[Federal Register Volume 62, Number 85 (Friday, May 2, 1997)]
[Rules and Regulations]
[Pages 24008-24013]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-11200]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 96-NM-150-AD; Amendment 39-10010; AD 97-09-14]
RIN 2120-AA64
Airworthiness Directives; Boeing Model 737-100, -200, -300, -400,
and -500 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 all Boeing Model 737-100, -200, -300, -400, and -500
series airplanes, that requires an inspection of reworked aileron/
elevator power control units (PCU's) and rudder PCU's to determine if
reworked PCU manifold cylinder bores containing chrome plating are
installed, and replacement of the cylinder bores with bores that have
been reworked using the oversize method or the steel sleeve method, if
necessary. This amendment is prompted by a review of the design of the
flight control systems on Model 737 series airplanes. The actions
specified by this AD are intended to prevent a reduced rate of movement
of the elevator, aileron, or rudder due to contamination of hydraulic
fluid from chrome plating chips; such reduced rate of movement, if not
corrected, could result in reduced controllability of the airplane.
DATES: Effective June 6, 1997.
The incorporation by reference of certain publications listed in
the regulations is approved by the Director of the Federal Register as
of June 6, 1997.
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: Don Kurle, Senior 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) 227-2798; fax (206) 227-1181.
SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal
Aviation Regulations (14 CFR part 39) to include an airworthiness
directive (AD) that is applicable to all Boeing Model 737-100, -200, -
300, -400, and -500 series airplanes was published in the Federal
Register on August 28, 1996 (61 FR 44241). That action proposed to
require an inspection of the aileron/elevator power control units (PCU)
and the rudder PCU to determine if reworked PCU manifold cylinder bores
containing chrome plating are installed, and replacement of the
cylinder bores with bores that have been reworked using the oversize
method or the steel sleeve method, if necessary.
Interested persons have been afforded an opportunity to participate
in the making of this amendment. Due consideration has been given to
the comments received.
Support for the Proposal
One commenter supports the proposed rule.
[[Page 24009]]
Request to Revise Statement of Findings of Critical Design Review
Team
One commenter requests the second paragraph of the Discussion
section that appeared in the preamble to the proposed rule be revised
to accurately reflect the findings of the Critical Design Review (CDR)
team. The commenter asks that the FAA delete the one sentence in that
paragraph, which read: ``The recommendations of the team include
various changes to the design of the flight control systems of these
airplanes, as well as correction of certain design deficiencies.'' The
commenter suggests that the following sentences should be added: ``The
team did not find any design issues that could lead to a definite cause
of the accidents that gave rise to this effort. The recommendations of
the team include various changes to the design of the flight control
systems of these airplanes, as well as incorporation of certain design
improvements in order to enhance its already acceptable level of
safety.''
The FAA does not find that a revision to this final rule in the
manner suggested by the commenter is necessary, since the Discussion
section of a proposed rule does not reappear in a final rule. The FAA
acknowledges that the CDR team did not find any design issue that could
lead to a definite cause of the accidents that gave rise to this
effort. However, as a result of having conducted the CDR of the flight
control systems on Boeing Model 737 series airplanes, the team
indicated that there are a number of recommendations that should be
addressed by the FAA for each of the various models of the Model 737.
In reviewing these recommendations, the FAA has concluded that they
address unsafe conditions that must be corrected through the issuance
of AD's. Therefore, the FAA does not concur that these design changes
merely ``enhance [the Model 737's] already acceptable level of
safety.''
Requests To Withdraw the Proposal: No Supporting Data
One commenter contends that the proposal is not justified since it
cannot be supported by data. The commenter does not consider that the
proposal contributes to improving the safety aspects of Model 737
airplanes. The commenter states that the CDR team's report does not
indicate that there is any evidence to tie the referenced service
documents to any in-service problems or accidents. The commenter adds
that the FAA has not indicated it has reviewed any routine component
tear-down reports that would support the proposed actions. The
commenter concludes that the FAA does not understand the enormity of
the proposed action. A second commenter states that it has incorporated
the repair on several PCU's and has not witnessed a single failure of
the chrome plating of the cylinder bore. The FAA infers from these
remarks that the commenters request the proposed rule be withdrawn.
In support of its request to withdraw the proposal, the Air
Transport Association (ATA) of America, points out that any performance
degradation that might result from chrome plate separation would be
determined readily by flight crews prior to departure. The ATA also
indicates that if the plating repair were suspect, an incident
involving separation would have been identified early in the service
life of the units. The ATA contends that service experience and tests
conducted by the National Transportation Safety Board (NTSB) confirm
that there is no justification to consider this issue as an existing
airworthiness concern.
