[Federal Register Volume 73, Number 113 (Wednesday, June 11, 2008)]
[Rules and Regulations]
[Pages 32991-32993]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E8-12761]



[[Page 32991]]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2007-29333; Directorate Identifier 2007-NM-141-AD; 
Amendment 39-15547; AD 2008-12-04]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-600, -700, -700C, -
800, and -900 Series Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: We are adopting a new airworthiness directive (AD) for certain 
Boeing Model 737-600, -700, -700C, -800, and -900 series airplanes. 
This AD requires various repetitive inspections to detect cracks along 
the chemically milled steps of the fuselage skin or missing or loose 
fasteners in the area of the preventative modification or repairs, 
replacement of the time-limited repair with the permanent repair if 
applicable, and applicable corrective actions if necessary, which would 
end certain repetitive inspections. This AD results from a fatigue test 
that revealed numerous cracks in the upper skin panel at the chemically 
milled step above the lap joint. We are issuing this AD to detect and 
correct such fatigue-related cracks, which could result in the crack 
tips continuing to turn and grow to the point where the skin bay flaps 
open, causing decompression of the airplane.

DATES: This AD is effective July 16, 2008.
    The Director of the Federal Register approved the incorporation by 
reference of a certain publication listed in this AD as of July 16, 
2008.

ADDRESSES: For service information identified in this AD, contact 
Boeing Commercial Airplanes, P.O. Box 3707, Seattle, Washington 98124-
2207.

Examining the AD Docket

    You may examine the AD docket on the Internet at http://www.regulations.gov; or in person at the Docket Management Facility 
between 9 a.m. and 5 p.m., Monday through Friday, except Federal 
holidays. The AD docket contains this AD, the regulatory evaluation, 
any comments received, and other information. The address for the 
Docket Office (telephone 800-647-5527) is the Document Management 
Facility, U.S. Department of Transportation, Docket Operations, M-30, 
West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue, SE., 
Washington, DC 20590.

FOR FURTHER INFORMATION CONTACT: Wayne Lockett, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 
1601 Lind Avenue, SW., Renton, Washington 98057-3356; telephone (425) 
917-6447; fax (425) 917-6590.

SUPPLEMENTARY INFORMATION: 

Discussion

    We issued a notice of proposed rulemaking (NPRM) to amend 14 CFR 
part 39 to include an airworthiness directive (AD) that would apply to 
certain Boeing Model 737-600, -700, -700C, -800, and -900 series 
airplanes. That NPRM was published in the Federal Register on September 
28, 2007 (72 FR 55118) (An extension of the comment period for that 
NPRM was published in the Federal Register on November 14, 2007 (72 FR 
64009)). That NPRM proposed to require various repetitive inspections 
to detect cracks along the chemically milled steps of the fuselage skin 
or missing or loose fasteners in the area of the preventative 
modification or repairs, replacement of the time-limited repair with 
the permanent repair if applicable, and applicable corrective actions 
if necessary, which would end certain repetitive inspections.

Comments

    We gave the public the opportunity to participate in developing 
this AD. We considered the comments received.

Request To Provide Exception for Previously Installed Repairs

    Southwest Airlines notes that the proposed AD does not state how to 
do the inspection in an area that has a previously installed repair. 
Southwest Airlines states that AD 2004-18-06, amendment 39-13784 (69 FR 
54206, September 8, 2004), which addresses chemically milled steps of 
the fuselage skin for Boeing Model 737-200, -200C, -300, -400, and -500 
series airplanes, contains an exception that addresses the issue of a 
previously installed repair. Southwest Airlines asks that we include a 
similar exception in this AD.
    We agree that the NPRM needs to be clarified regarding procedures 
for previously installed repairs, and have added new paragraphs (j) and 
(k) to this AD to explain the exceptions. We note that the exception to 
the procedures required by paragraph (g) of this AD is similar to the 
exception in AD 2004-18-06, except that for this AD, post-preventive 
modifications and repair supplemental inspections are required for 
repairs installed in accordance with Boeing Special Attention Service 
Bulletin 737-53-1232, dated April 2, 2007 (cited as the appropriate 
source of service information for accomplishing the actions in the 
NPRM). We have also re-identified subsequent paragraphs accordingly.

Request To Allow Optional Eddy Current Inspection Method

    Continental Airlines (Continental) requests that we allow the use 
of the eddy current inspection procedures given in the Boeing 737 Non-
Destructive Test (NDT) Manual, Part 6, Subjects 53-30-25 (c-scan eddy 
current inspection), as an alternative to Subjects 53-30-19 and 53-30-
23 listed in Boeing Special Attention Service Bulletin 737-53-1232, 
dated April 2, 2007. Continental notes that the eddy current procedure 
in Subject 53-30-25 was approved as an alternative method of compliance 
(AMOC) for AD 2005-13-27, amendment 39-14164 (70 FR 36821, June 27, 
2005), which mandates a similar fuselage skin inspection for Boeing 
Model 737-300, -400, and -500 series airplanes.
    We agree that the NDT method Continental specifies provides an 
acceptable means to find cracking in the internal surface of the 
fuselage skin at the edge of a sub-surface doubler. Therefore, we have 
revised this AD to include a new paragraph (l)(4) to the AMOC paragraph 
(paragraph (j) of the NPRM). Paragraph (l)(4) states that Boeing Model 
737 NDT Manual, Part 6, Subject 53-30-25, is an AMOC for Subjects 53-
30-19 and 53-30-23.

