[Federal Register Volume 62, Number 43 (Wednesday, March 5, 1997)]
[Rules and Regulations]
[Pages 9925-9928]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-5158]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 96-NM-146-AD; Amendment 39-9953; AD 97-05-09]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737 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 certain Boeing Model 737 series airplanes, that requires 
replacement of the flow restrictors of the aileron and elevator power 
control units (PCU's) with new flow restrictors. 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 reduced roll and/or pitch rate control of the 
airplane and consequent increased pilot workload as a result of 
fragments from a deteriorated flow restrictor filter screen becoming 
lodged in the PCU.

DATES: Effective April 9, 1997.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of April 9, 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 certain Boeing Model 737 series 
airplanes was published in the Federal Register on August 28, 1996 (61 
FR 44232). That action proposed to require replacement of the flow 
restrictors of the aileron and elevator power control units (PCU's) 
with new flow restrictors.
    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.

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.''

Request To Extend Compliance Time for Replacing Flow Restrictors

    Several commenters request that the proposed compliance time for

[[Page 9926]]

replacement of the flow restrictors be extended.
    The Air Transport Association (ATA) of America, on behalf of 
several of its members, requests that the proposed compliance time for 
accomplishment of paragraph (a) of the proposal be extended from within 
18 months to within five years after the effective date of the AD to 
align with regularly scheduled maintenance (``D'' checks).
    One commenter requests that the compliance time for paragraph (a) 
of the proposal be extended to 24 months to avoid grounding aircraft by 
scheduling maintenance outside of regularly scheduled visits. One ATA 
member requests a 4-year compliance time based on considerations 
including scheduling, airplane downtime, unit turn-around time, and 
availability of spare parts.
    One commenter states that the retrofit requires a 30-day turn-
around time. Another commenter indicates that although the replacement 
takes 3 work hours, it takes 42 total work hours to return the airplane 
to service since the affected units are CAT II sensitive line 
replaceable units. The commenters also point out that there has never 
been an in-service failure of the filter screen. The failure referenced 
in the proposal occurred during a shop functional test at 5,400 pounds 
per square inch (psi) and, in service, the unit would not be subjected 
to operational pressures greater than 3,000 psi. The commenters add 
that there is some uncertainty at this time as to whether the shop test 
should be accomplished at such a high pressure; such a test may cause 
more safety concerns than it addresses.
    One ATA member states that there is no service history or other 
evidence to indicate that the filter screens may fail when subjected to 
3,000 psi, nor is there any history of discrepant PCU operation 
attributed to failure of the filter screens. The commenter indicates 
that the affected PCU's have accumulated an average of 17,400 flight 
hours each (for a total of approximately 17 million flight hours) 
without an in-service failure due to disintegration of the flow 
restrictor filter screens. The commenter believes that an acceptable 
level of safety can be achieved by mandating the replacement of suspect 
flow restrictors at the next PCU overhaul, not to exceed 5 years after 
the effective date of the AD.
    Boeing agrees that, in order to preclude any failures from 
occurring during a functional test following maintenance action, the 
suspect PCU filter screens should be replaced. However, Boeing 
indicates that any maintenance action involving removing, 
disassembling, modifying, and reinstalling the PCU provides opportunity 
for a maintenance error. In addition, Boeing states that any suspect 
filter screens already installed in airplanes are very unlikely to 
fail. Boeing adds that there is added risk if a filter screen failed 
during functional testing, but was not discovered. In view of these 
considerations, Boeing recommends a compliance time of five years or 
15,000 hours.
    One commenter, an operator of affected airplanes of foreign 
registry, requests that the proposed compliance time be extended to 60 
months to allow sufficient time to accomplish the replacement without 
grounding airplanes.
    The FAA concurs with the commenters' request to extend the 
compliance time. The FAA has determined that, in light of the 
information presented by the commenters, the compliance time can be 
extended to five years or 15,000 flight hours (whichever occurs first) 
to allow the replacement to be performed at a base during regularly 
scheduled maintenance where special equipment and trained maintenance 
personnel will be available, if necessary. The FAA does not consider 
that this extension will adversely affect safety. Paragraph (a) of the 
final rule has been revised to specify the extended compliance time.