The FAA does not concur with the requests of these commenters to
withdraw the proposal. The FAA has received at least five reports from
operators of Model 737 series airplanes indicating that the chrome
plating separated from reworked cylinder bores of the aileron/elevator
PCU's. A number of aileron/elevator and rudder PCU's were repaired
using chrome plating on the aluminum cylinder bores. Separation of the
chrome plating could result in contamination of hydraulic fluid from
chrome plating chips. Such
[[Page 24010]]
contamination can result in a reduced rate of movement of the elevator,
aileron, or rudder, and consequent reduced controllability of the
airplane. The FAA's position is that this condition is a potential
unsafe condition that must be corrected in order to ensure the safety
of the affected fleet.
The FAA acknowledges that in some cases (depending on when chrome
plate separation occurred), prior to departure, flight crews could
determine any performance degradation that might result from chrome
plate separation. However, if the separation occurred during flight,
the flight crew may be unaware of the occurrence and, when the flight
crew's workload is heavy, the crew's ability to control the airplane
may be reduced. The FAA considers that this presents a potential unsafe
condition that must be corrected.
No commenter presented evidence that would indicate chrome
separation occurs early in the life of the unit. Further, the FAA
assumes the NTSB testing discussed by one commenter refers to chip
shear testing accomplished by the NTSB on the rudder PCU. While it
appears that a chrome chip should be able to be sheared by the
hydraulic action of the PCU and not cause a PCU jam, chrome chips can
still contaminate the interior of the rudder, aileron, and elevator
PCU's, which could cause sluggish flight control operation.
Request To Withdraw the Proposal: Revise Component Maintenance/
Overhaul Manuals
One commenter recommends revising the proposal to require a
Component Maintenance Manual (CMM) revision to require inspection at
the next shop visit to identify any units with chrome bores and rework
those in accordance with the service letter in order to eliminate what
the commenter finds to be an enormous financial and operational impact
that would be imposed on operators if the proposed rule is issued.
One commenter, Boeing, indicates that separation of chrome plating
from aluminum cylinder bores has not been a significant in-service
problem; in fact, there have been no reports of chrome plating
separation since 1985. Boeing asserts that since no direct safety
hazard related to chrome plating has been established, the proposal
should be withdrawn and, instead, removal of chrome plating should be
required through a revision to the PCU overhaul manuals for the rudder
and aileron/elevator.
The FAA does not concur with the commenters' requests to withdraw
this AD and revise the component maintenance or overhaul manuals
instead. The FAA considers issuance of an AD necessary in this instance
since an unsafe condition has been identified, and AD's are the means
by which accomplishment of procedures and adherence to specific
compliance times are made mandatory to correct that unsafe condition.
While the FAA has no objection to Boeing revising the component
maintenance or overhaul manuals to provide a procedure for an
inspection to identify any units with chrome bores and rework of those
units in accordance with the service letter, or for removal of chrome
plating, such revision will not affect the requirements of this AD.
Requests To Limit Applicability to Certain PCU's
In lieu of withdrawing the proposal, several commenters suggest
limiting the applicability of the proposed AD to certain PCU's:
One commenter states that no PCU's containing chrome plated
manifold cylinder bores were produced or reworked after April 1, 1985
(the date of issuance of Boeing Service Letter 737-SL-27-30);
therefore, only those PCU's manufactured or reworked prior to that date
should be subject to the requirements of the proposal.
Two other commenters state that, as of June 5, 1985, the chrome
plating procedure was removed from the PCU overhaul manuals. One of
these commenters asserts that any PCU's manufactured after that date
would not have been reworked or manufactured with chrome plating in the
cylinder bores; therefore, those PCU's should be excluded from the
applicability of the proposal.
Another commenter states that the applicability of the proposal
should be limited only to those units manufactured prior to 1980. The
commenter does not provide justification for selecting 1980 as a cutoff
date. This commenter adds that a records search should be allowed to
confirm that no chrome plate repairs to the bore have been
accomplished.
One commenter states that inspection should be required only for
valve bodies made from 2024 aluminum, since the repair procedures were
changed in 1987 and there have been no problems since the original
issue of the service letter. The only reported problems have been with
the old-style valve bodies made from 2024 aluminum. (Production of the
7075 aluminum valve body started in the late 1970's.)