Request To Clarify Paragraph (g) of the NPRM

    Boeing requests that we clarify the wording in paragraph (g) of the 
NPRM to indicate which corrective actions are required and when. Boeing 
specifically states that the word ``applicable'' is missing from 
paragraph (g) of the NPRM, and requests that the paragraph state 
``accomplishing all of the applicable actions specified in the 
Accomplishment Instructions of the service bulletin.'' Boeing explains 
that, without the word ``applicable,'' the AD would require 
accomplishment of all actions within the Accomplishment Instructions, 
even those that do not apply under certain conditions.
    We agree to clarify paragraph (g) for the stated reasons. We have 
revised paragraph (g) of this AD to include the word ``applicable'' in 
the requested place.

[[Page 32992]]

Request To Improve Detail in Service Bulletin

    The Air Transport Association (ATA) on behalf of its member Delta 
Airlines, requests that we encourage Boeing to improve the level of 
detail in Boeing Special Attention Service Bulletin 737-53-1232, dated 
April 2, 2007, specifically Part V of the Accomplishment Instructions, 
``Preventative Modification.'' The commenters explain that the current 
data and figures for the modification are vague and could lead to 
considerable variation among operators in interpretation and 
installation. The commenters also state that, as a minimum, Boeing 
should issue a set of engineering drawings for typical modification 
parts for each affected group of airplanes, and incorporate them into a 
revision of the service bulletin.
    We disagree that the level of detail in Part V of the service 
bulletin is insufficient. As shown in Part V and its associated 
figures, modification doublers and fillers are to be centered in the 
skin pocket with their width determined by the existing fastener 
spacing common to the lap splice. Adding engineering drawings to the 
information already in the service bulletin could result in confusion 
due to variations in fastener spacing common to the lap joints. We have 
not changed the AD in this regard.

Request To Extend Repetitive Interval To Match C-Check Interval

    The ATA, on behalf of its member Alaska Airlines, requests that we 
extend the repetitive inspection intervals proposed in the NPRM and 
express them in terms of C-check intervals. The commenters explain that 
the current repetitive inspection intervals are not sufficient to 
bridge successive C-checks, and will thus make it necessary to have a 
frequent and possibly repetitive inspection in the line environment. 
The commenters further state that the preventive modification proposed 
in the NPRM would lengthen the repetitive inspection interval from 
1,500 flight cycles to either 4,000 or 6,000 flight cycles. In the 
commenters' opinion, this action does not justify the cost or manpower 
for doing the preventive modification.
    We do not agree with the commenter's request to extend the 
repetitive intervals. We have determined that the proposed compliance 
time represents the maximum interval of time allowable for the affected 
airplanes to continue to safely operate before the modification is 
done. We determined the inspection intervals in this AD using damage 
tolerance methods to ensure that damage can be detected before it 
becomes critical on the structure. Also, compliance intervals cannot be 
based on nonspecific intervals such as a C-check. Since maintenance 
schedules vary among operators, there would be no assurance that 
corrective action would be done within the timeframe for safe operation 
of the airplane. Further, in developing appropriate compliance times 
for this AD, we considered the urgency associated with the subject 
unsafe condition, and the practical aspect of accomplishing the 
required actions within a period of time that corresponds to the normal 
scheduled maintenance for most affected operators. The repetitive 
intervals following preventative modification were part of these 
considerations. We have not changed the AD in this regard.

Conclusion

    We reviewed the relevant data, considered the comments received, 
and determined that air safety and the public interest require adopting 
the AD with the changes described previously. We also determined that 
these changes will not increase the economic burden on any operator or 
increase the scope of the AD.

Costs of Compliance

    There are about 871 airplanes of the affected design in the 
worldwide fleet. This AD affects about 378 airplanes of U.S. registry. 
The inspections take between 11 and 25 work hours per airplane 
depending on the airplane configuration, at an average labor rate of 
$80 per work hour. Based on these figures, the estimated cost of the AD 
for U.S. operators is between $332,640 and $756,000, or between $880 
and $2,000 per airplane, per 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

    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.
    You can find our regulatory evaluation and the estimated costs of 
compliance in the AD Docket.

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 AD:

2008-12-04 Boeing: Amendment 39-15547. Docket No. FAA-2007-29333; 
Directorate Identifier 2007-NM-141-AD.

Effective Date

    (a) This airworthiness directive (AD) is effective July 16, 
2008.

Affected ADs

    (b) None.

Applicability

    (c) This AD applies to Boeing Model 737-600, -700, -700C, -800, 
and -900 series airplanes, certificated in any category; as 
identified in Boeing Special Attention Service Bulletin 737-53-1232, 
dated April 2, 2007.

