[Federal Register Volume 70, Number 30 (Tuesday, February 15, 2005)]
[Proposed Rules]
[Pages 7693-7695]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 05-2834]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2005-20356; Directorate Identifier 2004-NM-115-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-100, -200, -200C, -
300, -400, and -500 Series Airplanes

AGENCY: Federal Aviation Administration (FAA), Department of 
Transportation (DOT).

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: The FAA proposes to adopt a new airworthiness directive (AD) 
for all Boeing Model 737-100, -200, -200C, -300, -400, and -500 series 
airplanes. This proposed AD would require repetitive inspections of the 
stiffeners at left buttock line (LBL) and right buttock line (RBL) 6.15 
for cracks; and replacement of both stiffeners with new, improved 
stiffeners if any stiffener is found cracked. This proposed AD would 
also allow replacement of both stiffeners at LBL and RBL 6.15 with new, 
improved stiffeners, which terminates the repetitive inspections. This 
proposed AD is prompted by reports of cracks in the stiffeners at LBL 
and RBL 6.15 on the rear spar of the wing center section. We are 
proposing this AD to detect and correct cracks in the stiffeners at LBL 
and RBL 6.15, which could result in damage to the keel beam structure 
and consequently reduce the capability of the airplane to sustain 
flight loads.

DATES: We must receive comments on this proposed AD by April 1, 2005.

ADDRESSES: Use one of the following addresses to submit comments on 
this proposed AD.
     DOT Docket Web site: Go to http://dms.dot.gov and follow 
the instructions for sending your comments electronically.
     Government-wide rulemaking Web site: Go to http://www.regulations.gov and follow the instructions for sending your 
comments electronically.
     Mail: Docket Management Facility, U.S. Department of 
Transportation, 400 Seventh Street SW., Nassif Building, room PL-401, 
Washington, DC 20590.
     By fax: (202) 493-2251.
     Hand Delivery: Room PL-401 on the plaza level of the 
Nassif Building, 400 Seventh Street SW., Washington, DC, between 9 a.m. 
and 5 p.m., Monday through Friday, except Federal holidays.
    For service information identified in this proposed AD, contact 
Boeing Commercial Airplanes, P.O. Box 3707, Seattle, Washington 98124-
2207.
    You can examine the contents of this AD docket on the Internet at 
http://dms.dot.gov, or at the Docket Management Facility, U.S. 
Department of Transportation, 400 Seventh Street SW., room PL-401, on 
the plaza level of the Nassif Building, Washington, DC. This docket 
number is FAA-2005-20356; the directorate identifier for this docket is 
2004-NM-115-AD.

FOR FURTHER INFORMATION CONTACT: Nancy Marsh, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA,

[[Page 7694]]

Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (425) 917-6440; fax (425) 917-6590.

SUPPLEMENTARY INFORMATION: 

Comments Invited

    We invite you to submit any relevant written data, views, or 
arguments regarding this proposed AD. Send your comments to an address 
listed under ADDRESSES. Include ``Docket No. FAA-2005-20356; 
Directorate Identifier 2004-NM-115-AD'' in the subject line of your 
comments. We specifically invite comments on the overall regulatory, 
economic, environmental, and energy aspects of the proposed AD. We will 
consider all comments submitted by the closing date and may amend the 
proposed AD in light of those comments.
    We will post all comments we receive, without change, to http://dms.dot.gov, including any personal information you provide. We will 
also post a report summarizing each substantive verbal contact with FAA 
personnel concerning this proposed AD. Using the search function of 
that Web site, anyone can find and read the comments in any of our 
dockets, including the name of the individual who sent the comment (or 
signed the comment on behalf of an association, business, labor union, 
etc.). You can review DOT's complete Privacy Act Statement in the 
Federal Register published on April 11, 2000 (65 FR 19477-78), or you 
can visit http://dms.dot.gov.

Examining the Docket

    You can examine the AD docket in person at the Docket Management 
Facility office between 9 a.m. and 5 p.m., Monday through Friday, 
except Federal holidays. The Docket Management Facility office 
(telephone (800) 647-5227) is located on the plaza level of the Nassif 
Building at the DOT street address stated in the ADDRESSES section. 
Comments will be available in the AD docket shortly after the DMS 
receives them.