Boeing suggests that only those PCU's manufactured prior to June
1984 should be included in the applicability of the proposal. This date
is one year prior to the revisions of the overhaul manual, which
eliminated chrome plating as a repair procedure. (Since the average
overhaul interval is approximately 15,000 flight hours, it is
conservative to assume that no overhauls would occur within one year of
manufacture.) Boeing indicates that only serial numbers prior to 1252A
(for the rudder PCU) and those prior to 5360A (for the aileron/elevator
PCU) would need to be inspected. In addition, Boeing recommends that
any aileron/elevator actuators having a part number that includes an
``ss'' should be eliminated from the applicability of the proposal
since those PCU's have a steel sleeve (i.e., those PCU's could not have
chrome plating on aluminum).
One commenter states that the proposed rule should include an
exemption for PCU's that have been inspected previously and found to
have no chrome, or units on which the steel sleeve repair has been
incorporated.
The FAA concurs that the applicability of the final rule should be
revised. At the time the proposal was issued, the part and serial
numbers of PCU's that have been overhauled or repaired were not
available; therefore, the FAA was unable to include them in the
applicability of the proposal. However, Boeing has provided this
information in its comments to the proposed rule. The FAA has revised
the applicability of the final rule by specifying the part and serial
numbers of affected PCU's. In effect, such revision limits the
applicability of this AD to those PCU's manufactured prior to June
1984, and specifically excludes those aileron and elevator PCU's having
a part number that contains an ``ss'' (i.e., those that have been
reworked with a steel sleeve). In addition, paragraph (a) of the final
rule has been revised to specify the part and serial numbers of
affected PCU's.
As for allowing a records search to confirm that no chrome plate
repairs to the bore have been accomplished, the FAA finds that no
change to the final rule is necessary. The applicability of this final
rule specifies that the AD applies only to certain Model 737 series
airplanes that are equipped with an aileron, elevator, or rudder PCU
having a particular part and serial number. This AD does not preclude
an operator from performing a records search to determine if an
airplane in its fleet is subject to the requirements of this AD.
Request To Limit Applicability of Proposal to Rudder PCU's
One commenter requests that the requirements of the proposal be
limited to rudder PCU's only, rather than
[[Page 24011]]
aileron, elevator, and rudder PCU's. The commenter states that the
adoption of the proposed rule would overburden existing competent
repair facilities and would expose the airlines and the public to a
hazardous condition far greater than any condition that exists
presently from the identified unsafe condition. This commenter believes
the proposal implies that a simple inspection can determine the status
of chrome plated bores on the affected units; however, the commenter
indicates that, due to the fact that the chrome sleeving process was
used in both manufacturing and repair of the units, that implication is
incorrect. The commenter states that limiting the inspection to rudder
PCU's--especially those manufactured before chrome sleeving was
discontinued--would reduce the risk of unintended consequences
resulting from the overburdening of competent repair facilities.
The FAA does not agree that the applicability of the AD should be
revised to include only rudder PCU's. The FAA has determined that
sluggish ailerons and elevators pose a potential unsafe condition
similar to that of the rudder. Therefore, the FAA finds that it is
appropriate to address this potential unsafe condition as it applies to
aileron and elevator PCU's, as well as rudder PCU's.
Requests To Extend Compliance Time
The ATA, on behalf of several of its members, requests that the
proposed compliance time be extended from 18 months to at least five
years.
One ATA member states that it would be physically impossible and
unnecessary for operators to accomplish the required actions within the
proposed compliance time of 18 months. This commenter indicates that a
review of its maintenance records for the past 15 years showed that it
has never repaired either an aileron or rudder cylinder due to a worn
bore.
One ATA member states that it is important that ample time be
provided to accomplish the intent of the proposal because such
accomplishment requires the removal of PCU's from airplanes and partial
disassembly of PCU's in order to determine the type of rework of the
cylinder bore, which requires scheduling, airplane downtime, unit
turnaround time, and availability of spare PCU's. Another ATA member
states that removal of all PCU's would require industry to process
almost 750 PCU's per month for the next 18 months.
One commenter asks that the compliance time be extended to the next
shop overhaul in light of the fact that there is no documented unsafe
condition or in-service concern.
Boeing suggests an extension of the compliance time to five years
or 15,000 flight hours so that the majority of PCU's can be inspected
as a part of normal maintenance actions. Boeing adds that the
possibility of maintenance errors during PCU replacement will result in
a net degradation in airplane safety as a result of the inspection
schedule established by the proposed rule.