[[Page 32993]]

Unsafe Condition

    (d) This AD results from a fatigue test that revealed numerous 
cracks in the upper skin panel at the chemically milled step above 
the lap joint. We are issuing this AD to detect and correct such 
fatigue-related cracks, which could result in the crack tips 
continuing to turn and grow to the point where the skin bay flaps 
open, causing decompression of the airplane.

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

    (f) The term ``service bulletin,'' as used in this AD, means 
Boeing Special Attention Service Bulletin 737-53-1232, dated April 
2, 2007.

Inspections and Replacement, As Applicable

    (g) At the applicable compliance times listed in Tables 1, 2, 
and 3 of paragraph 1.E., ``Compliance,'' of the service bulletin, or 
within the time specified in paragraph (g)(1) or (g)(2) of this AD, 
as applicable, whichever occurs later, and thereafter at the 
applicable repeat intervals listed in Tables 1, 2, and 3: Do the 
applicable inspections and replacement by accomplishing all the 
applicable actions specified in the Accomplishment Instructions of 
the service bulletin.
    (1) For airplanes specified in Tables 1 and 2 of paragraph 1.E., 
``Compliance,'' of the service bulletin: Do the applicable initial 
inspection required by paragraph (g) of this AD within 36 months 
after the effective date of this AD.
    (2) For airplanes specified in Table 3 of paragraph 1.E., 
``Compliance,'' of the service bulletin: Do the applicable initial 
inspection and replacement required by paragraph (g) of this AD 
within 24 months after the effective date of this AD.

Corrective Actions

    (h) If any crack or loose or missing fastener is found during 
any applicable inspection required by paragraph (g) of this AD, 
before further flight, do the applicable corrective action in 
accordance with the service bulletin; except, where the service 
bulletin specifies to contact Boeing for appropriate action, before 
further flight, repair the crack using a method approved in 
accordance with the procedures specified in paragraph (l) of this 
AD.

Terminating Action for Certain Repetitive Inspections

    (i) For airplanes on which the preventative modification 
specified in the service bulletin has not been installed: 
Accomplishing the preventative modification, time-limited repair, or 
permanent repair in accordance with the service bulletin ends the 
applicable repetitive external detailed inspections required by 
paragraph (g) of this AD.

Exceptions to the Service Bulletin Procedures for Previously Installed 
Repairs

    (j) For any airplane subject to the requirements of paragraph 
(g) of this AD: Inspections done at the compliance times specified 
in Table 1 of paragraph 1.E., ``Compliance,'' of the service 
bulletin are not required in areas that are spanned by an FAA-
approved repair that has a minimum of 3 rows of fasteners above and 
below the chemically milled step. Post-repair supplemental 
inspections are to be done at the times specified in Table 2 of 
paragraph 1.E., ``Compliance,'' of the service bulletin.
    (k) For any airplane that has an external doubler covering the 
chemically milled step, but the doubler does not span the step by a 
minimum of 3 rows of fasteners above and below the chemically milled 
step: Instead of requesting approval for an alternative method of 
compliance (AMOC) in accordance with the procedures specified in 
paragraph (l) of this AD, one method of compliance with the 
inspection requirement of paragraph (g) of this AD is to inspect all 
chemically milled steps covered by the repair using non-destructive 
test (NDT) methods in accordance with the Boeing 737 NDT Manual, 
Part 6, Subject 53-30-20. These repairs are to be considered time-
limited and are subject to the post-repair supplemental inspections 
and replacement at the times specified in Table 3 of paragraph 1.E., 
``Compliance,'' of the service bulletin.

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) To request a different method of compliance or a different 
compliance time for this AD, follow the procedures in 14 CFR 39.19. 
Before using any approved AMOC on any airplane to which the AMOC 
applies, notify your appropriate principal inspector (PI) in the FAA 
Flight Standards District Office (FSDO), or lacking a PI, your local 
FSDO.
    (3) 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 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.
    (4) Use of Boeing Model 737 NDT Manual, Part 6, Subject 53-30-
25, is an AMOC for Boeing Model 737 NDT Manual, Part 6, Subjects 53-
30-19 and 53-30-23, as specified in the service bulletin.

Material Incorporated by Reference

    (m) You must use Boeing Special Attention Service Bulletin 737-
53-1232, dated April 2, 2007, to do the actions required by this AD, 
unless the AD specifies otherwise.
    (1) The Director of the Federal Register approved the 
incorporation by reference of this service information under 5 
U.S.C. 552(a) and 1 CFR part 51.
    (2) For service information identified in this AD, contact 
Boeing Commercial Airplanes, P.O. Box 3707, Seattle, Washington 
98124-2207.
    (3) You may review copies of the service information 
incorporated by reference at the FAA, Transport Airplane 
Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the 
National Archives and Records Administration (NARA). For information 
on the availability of this material at NARA, call 202-741-6030, or 
go to: http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html.

    Issued in Renton, Washington, on May 29, 2008.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
 [FR Doc. E8-12761 Filed 6-10-08; 8:45 am]
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