[Federal Register Volume 63, Number 209 (Thursday, October 29, 1998)]
[Proposed Rules]
[Pages 57953-57955]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-28969]
[[Page 57953]]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 98-NN-57-AD]
RIN 2120-AA64
Airworthiness Directives; Boeing Model 737 Series Airplanes
AGENCY: Federal Aviation Administration, DOT.
ACTION: Notice of proposed rulemaking (NPRM).
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SUMMARY: This document proposes the adopting of a new airworthiness
directive (AD) that is applicable to certain Boeing Model 737 series
airplanes. This proposal would require a one-time inspection of the
main landing gear (MLG) axle flange to detect cracking, and follow-on
corrective actions. For certain airplanes, this proposal also would
require replacement of the original brake mounting gasket with a more
durable aluminum-nickle-bronze gasket, and installation of new shear
studs, if necessary. For certain airplanes, the proposal would require
modification of the mounting flange holes of the torque tube. This
proposal is prompted by reports of cracking in the axle flange and by
reports of deterioration of the brake mounting gasket. The actions
specified by the proposed AD are intended to prevent fracture of the
MLG axle and separation of the wheel from the MLG, and consequent
reduced controllability of the airplane.
DATES: Comments must be received by December 14, 1998.
ADDRESSES: Submit comments in triplicate to the Federal Aviation
Administration (FAA), Transport Airplane Directorate, ANM-114,
Attention: Rule Docket No. 98-NM-57-AD, 1601 Lind Avenue, SW., Renton,
Washington 98055-4056. Comments may be inspected at this location
between 9:00 a.m. and 3:00 p.m., Monday through Friday except Federal
holidays.
The service information referenced in the proposed rule may be
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle,
Washington 98124-2207. This information may be examined at the FAA,
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton,
Washington.
FOR FURTHER INFORMATION CONTACT: Rick Kawaguchi, Aerospace Engineer,
Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle
Aircraft Certification Office, 1601 Lind Avenue, SW., Renton,
Washington 98055-4056; telephone (425) 227-1153; fax (425) 227-1181.
SUPPLEMENTARY INFORMATION:
Comments Invited
Interested persons are invited to participate in the making of the
proposed rule by submitting such written data, views, or arguments as
they may desire. Communications shall identify the Rules Docket number
and be submitted in triplicate to the address specified above. All
communications received on or before the closing date for comments,
specified above, will be considered before taking action on the
proposed rule. The proposals contained in this notice may be changed in
light of the comments received.
Comments are specifically invited on the overall regulatory,
economic, environmental, and energy aspects of the proposed rule. All
comments submitted will be available, both before and after the closing
date for comments, in the Rules Docket for examination by interested
persons. A report summarizing each FAA-public contact concerned with
the substance of this proposal will be filed in the Rules Docket.
Commenters wishing the FAA to acknowledge receipt of their comments
submitted in response to this notice must submit a self-addressed,
stamped postcard on which the following statement is made: ``Comments
to Docket Number 98-NM-57-AD.'' The postcard will date stamped and
returned to the commenter.
Availability of NPRMs
Any person may obtain a copy of this NPRM by submitting a request
to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules
Docket No. 98-NM-57-AD, 1601 Lind Avenue, SW., Renton, Washington
98055-4056.
Discussion
The FAA has received reports indicating that, since the
introduction of the Boeing Model 737 series airplane into service,
numerous airplanes have lost a main landing gear (MLG) wheel due to
fracturing of the axle. Although the total number of such wheel losses
is small, the rate at which fractures occur has increased in the last
several years. The axle fractures (and resultant wheel losses) are
attributed to a variety of conditions, including the deterioration of
the original fiberglass brake mounting gasket and fretting damage of
the stud holes in the adjacent axle flange. (The gasket is installed
between the brake assembly and the MLG axle flange; the flange itself
is an integral part of the MLG axle.)
Investigation has revealed that the deterioration of the original
fiberglass brake mounting gasket is caused by heat and vibration
generated by the MLG brake assemblies. Such deterioration of the gasket
leads to a loss of clamp-up forces between the brake assembly and the
MLG axle flange. This is turn leads to loosening of the brake assembly
and fretting damage of the axle flange. It is typical for such fretting
damage of the axle flange to lead to the initiation of a crack in a
stud hole of the axle flange; such cracking eventually grows and
spirals outward from the flange until a complete fracture of the MLG
axle occurs. Deterioration of the brake mounting gasket, if not
corrected, could lead to fracture of the MLG axle and separation of the
wheel from the MLG, and consequent reduced controllability of the
airplane.
Explanation of Relevant Service Information
The FAA has reviewed and approved Boeing Service Bulletin 737-32-
1253, dated November 7, 1991, which describes procedures for the
replacement of the original brake mounting gasket with a more durable
aluminum-nickel-bronze gasket. The service bulletin also specifies a
configuration in the new gasket installation. Specifically, the service
bulletin instructs operators to use a 10-bolt, 2-stud mounting
configuration for attaching the new gasket to the adjacent MLG axle
flange. This new mounting configuration allows the clamp-up forces
between the brake assembly and the MLG axle flange to be maintained at
levels enough to prevent future fretting of the axle flange.