The FAA concurs with the commenters' requests to extend the
compliance time. In light of the information presented by the
commenters, the FAA finds that extending the compliance time to within
five years or 15,000 flight hours after the effective date of the AD,
or at the next time the PCU is sent to a repair facility (whichever of
these times occurs first), will not adversely affect safety. In
addition, this revised compliance time will allow the inspection to be
performed at a base during regularly scheduled maintenance where
special equipment and trained maintenance personnel will be available
if necessary. Paragraph (a) of the final rule has been revised to
specify this revised compliance time.
Request To Revise Cost Impact Information
Two commenters believe that the cost impact information presented
in the proposal has been underestimated greatly, and that the proposal
places an unreasonable financial burden on operators.
One of these commenters indicates that the inspection of the PCU
cylinder bores requires removal of PCU's from the airplane and
disassembly of those units. The commenter presents the following cost
estimates:
28 work hours for removal and reinstallation of five PCU's
per airplane;
20 work hours (per PCU) for disassembly, inspection,
assembly, and testing; and
$1,100 (per PCU) for parts required for reassembly of the
units after inspection. Using these figures, the commenter estimates
the cost impact on U.S. operators to be approximately $14.3 million, or
$13,180 per airplane.
The other commenter states that the proposal does not account for
any return-to-service checks after the units have been changed,
overhaul costs once the units are in the shop, or costs of frequent
repetitive checks and short compliance periods for changing the units.
The FAA infers from these remarks that the commenters request the
cost impact information, below, be revised.
The FAA does not concur. The cost impact information, below,
describes only the ``direct'' costs of the specific actions required by
this AD. The number of work hours necessary to accomplish the required
action (i.e., the inspection), specified as 5 in the cost impact
information, was provided to the FAA by the manufacturer based on the
best data available to date. This number represents the time necessary
to perform only the action (inspection) that is actually required by
this AD. The FAA recognizes that, in accomplishing the requirements of
any AD, operators may incur ``incidental'' costs in addition to the
``direct'' costs. The cost analysis in AD rulemaking actions, however,
typically does not include incidental costs, such as the time required
to gain access and close up; planning time; or time necessitated by
other administrative actions. Because incidental costs may vary
significantly from operator to operator, they are almost impossible to
calculate.
Additionally, the revised compliance time presented in this AD
should coincide with normal overhaul schedules (within 5 years or
15,000 flight hours). The FAA estimates that the PCU inspections (and
any ``on condition'' replacements) will be accomplished during normal
overhauls, which will minimize the economic impact on operators and
accomplish the safety objectives addressed in this AD.
Request To Clarify Inspection of Reworked or Overhauled PCU's
One commenter requests that the FAA revise the proposal to clarify
that only reworked or overhauled PCU's must be inspected. The commenter
suggests the following wording for the Summary section of the preamble
to the proposal: ``* * * This proposal would require an inspection of
reworked aileron/elevator PCU's and rudder PCU's to determine * * *.''
The commenter asks that paragraph (a) of the proposal be revised to
state clearly that ``reworked'' or ``overhauled'' PCU's must be
inspected. The commenter considers that foreign operators and
airworthiness authorities may misinterpret the intent of this AD as
proposed.
The FAA concurs with the commenter's request. The intent of this
final rule is that operators inspect only reworked or overhauled PCU's
to determine if chrome plating is applied in the cylinder bores. The
Summary section of the preamble to the final rule has been revised to
clarify this intent. Additionally, paragraph (a) of the final
[[Page 24012]]
rule has been revised to specify that only reworked or overhauled PCU's
must be inspected.
Request To Address Cause of Chrome Plating Separation
One commenter contends that chrome plating on aluminum is
successful (the component will have the required integrity for
airworthiness) when the base metal has been subjected to the proper
pretreatment (cleaned), proper chrome plating, and properly executed
post plating operations such as finish grinding and nondestructive
testing. The commenter states that poor maintenance techniques,
environmental factors, or overlooked design parameters present a more
relevant and detrimental concern to flight safety than a properly
applied chrome on aluminum repair. The commenter believes that removal
of the chrome repair is treating the effect without fully understanding
the cause and addressing the underlying issues.
The FAA infers from these remarks that the commenter requests that
the FAA address the cause for chrome plating separation, rather than
remove the chrome plating repair as an option.
The FAA agrees that if the repair is done properly, it could
provide satisfactory service. In any event, the FAA is aware of
instances of failure of the repair. The FAA finds that issuance of this
AD is necessary to ensure that all chrome plating repairs are removed
from the affected Model 737 fleet so that an acceptable level of safety
for these airplanes is attained. However, the FAA would consider a
request for approval of an alternative method of compliance, provided
that a satisfactory repeatable repair procedure using chrome plating
can be developed.
