[Federal Register Volume 61, Number 168 (Wednesday, August 28, 1996)]
[Proposed Rules]
[Pages 44234-44237]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-21879]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 96-NM-147-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 adoption of a new airworthiness 
directive (AD) that is applicable to all Boeing Model 737-100, -200, -
300, -400, and -500 series airplanes. This proposal would require 
operational tests of the standby rudder power control unit (PCU) to 
ensure correct operation of the rudder, and correction of any 
discrepancy found; and repetitive inspections to detect galling on the 
input shaft and bearing of the standby PCU, and replacement of the 
standby rudder actuator with a serviceable actuator, if necessary. This 
proposal also would require eventual replacement of the input bearing 
of the standby PCU with an improved bearing, which constitutes 
terminating action for the inspections to detect galling. This proposal 
is prompted by a review of the design of the flight control systems on 
Model 737 series airplanes. The actions specified by the proposed AD 
are intended to prevent corrosion of the servo valve and bypass valve 
sleeves of the standby PCU, and galling on the input shaft and bearing 
of the standby PCU, which could result in uncommanded movement of the 
rudder or increased pedal forces. These conditions, if not corrected, 
could result in reduced controllability of the airplane.

DATES: Comments must be received by October 24, 1996.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 96-NM-147-AD, 1601 Lind Avenue, SW., 
Renton, Washington 98055-4056. Comments may be inspected at this

[[Page 44235]]

location between 9:00 a.m. and 3:00 p.m., Monday through Friday, except 
Federal holidays.
    The service information referenced in the proposed rule may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the FAA, 
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington.

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 96-NM-147-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. 96-NM-147-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    In October 1994, the FAA organized a team to conduct a Critical 
Design Review (CDR) of the flight control systems installed on Boeing 
Model 737 series airplanes in an effort to confirm the continued 
operational safety of these airplanes. The formation of the CDR team 
was prompted by questions that arose following an accident involving a 
Model 737-200 series airplane that occurred near Colorado Springs, 
Colorado, and one involving a Model 737-300 series airplane that 
occurred near Pittsburgh, Pennsylvania. The CDR team's analysis of the 
flight control systems was performed independent of the investigations 
of these accidents, which are conducted by the National Transportation 
Safety Board (NTSB). The cause of the accidents has not yet been 
determined.
    The CDR team was composed of representatives from the FAA, the 
NTSB, other U.S. government organizations, and foreign airworthiness 
authorities. The team analyzed conclusions from previous reviews and 
analyses of the design of the flight control systems on Model 737 
series airplanes. The team completed its review in May 1995. The 
recommendations of the team include various changes to the design of 
the flight control systems of these airplanes, as well as correction of 
any design deficiencies. This proposed AD is one of nine rulemaking 
actions being issued by the FAA to address the recommendations of the 
CDR team.

Reports Received by FAA

    The FAA received a report indicating that significant corrosion was 
found on the outer diameter and radial passages of both the servo valve 
and bypass valve sleeves of the standby rudder power control unit 
(PCU). Although the bypass valve was functional, the servo valve was 
seized, and the input ball of the input shaft was sheared. The slides 
removed from these valves also exhibited heavy corrosion deposits on 
the outer diameter surfaces and gray/black hydraulic fluid stains 
within the standby PCU. In addition, water was found in the PCU. The 
corrosion has been attributed to high moisture content in the standby 
PCU, which may have condensed in the PCU prior to installation and was 
not flushed out by hydraulic fluid cycling. Investigation of the 
fracture surface indicated that the fracture of the ball of the input 
shaft was caused by stress corrosion cracking. When the standby rudder 
system is powered, and the servo valve of the standby PCU is jammed in 
an off neutral position, uncommanded movement of the rudder could 
occur.
    The FAA also received reports of galling on the input shaft and 
bearing of the standby rudder PCU. Galling is defined as fretting or 
chafing of a mating surface by sliding contact with another surface or 
body. The friction between the sliding surfaces causes the material 
from one surface to be welded or deposited onto the other surface, 
which ultimately destroys the surface area, and forces an uncommanded 
motion of the rudder. In response to these reports, the airplane 
manufacturer increased the clearance between the input shaft and 
bearing. However, this change did not eliminate the galling condition. 
Further, some reported incidents of uncommanded yaw were traced to 
galling on the input shaft and bearing. Galling on the input shaft and 
bearing of the standby rudder PCU could result in increased rudder 
pedal forces and erratic operation of the yaw damper.
    Uncommanded movement of the rudder due to corrosion of the servo 
valve and bypass valve sleeves of the standby rudder PCU, or increased 
rudder pedal forces and uncommanded motion of the rudder, due to 
galling on the input shaft and bearing of the standby PCU; if not 
corrected, could result in reduced controllability of the airplane.

