Airworthiness Directives; Boeing Model 737-200, -300, -400, and -500 Series Airplanes, 252-256 [E6-22462]

Agencies

• Federal Aviation Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 72, Number 2 (Thursday, January 4, 2007)]
[Rules and Regulations]
[Pages 252-256]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E6-22462]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2005-22629; Directorate Identifier 2005-NM-089-AD; 
Amendment 39-14867; AD 2006-26-09]
RIN 2120-AA64


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

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

ACTION: Final rule.

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SUMMARY: The FAA is adopting a new airworthiness directive (AD) for 
certain Boeing Model 737-200, -300, -400, and -500 series airplanes. 
This AD requires a one-time inspection of the frames between station 
360 and station 907 to determine if a subject support bracket for the 
air conditioning outlet extrusion is installed, and related repetitive 
investigative actions and repair if necessary. This AD also provides an 
optional preventive modification that ends the repetitive investigative 
actions. This AD also requires a one-time post-modification/repair 
inspection for cracking of each repaired/modified frame. This AD 
results from numerous reports indicating that frame cracks have been 
found at the attachment holes for support brackets for the air 
conditioning outlet extrusion. We are issuing this AD to detect and 
correct such cracking, which, if the cracking were to continue to grow, 
could result in a severed frame. A severed frame, combined with 
existing multi-site damage at the stringer 10 lap splice, could result 
in rapid decompression of the airplane.

DATES: This AD becomes effective February 8, 2007.
    The Director of the Federal Register approved the incorporation by 
reference of a certain publication listed in the AD as of February 8, 
2007.

ADDRESSES: You may examine the AD docket on the Internet at https://
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, P.O. Box 3707, Seattle, 
Washington 98124-2207, for the service information identified in this 
AD.

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:

Examining the Docket

    You may examine the airworthiness directive (AD) docket on the 
Internet at https://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 certain Boeing Model 
737-200, -300, -400, and -500 series airplanes. That NPRM was published 
in the Federal Register on October 6, 2005 (70 FR 58358). That NPRM 
proposed to require a one-time inspection of frames between station 360 
and station 907 to determine if a subject support bracket for the air 
conditioning outlet extrusion is installed, and related repetitive 
investigative actions and repair if necessary. That NPRM also proposed 
to provide an optional preventive modification that would end the 
repetitive investigative actions. That NPRM also proposed to require a 
one-time post-modification/repair inspection for cracking of each 
repaired/modified frame.

Comments

    We provided the public the opportunity to participate in the 
development of this AD. We have considered the comments received.

Request To Extend Certain Compliance Times

    KLM Royal Dutch Airlines (KLM), and the Air Transport Association 
(ATA), on behalf of United Airlines (UAL) and US Airways, ask that the 
compliance time for the inspection be changed to coincide with 
scheduled maintenance checks.
    UAL notes that the 6,000-flight-cycle interval for the post-
modification/repair inspection (between 18,000 and 24,000 flight 
cycles) does not fall into a compatible maintenance opportunity. UAL 
states that, when given the opportunity by Boeing to review the 
preliminary service bulletin, the requirement for this inspection was 
``within 30,000 flight cycles.'' UAL asks if there is an alternative 
inspection method, such as an open hole eddy current inspection, which 
would extend the 6,000-flight-cycle repetitive inspection interval to 
9,000 flight cycles to align with a heavy maintenance check.
    US Airways adds that the repeat inspection interval will have an 
adverse impact on operations. US Airways also adds that the repeat 
inspection interval seems to be arbitrary and unreasonable, and it 
imposes undue costs to the airline. US Airways has been addressing this 
issue since 1999, and notes that the existing maintenance program 
currently has a repeat inspection interval of 12,500 flight hours or 
approximately 9,375 flight cycles for the inspection for frame cracks 
in this location. US Airways adds that the inspection program has 
proven adequate to find and repair these cracks before they have an 
adverse impact on the structural integrity of the airplane. US Airways 
concludes that the increased inspection interval mentioned previously 
also minimizes impact to fleet operations, while still maintaining a 
sufficient level of safety. US Airways requests that the repeat 
inspection interval be increased to align with the existing scheduled 
heavy maintenance visits.
    KLM states that page 3 of the NPRM, under ``Relevant Service 
Information,'' specifies a compliance time of 5,000 flight cycles after 
the date of the service bulletin for the initial inspection, and an 
interval of 6,000 flight cycles for the repetitive inspections. KLM 
adds that the inspection is applicable to all frames, which amounts to 
35 frames on the left- and right-hand sides, for a total of 70 
inspection areas on a Boeing Model 737-300 airplane. Due to the extent 
of this work, the inspection in the NPRM must be accomplished during a 
planned maintenance check, preferably a D-check when the support 
brackets are

