AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

SUMMARY: We are adopting a new airworthiness directive (AD) for certain
The Boeing Company Model 737-600, -700, -700C, -800, and -900 series
airplanes. This AD was prompted by a report of cracks found in the skin at
body station (STA) 540 just below stringer S-22L on a Model 737-700 series
airplane. This AD requires repetitive detailed and high frequency eddy current
inspections for cracking of the skin around the eight fasteners common to the
ends of the STA 540 bulkhead chords between stringers S-22 and S-23, left
and right sides; and corrective actions and preventive modification if
necessary. We are issuing this AD to detect and correct fatigue cracking in
the skin, which can result in rapid decompression of the cabin.

DATES: This AD is effective November 4, 2013.
The Director of the Federal Register approved the incorporation by
reference of a certain publication listed in the AD as of November 4,
2013.

ADDRESSES: For service information identified in this AD, contact
Boeing Commercial Airplanes, Attention: Data & Services Management,
P.O. Box 3707, MC 2H-65, Seattle, WA 98124-2207; telephone 206-544-
5000, extension 1; fax 206-766-5680; Internet https://www.myboeingfleet.com.
You may review copies of the referenced service information at the FAA,
Transport Airplane Directorate, 1601 Lind Avenue SW., Renton, WA. For
information on the availability of this material at the FAA, call 425-227-1221.

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 (phone: 800-647-5527) is 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: Alan Pohl, Aerospace Engineer,
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office,
1601 Lind Avenue SW., Renton, WA 98057-3356; phone: 425-917-6450; fax:
425-917-6590; email: alan.pohl@faa.gov.

SUPPLEMENTARY INFORMATION:

Discussion

We issued a notice of proposed rulemaking (NPRM) to amend 14 CFR
part 39 to include an AD that would apply to the specified products.
The NPRM published in the Federal Register on July 25, 2012 (77 FR
43547). The NPRM proposed to require repetitive detailed and high
frequency eddy current (HFEC) inspections for cracking of the skin
around the eight fasteners common to the ends of the STA 540 bulkhead
chords between stringers S-22 and S-23, left and right sides; and
corrective actions and preventive modification if necessary.

Comments

We gave the public the opportunity to participate in developing
this AD. The following presents the comments received on the proposal
(77 FR 43547, July 25, 2012) and the FAA's response to each comment.

Concurrence

The Boeing Company concurred with the content of the NPRM (77 FR
43547, July 25, 2012).

Support of Compliance Time

AirTran/Southwest Airlines stated that the inspection threshold and
intervals will fit within its planned scheduled maintenance checks. The
commenter also stated that the number of man-hours and elapsed time to
accomplish the NPRM (77 FR 43547, July 25, 2012) will not impact the
overall span-time of its planned scheduled maintenance check.

Request To Change the Compliance Time

American Airlines requested that all airplanes have the same
compliance time of 26,500 total flight cycles with a grace period of
6,500 flight cycles. The commenter explained that since the NPRM (77 FR
43547, July 25, 2012) is for the same type of airplanes with the same
condition, they should have the same compliance time regardless of the
amount of flight cycles at the time of the AD release date. The
commenter noted that the NPRM specifies a compliance time of 18,000
total flight cycles with a grace period of 4,000 flight cycles for
airplanes with less than 27,500 total flight cycles. The commenter also
stated that the 4,000 flight cycle grace period does not allow enough
time for operators to have two good opportunities to accomplish the
inspections during normal maintenance visits.
We disagree with changing the compliance times. In developing
appropriate compliance times for this action, 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 shorter compliance time for airplanes with higher number
of total flight cycles addresses the increased likelihood of cracking
or larger cracks being present. Under the provisions of paragraph (l)
of this final rule, we will consider requests for approval of an
adjustment of the compliance time if sufficient data are submitted to
substantiate that the new compliance time would provide an acceptable
level of safety. No change has been made to this final rule in this
regard.