FAA's Findings

    In light of this information, the FAA finds that certain procedures 
and corrective actions must be accomplished to ensure correct operation 
of the rudder when the standby hydraulic system is powered, and to 
detect galling on the input shaft and bearing of the standby rudder 
PCU. In addition, the FAA finds that the input bearing of the standby 
PCU must be replaced eventually with an improved bearing. The FAA has 
determined that these actions are necessary to ensure the safety of the 
affected fleet.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Service Letter 737-SL-27-
103, dated October 13, 1995, which describes procedures for repetitive 
operational tests to cycle hydraulic fluid through the standby rudder 
PCU and to ensure correct operation of the rudder when the standby 
hydraulic system is powered, and correction of any discrepancy found. 
Cycling of fluid through the standby rudder PCU will minimize the 
possibility of moisture collection and corrosion within the unit.

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, the 
proposed AD would

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require repetitive operational tests to cycle hydraulic fluid through 
the standby rudder PCU and to ensure correct operation of the rudder 
when the standby hydraulic system is powered, and correction of any 
discrepancy found. The operational tests and correction of 
discrepancies would be required to be accomplished in accordance with 
the service letter described previously.
    Additionally, the proposed AD would require repetitive inspections 
to detect galling on the input shaft of the standby rudder PCU, and 
replacement of the standby rudder actuator with a serviceable actuator, 
if necessary. The actions would be required to be accomplished in 
accordance with certain procedures specified in this proposed AD.
    The proposed AD also would require eventual replacement of the 
input bearing of the standby rudder PCU with an improved bearing. 
Accomplishment of the replacement constitutes terminating action for 
the repetitive inspections to detect galling on the input shaft of the 
standby rudder PCU. The replacement would be required to be 
accomplished in accordance with a method approved by the FAA.

Explanation of Proposed Compliance Times

    In developing an appropriate compliance time for the proposed 
operational tests, the FAA's intent is that the actions be performed 
during a regularly scheduled maintenance visit for the majority of the 
affected fleet, when the airplanes would be located at a base where 
special equipment and trained personnel would be readily available, if 
necessary. The FAA has determined that an interval of 250 hours time-
in-service corresponds closely to the interval representative of most 
of the affected operators' regularly scheduled ``A'' checks. The FAA 
considers that this interval represents an interval in which the tests 
can be accomplished in a timely manner within the fleet and still 
maintain an adequate level of safety.
    Similarly, in developing an appropriate compliance time for the 
proposed inspections to detect galling, the FAA's intent is that the 
inspections be accomplished during a regularly scheduled ``C'' check of 
the airplane. In addition, the FAA considered the availability of 
replacement standby rudder actuators that may be needed if galling is 
detected. The FAA finds that an interval of 3,000 hours time-in-service 
correlates with that representative of normal maintenance schedules and 
will provide an acceptable level of safety.

Cost Impact

    There are approximately 2,830 Model 737 series airplanes of the 
affected design in the worldwide fleet. The FAA estimates that 1,037 
airplanes of U.S. registry would be affected by this proposed AD
    It would take approximately 1 work hour per airplane to accomplish 
the proposed operational tests, at an average labor rate of $60 per 
work hour. Based on these figures, the cost impact of the proposed 
operational tests on U.S. operators is estimated to be $62,220, or $60 
per airplane, per test cycle.
    The FAA estimates that it would take approximately 2 work hours per 
airplane to accomplish the proposed inspections, at an average labor 
rate of $60 per work hour. Based on these figures, the cost impact of 
the proposed inspections on U.S. operators is estimated to be $124,440, 
or $60 per airplane, per inspection cycle.
    The cost impact figures discussed above are based on assumptions 
that no operator has yet accomplished any of the proposed requirements 
of this AD action, and that no operator would accomplish those actions 
in the future if this AD were not adopted.
    The FAA currently has no specific cost estimates associated with 
the proposed replacement of the input bearing, since the improved 
bearing has not been developed yet. The proposed compliance time of 3 
years for this replacement should allow the time necessary for design 
of an acceptable replacement part, and should coincide with normal 
maintenance schedules, thereby minimizing the costs and schedule impact 
of such a change on operators. As indicated earlier in this preamble, 
the FAA specifically invites the submission of comments and other data 
regarding this economic aspect of the proposal.

