[Federal Register Volume 63, Number 8 (Tuesday, January 13, 1998)]
[Rules and Regulations]
[Pages 1903-1905]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-714]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 97-NM-45-AD; Amendment 39-10283; AD 98-02-01]
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 removing the yaw damper coupler;
replacing its internal rate gyroscope with a new or overhauled unit;
and performing a test to verify the integrity of the yaw damper
coupler, and repair, if necessary. This amendment is prompted by an FAA
determination that requiring replacement of the internal rate gyroscope
will significantly increase the reliability of the yaw damper coupler
system. The actions specified by this AD are intended to prevent sudden
uncommanded yawing of the airplane due to potential failures within the
yaw damper system, and consequent injury to passengers and crewmembers.
EFFECTIVE DATE: February 17, 1998.
ADDRESSES: Information pertaining to this rulemaking action may be
examined at the Federal Aviation Administration (FAA), Transport
Airplane Directorate, Rules Docket, 1601 Lind Avenue, SW., Renton,
Washington.
FOR FURTHER INFORMATION CONTACT: T. Tin Truong, Aerospace Engineer,
Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft
Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-
4056; telephone (425) 227-2552; fax (425) 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 June 25, 1997 (62 FR 34185). That action proposed to
require removing the yaw damper coupler; replacing its internal rate
gyroscope with a new or overhauled unit; and performing a test to
verify the integrity of the yaw damper coupler, and repair, if
necessary.
Interested persons have been afforded an opportunity to participate
in the
[[Page 1904]]
making of this amendment. Due consideration has been given to the
comments received.
Support for the Proposal
Three commenters support the proposal.
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.''
Connection Between the Proposed Rule and AD 97-14-03
Several commenters request that the FAA clarify how the
requirements of AD 97-14-03, amendment 39-10060 (62 FR 34623, June 27,
1997), which requires replacement of the yaw damper coupler with a new
unit (that has yet to be certified), and the proposal affect each
other. The commenters state that the planned design required by AD 97-
14-03 will eliminate the subject of the proposed rule (use of an
electro-mechanical internal rate gyro). One commenter suggests that
accomplishment of the requirements of AD 97-14-03 be considered as an
alternative method of compliance for the actions specified in the
proposal. Another commenter requests that accomplishment of the
requirements of AD 97-14-03 be considered terminating action for the
requirements of the proposal. Further, one commenter requests that a
note be added to the proposed AD indicating whether the actions
required by AD 97-14-03 terminate the test and replacement required by
this proposed rule, or whether those test and replacement requirements
must be continued.
The FAA clarifies that the requirements of this AD and AD 97-14-03
are related. This final rule requires, in part, removal of the yaw
damper coupler, and replacement of its internal rate gyroscope with a
new or overhauled unit. AD 97-14-03 requires replacement of the yaw
damper coupler with a new unit. However, since that new unit has not
yet been certified, the FAA cannot consider the requirements of AD 97-
14-03 to be terminating action for the requirements of this AD, and the
actions required by paragraph (a) of this AD must be accomplished on a
repetitive basis. Once a new yaw damper coupler is designed, developed,
and certified, the FAA may consider installation of that new unit to be
terminating action for the requirements of this AD.
Testing of the Yaw Damper Coupler
One commenter requests clarification concerning the requirement for
testing of the yaw damper coupler specified in the proposal.
Specifically, the commenter asks whether the yaw damper coupler must be
tested in a shop or on the airplane. The commenter also requests
clarification concerning which documents should be referenced for test
procedures (i.e., the Airplane Maintenance Manual or the Component
Maintenance Manual). The commenter also suggests that the test
procedures be provided in a logical sequence based on whether the test
is accomplished on the airplane or in a shop. (The commenter submitted
sample procedures for tests accomplished on the airplane or in a shop.)
The FAA concurs that clarification is necessary. Since the
manufacturer currently has no service information that describes
maintenance procedures for the yaw damper coupler, this AD requires
that maintenance actions be accomplished in accordance with a method
approved by the FAA. Therefore, the individual operator is responsible
to establish logical, sequential maintenance procedures (for
accomplishment of actions either in a shop or on the airplane), and to
submit those procedures to the FAA for approval.
Last Maintenance Activity
One commenter requests clarification of the phrase ``since last
maintenance activity.'' The commenter states that because this phrase
is unclear, the FAA should publish another proposal.