Request for Increased Repetitive Inspection Intervals

American Airlines requested that the repetitive inspection interval
of 4,000 flight cycles specified in the NPRM (77 FR 43547, July 25,
2012) be changed to at least 8,000 flight cycles to coordinate with
heavy maintenance visits to provide the least amount of impact during
the maintenance visit. The commenter stated that it does not believe
that we have provided sufficient evidence to warrant such a tight
repetitive inspection interval if no cracks are found after the initial
inspection. The commenter also noted that since this crack has only
been found on one airplane, it is not certain how susceptible the rest
of the fleet is to develop skin cracks at body station (BS)540.
We disagree with increasing the repetitive inspection interval. In
developing an appropriate repetitive inspection interval for this
action, 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 interval was
determined using the same methodology as for other cracks of primary
structure addressed in other airworthiness directives. No data has been
offered that would substantiate a change to this final rule. Under the
provisions of paragraph (l) of this final rule, we will consider
requests for approval of an adjustment of the repetitive inspection
interval if sufficient data are submitted to substantiate that the new
interval would provide an acceptable level of safety. No change has
been made to this final rule in this regard.

Request To Change Cost Estimate

American Airlines requested that we change the Cost of Compliance
table to account for the removal and installation of the ram air
transition duct and the recirculation air filter housing. American Airlines
stated the ram air transition duct must be removed to accomplish the
inspection of the skin around the 8 fasteners and will add an additional
2 work-hours (open and close) for each airplane. American Airlines re-
quested that the labor cost for the inspection be changed to 5 work-
hours rather than the estimated 3 work-hours specified in the NPRM (77
FR 43547, July 25, 2012) to include the removal and installation of the
ram air transition duct. American Airlines also stated that the recirculation
air filter housing must be removed to accomplish the preventative
modification and will add an additional 6 work-hours (open and close)
for each airplane. American Airlines also noted that the current price
for the modification kit is $993, rather than $894 as referenced in the
NPRM (77 FR 43547, July 25, 2012).
We partially agree with the request to change the Cost of
Compliance table. We disagree with the figures used by the commenter.
The work-hours, however, have been revised in Boeing Special Attention
Service Bulletin 737-53-1294, Revision 1, dated June 14, 2013. The Cost
of Compliance table has been revised accordingly.

Request To Allow the Use of Grip Length Adjustment Washers

AirTran/Southwest Airlines requested that we add Note 6 of the
Accomplishment Instructions of Boeing Special Attention Service
Bulletin 737-53-1294, dated March 31, 2011, to allow the use of grip
length adjustment washers to accomplish the NPRM (77 FR 43547, July 25,
2012).
We disagree. Note 5 of the Accomplishment Instructions of Boeing
Special Attention Service Bulletin 737-53-1294, Revision 1, dated June
14, 2013 (previously Note 6 of the Accomplishment Instructions of
Boeing Special Attention Service Bulletin 737-53-1294, dated March 31,
2011), states, ``If the length of any fastener specified in this
service bulletin does not meet the installation standards in SRM
[structural repair manual] Chapter 51, then a fastener of the same
specification, or an approved substitute, with a length which meets the
installation standards in SRM Chapter 51 may be used.'' Since the
installation standards of Section 51 of the SRM include the use of grip
length adjustment washers, no additional authorization is necessary. No
change has been made to this final rule in this regard.

Request To Remove or Modify Paragraph (i)(4) of the NPRM (77 FR
43547, July 25, 2012)

