[Federal Register Volume 70, Number 186 (Tuesday, September 27, 2005)]
[Rules and Regulations]
[Pages 56358-56361]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 05-19144]



[[Page 56358]]

-----------------------------------------------------------------------

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2005-20356; Directorate Identifier 2004-NM-115-AD; 
Amendment 39-14294; AD 2005-20-01]
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: Final rule.

-----------------------------------------------------------------------

SUMMARY: The FAA is adopting a new airworthiness directive (AD) for all 
Boeing Model 737-100, -200, -200C, -300, -400, and -500 series 
airplanes. This AD requires 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 AD also allows replacement of both 
stiffeners at LBL and RBL 6.15 with new, improved stiffeners, which 
terminates the repetitive inspections. This 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 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.

DATES: This AD becomes effective November 1, 2005.
    The incorporation by reference of a certain publication listed in 
the AD is approved by the Director of the Federal Register as of 
November 1, 2005.

ADDRESSES: You may examine the AD docket on the Internet at http://dms.dot.gov or in person at the Docket Management Facility, U.S. 
Department of Transportation, 400 Seventh Street, SW., Nassif Building, 
room PL-401, Washington, DC.
    Contact Boeing Commercial Airplanes, PO Box 3707, Seattle, 
Washington 98124-2207, for service information identified in this AD.

FOR FURTHER INFORMATION CONTACT: Nancy Marsh, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 
1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 
917-6440; fax (425) 917-6590.

Examining the Docket

    You may examine the AD docket on the Internet at http://dms.dot.gov 
or 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 street address stated in the 
ADDRESSES section.

Discussion

    The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 
CFR part 39 to include an AD that would apply to all Boeing Model 737-
100, -200, -200C, -300, -400, and -500 series airplanes. That NPRM was 
published in the Federal Register on February 15, 2005 (70 FR 7693). (A 
correction of the NPRM was published in the Federal Register on May 19, 
2005 (70 FR 28988).) That NPRM proposed to 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. That 
NPRM also proposed to allow replacement of both stiffeners at LBL and 
RBL 6.15 with new, improved stiffeners, which would terminate the 
repetitive inspections.

Comments

    We provided the public the opportunity to participate in the 
development of this AD. We have considered the comments that have been 
submitted on the proposed AD.

Support for the Proposed AD

    Two commenters support the proposed AD.

Request To Use Operator Equivalent Procedures

    One commenter requests that we revise paragraph (h) of the proposed 
AD to allow the use of FAA-approved, operator equivalent procedures for 
draining and gaining access to the center fuel tanks. The commenter 
states that Parts II and III of Boeing Alert Service Bulletin 737-
57A1269, Revision 1, dated September 16, 2004, contain work steps for 
de-fueling and purging the center tanks. The commenter further states 
that mandating how the fuel tanks are purged does not directly affect 
the means of correcting the unsafe condition addressed in the proposed 
AD.
    We agree that the procedures specified in Parts II and III are 
intended for gaining access to the center tanks. We also agree that 
using an equivalent procedure to gain access would not adversely affect 
the means of correcting the unsafe condition, which is to detect and 
correct cracks in the stiffeners at LBL and RBL 6.15. Therefore, we 
have revised the first sentence of paragraph (h) of this AD to require 
accomplishing the applicable actions in Part IV through Part IX of the 
service bulletin.

Request for Credit for Previous Inspections

    One commenter requests that inspections performed in accordance 
with Boeing All Operator Telex (AOT) M-7200-01-00426, dated February 
19, 2001, be considered acceptable for compliance with the inspections 
specified in paragraph (g) of the proposed AD. The commenter states 
that both Boeing AOT M-7200-01-00426 and Boeing Alert Service Bulletin 
737-57A1269, Revision 1, dated September 16, 2004, provide instructions 
for doing a detailed inspection of the stiffeners at LBL and RBL 6.15 
on the rear spar of the wing center section within the same compliance 
time.
    We agree that the detailed inspections specified in Boeing AOT M-
7200-01-00426 are acceptable for compliance with the corresponding 
requirements of this AD. We have added a new paragraph (k) to this AD 
to give credit and re-lettered the subsequent paragraphs accordingly.

Request To Use New Stiffeners of the Existing Type Design

    Two commenters request that we revise paragraph (h) of the proposed 
AD to add the option of replacing a cracked stiffener with a new 
stiffener of the existing type design (made from 7075-T6511 aluminum 
extrusion). One commenter states that since we have determined a 
repetitive inspection interval of 4,500 flight cycles provides an 
adequate level of safety for detecting cracks in the existing 
stiffeners, then replacement with new stiffeners of the existing type 
design should also provide an adequate level of safety if the 
repetitive inspections are continued. Although there is an ample supply 
of new stiffeners of the existing type design available, both 
commenters are concerned that there is an insufficient supply of new, 
improved stiffeners (made from 2024-T351 aluminum alloy plate) to 
comply with the proposed replacements.
    We do not agree. The manufacturer has confirmed that there is a 
sufficient supply of new, improved stiffeners available to comply with 
this AD. Therefore, no change to this AD is necessary in this regard.

