[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
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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