[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]


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

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.

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

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]
BILLING CODE 4910-13-U