[Federal Register Volume 62, Number 124 (Friday, June 27, 1997)]
[Rules and Regulations]
[Pages 34623-34626]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-16853]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 97-NM-28-AD; Amendment 39-10060; AD 97-14-03]
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 installation of a newly designed 
rudder-limiting device and yaw damper system. This amendment is 
prompted by a report indicating that a full rudder input, either 
commanded or uncommanded, could result in a rapid roll upset; and by 
reports of malfunctions of the yaw damper system. The actions specified 
by this AD are intended to prevent excessive rudder authority and 
consequent reduced controllability of the airplane; and malfunctions of 
the yaw damper system, which could result in sudden uncommanded yawing 
of the airplane and consequent injury to passengers and crewmembers.

EFFECTIVE DATE: August 1, 1997.

ADDRESSES: Information concerning this amendment may be obtained from 
or 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, Transport Airplane 
Directorate, 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 March 14, 1997 (62 FR 12121). That action proposed to 
require installation of a newly designed rudder-limiting device and yaw 
damper system.
    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

    Three commenters support the proposed AD.

Request To Revise Discussion Section of Proposal

    One commenter requests that the second paragraph of the Discussion 
section that appeared in the preamble to the proposed rule be revised 
to remove any reference to wear of any bearing in the yaw damper 
coupler as the cause of the identified unsafe condition. The commenter 
states that its evaluations of the rate gyroscope from uncommanded yaw 
incidents do not support the conclusion that rudder kicks can be caused 
by wear of rotor bearings in the yaw damper coupler; therefore this 
commenter does not support replacement of the existing yaw damper 
couplers. The commenter also suggests that the word ``gimbal'' (in 
reference to the bearings) should be referenced in the proposal in lieu 
of ``rotor.''
    The FAA concurs partially. The FAA is aware of a number of 
incidents of failure of the rate gyroscope of the yaw damper coupler as 
a result of wear of the rotor bearing. Such wear causes increased 
vibration within the yaw damper coupler, which can lead to brinnels 
(i.e., dents) in the gimbal bearings. This situation can cause faults 
in the gyroscope at certain input rates, which could result in the 
identified unsafe condition. Therefore, while wear of the rotor bearing 
alone does not cause rudder kicks, it does contribute to the unsafe 
condition.
    The FAA agrees that the word ``gimbal'' could be referenced in 
place of ``rotor.'' However, the Discussion section of a proposal does 
not reappear in a final rule. Therefore, the FAA finds that no change 
to this final rule is necessary.

Request To Extend the Comment Period of the Proposal

    Several commenters request an extension of the public comment 
period for the proposed AD. These commenters state that such an 
extension will enable operators to better understand the issues 
surrounding the proposed actions and to review material that Boeing 
will present. The FAA does not concur. The FAA is unaware of material 
from Boeing and, therefore, is unable to extend the public comment 
period based on this request. Further, the FAA finds that to delay 
issuance of this final rule would be inappropriate, since the FAA has 
determined that an unsafe condition exists and the actions required by 
this AD are necessary to ensure continued safety.

Request To Delay Issuance of Final Rule

    One commenter requests that the FAA delay issuance of the final 
rule until Boeing can release the service bulletins containing 
procedures for installation of a newly designed yaw damper system and 
rudder-limiting device. The commenter states that neither Boeing nor 
its suppliers have completed engineering the proposed design changes; 
therefore, the commenter is unable to provide meaningful or technically 
relevant comments regarding the actions specified in the proposed AD.
    In light of the critical nature of the addressed unsafe condition, 
the FAA does not consider that delaying this action until after the 
release of Boeing's planned service bulletins is warranted. 
Furthermore, the FAA disagrees with the commenter's assertion that it 
is unable to submit meaningful comments on this AD until Boeing's 
design changes are completed. On the contrary, the proposed AD provided 
extensive information on the nature of the unsafe condition, the 
proposed corrective actions, and the proposed compliance times for 
those actions. The only information not provided (because it was not 
available) was reference to a specific service document providing 
details on specific methods for accomplishing the proposed actions.
    The FAA considers that this proposed AD has complied fully with the 
requirements of the Administrative Procedure Act to provide the public 
with a reasonable opportunity to comment by including in the proposal 
``either the terms or substance of the proposed rule or a description 
of the subjects and issues involved.''