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 adding the following new 
airworthiness directive:

Boeing: Docket 96-NM-147-AD.

    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 (d) 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 movement of the rudder or increased 
rudder pedal forces, and consequent reduced controllability of the 
airplane, accomplish the following:
    (a) Within 250 hours time-in-service after the effective date of 
this AD, and thereafter at intervals not to exceed 250 hours time-
in-service: Perform an operational test to cycle hydraulic fluid 
through the standby rudder power control unit (PCU) and to ensure 
correct operation of the rudder when the standby hydraulic system is 
powered, in accordance with Boeing Service Letter 737-SL-27-103, 
dated October 13, 1995. Prior to

[[Page 44237]]

further flight, correct any discrepancy that is found, in accordance 
with the service letter.
    (b) Within 3,000 hours time-in-service after the effective date 
of this AD, and thereafter at intervals not to exceed 3,000 hours 
time-in-service: Perform an inspection to detect galling on the 
input shaft and bearing of the standby rudder PCU by accomplishing 
paragraphs (b)(1) through (b)(10) of this AD.
    (1) Shut off all hydraulic power.
    (2) Gain access to the standby rudder actuator.
    (3) Disconnect the input rod from the standby actuator.
    (4) Using a push/pull spring scale (minimum +/- 10% accuracy at 
1.0 pound; preferably one having a peak load memory function), push 
on the standby rudder actuator input lever with sufficient force to 
move the lever from the neutral position up to, but not touching, 
the aft stop. The scale must be contacting the input lever at 
approximately the clevis bolt centerline. While applying the load 
required to move the lever, the scale must be maintained at an angle 
perpendicular to the lever arm (not to exceed 20 degrees from 
perpendicular). The force required to move the input lever 
throughout this range of motion must not exceed one pound.
    (5) Repeat the test specified in paragraph (b)(4) of this AD, 
moving the lever arm from the aft stop position up to the forward 
stop, but not touching. The force required to move the input lever 
throughout this range of motion must not exceed one pound.
    (6) Repeat the test specified in paragraph (b)(4) of this AD, 
moving the lever arm from the forward stop position back to the 
neutral position. The force required to move the input lever 
throughout this range of motion must not exceed one pound.
    (7) If the actuator force encountered during any of the 
procedures required by paragraph (b)(4), (b)(5), or (b)(6) of this 
AD exceeds one pound, prior to further flight, replace the standby 
rudder actuator with a serviceable actuator, and test the standby 
rudder actuator in accordance with the procedure specified in 
paragraph (b)(9) of this AD.
    (8) If the actuator force encountered during any of the 
procedures required by paragraph (b)(4), (b)(5), or (b)(6) of this 
AD is one pound or less, prior to further flight, reconnect the 
input rod to the standby rudder actuator, and test the standby 
rudder actuator in accordance with the procedure specified in 
paragraph (b)(9) of this AD.
    (9) Perform a functional test of the standby rudder actuator in 
accordance with Maintenance Manual 737-100/-200, Chapter 27-21-141, 
removal/installation (for Model 737-100 and -200 series airplanes); 
or maintenance Manual 737-300/-400/-500, Chapter 27-21-24, removal/
installation (for Model 737-300, -400, and -500 series airplanes).
    (10) Restore the airplane to its normal condition.
    (c) Within 3 years after the effective date of this AD, replace 
the input bearing of the standby rudder PCU with an improved bearing 
in accordance with a method approved by the Manager, Seattle 
Aircraft Certification Office (ACO), FAA, Transport Airplane 
Directorate. Accomplishment of the replacement terminates the 
repetitive inspections required by paragraph (b) of this AD.
    (d) 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 2: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

    (e) 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 August 21, 1996.
Ronald T. Wojnar,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 96-21879 Filed 8-23-96; 9:01am]
BILLING CODE 4910-13-U