[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