Request To Extend Compliance Time for Disallowing Installation of Flow 
Restrictors

    The ATA also requests that the proposed compliance time for 
disallowing installation of flow restrictors, as specified in paragraph 
(b) of the proposal, be extended from ``as of the effective date of 
this AD'' to within two years after the effective date of the AD. The 
commenter does not provide specific justification for this request.
    The FAA does not concur. Since the service information referenced 
in this final rule was issued in June 1992, the FAA finds that ample 
opportunity has been provided for removal of the affected flow 
restrictors from operators' inventories and replacement with acceptable 
parts.

Requests To Withdraw the Proposal

    Several commenters request that the proposed rule be withdrawn.
    One commenter believes the proposal is not justified since it 
cannot be supported by data. The commenter indicates the proposal does 
not contribute to improving the safety aspects of Model 737 aircraft. 
The commenter states that the Critical Design Review (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 that 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 concludes that the proposal does not address an 
unsafe condition, even in a worst case situation; that an unsafe 
condition is extremely unlikely to occur in service; and that an unsafe 
condition would most likely be detected during a preflight check.
    Another commenter, Boeing, states that the proposal does not 
correct an unsafe condition; rather, it eliminates the potential for a 
failure condition that could degrade controllability (but not prevent 
continued safe flight and landing). Boeing indicates that there have 
been no reported in-service failures of the suspect filter screens. 
Based on ``the limited safety concern,'' Boeing states that it is 
appropriate for removal and rework of the suspect units as part of 
routine maintenance. Boeing suggests that, if the FAA does not withdraw 
the proposal, the PCU overhaul manual could be revised to provide a 
procedure for inspection and replacement of suspect flow restrictors.
    One commenter states that both Boeing and FAA analyses indicate a 
worst case scenario (with an accompanying independent hydraulic 
failure) to be reversion to manual control--a situation checked many 
times each year during maintenance test flights by carriers. The 
commenter also states that the instance in which the filter collapsed 
occurred at proof test pressures that would never be encountered in 
service (according to Boeing and the component manufacturer).
    The FAA does not concur with these requests to withdraw the 
proposed rule. The FAA has not received any data to demonstrate the 
reliability or strength of the faulty filters. However, the FAA is 
aware that these filters were not strong enough to pass proof testing 
at the PCU manufacturer's facility. Neither the filter or PCU 
manufacturer attempted to quantify the actual strength of the filter 
screen. In addition, while it is true that there have been no reported 
in-service failures, a screen failure would not necessarily be reported 
since the FAA does not require reports of screen failures.
    As discussed in the preamble to the proposal, the FAA has 
determined that sufficient data exist to demonstrate that contamination 
of the PCU at the main control valve due to deterioration of a

[[Page 9927]]

filter screen from a flow restrictor can result in fragments of the 
screen migrating to the main control valve, the damping orifice, or the 
bypass valve. Fragments from a deteriorated flow restrictor filter 
screen could become lodged in the PCU. As suggested by one of the 
commenters, even if manual reversion is checked during maintenance test 
flights several times each year, this condition is considered unsafe 
since it would result in reduced roll and/or pitch rate control of the 
airplane and consequent increased pilot workload. The FAA has 
determined that replacement of the flow restrictors of the aileron and 
elevator PCU's with new flow restrictors, as required by this AD 
action, will adequately address that unsafe condition.
    The FAA has no objection to Boeing revising the PCU overhaul manual 
to provide a procedure for inspection and replacement of suspect flow 
restrictors; such revision will not affect the requirements of this AD.

Request To Allow Records Search

    One commenter requests that a note be added to the proposal to 
specify that compliance with the AD can be demonstrated by 
accomplishing a records search to determine whether any of the suspect 
units are installed on the airplane.
    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 or 
elevator PCU having a particular part 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 Revise Cost Impact Information

