the interim. 
    Additionally, the commenter should not assume that all operators will 
    wait until the end of the compliance time before replacement the PCU's. 
    In fact, the FAA has been advised that the PCU manufacturer has already 
    begun rework activity and some airlines have already begun replacement 
    procedures.
        One commenter requests that paragraph (a)(2) of the proposed rule 
    be revised to provide operators with the option of installing a 
    serviceable, non-modified PCU, rather than only a modified PCU, if a 
    discrepancy is detected during any test. Operators should be allowed to 
    use this non-modified PCU, provided that it is repetitively tested 
    until replacement of all PCU's is required in 5 years. Such a revision 
    to the rule would prevent unnecessary grounding of an airplane if a 
    discrepancy is detected and a modified PCU is not available. The FAA 
    concurs and has revised the final rule accordingly.
        Another commenter requests that the proposed rule be revised to 
    address third-party repaired parts. This commenter states that at least 
    one repair facility is producing FAA-approved replacement slide and 
    sleeve assemblies to overhaul the Parker-Hannifin main rudder PCU dual 
    servo valves. The commenter believes that it is the FAA's 
    responsibility to ensure that third-party replacement parts are 
    reworked in a controlled manner to the same level of safety as that 
    provided by the retrofit plan developed by the original equipment 
    manufacturer (OEM), since the replacement parts were approved solely by 
    the FAA without support from the OEM.
        The FAA does not concur that such a revision to the rule is 
    necessary. Paragraph (c) of the final rule contains a provision that 
    allows third-party replacement part manufacturers to submit proposed 
    design changes to the FAA for approval as alternative methods of 
    compliance with the AD.
        One commenter suggests that the discussion of the requirements of 
    the proposed rule be revised to clarify that the test of the main 
    rudder PCU is necessary not only to detect excessive internal leakage 
    of hydraulic fluid, but to detect and correct possible stalling and 
    reversal as well. The FAA concurs. Although the test is accomplished to 
    detect excessive internal leakage, the AD requires that any 
    discrepancy, such as stalling and reversal, that is detected during the 
    test must be corrected prior to further flight. The AD references 
    Boeing Service Letter 737-SL-27-82-B for a description of the possible 
    discrepancies that could be found during the required test. The wording 
    to the preamble of this final rule has been revised to include 
    reference to the possible discrepancies of stalling and reversal; 
    however, the wording of the AD itself needs no revision.
        This same commenter suggests that the description of the unsafe 
    condition on which this AD action is based could be worded more 
    accurately. This commenter states that the actions specified by the AD 
    are intended to prevent secondary slide overtravel from occurring, 
    which could cause the rudder actuator piston and the rudder to 
    ``operate with reduced force capability or to move in a direction 
    opposite to the intended direction.'' The FAA concurs with the 
    commenter's suggestion and has revised the appropriate wording 
    accordingly.
        Two commenters suggest that the cost impact information in the 
    preamble to the notice was not totally accurate in showing the complete 
    costs to operators, especially those costs related to the required 
    repetitive tests. One commenter states that each test would require 
    approximately 8 work hours to accomplish, and that, based on the 750-
    flight hour repetitive test interval, most airplanes would be required 
    to be tested between 6 and 10 times over the next 5 years (until 
    replacement of the PCU is completed). Another commenter states that the 
    total time required for removing and installing the PCU is 20 work 
    hours. The FAA concurs that the economic information should be 
    clarified. The cost impact figures, as stated in the preamble to the 
    notice, were based on the latest data that the FAA had at that time. 
    The cost impact information, below, has been revised to delineate the 
    costs of the required actions, based on this latest information 
    provided by the commenters.
        Paragraphs (a)(1) and (a)(2) of the final rule have been revised to 
    correctly reference paragraph ``3.B.'' of Boeing Service Letter 737-SL-
    27-82-B for the description of possible discrepancies that could be 
    found during the required test. The notice had incorrectly referenced 
    paragraph ``B.'' rather than ``3.B.''
        After 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 
    significantly increase the economic burden on any operator nor increase 
    the scope of the AD.
        There are approximately 2,448 Model 737 series airplanes of the 
    affected design in the worldwide fleet. The FAA estimates that 729 
    airplanes of U.S. registry will be affected by this AD.
        It will take approximately 8 work hours per airplane to accomplish 
    the required test actions, at an average labor rate of $55 per work 
    hour. Based on these figures, the total cost impact of the tests 
    required by this AD on U.S. operators is estimated to be $320,760, or 
    $440 per airplane, per test.
        According to information provided by commenters to the notice that 
    preceded this rule, some airplanes may require to be tested between 6 
    and 10 times prior to the required replacement of the PCU (within 5 
    years). In the case of those airplanes requiring 6 tests, the total 
    cost impact of the required repetitive tests would be $2,640 per 
    airplane over 5 years; in the case of those airplanes requiring 10 
    tests, the total cost impact of the required repetitive tests would be 
    $4,400 per airplane over 5 years.
        The number of required work hours, as indicated above, is presented 
    as if the tests required by this AD were to be conducted as ``stand 
    alone'' actions. However, in actual practice, these tests could be 
    accomplished coincidentally or in combination with normally scheduled 
    airplane inspections and other maintenance program tasks. Therefore, 
    the actual number of necessary ``additional'' work hours would be 
    minimal in many instances. Additionally, any costs associated with 
    special airplane scheduling should be minimal.
        It will take approximately 20 work hours per airplane to accomplish 
    the required replacement of the PCU (removal and installation), at an 
    average labor rate of $55 per work hour. Required parts will be 
    supplied by the manufacturer at no cost to operators. Based on these 
    figures, the total cost impact of the replacement required by this AD 
    is estimated to be $801,900, or $1,100 per airplane.
        The 5-year compliance time for the replacement of the PCU, as 
    specified in paragraph (b) of this AD, will allow ample time for the 
    replacement to be accomplished coincidentally with scheduled major 
    airplane inspection and maintenance activities, thereby minimizing the 
    costs associated with special airplane scheduling.
        The total cost impact figures described 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. However, the 
    FAA has been advised that several operators already have accomplished 
    at least the initial required test of the PCU's on their affected 
    fleets, and certain operators already have replaced some PCU's. 
    Therefore, the future economic cost impact of this rule on U.S. 
    operators is less than that indicated above.
        The 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.
        For 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.
    
