[Federal Register Volume 62, Number 50 (Friday, March 14, 1997)]
[Proposed Rules]
[Pages 12126-12129]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-6437]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 97-NM-29-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-100, -200, -300, -400, 
and -500 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.


ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the supersedure of 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 action would add requirements for 
replacement of the PCU and the vernier control rod bolt with newly 
designed units. This action also would add a requirement for leak tests 
of the PCU, and replacement of the PCU with a serviceable or newly 
designed unit, if necessary. This proposal 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 the proposed AD are intended to 
prevent such fracturing, which could result in uncommanded movements of 
the rudder, and consequent reduced controllability of the airplane.

DATES: Comments must be received by April 23, 1997.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 97-NM-29-AD, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056. Comments may be inspected at this location 
between 9:00 a.m. and 3:00 p.m., Monday through Friday, except Federal 
holidays.


[[Page 12127]]


FOR FURTHER INFORMATION CONTACT: Kenneth W. Frey, Aerospace Engineer, 
Systems and Equipment Branch, ANM-130S, FAA, Transport Airplane 
Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, 
SW., Renton, Washington 98055-4056; telephone (206) 227-2673; fax (206) 
227-1181.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to participate in the making of the 
proposed 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 above. All 
communications received on or before the closing date for comments, 
specified above, will be considered before taking action on the 
proposed rule. The proposals contained in this notice may be changed in 
light of the comments received.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed 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 summarizing each FAA-public contact concerned with 
the substance of this proposal will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this notice must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 97-NM-29-AD.'' The postcard will be date stamped and 
returned to the commenter.

Availability of NPRMs

    Any person may obtain a copy of this NPRM by submitting a request 
to the FAA, Transport Airplane Directorate, ANM-103, Attention: Rules 
Docket No. 97-NM-29-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    On January 3, 1994, the FAA issued AD 94-01-07, amendment 39-8789 
(59 FR 4570, February 1, 1994), applicable to certain Boeing Model 737 
series airplanes, to require repetitive periodic 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 PCU with an improved model. That action was prompted by results of 
an investigation, which revealed that there was a remote possibility 
that the secondary slide in the servo valve of certain PCU's could go 
past the intended maximum-travel position. The requirements of that 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.
    On November 7, 1996, the FAA issued AD 96-23-51, amendment 39-9818 
(61 FR 59317, November 22, 1996), applicable to all Boeing Model 737 
series airplanes, to require repetitive periodic tests to verify proper 
operation of the main rudder PCU, and replacement of the PCU with a new 
unit, if necessary. That action was prompted by tests of the PCU 
conducted by the manufacturer, which demonstrated another very remote 
potential failure scenario that was previously unknown. The 
requirements of that AD are intended to prevent rudder motion in the 
opposite direction of the rudder command.

Actions Since Issuance of Previous Rules

    In the preamble to AD 96-23-51, the FAA indicated that it 
considered that AD to be interim action, and that further rulemaking 
action would be considered once final action was identified. Since the 
issuance of that AD, Boeing has advised the FAA that it is designing 
new main rudder PCU's and a new bolt for the vernier control rod for 
installation on the latest versions of Model 737 series airplanes 
currently undergoing certification. These new PCU's and bolts are 
capable of being installed on the existing fleet of Model 737 series 
airplanes. At this time, the testing and design analyses necessary for 
FAA approval have not yet been completed; therefore, Boeing has not yet 
released a service bulletin reflecting these changes. The FAA 
anticipates that these tests and analyses will be completed and the 
service bulletin approved prior to issuance of a final rule.
    In addition, the FAA also received reports indicating that the 
outer bolts for the vernier control rod fractured in two cases. 
Fracturing of the outer bolt was caused by the shank of the bolt 
running into the threads on the nutplate during installation of the 
vernier control rod. These bolts have a dual load path. If the second 
load path of the bolt fractures, the manual input link to the main 
rudder PCU would be disconnected. Such fracturing, if not corrected, 
could result in uncommanded movements of the rudder, and consequent 
reduced controllability of the airplane.

FAA's Determinations

    In light of this information, the FAA has determined the following:
    1. The main rudder PCU's must be replaced with newly designed 
units. These new PCU's will have a valve that is similar to the valve 
installed on the existing units in that the valve is dual-concentric in 
design; however, the new units will have different characteristics for 
the flow of hydraulic fluid. Installation of the new units will 
eliminate the possibility of improper flow of hydraulic fluid. 
Replacement of the existing units with new units constitutes 
terminating action for the actions required by those existing AD's.
    2. The bolt for the vernier control rod must be replaced with a 
newly designed bolt. Installation of the new bolt will eliminate the 
possibility of the shank of the bolt running into the threads on the 
nutplate.
    3. Although the FAA has received no reports indicating that an in-
flight engine out or loss of hinge moment has resulted in reduced 
controllability of an airplane, high internal leakage in the main 
rudder PCU can exist. This high internal leakage could be caused by a 
jam in the slides of the servo valve or by other failures or wear 
within the PCU. Such leakage could result in reduced hinge moment 
capability of the rudder PCU, which could result in reduced 
controllability of the airplane at any time large rudder inputs are 
required (such as failure of the engine during takeoff). In light of 
this, the FAA finds that periodic inspections must be performed to 
detect high internal leakage of the main rudder PCU in a timely manner.

Explanation of Requirements of Proposed Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other products of this same type design, this 
proposed AD would supersede AD 94-01-07 and AD 96-23-51. The following 
requirements from the superseded AD's have been carried over into the 
proposed AD:

--Tests of the main rudder 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.