In addition, AlliedSignals has issued Service Bulletin 2601042-32-
003, dated March 15, 1997, which describes procedures for modification
of the mounting flange holes of the torque tube. The modification
includes increasing the counterbore depth of the mounting flange holes
of the torque tube, and installing a chamfer to properly interface with
the attachment studs on the MLG axle flange. This service bulletin was
issued when it became evident that incorporation of Boeing Service
Bulletin 737-32-1253 could cause an interference problem on certain
AlliedSignal brake assemblies.
In addition, Boeing has issued All Operators Telex (AOT) M-7272-96-
1442, dated March 29, 1996, which provides background information on
the fractures of the MLG axle that have occurred in the fleet. The
section of this AOT titled ``Recommended Operator
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Action'' specifies that certain actions be accomplished in conjunction
with the modification specified in Boeing Service Bulletin 737-32-1253.
Specifically, the ``Recommends Operator Action'' section lists the
corrective actions to be taken if corrosion or fretting damage is found
on the axle flange. The corrective actions include removing any
corrosion found on the axle flange, blending out any fretting or
cracking damage, and performing either a magnetic inspection or a high
frequency eddy current inspection to ensure that the repaired part is
free of cracks.
Accomplishment of the actions specified in the service bulletins
and AOT is intended to adequately address the identified unsafe
condition.
Explanation of Requirements of Proposed Rule
Since an unsafe condition has been identified that is likely to
exist or develop on other products of this same type design, the
proposed AD would require a one-time inspection of the MLG axle flange
to detect cracking, and follow-on corrective actions. For certain
airplanes, this proposal also would require replacement of the original
brake mounting gasket with a more durable aluminum-nickel-bronze
gasket. For airplanes equipped with the new gaskets, but not with the
new shear studs, the proposal would require installing new shear studs
concurrently with the other actions proposed by this AD. For certain
airplanes, the proposal also would require modification of the mounting
flange holes of the torque tube. The actions would be required to be
accomplished in accordance with the Boeing and AlliedSignal service
bulletins, and the Boeing AOT described previously, except as discussed
below.
Differences Between the Proposed Rule and the Service Information
Operators should note that although the AOT recommends that
operators accomplish a magnetic particle or high frequency eddy current
inspection for cracking only after the MLG axle flange has been
repaired (following the discovery of corrosion or fretting), this
proposed AD would require the accomplishment of one of these
inspections even if the axle flange shows no signs of corrosion or
fretting.
Additionally, the AOT specifies that operators are to contact the
manufacturer for certain follow-on repair instructions. However, this
proposed AD would require that such repair be accomplished in
accordance with a method approved by the FAA.
Cost Impact
There are approximately 2,015 airplanes of the affected design in
the worldwide fleet. The FAA estimates that 893 airplanes of U.S.
registry would be affected by this proposed AD.
The FAA estimates that it would take approximately 4 work hours per
airplane to accomplish the proposed inspection, and that the average
labor rate is $60 per work hour. Based on these figures, the cost
impact of the proposed inspection on U.S. operators is estimated to be
$214,320 or $240 per airplane.
It would take approximately 32 work hours per airplane at an
average labor rate of $60 per work hour should an operator be required
to accomplish the proposed brake modification. Required parts would
cost approximately $2,052 per airplane. Based on these figures, the
cost of the proposed brake modification on U.S. operators is estimated
to be $2,972 per airplane.
Additionally, the FAA estimates that it would take approximately 5
work hours per airplane to accomplish the proposed torque tube
modification and that the average labor rate is $60 per work hour. The
FAA estimates that this action would be required to be accomplished on
approximately 400 U.S.-registered airplanes. Based on these figures,
the cost impact of this proposed modification on U.S. operators is
estimated to be $120,000, or $300 per airplane.
The cost impact figures discussed above are based on assumptions
that no operator has yet accomplished any of the proposed 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 proposed herein would not have substantial direct
effect 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
proposal would not have sufficient federalism implications to warrant
the preparation of a Federalism Assessment.
For the reasons discussed above, I certify that this proposed
regulation (1) is not a ``significant regulatory action'' under
Executive Order 12866; (2) is not a ``significant rule'' under the DOT
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979);
and (3) if promulgated, 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 copy of the draft
regulatory evaluation prepared for this action is contained in the
Rules Docket. A copy of it may be obtained by contacting 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.
The Proposed Amendment
Accordingly, pursuant to the authority delegated to me by the
Administrator, the Federal Aviation Administration proposes to amend
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:
Boeing: Docket 98-NM-57-AD.
