[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]



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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