[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]
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