[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]


-----------------------------------------------------------------------

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.

-----------------------------------------------------------------------

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