[[Page 56359]]

Request To Replace a Stiffener, Only if Cracked

    Two commenters request that we revise paragraph (h) of the proposed 
AD to state that, if only one of the two stiffeners is found cracked, 
operators would be required to replace only the cracked stiffener 
instead of both stiffeners. As justification, the first commenter 
states that it frequently finds only one cracked stiffener during 
inspections of the stiffeners at LBL and RBL 6.15. Both commenters 
believe that the proposed AD should allow the option of replacing only 
the cracked stiffener provided that the repetitive inspections for 
cracking are continued until both stiffeners are eventually replaced. 
The second commenter supports this change because replacing both 
stiffeners requires additional labor and material. The commenter also 
states that the aggressive initial inspection threshold will force 
operators to inspect affected airplanes outside of a heavy maintenance 
visit. The commenter asserts that the additional impact of replacing 
both stiffeners will strain available resources.
    We do not agree because the new, improved stiffeners are much more 
rigid than the stiffeners of the existing type design. Replacing only 
one of the two stiffeners will lead to changes in the loading of the 
structure and premature fatigue of the new, improved stiffener. 
However, we acknowledge that replacing a cracked stiffener with a new 
stiffener of the existing type design will not adversely affect the 
relative stiffness of the two keel beam stiffeners, since they would be 
the same type design. If service information containing repair 
instructions and subsequent inspection requirements for replacing a 
cracked stiffener with a new stiffener of the existing type design is 
developed, under the provisions of paragraph (l) of this AD, we may 
consider requests for approval of an AMOC. Sufficient data must be 
submitted to substantiate that such a design change would provide an 
acceptable level of safety. Therefore, no change to this AD is 
necessary in this regard.

Request To Allow Temporary Repairs

    Three commenters request that we revise the proposed AD to allow 
operators to make temporary repairs until cracked stiffeners can be 
replaced. One commenter suggests adding an interim repair plan to the 
proposed AD to give operators time to schedule the terminating action 
(replacement of cracked stiffeners with new, improved stiffeners). The 
commenter proposes that an interim repair plan could consist of stop-
drilling small cracks where possible and reducing the repetitive 
inspection intervals to monitor crack growth, until the terminating 
action could be accomplished. The commenter is concerned it will not be 
able to comply with the requirements of the proposed AD because of the 
short initial inspection threshold and number of affected airplanes in 
its fleet.
    The second commenter states that repairs done in accordance with 
Boeing AOT M-7200-01-00426, dated February 19, 2001, and Repair Sketch 
LOR-760 will take less time than replacement of the stiffeners, 
especially since most of its affected airplanes will be inspected 
outside of a heavy maintenance visit. The third commenter asks if we 
would consider the two temporary repairs, which do not require access 
into the center tank, as an AMOC to the proposed AD.
    We partially agree. The FAA is working with the manufacturer to 
establish appropriate inspection and replacement requirements for this 
interim repair. Once this evaluation is concluded we may, under the 
provisions of paragraph (l) of this AD, we approve the subject interim 
repairs as an AMOC. We do not consider that delaying this final rule is 
warranted.

Request To Revise Compliance Time

    One commenter requests that we extend the compliance time of the 
initial inspection, from 180 days to 15 months for airplanes that have 
accumulated less than 30,000 total flight cycles, to allow affected 
operators to perform the inspection during a regularly scheduled 
maintenance interval. The proposed AD reported that cracked stiffeners 
were found on two airplanes with over 40,000 total flight cycles and on 
a third airplane with just over 20,000 total flight cycles. The 
commenter believes that the data are not consistent enough to warrant a 
short compliance time for airplanes that have accumulated fewer than 
40,000 total flight cycles. To comply with the proposed AD, the 
operator states that it would have to inspect more than 1 airplane per 
week, since the proposed AD affects the majority of its fleet. The 
operator also states that its operations would be negatively impacted 
if several of its airplanes required the terminating action, estimated 
at 250 work hours.
    We do not agree with the commenter's request. The commenter 
provides no technical justification for revising this inspection 
interval. Furthermore, since issuing the proposed AD, we have received 
numerous additional reports of cracked stiffeners. Eight of those 
reports included airplanes that have accumulated fewer than 30,000 
total flight cycles. We have determined that the compliance time, as 
proposed, represents the maximum interval of time allowable for the 
affected airplanes to continue to operate safely before the inspection 
is accomplished.