Discussion

    We have received reports indicating that cracks have been found in 
the stiffeners at left buttock line (LBL) 6.15 and at right buttock 
line (RBL) 6.15 on the rear spar of the wing center section on several 
Boeing Model 737-300 series airplanes. On two of those airplanes, the 
stiffeners at LBL and RBL 6.15 were cracked all the way through, and 
the keel beam structure was damaged. These airplanes had accumulated 
between 20,697 and 47,496 total flight cycles. In another instance, on 
a Model 737-200 series airplane, the stiffener at RBL 6.15 was also 
cracked all the way through, just below the lower spar chord. That 
airplane had accumulated 40,888 total flight cycles.
    The stiffeners on certain Model 737-100, -200C, -400, and -500 
series airplanes are identical to those on the affected Model 737-200 
and -300 series airplanes. Therefore, all of these models may be 
subject to the same unsafe condition.
    The existing stiffeners are made from 7075-T6511 aluminum extrusion 
and have only one flange for attachment to the rear spar. These 
stiffeners do not provide the necessary strength to prevent cracks at 
LBL and RBL 6.15. This condition, if not detected and corrected, could 
result in damage to the keel beam structure and consequently reduce the 
capability of the airplane to sustain flight loads.

Relevant Service Information

    We have reviewed Boeing Alert Service Bulletin 737-57A1269, 
Revision 1, dated September 16, 2004. The service bulletin describes 
procedures for doing repetitive detailed inspections of the stiffeners 
at LBL and RBL 6.15 for cracks; and replacing both stiffeners with new, 
improved stiffeners if any stiffener is found cracked. Replacement of a 
stiffener includes:
     Doing an eddy current inspection of all open fastener 
holes after removing the stiffener, after removing the gusset and 
grommet, and after removing the stiffener;
     Installing nutplates and ground studs; and
     Drilling holes, machining the spotface, and applying a 
primer for pre-installation of the stiffener.
    Replacement of both stiffeners at LBL and RBL 6.15 with new, 
improved stiffeners eliminates the need for repetitive inspections. 
Accomplishing the actions specified in the service bulletin is intended 
to adequately address the unsafe condition.

FAA's Determination and Requirements of the Proposed AD

    We have evaluated all pertinent information and identified an 
unsafe condition that is likely to exist or develop on other airplanes 
of this same type design. Therefore, we are proposing this AD, which 
would require repetitive detailed inspections of the stiffeners at LBL 
and RBL 6.15 for cracks; and replacement of both stiffeners with new, 
improved stiffeners if any stiffener is found cracked. This proposed AD 
would also allow replacement of stiffeners at LBL and RBL 6.15 with 
new, improved stiffeners, which terminates the repetitive inspections. 
The proposed AD would require you to use the service information 
described previously to perform these actions, except as discussed 
under ``Difference Between the Proposed AD and the Service Bulletin.''

Difference Between the Proposed AD and the Service Bulletin

    The service bulletin specifies that you may contact the 
manufacturer for instruction on how to repair certain conditions, but 
this proposed AD would require you to repair those conditions in one of 
the following ways:
     Using a method that we approve; or
     Using data that meet the certification basis of the 
airplane, and that have been approved by an Authorized Representative 
for the Boeing Delegation Option Authorization Organization who has 
been authorized by the FAA to make those findings.

Costs of Compliance

    This proposed AD would affect about 3,132 airplanes worldwide. The 
following table provides the estimated costs, at an average labor rate 
of $65 per hour, for U.S. operators to comply with this proposed AD.

                                                 Estimated Costs
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                                                                                  No. of U.S.-
            Action               Work hours         Parts           Cost per       registered      Fleet cost
                                                                    airplane        airplanes
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Inspection, per inspection                1   None............  $65, per                1,384   $89,960, per
 cycle.                                                          inspection                      inspection
                                                                 cycle.                          cycle.
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[[Page 7695]]

Authority for This Rulemaking

    The FAA's authority to issue rules regarding aviation safety is 
found in Title 49 of the United States Code. Subtitle I, Section 106 
describes the authority of the FAA Administrator. Subtitle VII, 
Aviation Programs, describes in more detail the scope of the agency's 
authority.
    This rulemaking is promulgated under the authority described in 
Subtitle VII, Part A, Subpart III, Section 44701, ``General 
requirements.'' Under that section, Congress charges the FAA with 
promoting safe flight of civil aircraft in air commerce by prescribing 
regulations for practices, methods, and procedures the Administrator 
finds necessary for safety in air commerce. This regulation is within 
the scope of that authority because it addresses an unsafe condition 
that is likely to exist or develop on products identified in this AD.