    List of Subjects in 14 CFR Part 39
    
        Air transportation, Aircraft, Aviation safety, Incorporation by 
    reference, Safety.
    
    Adoption of the Amendment
    
        Accordingly, pursuant to the authority delegated to me by the 
    Administrator, the Federal Aviation Administration amends 14 CFR part 
    39 of the Federal Aviation Regulations as follows:
    
    PART 39--AIRWORTHINESS DIRECTIVES
    
        1. The authority citation for part 39 continues to read as follows:
    
        Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 
    106(g); and 14 CFR 11.89.
    
    
    Sec. 39.13  [Amended]
    
        2. Section 39.13 is amended by adding the following new 
    airworthiness directive:
    
    94-01-07 Boeing: Amendment 39-8789. Docket 93-NM-79-AD.
    
        Applicability: Model 737 series airplanes; line positions 1 
    through 2453, inclusive; certificated in any category.
        Compliance: Required as indicated, unless accomplished 
    previously.
        To prevent the rudder actuator piston and the rudder to operate 
    with reduced force capability or to move in a direction opposite to 
    the intended direction, which could result in reduced 
    controllability of the airplane, accomplish the following:
        (a) Within 750 flight hours after the effective date of this AD, 
    perform a test of the main rudder power control unit (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.
        (1) If 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.
        (2) If 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:
        (i) Replace 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.
        (ii) Replace 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 this AD.
        (b) Within 5 years after the effective date of this AD, replace 
    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. Such replacement constitutes terminating 
    action for the tests required by this AD.
        (c) An 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.
    
        Note: Information concerning the existence of approved 
    alternative methods of compliance with this AD, if any, may be 
    obtained from the Seattle ACO.
    
        (d) Special flight permits may be issued in accordance with FAR 
    21.197 and 21.199 to operate the airplane to a location where the 
    requirements of this AD can be accomplished, provided that the 
    airplane has not failed the internal leakage test required by this 
    AD.
        (e) The tests shall be done in accordance with Boeing Service 
    Letter 737-SL-27-82-B, dated July 13, 1993. The replacement shall be 
    done in accordance with Boeing Service Bulletin 737-27-1185, dated 
    April 15, 1993. 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.
        (f) This amendment becomes effective on March 3, 1994.
    
        Issued in Renton, Washington, on January 3, 1994.
    Darrell M. Pederson,
    Acting Manager, Transport Airplane Directorate, Aircraft Certification 
    Service.
    [FR Doc. 94-347 Filed 1-31-94; 8:45 am]
    BILLING CODE 4910-13-P
    
    
    

Document Information

Effective Date:
3/3/1994
Published:
02/01/1994
Department:
Transportation Department
Entry Type:
Uncategorized Document
Action:
Final rule.
Document Number:
94-347
Dates:
Effective March 3, 1994.
Pages:
0-0 (1 pages)
Docket Numbers:
Federal Register: February 1, 1994, Docket No. 93-NM-79-AD, Amendment 39-8789, AD 94-01-07
CFR: (1)
14 CFR 39.13