Requests To Reduce Compliance Time for Modification

    One commenter requests a revision to the proposed compliance time 
of 3 years for accomplishment of the requirements of this proposed AD. 
The commenter requests that the requirements proposed by the AD be 
accomplished by

[[Page 34624]]

December 31, 1997. The commenter states that the National 
Transportation Safety Board (NTSB) and FAA have known about the 
problems associated with the rudder power control unit (PCU) since 1986 
or earlier. The commenter asserts that further delays will only 
increase the possibility of another catastrophic accident.
    The FAA does not concur with the commenter's request to reduce the 
compliance time. In response to the comment that the FAA has known 
about the problems associated with the main rudder PCU since 1986 or 
earlier, the FAA finds this statement to be incorrect. The FAA learned 
of the design deficiencies in the main rudder PCU servo valve and 
control rod bolts in the last quarter of 1996, and has specifically 
addressed concerns associated with the main rudder PCU in a notice of 
proposed rulemaking that was issued on March 7, 1997 (reference Docket 
No. 97-NM-29-AD).
    In the case of this AD, the FAA finds that a compliance time of 
less than 3 years would significantly increase the possibility of new 
design or manufacturing errors. Further, the FAA points out that once 
Boeing has developed the design changes for the rudder-limiting device 
and yaw damper system, time will be necessary to test the new design 
changes to ensure those changes meet certification requirements for FAA 
approval.
    Further, in developing an appropriate compliance time for the 
required modifications, the FAA considered not only the degree of 
urgency associated with addressing the unsafe condition, but the 
availability of required parts and the practical aspect of 
accomplishing the replacements within an interval of time that 
parallels normal scheduled maintenance for the majority of affected 
operators. In consideration of all of these factors, the FAA has 
determined that 3 years represents an appropriate interval of time 
allowable wherein the modifications can be accomplished during 
scheduled maintenance intervals for the majority of affected operators, 
and an acceptable level of safety can be maintained.

Requests To Eliminate Rudder Authority at Altitudes Above 1,500 
Feet

    Three commenters note that paragraph (a)(1) of the proposed AD 
requires installation of the newly designed rudder-limiting device that 
reduces the rudder authority at altitudes above 1,500 feet above ground 
level (AGL).
    One of these commenters requests that the rudder limiting device be 
changed from an altitude-based device to one based on airplane speed 
and the asymmetrical thrust of the engines. This commenter states that 
excessive rudder authority should be restricted at any altitude and 
speed. This commenter also states that a malfunction on the rudder 
system could occur at altitudes above 1,500 feet above ground level 
(AGL) when the rudder limiting device is activated. Such a failure 
could be transparent to the flightcrew until the airplane descends 
below 1,500 feet AGL, at which point the rudder-limiting device will no 
longer be in effect.
    The second commenter also requests that airspeed (or dynamic 
pressure) be the triggering point for activation of the rudder limiter. 
This commenter contends that an active rudder-limiting device is 
necessary to reduce the rudder authority. The commenter points out that 
such a reduction should occur in any situation in which a full rudder 
deflection (i.e., hardover) can result in a rolling movement due to a 
sideslip that exceeds the maximum rolling moment available by control 
wheel inputs. The commenter states that this scenario can exist both 
above and below 1,500 feet AGL. The commenter also states that an 
airspeed driven rudder limiter would be consistent with past practices 
and industry standards.
    The third commenter also requests that the proposal be revised to 
require rudder limiting ``at flight conditions where full rudder 
authority is not required.'' The commenter states that the requirements 
of paragraph (a)(1) of the proposal (i.e., at altitudes above 1,500 
feet AGL) are too restrictive. The commenter asserts that it will be 
possible to reduce this altitude.
    The FAA finds that clarification is necessary. The FAA finds that, 
as paragraph (a)(1) is currently worded, operators could only install a 
newly designed rudder-limiting device that reduces that rudder 
authority at altitudes above 1,500 feet AGL. However, the FAA finds the 
various designs may reduce rudder authority; thus, basing the rudder-
limiting device on an altitude is too restrictive. Therefore, the FAA 
has determined that revising paragraph (a)(1) of the final rule to 
replace the phrase ``at altitudes above 1,500 feet above ground level 
(AGL)'' with the phrase ``at flight conditions where full rudder 
authority is not required'' will allow operators to submit various 
designs that reduce rudder authority to the FAA for approval. The FAA 
has revised paragraph (a)(1) of the final rule accordingly.

Request That Proposed Modifications Terminate Another AD

    One commenter requests that the requirements of the proposed AD 
constitute terminating action for the requirements of Notice of 
Proposed Rulemaking (NPRM) Docket No. 96-NM-151-AD that address the yaw 
damper coupler/rate gyroscope.
    The FAA finds that clarification is necessary. The FAA points out 
that the NPRM referenced by the commenter proposed to require actions 
associated with the yaw damper engage solenoid valve and the yaw damper 
coupler/rate gyroscope. Additionally, since receipt of the comment, the 
FAA has issued the final rule for that NPRM [reference AD 97-09-15, 
amendment 39-10011 (62 FR 24325, May 5, 1997)]. That AD addresses only 
actions associated with the yaw damper engage solenoid valve.
    In the preamble of AD 97-09-15, the FAA indicated that it is 
considering issuance of a separate rulemaking action to address actions 
relative to the yaw damper coupler/rate gyroscope. The FAA is 
considering whether accomplishing the actions required by this final 
rule would constitute terminating action for the requirements of that 
separate proposed AD.