Regulatory Findings

    We have determined that this proposed AD would not have federalism 
implications under Executive Order 13132. This proposed AD 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.
    For the reasons discussed above, I certify that the 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. 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.
    We prepared a regulatory evaluation of the estimated costs to 
comply with this proposed AD. See the ADDRESSES section for a location 
to examine the regulatory evaluation.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, under the authority delegated to me by the 
Administrator, FAA proposes to amend 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. The FAA amends Sec.  39.13 by adding the following new 
airworthiness directive (AD):

Boeing: Docket No. FAA-20356; Directorate Identifier 2004-NM-115-AD.

Comments Due Date

    (a) The Federal Aviation Administration (FAA) must receive 
comments on this AD action by April 1, 2005.

Affected ADs

    (b) None.

Applicability

    (c) This AD applies to all Boeing Model 737-100, -200, -200C, -
300, -400, and -500 series airplanes, certificated in any category.

Unsafe Condition

    (d) This AD was prompted by cracks in the stiffeners at left 
buttock line (LBL) and right buttock line (RBL) 6.15 on the rear 
spar of the wing center section. We are issuing this AD to detect 
and correct cracks in the stiffeners at LBL and RBL 6.15, which 
could result in damage to the keel beam structure and consequently 
reduce the capability of the airplane to sustain flight loads.

Compliance

    (e) You are responsible for having the actions required by this 
AD performed within the compliance times specified, unless the 
actions have already been done.

Service Bulletin Reference

    (f) The term ``service bulletin,'' as used in this AD, means the 
Accomplishment Instructions of Boeing Alert Service Bulletin 737-
57A1269, Revision 1, dated September 16, 2004.

Initial and Repetitive Inspections

    (g) Before accumulating 15,000 total flights cycles, or within 
180 days after the effective date of this AD, whichever occurs 
later: Do a detailed inspection of the stiffeners at LBL and RBL 
6.15 for cracks, in accordance with Part I of the service bulletin. 
Thereafter at intervals not to exceed 4,500 flight cycles, repeat 
the detailed inspection until the stiffeners at LBL and RBL 6.15 
have been replaced, in accordance with paragraph (h) or (i) of this 
AD.

    Note 1: For the purposes of this AD, a detailed inspection is: 
``An intensive examination of a specific item, installation, or 
assembly to detect damage, failure, or irregularity. Available 
lighting is normally supplemented with a direct source of good 
lighting at an intensity deemed appropriate. Inspection aids such as 
mirror, magnifying lenses, etc., may be necessary. Surface cleaning 
and elaborate procedures may be required.''

Replacement of Cracked Stiffener

    (h) If any crack is found during any inspection required by this 
AD, before further flight, replace both stiffeners with new, 
improved stiffeners by doing all of the applicable actions in Part 
II through Part IX of the service bulletin; except where the service 
bulletin specifies to contact Boeing for appropriate action: Before 
further flight, repair according to a method approved by the 
Manager, Seattle Aircraft Certification Office (ACO), FAA, or 
according to data meeting the certification basis of the airplane 
approved by an Authorized Representative for the Boeing Delegation 
Option Authorization Organization who has been authorized by the 
Manager, Seattle ACO, to make those findings. For a repair method to 
be approved, the approval must specifically reference this AD. 
Accomplishing the replacement terminates the repetitive inspections 
required by paragraph (g) of this AD.

Optional Terminating Action

    (1) Replacement of both stiffeners at LBL and RBL 6.15 in 
accordance with paragraph (h) of this AD terminates the repetitive 
inspections required by this AD.

Credit for Previous Service Bulletin

    (j) The actions done before the effective date of this AD in 
accordance with Boeing Alert Service Bulletin 737-57A1269, dated 
December 4, 2003, are acceptable for compliance with the 
corresponding actions required by this AD.

Alternative Methods of Compliance (AMOCs)

    (k)(1) The Manager, Seattle ACO, FAA, has the authority to 
approve AMOCs for this AD, if requested in accordance with the 
procedures found in 14 CFR 39.19.
    (2) An AMOC that provides an acceptable level of safety may be 
used for any repair required by this AD, if it is approved by an 
Authorized Representative for the Boeing Delegation Option 
Authorization Organization who has been authorized by the Manager, 
Seattle ACO, to make those findings. For a repair method to be 
approved, the repair must meet the certification basis of the 
airplane, and the approval must specifically refer to this AD.

    Issued in Renton, Washington, on February 6, 2005.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 05-2834 Filed 2-14-05; 8:45 am]
BILLING CODE 4910-13-M