Request To Revise ``Cost of Compliance''

    One commenter estimates that the proposed inspection would take 
about 4 work hours, not 1 work hour as we specified in the proposed AD. 
We infer that the commenter would like us to revise the ``Cost of 
Compliance'' section.
    We do not agree, since the commenter has not provided justification 
for the increase in work hours. Our cost estimate is based on 
information that the manufacturer has provided to us, and we point out 
that 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. Therefore no change to this AD is necessary in this regard.

Explanation of Changes Made to This AD

    We have simplified paragraph (h) of this AD by referring to the 
``Alternative Methods of Compliance (AMOCs)'' paragraph of this AD for 
repair methods. Also, we have revised the ``Alternative Methods of 
Compliance (AMOCs)'' paragraph in this AD to clarify the delegation 
authority for Authorized Representatives for the Boeing Commercial 
Airplanes Delegation Option Authorization.

Conclusion

    We have carefully reviewed the available data, including the 
comments that have been submitted, and determined that air safety and 
the public interest require adopting the AD with the changes described 
previously. We have determined that these changes will neither increase 
the economic burden on any operator nor increase the scope of the AD.

Costs of Compliance

    This AD affects 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 AD.

[[Page 56360]]



                                                 Estimated Costs
----------------------------------------------------------------------------------------------------------------
                                                                                  Number of
                                                                                    U.S.-
             Action                Work hours     Parts      Cost per airplane    registered      Fleet cost
                                                                                  airplanes
----------------------------------------------------------------------------------------------------------------
Inspection, per inspection cycle            1         None  $65, per inspection        1,384  $89,960, per
                                                             cycle.                            inspection cycle.
----------------------------------------------------------------------------------------------------------------

Authority for This Rulemaking

    Title 49 of the United States Code specifies the FAA's authority to 
issue rules on aviation safety. 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.
    We are issuing this rulemaking 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 
rulemaking action.

Regulatory Findings

    We have determined that this AD will not have federalism 
implications under Executive Order 13132. This AD will 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 this AD:
    (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.
    We prepared a regulatory evaluation of the estimated costs to 
comply with this 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, Incorporation by 
reference, Safety.

Adoption of the Amendment

0
Accordingly, under the authority delegated to me by the Administrator, 
the FAA amends 14 CFR part 39 as follows:

PART 39--AIRWORTHINESS DIRECTIVES

0
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]

0
2. The FAA amends Sec.  39.13 by adding the following new airworthiness 
directive (AD):

2005-20-01 Boeing: Amendment 39-14294. Docket No. FAA-2005-20356; 
Directorate Identifier 2004-NM-115-AD.

Effective Date

    (a) This AD becomes effective November 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 flight 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 with new, improved stiffeners, 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 Stiffeners

    (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 
IV through Part IX, as applicable, of the service bulletin; except 
where the service bulletin specifies to contact Boeing for 
appropriate action: Before further flight, repair using a method 
approved in accordance with the procedures specified in paragraph 
(l) of this AD. Accomplishing the replacement terminates the 
repetitive inspections required by paragraph (g) of this AD.

Optional Terminating Action

    (i) Replacement of both stiffeners at LBL and RBL 6.15 with new, 
improved stiffeners 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.

Credit for Previous Inspections

    (k) Inspections done before the effective date of this AD in 
accordance with Boeing All Operator Telex M-7200-01-00426, dated 
February 19, 2001, are acceptable for compliance with the 
requirements of paragraph (g) of this AD.

Alternative Methods of Compliance (AMOCs)

    (l)(1) The Manager, Seattle Aircraft Certification Office (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

[[Page 56361]]

required by this AD, if it is approved by an Authorized 
Representative for the Boeing Commercial Airplanes 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.

Material Incorporated by Reference

    (m) You must use Boeing Alert Service Bulletin 737-57A1269, 
Revision 1, dated September 16, 2004, to perform the actions that 
are required by this AD, unless the AD specifies otherwise. The 
Director of the Federal Register approved the incorporation by 
reference of this document in accordance with 5 U.S.C. 552(a) and 1 
CFR part 51. Contact Boeing Commercial Airplanes, P.O. Box 3707, 
Seattle, Washington 98124-2207, for a copy of this service 
information. You may review copies at the Docket Management 
Facility, U.S. Department of Transportation, 400 Seventh Street, 
SW., room PL-401, Nassif Building, Washington, DC; on the Internet 
at http://dms.dot.gov; or at the National Archives and Records 
Administration (NARA). For information on the availability of this 
material at the NARA, call (202) 741-6030, or go to http://www.archives.gov/federal-register/cfr/ibr-locations.html.

    Issued in Renton, Washington, on September 16, 2005.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 05-19144 Filed 9-26-05; 8:45 am]
BILLING CODE 4910-13-P