Request That Parts Be Available for Concurrent Accomplishment of 
Modifications

    One commenter requests that parts for both modification of the yaw 
damper system (required by this proposed AD) and modification of the 
rudder PCU (proposed by NPRM Docket No. 97-NM-29-AD) be made available 
at the same time. The commenter states that such parts availability 
will allow accomplishment of both modifications at the same time, which 
would minimize the down time of the airplane.
    The FAA has no way of ensuring that parts can be made available at 
a specific time so that these modifications can be accomplished 
concurrently. The FAA acknowledges that accomplishment of both 
modifications at the same time would minimize down time of the 
airplane. The FAA points out that the compliance time for this AD is 3 
years, and the proposed compliance time for NPRM Docket No. 97-NM-29-AD 
is 2 years. Based on parts availability, it is an operator's 
prerogative to special schedule its fleet of airplanes to accomplish 
both modifications concurrently, provided that the required actions are 
accomplished within the specified compliance times. The FAA finds that 
no change to this final rule is necessary.

[[Page 34625]]

Request To Add a New Requirement for ON/OFF Switches

    One commenter requests that the shut-off valves of the rudder 
hydraulic supply be installed and controlled by ON/OFF switches in the 
control cabin. The commenter states that such switches are installed on 
Boeing Model 727 series airplanes. The FAA does not concur with the 
commenter's request. The FAA does not consider it appropriate to 
include various provisions in an AD applicable to a single operator's 
unique use of an affected airplane. However, paragraph (b) of this AD 
contains a provision for requesting approval of an alternative method 
of compliance to address these types of unique circumstances.

Request To Add a New Requirement To Revise Operating Procedures

    One commenter requests that the FAA require a revision to operating 
procedures of Boeing Model 737 series airplanes that would give pilots 
a reliable margin of safety until operators could accomplish the 
proposed installation of the newly designed rudder limiter. The 
commenter points out that, for certain weight and approach flap 
combinations of the airplane, the approach speeds that Boeing 
recommended are at or very near the ``cross over point'' (a speed below 
which the lateral controls become inadequate to counter a fully 
deflected rudder). The commenter contends that increasing the 
recommended approach speed by an additional 10 knots will increase the 
controllability of the airplane and will provide the flightcrew with 
additional time to take appropriate action in the event of a rudder 
hardover.
    The FAA does not concur with the commenter's request. On December 
23, 1996, the FAA issued AD 96-26-07, amendment 39-9871 (62 FR 15, 
January 2, 1997), which is applicable to all Boeing Model 737 series 
airplanes. That AD requires revising the FAA-approved Airplane Flight 
Manual to include procedures that will enable the flightcrew to take 
appropriate action to maintain control of the airplane during an 
uncommanded yaw or roll condition, and to correct a jammed or 
restricted flight control condition. The FAA has determined that the 
requirements of AD 96-26-07 adequately address the controllability 
issue raised by the commenter.

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 2,900 Boeing Model 737 series airplanes of 
the affected design in the worldwide fleet. The FAA estimates that 
1,350 airplanes of U.S. registry will be affected by this AD.
    The FAA estimates that it will take approximately 87 work hours per 
airplane to accomplish the required installation of a newly designed 
rudder-limiting device, at an average labor rate of $60 per work hour. 
Required parts will be supplied by the manufacturer at no cost to 
operators. Based on these figures, the cost impact of the required AD 
on U.S. operators is estimated to be $7,047,000, or $5,220 per 
airplane.
    The FAA also estimates that it will take approximately 20 work 
hours per airplane to accomplish the required installation of a newly 
designed yaw damper system, at an average labor rate of $60 per work 
hour. Required parts will be supplied by the manufacturer at no cost to 
operators. Based on these figures, the cost impact of the required AD 
on U.S. operators is estimated to be $1,620,000, or $1,200 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:

97-14-03  Boeing: Amendment 39-10060. Docket 97-NM-28-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 
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 (b) 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 excessive rudder authority and consequent 
reduced controllability of the airplane; and malfunctions of the yaw 
damper system, which could result in sudden uncommanded yawing of 
the airplane and consequent injury to passengers and crewmembers; 
accomplish the following:
    (a) Within 3 years after the effective date of this AD, 
accomplish paragraphs (a)(1) and (a)(2) of this AD in accordance 
with a method approved by the Manager, Seattle Aircraft 
Certification Office (ACO), FAA, Transport Airplane Directorate.
    (1) Install a newly designed rudder-limiting device that reduces 
the rudder authority at flight conditions where full rudder 
authority is not required.
    (2) Install a newly designed yaw damper system that improves the 
reliability and fault monitoring capability.

[[Page 34626]]

    (b) 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.

    (c) 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.
    (d) This amendment becomes effective on August 1, 1997.

    Issued in Renton, Washington, on June 23, 1997.
S.R. Miller,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 97-16853 Filed 6-26-97; 8:45 am]
BILLING CODE 4910-13-U