[Federal Register Volume 66, Number 47 (Friday, March 9, 2001)]
[Proposed Rules]
[Pages 14096-14099]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-5807]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-310-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-100, -200, and -200C-
Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to certain Boeing Model 737-100, -
200, and -200C series airplanes. This proposal would require inspection 
of certain floor beams and transverse beams, and corrective actions, if 
necessary. The actions specified in the proposed AD are intended to 
detect and correct cracking at the aileron control quadrant cutouts and 
in the cabin floor beams and pressure web transverse beams above the 
main wheelwell, which could result in rapid loss of cabin pressure and 
reduced structural integrity of the airframe.

DATES: Comments must be received by April 23, 2001.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 99-NM-310-AD, 1601 Lind Avenue, SW.,

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Renton, Washington 98055-4056. Comments may be inspected at this 
location between 9 a.m. and 3 p.m., Monday through Friday, except 
Federal holidays. Comments may be submitted via fax to (425) 227-1232. 
Comments may also be sent via the Internet using the following address: 
[email protected]. Comments sent via fax or the Internet must 
contain ``Docket No. 99-NM-310-AD'' in the subject line and need not be 
submitted in triplicate. Comments sent via the Internet as attached 
electronic files must be formatted in Microsoft Word 97 for Windows or 
ASCII text.
    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: Scott Fung, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 
1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 
227-1221; 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 action 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 action must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 99-NM-310-AD.'' The postcard will be 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. 99-NM-310-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The FAA has received reports indicating that, on numerous Boeing 
Model 737 series airplanes, cracks have been detected in the left and 
right buttock line (LBL and RBL) 24.8 floor beams in the area of the 
aileron control quadrant cutout, and in the floor beams and pressure 
web transverse beams above the main wheelwell. This cracking has been 
attributed to stress concentration at the aileron control quadrant 
cutout and to fatigue at beam intersections resulting from 
pressurization flexure, respectively. This condition, if not corrected, 
could result in rapid loss of cabin pressure and reduced structural 
integrity of the airframe.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Service Bulletin 737-57-
1139, Revision 4, dated April 16, 1992. That service bulletin describes 
procedures for repetitive detailed visual inspections to detect 
cracking of the LBL and RBL 24.8 floor beams at the aileron control 
quadrant cutout; corrective actions, if necessary; and eventual 
modification of that area. That service bulletin also describes 
procedures for repetitive detailed visual inspections for cracking of 
the transverse beams and floor beams at the beam intersections, and 
eventual modification of that area. The modifications eliminate the 
need for the repetitive inspections. For any cracking of the LBL and 
RBL 24.8 floor beams at the aileron control quadrant cutout, if the 
cracking is within certain limits specified in the service bulletin, 
corrective actions include repair and accomplishment of the 
modification of the LBL and RBL 24.8 floor beams. For any cracking of 
the LBL and RBL 24.8 floor beams at the aileron control quadrant cutout 
that is outside the limits specified in the service bulletin, or any 
cracking of the transverse beams and floor beams at the beam 
intersections, the service bulletin specifies to contact Boeing for 
repair instructions.

Other Relevant Rulemaking

    The FAA previously has issued AD 90-06-02, amendment 39-6489 (55 FR 
8372, March 7, 1990), and AD 93-17-08, amendment 39-8679 (58 FR 46076, 
September 1, 1993), which apply to certain Boeing Model 737 series 
airplanes. AD 90-06-02 requires incorporation of structural 
modifications listed in Boeing Document No. D6-38505, Revision C, dated 
December 11, 1989; and AD 93-17-08 requires incorporation of structural 
modifications listed in Appendices A.3 and B.3 of Boeing Document No. 
D6-38505, Revision F, dated April 23, 1992. The modifications specified 
in Boeing Service Bulletin 737-57-1139, Revision 4, are listed in 
Boeing Document No. D6-38505, Revisions C and F. Because the 
modifications in Boeing Service Bulletin 737-57-1139, Revision 4, are 
already required by AD 90-06-02 and AD 93-17-08, this proposed AD would 
require only the inspections in the service bulletin, not the 
modifications. ``Note 3'' has been included in the body of this notice 
of proposed rulemaking to clarify that the modifications in the service 
bulletin are already required by other AD's. In addition, 
accomplishment of the modifications in the service bulletin in 
accordance with AD 90-06-02 and AD 93-17-08 is terminating action for 
the inspections in this proposed AD, and paragraphs (c)(1) and (c)(2) 
of this proposed AD clarify this point.

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 accomplishment of the inspections specified 
in the service bulletin described previously, except as discussed 
below.

Differences Between Proposed Rule and Service Bulletin

    Operators should note that, although the service bulletin specifies 
that the manufacturer may be contacted for disposition of certain 
repair conditions, this proposed AD would require the repair of those 
conditions to be accomplished in accordance with a method approved by 
the FAA, or in accordance with data meeting the type certification 
basis of the airplane approved by a Boeing Company Designated 
Engineering Representative who has been authorized by the FAA to make 
such findings.

Cost Impact

    There are approximately 971 airplanes of the affected design in the 
worldwide fleet. The FAA estimates that 333 airplanes of U.S. registry 
would be affected by this proposed AD, and that it would take 
approximately 10 work

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hours per airplane to accomplish the proposed inspections, at an 
average labor rate of $60 per work hour. Based on these figures, the 
cost impact of the proposed inspections on U.S. operators is estimated 
to be $199,800, or $600 per airplane, per inspection cycle.
    The cost impact figure discussed above is 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. The cost impact figures 
discussed in AD rulemaking actions represent only the time necessary to 
perform the specific actions actually required by the AD. These figures 
typically do not include incidental costs, such as the time required to 
gain access and close up, planning time, or time necessitated by other 
administrative actions.