    It should be noted that paragraph (b) of AD 94-01-07 requires 
replacement of the PCU with a unit having part number

[[Page 12128]]

65-44861-11 or 65C37052-2, -3, -4, -5, -6, -7, -8, or -9. However, 
paragraph (b) of this proposed AD would allow for this replacement as 
an optional terminating action (instead of a required action) for the 
tests required by paragraph (a) of AD 94-01-07.
    The proposed AD would add requirements for replacement of the PCU 
and vernier control rod bolt with newly designed units. Additionally, 
the proposed AD would add a requirement for repetitive leak tests of 
the PCU, and replacement of the PCU with a serviceable or newly 
designed unit, if necessary. These new actions would be required to be 
accomplished in accordance with a method approved by the FAA.
    In developing an appropriate compliance time for the new 
requirements of this proposed AD, the FAA considered the safety 
implications, the time necessary for design and production of the new 
PCU's and bolts, and normal maintenance schedules for timely 
accomplishment of the proposed actions. In light of these items, the 
FAA has determined that a compliance time of two years for installation 
of the newly designed parts, and 6,000 flight hours for accomplishment 
of the repetitive leak tests, is appropriate.

Cost Impact

    There are approximately 2,900 Model 737 series airplanes of the 
affected design in the worldwide fleet. The FAA estimates that 1,350 
airplanes of U.S. registry would be affected by this proposed AD.
    The 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 per airplane, per test.
    The 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.
    The 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.
    The replacement of the PCU that is proposed in this AD action would 
take approximately 9 work hours per airplane to accomplish, at an 
average labor rate of $60 per work hour. Required parts would be 
supplied by the manufacturer at no cost to operators. Based on these 
figures, the cost impact of the proposed replacement of the PCU on U.S. 
operators is estimated to be $729,000, or $540 per airplane.
    The replacement of the vernier control rod bolt that is proposed in 
this AD action would take approximately 1 work hour per airplane to 
accomplish, at an average labor rate of $60 per work hour. Required 
parts would be supplied by the manufacturer at no cost to operators. 
Based on these figures, the cost impact of the proposed replacement of 
the vernier control rod bolt on U.S. operators is estimated to be 
$81,000, or $60 per airplane.
    The leak tests that are proposed in this AD action would 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 proposed requirements of this AD on U.S. operators is 
estimated to be $648,000, or $480 per airplane, per leak test.
    The cost impact figures discussed above are based on assumptions 
that no operator has yet accomplished any of the current or proposed 
requirements of this AD action, and that no operator would accomplish 
those actions in the future if this AD were not adopted.

Regulatory Impact

    The regulations proposed herein would 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 
proposal would not have sufficient federalism implications to warrant 
the preparation of a Federalism Assessment.
    For the reasons discussed above, I certify that this proposed 
regulation (1) is not a ``significant regulatory action'' under 
Executive Order 12866; (2) is not a ``significant rule'' under the DOT 
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); 
and (3) if promulgated, 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 copy of the draft 
regulatory evaluation prepared for this action is contained in the 
Rules Docket. A copy of it may be obtained by contacting the Rules 
Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration proposes to amend 
part 39 of the Federal Aviation Regulations (14 CFR part 39) as 
follows:

PART 39--AIRWORTHINESS DIRECTIVES

    1. The authority citation for part 39 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

    2. 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), to read as follows:

Boeing: Docket 97-NM-29-AD. Supersedes AD 94-01-07, Amendment 39-
8789, and AD 96-23-51, Amendment 39-9818.

    Applicability: All Model 737-100, -200, -300, -400, and -500 
series airplanes, certificated in any category.

    Note 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 (g) 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.
    Compliance: Required as indicated, unless accomplished 
previously.
    To prevent uncommanded movements of the rudder, and consequent 
reduced controllability of the airplane, accomplish the following:

Restatement of Requirements of AD 94-01-07:

    (a) Within 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.
    (1) If no discrepancy, as described in paragraph 3.B. of the 
Service Letter, is

[[Page 12129]]

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 paragraph (a) of this AD.
    (b) Replacement 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.

Restatement of Requirements of AD 96-23-51:

    (c) Within 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.
    (1) If the rudder PCU operates properly, repeat the test 
thereafter at intervals not to exceed 250 flight hours.
    (2) If 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.

New Requirements of this AD:

    (d) Within 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.
    (1) Replace any main rudder PCU having Boeing part number (P/N) 
65-44861-( ) or P/N 65C37052-( ) with a new main rudder PCU that has 
been approved by the Manager, Seattle ACO.
    (2) Replace the vernier control rod bolt having Boeing P/N 69-
27229-( ) with a new bolt that has been approved by the Manager, 
Seattle ACO.
    (e) Perform 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.

    Note 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.

    (1) For 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 6,000 flight hours.
    (2) For airplanes other than those identified in paragraph 
(e)(1) of this AD: Within 6,000 flight hours after accomplishment of 
the replacement required by paragraph (d)(1) of this AD, and 
thereafter at intervals not to exceed 6,000 flight hours.
    (f) Once 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 a newly designed unit.
    (g) 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 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.

    Note 3: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

    (h) Special 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.

    Issued in Renton, Washington, on March 7, 1997.
Ronald T. Wojnar,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 97-6437 Filed 3-13-97; 8:45 am]
BILLING CODE 4910-13-P