Request To Revise Preamble of Proposal
Boeing requests that the wording of the ``Reports Received by FAA''
section of the preamble to the proposed rule be revised. The commenter
notes that this section of the preamble states that chrome plating
chips could block or jam the rudder PCU control valve and thereby cause
partial or full rudder deflection. Boeing indicates that this statement
is incorrect. Boeing remarks that testing conducted by the NTSB systems
group showed that a chrome chip in the control valve could be sheared
by a force of six pounds. This force would be provided by the rudder
feel and centering unit (in combination with system friction) before
any significant rudder deflected had occurred.
The commenter also states that this section of the preamble refers
only to the rudder PCU, but also should refer to the aileron and
elevator PCU's.
The FAA concurs with the remarks submitted by the commenter.
However, the section of the preamble to the proposed rule referenced by
the commenter does not reappear in this final rule. Therefore, no
change to the final rule is necessary.
Request To Correct PCU Part Number
One commenter requests that the part number referenced in the
proposal for the rudder PCU be corrected to 65-44861. The FAA concurs
with this request. The FAA has revised paragraphs (a) and (c) of this
final rule to correct this inadvertent typographical error.
Conclusion
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
increase the economic burden on any operator nor increase the scope of
the AD.
Cost Impact
There are approximately 2,675 Model 737 series airplanes of the
affected design in the worldwide fleet. The FAA estimates that 1,091
airplanes of U.S. registry will be affected by this AD, that it will
take approximately 5 work hours per airplane to accomplish the required
inspection, and that the average labor rate is $60 per work hour. Based
on these figures, the cost impact of the AD on U.S. operators is
estimated to be $327,300, or $300 per airplane.
The cost impact figure discussed above is 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.
Should an operator be required to accomplish the necessary
replacement, it would take approximately 18 work hours per airplane to
accomplish, at an average labor rate of $60 per work hour. Required
parts will cost approximately $15,800 per airplane. Based on these
figures, the cost impact of any necessary replacement action is
estimated to be $16,880 per airplane.
Regulatory Impact
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 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:
97-09-14 Boeing: Amendment 39-10010. Docket 96-NM-150-AD.
Applicability: Model 737-100, -200, -300, -400, and -500 series
airplanes equipped with a rudder power control unit (PCU) having
part number (P/N) 65-44861-( ) and a serial number less than 1252A;
or an aileron or elevator PCU having P/N 65-44761-( ) (except those
having P/N's that contain an ``ss'') and a serial number less than
5360A; 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
[[Page 24013]]
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 a reduced rate of movement of the elevator, aileron,
or rudder, which, if not corrected, could result in reduced
controllability of the airplane, accomplish the following:
(a) Perform an inspection of reworked or overhauled aileron and
elevator PCU's having P/N 65-44761-( ) (except those having P/N's
that contain an ``ss'') and a serial number less than 5360A; and
rudder PCU's having part number (P/N) 65-44861-( ) and a serial
number less than 1252A; to determine if reworked PCU manifold
cylinder bores containing chrome plating are installed, in
accordance with Boeing Service Letter 737-SL-27-30, dated April 1,
1985. Accomplish the inspection at the earlier of the times
specified in paragraphs (a)(1) and (a)(2) of this AD.
(1) Within 5 years or 15,000 flight hours after the effective
date of this AD, whichever occurs first.
(2) At the next time the PCU is sent to a repair facility.
(b) If any reworked PCU manifold cylinder bores containing
chrome plating are installed: Prior to further flight, replace the
cylinder bores with bores that have been reworked using the oversize
method or the steel sleeve method specified in Boeing
Service Letter 737-SL-27-30, dated April 1, 1985. Accomplish the
replacement in accordance with the service letter.
(c) As of the effective date of this AD, no person shall install
a reworked PCU manifold cylinder bore containing chrome plating on
an aileron or elevator PCU having P/N 65-44761-( ), or on a rudder
PCU having P/N 65-44861-( ), of any airplane unless the cylinder
bore has been reworked using the oversize method or the steel sleeve
method specified in Boeing Service Letter 737-SL-27-30, dated April
1, 1985.
(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 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 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.
(f) The inspection and repair shall be done in accordance with
Boeing Service Letter 737-SL-27-30, dated April 1, 1985. 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.
(g) This amendment becomes effective on June 6, 1997.
Issued in Renton, Washington, on April 24, 1997.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 97-11200 Filed 5-1-97; 8:45 am]
BILLING CODE 4910-13-U