Regulatory Impact

    The regulations proposed herein would not have a 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, it 
is determined that this proposal would not have federalism implications 
under Executive Order 13132.
    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 99-NM-310-AD.

    Applicability: Model 737-100, -200, and -200C series airplanes; 
line numbers 1 through 1585 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 detect and correct cracks in the floor beams at the 
aileron control quadrant cutout and in the floor beams and pressure 
web transverse beams above the main wheelwell, which could result in 
rapid loss of cabin pressure and reduced structural integrity of the 
airplane, accomplish the following:

Initial Inspection and Follow-On Actions: Groups 1, 2, and 5

    (a) For airplanes in Groups 1, 2, and 5; as listed in Boeing 
Service Bulletin 737-57-1139, Revision 4, dated April 16, 1992: 
Prior to the accumulation of 12,000 total flight cycles, or within 
3,000 flight cycles after the effective date of this AD, whichever 
occurs later, perform a detailed visual inspection to detect 
cracking of the left and right buttock line (LBL and RBL) 24.8 floor 
beams in the area of the aileron control quadrant cutout, in 
accordance with Part II of the Accomplishment Instructions of the 
service bulletin.

    Note 2: For the purposes of this AD, a detailed visual 
inspection is defined as: ``An intensive visual examination of a 
specific structural area, system, installation, or assembly to 
detect damage, failure, or irregularity. Available lighting is 
normally supplemented with a direct source of good lighting at 
intensity deemed appropriated by the inspector. Inspection aids such 
as mirror, magnifying lenses, etc. may be used. Surface cleaning and 
elaborate access procedures may be required.

    (1) If no cracking is detected, repeat the inspection thereafter 
at intervals not to exceed 3,000 flight cycles, until the 
modification in paragraph (c)(1) of this AD is done.
    (2) If cracking is detected that is within the limits specified 
in Part II, Paragraphs C.1. and C.2., of the Accomplishment 
Instructions of the service bulletin, prior to further flight, 
repair the crack per the service bulletin, and accomplish the 
modification specified in paragraph (c)(1) of this AD.
    (3) If cracking is detected that is outside the limits 
identified in Part II, Paragraphs C.1. and C.2., of the 
Accomplishment Instructions of the service bulletin, prior to 
further flight, repair in accordance with a method approved by the 
Manager, Seattle Aircraft Certification Office (ACO), FAA; or in 
accordance with a method approved by a Boeing Company Designated 
Engineering Representative (DER) who has been authorized by the 
Manager, Seattle ACO, to make such findings. For the repair method 
to be approved by the Manager, Seattle ACO, as required by this 
paragraph, the approval letter must specifically reference this AD.

Initial Inspection and Follow-On Actions: Groups 1, 2, 3, and 4

    (b) For airplanes in Groups 1, 2, 3, and 4; as listed in Boeing 
Service Bulletin 737-57-1139, Revision 4, dated April 16, 1992: 
Prior to the accumulation of 20,000 total flight cycles, or within 
6,000 flight cycles after the effective date of this AD, whichever 
occurs later, perform a detailed visual inspection to detect 
cracking of the transverse beams and floor beams at the beam 
intersections in accordance with Part II of the Accomplishment 
Instructions of the service bulletin.
    (1) If no cracking is detected, repeat the inspection thereafter 
at intervals not to exceed 6,000 flight cycles, until the 
modification in paragraph (c)(2) of this AD is done.
    (2) If any cracking is detected, prior to further flight, repair 
in accordance with a method approved by the Manager, Seattle ACO, or 
in accordance with a method approved by a Boeing Company DER who has 
been authorized by the Manager, Seattle ACO, to make such findings. 
For the repair method to be approved by the Manager, Seattle ACO, as 
required by this paragraph, the approval letter must specifically 
reference this AD.

Modifications (Terminating Action)

    (c) The following modifications in accordance with Boeing 
Service Bulletin 737-57-1139, Revision 4, dated April 16, 1992, 
constitute terminating action for certain requirements of this AD.
    (1) For airplanes in Groups 1, 2, and 5; as listed in the 
service bulletin: Modification of the LBL and RBL 24.8 floor beams 
in the area of the aileron control quadrant cutout in accordance 
with Part I of the Accomplishment Instructions of the service 
bulletin constitutes terminating action for the repetitive 
inspection requirements of paragraph (a) of this AD.
    (2) For airplanes in Groups 1, 2, 3, and 4; as listed in the 
service bulletin: Modification of the transverse beams and floor 
beams at the beam intersections in accordance with Part III or Part 
I, as applicable, of the

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Accomplishment Instructions of the service bulletin constitutes 
terminating action for the repetitive inspections required by 
paragraph (b) of this AD.

    Note 3: The modifications specified in Boeing Service Bulletin 
737-57-1139, Revision 4, dated April 16, 1992, are required by AD 
90-06-02, amendment 39-6489, and AD 93-17-08, amendment 39-8679.

Alternative Methods of Compliance

    (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 4: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

Special Flight Permits

    (e) 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.


    Issued in Renton, Washington, on March 5, 2001.
Donald L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 01-5807 Filed 3-8-01; 8:45 am]
BILLING CODE 4910-13-P