AirTran/Southwest Airlines requested that paragraph (i)(4) of the
NPRM (77 FR 43547, July 25, 2012) be removed. AirTran/Southwest
Airlines requested that we allow the operator to determine the sequence
in which steps are to be accomplished for the inspections and
modifications, otherwise, the operators may inadvertently violate the
AD by performing unrelated tasks out of sequence.
American Airlines requested that we remove or modify paragraph
(i)(4) of the NPRM (77 FR 43547, July 25, 2012) stating that paragraph
(i)(4) is more restrictive than necessary to ensure safety of flight.
American Airlines stated that not being able to accomplish some steps
out of order will prevent accomplishment of the AD in a timely manner.
American Airlines suggested modifying paragraph (i)(4) of the NPRM (77
FR 43547, July 25, 2012) to allow the modifications and repairs to be
accomplished in any order as long as the steps within those actions are
accomplished in order.
We agree to remove paragraph (i)(4) of the NPRM (77 FR 43547, July
25, 2012). We have received Boeing Special Attention Service Bulletin
737-53-1294, Revision 1, dated June 14, 2013, which removes
instructions regarding the sequencing of steps and changes certain part
numbers. We have revised paragraphs (c), (g), (h), (i), and (j) of this
final rule to refer to Boeing Special Attention Service Bulletin 737-
53-1294, Revision 1, dated June 14, 2013. We have also added new
paragraph (k) to this final rule to allow credit for the actions
required by paragraphs (g), (h), (i), and (j) of this AD, if those
actions were performed before the effective date of this final rule
using Boeing Special Attention Service Bulletin 737-53-1294, dated
March 31, 2011. Subsequent paragraphs have been redesignated
accordingly.

Request To Allow Removal of Additional or Fewer Parts, and Include
Jacking and Shoring Limitations

AirTran/Southwest Airlines requested that we include a statement
stating that it is acceptable to remove additional, or fewer, parts as
necessary; however, jacking and shoring limitations must be observed.
We partially agree with the request. We agree that clarification is
needed regarding removal of additional or fewer parts. We infer that
this comment concerns instructions in Boeing Special Attention Service
Bulletin 737-53-1294, dated March 31, 2011, regarding access and
restoration, which are not required to address the unsafe condition.
However, we disagree with requiring jacking and shoring limitations in
this final rule because those actions are not required to address the
unsafe condition. Operators may perform those actions in accordance
with approved maintenance procedures. We have added new paragraph
(i)(4) to this final rule to state that access and close actions
identified in Boeing Special Attention Service Bulletin 737-53-1294,
Revision 1, dated June 14, 2013, are not required by this final rule.
We have also revised paragraphs (g) and (h) of this final rule to refer
to paragraph (i)(4) of this final rule.

STC Winglet Comment

Aviation Partners Boeing stated that the installation of winglets
per STC ST00830SE does not affect them.
We have redesignated paragraph (c) of the NPRM (77 FR 43547, July
25, 2012) as paragraph (c)(1) in this AD and added paragraph (c)(2) to
this AD to state that installation of STC ST00830SE (http://rgl.faa.gov/
Regulatory_and_Guidance_Library/rgstc.nsf/0/408E 012E008616A786257
8880060456C?OpenDocument&Highlight=st00830se) does not affect the
ability to accomplish the actions required by this final rule. Therefore, for
airplanes on which STC ST00830SE is installed, a ``change in product''
alternative method of compliance (AMOC) approval request is not necessary
to comply with the requirements of 14 CFR 39.17. For all other AMOC requests,
the operator must request approval for an AMOC in accordance with the
procedures specified in paragraph (l) of this final rule.

Conclusion

We reviewed the relevant data, considered the comments received,
and determined that air safety and the public interest require adopting
this AD with the change described previously and minor editorial
changes. We have determined that these minor changes:
Are consistent with the intent that was proposed in the
NPRM (77 FR 43547, July 25, 2012) for correcting the unsafe condition;
and
Do not add any additional burden upon the public than was
already proposed in the NPRM (77 FR 43547, July 25, 2012).
We also determined that these changes will not increase the
economic burden on any operator or increase the scope of this AD.

Costs of Compliance

We estimate that this AD affects 903 airplanes of U.S. registry. We
estimate the following costs to comply with this AD:

Estimated Costs

We estimate the following costs to do any necessary repairs and
inspections that would be required based on the results of the
inspection. We have no way of determining the number of aircraft that
might need these repairs:

On-Condition Costs

According to the manufacturer, some of the costs of this AD may be
covered under warranty, thereby reducing the cost impact on affected
individuals. We do not control warranty coverage for affected
individuals. As a result, we have included all costs in our cost
estimate.

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),
(3) Will not affect intrastate aviation in Alaska, and
(4) 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.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Incorporation by
reference, Safety.

Adoption of the Amendment

Accordingly, under the authority delegated to me by the
Administrator, the FAA amends 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):