Applicability: Model 737-100, -200, -300, -400, and -500 series
airplanes; line positions 1 through 2135 inclusive; 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 (d) 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 fracture of the main landing gear (MLG) axle and the
separation of the wheel from the MLG, and consequent reduced
controllability of the airplane, accomplish the following:
(a) For Model 737-100 and -200 series airplanes equipped with
AlliedSignal (ALS/Bendix) brake assembly installations having Boeing
part numbers (P/N) 10-61063-14, -18, or -21, on which the original
gaskets have been replaced with aluminum-nickel-bronze gaskets in
accordance with Boeing Service Bulletin 737-32-1253, dated November
7, 1991: Within 200 days or 1,500 flight cycles after the effective
date of this
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AD, whichever occurs later, accomplish the requirements of
paragraphs (a)(1), (a)(2), (a)(3), and (a)(4) of this AD.
(1) Perform either a one-time magnetic particle inspection or a
one-time high frequency eddy current inspection of the MLG axle
flange to detect cracking, except that a high frequency eddy current
inspection may only be accomplished if the axle flange has not been
repaired previously and coated with a nickel sulfamate finish. The
magnetic particle inspection or high frequency eddy current
inspection is to be accomplished in accordance with procedures
specified in paragraph B. of the ``Recommended Operator Action''
section of Boeing All Operators Telex (AOT) M-7272-76-1442, dated
Mach 29, 1996. If any cracking is detected, prior to further flight,
repair the MLG axle flange in accordance with a method approved by
the Manager, Seattle Aircraft Certification Office (ACO), FAA,
Transport Airplane Directorate.
(2) If any corrosion or fretting is found during accomplishment
of the inspection required by paragraph (a)(1) of this AD: Prior to
further flight, accomplish the repair procedures specified in the
``Recommended Operator Action'' section of Boeing AOT M-7272-96-
1442, dated March 29, 1996.
(3) Accomplish the modification of the torque tube mounting
holes on the mounting flange, in accordance with AlliedSignal
Service Bulletin 2601042-32-003, dated March 15, 1997.
(4) If shear studs were replaced at the time the new aluminum-
nickel-bronze gaskets were installed: Replace the shear studs in
accordance with Boeing Service Bulletin 737-32-1253, dated November
7, 1991.
(b) For Model 737-100 and -200 series airplanes equipped with
AlliedSignal (ALS/Bendix) brake assembly installations having Boeing
P/N 10-61063-14, -18, or -21, on which the original gaskets have not
been replaced with new aluminum-nickel-bronze gaskets in accordance
with Boeing Service Bulletin 737-32-1253, dated November 6, 1991:
Within 200 days or 1,500 flight cycles after the effective date of
this AD, whichever occurs later, accomplish the requirements of
paragraphs (b)(1), (b)(2), (b)(3), and (b)(4) of this AD.
(1) Perform either a one-time magnetic particle inspection or a
one-time high frequency eddy current inspection of the MLG axle
flange to detect cracking. The magnetic particle inspection or high
frequency eddy current inspection is to be accomplished in
accordance with procedures specified in paragraph B. of the
``Recommended Operator Action'' section of Boeing AOT M-7272-96-
1442, dated March 29, 1996. If any cracking is detected, prior to
further flight, repair the MLG axle flange in accordance with a
method approved by the Manager, Seattle ACO.
(2) If any corrosion or fretting is found during accomplishment
of the inspection required by paragraph (b)(1) of this AD: Prior to
further flight, accomplish the repair procedures specified in the
``Recommended Operator Action'' section of Boeing AOT M-7272-96-
1442, dated March 29, 1996.
(3) Accomplish the modification of the torque tube mounting
holes of the mounting flange, in accordance with AlliedSignal
Service Bulletin 2601042-32-003, dated March 15, 1997.
(4) Accomplish the modification of the affected brake assemblies
in accordance with Boeing Service Bulletin 737-32-1253, dated
November 7, 1991.
(c) For Model 737-100, -200, -300, -400, and -500 series
airplanes other than those identified in paragraphs (a) and (b) of
this AD: Within 200 days or 1,500 flight cycles after the effective
date of this AD, whichever occurs later, accomplish the requirements
of paragraphs (c)(1), (c)(2), and (c)(3) of this AD.
(1) Perform either a one-time magnetic particle inspection or a
one-time high frequency eddy current inspection of the MLG axle
flange to detect cracking. The magnetic particle inspection or high
frequency eddy current inspection is to be accomplished in
accordance with procedures specified in paragraph B. of the
``Recommended Operator Action'' section of Boeing AOT M-7272-96-
1442, dated March 29, 1996. If any cracking is detected, prior to
further flight, repair the MLG axle flange in accordance with a
method approved by the Manager, Seattle ACO.
(2) If any corrosion or fretting is found during accomplishment
of the inspection required by paragraph (c)(1) of this AD: Prior to
further flight, accomplish the repair procedures specified in the
``Recommended Operator Action'' section of Boeing AOT M-7272-96-
1442, dated March 29, 1996.
(3) Accomplish the modification of the affected brake assemblies
in accordance with Boeing Service Bulletin 737-32-1253, dated
November 7, 1991.
(d) 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.
(e) Special flight permits may be issued in accordance with
sessions 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.
Issued in Renton, Washington, on October 21, 1998.
S.R. Miller,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 98-28969 Filed 10-28-98; 8:45 am]
BILLING CODE 4910-13-M