The FAA clarifies that the phrase ``since last maintenance
activity'' applies to maintenance activity in which it was positively
established that the yaw damper coupler was functioning properly and
did not require repair. However, the FAA considers that the phrase is
understandable and is commonly used throughout the aviation industry.
Therefore, the FAA does not concur that this phrase is unclear, or that
publication of another proposal is warranted.
Significant Increase in Reliability of Yaw Damper Coupler System
One commenter, the manufacturer, requests that the word
``significantly'' be omitted from the following phrase, which appeared
in the Discussion section of the proposal: ``The FAA made this
determination * * * replacement of the internal rate gyroscope * * *
will significantly increase the reliability of the yaw damper coupler
system.'' The commenter states that the data it provided the FAA
indicate that there would be a maximum increase in reliability of 30 to
40 percent, which the commenter considers to be a moderate (rather than
significant) increase in reliability.
The FAA does not concur. There are no specific quantitative or
standard definitions of the terms ``significant'' and ``moderate.'' In
this case, the FAA considers it appropriate to define an increase in
reliability of 30 to 40 percent as ``significant.'' Additionally, since
the Discussion section of a proposal does not reappear in a final rule,
the FAA finds that no change to this final rule is necessary.
Rudder Limiting Device
One commenter, the manufacturer, requests that reference to the
``rudder limiting device'' be removed from the Discussion section of
the proposal. The commenter states that the discussion of the rudder
limiting device is confusing
[[Page 1905]]
because it is not related to the yaw damper failure modes. In addition,
the commenter points out that certain information discussing the rudder
limiting devices is outdated.
The FAA acknowledges that there may have been some confusion about
including a discussion of the rudder limiting device; however, the FAA
considers that the confusion would not be so great as to warrant not
including that information. Furthermore, the Discussion section of the
proposal does not reappear in the final rule. Therefore, the FAA finds
that no change to this final rule is necessary.
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 as proposed.
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 proposed AD, that
it would take between 8 and 13 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 $2,500 per airplane. Based
on these figures, the cost impact of the AD on U.S. operators is
estimated to be between $3,251,180 and $3,578,480, or between $2,980
and $3,280 per airplane.
The cost impact figures discussed above are 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, 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:
98-02-01 Boeing: Amendment 39-10283. Docket 97-NM-45-AD.
Applicability: All Model 737-100, -200, -300, -400, and -500
series airplanes, certificated in any category.
Note 1: This AD applies to each airplane identified in the
preceding applicability provision, regardless of whether it has been
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 sudden uncommanded yawing of the airplane due to
potential failures within the yaw damper system, and consequent
injury to passengers and crewmembers, accomplish the following:
(a) Remove the yaw damper coupler, replace the internal rate
gyroscope with a new or overhauled unit, and perform a test to
verify the integrity of the yaw damper coupler, all in accordance
with a method approved by the Manager, Seattle Aircraft
Certification Office (ACO), FAA, Transport Airplane Directorate, at
the applicable time specified in paragraph (a)(1) or (a)(2) of this
AD.
(1) For airplanes on which the yaw damper coupler has
accumulated less than 12,000 hours time-in-service since its last
maintenance activity as of the effective date of this AD: Perform
the actions within 6,000 hours time-in-service after the effective
date of this AD; and thereafter at intervals not to exceed 9,000
hours time-in-service.
(2) For airplanes on which the yaw damper coupler has
accumulated 12,000 or more hours time-in-service since its last
maintenance activity as of the effective date of this AD: Perform
the actions within 3,000 hours time-in-service after the effective
date of this AD; and thereafter at intervals not to exceed 9,000
hours time-in-service.
(b) If the yaw damper coupler fails the test required by
paragraph (a) of this AD, prior to further flight, repair the
coupler in accordance with a method approved by the Manager, Seattle
ACO.
(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 ACO. Operators shall submit
their requests through an appropriate FAA Principal Maintenance
Inspector, who may add comments and then send it to the Manager,
Seattle ACO.
Note 2: Information concerning the existence of approved
alternative methods of compliance with this AD, if any, may be
obtained from the Seattle ACO.
(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) This amendment becomes effective on February 17, 1998.
Issued in Renton, Washington, on January 6, 1998.
James V. Devany,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 98-714 Filed 1-12-98; 8:45 am]
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