    One commenter states that imposition of the proposal would 
overburden competent repair facilities and expose the airlines and the 
flying public to unnecessary risk as a result. In support of its 
position, the commenter states that the cost impact information in the 
proposal indicates the screens referenced in the service letter cited 
in the AD are line replaceable when they are not. The commenter also 
asserts that the costs specified in the proposal are unrealistically 
low; however, the commenter does not provide any suggested cost 
estimates or data to substantiate this remark.
    The FAA infers from these remarks that the commenter requests that 
the cost impact information be revised. In this case, the FAA does not 
concur.
    First, the FAA points out that comments are more likely to be 
persuasive to the extent that they provide specific and detailed 
information regarding actual costs. However, when commenters submit 
simple generalizations about the costs, there is little that the FAA 
can consider.
    Second, 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 actions and 
the cost for required parts were 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 actions 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 FAA realizes that such is the case for this AD, 
since the filter screen is not a line replaceable unit. 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.
    Third, the FAA finds that the revised compliance time specified in 
paragraph (a) of this AD should allow ample time for the required 
actions to be accomplished coincidentally with scheduled major airplane 
inspection and maintenance activities, thereby minimizing any burden on 
repair facilities and any additional costs.

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 change previously 
described. The FAA has determined that this change will neither 
increase the economic burden on any operator nor increase the scope of 
the AD.

Cost Impact

    There are approximately 244 Model 737 series airplanes of the 
affected design in the worldwide fleet. The FAA estimates that 146 
airplanes of U.S. registry will be affected by this AD, that it will 
take approximately 12 work hours per airplane to accomplish the 
required actions, and that the average labor rate is $60 per work hour. 
Required parts will cost approximately $2,960 per airplane. Based on 
these figures, the cost impact of the AD on U.S. operators is estimated 
to be $537,280, or $3,680 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.

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.

[[Page 9928]]

Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding the following new 
airworthiness directive:

97-05-09  Boeing: Amendment 39-9953. Docket 96-NM-146-AD.

    Applicability: Model 737 series airplanes equipped with an 
aileron or elevator power control unit (PCU) having part number (P/
N) 65-45180-29, serial numbers 182 through 1297 inclusive; 
certificated in any category.

    Note 1: Originally, aileron or elevator PCU's having P/N's and 
serial numbers identified in the applicability of this AD may have 
been installed on Model 737 series airplanes having line numbers 
1793 through 2036 inclusive. In addition, some of these PCU's may 
have been used as spares; therefore, specific airplane line numbers 
equipped with such PCU's cannot be provided in this AD.
    Note 2: PCU's having P/N 65-45180-29 consist of a PCU assembly 
having P/N 65-44761-21 plus associated hydraulic fittings. Both PCU 
P/N's 65-45180-29 and 65-44761-21 are serialized. PCU's subject to 
the requirements of this AD may be more easily identified using 
serial numbers for P/N 65-44761-21. The following serial numbers 
correspond to P/N 65-44761-21:

8550A,
8552A,
8556A,
8557A,
8561A,
8563A through 8718A inclusive,
8720A through 8726A inclusive,
8728A through 8745A inclusive,
8749A,
8750A through 8758A inclusive,
8760A through 8873A inclusive,
8876A through 9004A inclusive,
9007A through 9012A inclusive,
9014A through 9040A inclusive,
9042A through 9066A inclusive,
9068A through 9340A inclusive,
9342A through 9388A inclusive,
9390A through 9529A inclusive,
9531A through 9676A inclusive, and
9678A through 9688A inclusive.

    Note 3: 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 (c) 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 reduced roll and/or pitch rate control of the aileron 
and consequent increased pilot workload, accomplish the following:
    (a) Within 5 years or 15,000 flight hours after the effective 
date of this AD, whichever occurs first: Replace the four flow 
restrictors, part number (P/N) JETA1875500D, on the aileron and 
elevator power control units (PCU's), P/N 65-45180-29, serial 
numbers 182 through 1297 inclusive, with flow restrictors having P/N 
JETX0527100B, in accordance with Boeing Service Letter 737-SL-27-71-
A, dated June 19, 1992, including Attachment 1.
    (b) As of the effective date of this AD, no person shall install 
a flow restrictor having P/N JETA1875500D on an aileron or elevator 
PCU having P/N 65-45180-29, serial numbers 182 through 1297 
inclusive, of any airplane.
    (c) 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 4: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

    (d) 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.
    (e) The replacement shall be done in accordance with Boeing 
Service Letter 737-SL-27-71-A, dated June 19, 1992, including 
Attachment 1. 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.
    (f) This amendment becomes effective on April 9, 1997.

    Issued in Renton, Washington, on February 25, 1997.
James V. Devany,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 97-5158 Filed 3-4-97; 8:45 am]
BILLING CODE 4910-13-U