[[Page 253]]

accessible. Based on the current inspection interval, the inspection 
must be accomplished during a C-check, which necessitates additional 
work. KLM asks if we have considered possible cycle interval changes in 
order to relieve the economic burden of this inspection.
    We agree with the commenters' request to extend the inspection 
interval. We have worked with Boeing to expand the standard analysis 
methodology to better model service experience. The new analysis 
methodology allows for longer compliance times and longer grace periods 
for airplanes that did not have lower row lap splice cracking concerns.
    The new compliance times are identified in paragraph 1.E., 
``Compliance,'' of Revision 1 of Boeing Special Attention Service 
Bulletin 737-53-1216, dated June 8, 2006. The new compliance times for 
the initial general visual, medium frequency eddy current (MFEC) and 
high frequency eddy current (HFEC) inspections, as applicable, are 
prior to the accumulation of 40,000 total flight cycles, or within 
5,000 or 9,000 flight cycles (depending on the airplane configuration) 
after issuance of the service bulletin, whichever occurs later. The 
service bulletin specifies a repetitive interval (for all subject 
frames) of 9,000 flight cycles. We have reviewed the procedures in 
Revision 1 and have determined that they are essentially the same as 
those in the original issue of the service bulletin (which was 
referenced in the NPRM). The effectivity section in Revision 01 shows 
changes of airplane operators; however, Revision 01 does not 
necessitate additional work. Therefore, we have revised this AD to 
refer to Revision 1 of the service bulletin as the appropriate source 
of service information for accomplishing the required actions at the 
new extended compliance times. We have also added a statement to 
paragraph (l) of this AD that gives credit for actions accomplished 
before the effective date of this AD in accordance with the original 
issue of the service bulletin.

Request To Adopt an Alternative Compliance/Inspection Schedule

    Southwest Airlines (SWA) requests that we consider an alternative 
inspection method--an external detailed visual inspection--that would 
extend the grace period from 5,000 flight cycles to a total of 10,000 
flight cycles, particularly for airplanes that are not susceptible to 
multi-site damage. SWA notes that the areas of inspection are not 
easily accessible as those areas are located behind the overhead bins. 
SWA adds that the majority of operators do not have convenient 
scheduled maintenance visits that result in access to the interior area 
behind the overhead bins within a span of 5,000 or 6,000 flight cycles. 
SWA suggests revising the repetitive inspection requirements (every 
6,000 flight cycles) to longer thresholds (every 10,000 flight cycles) 
for airplanes over 30,000 flight cycles, provided that the external 
inspections are being accomplished. SWA proposes an alternative 
inspection option for those airplanes that are not susceptible to 
multi-site damage, as follows:
     Airplanes with less than 40,000 total flight cycles.
     Airplanes on which Boeing Service Bulletin 737-53A1177, 
Revision 6, has been done for lap joint repairs, including window belt 
replacements.
     Airplanes having line numbers 2553 and above, on which the 
lower row of fasteners of the stringer 10 lap joint is not susceptible 
to cracking.
    SWA provided an example of an alternative compliance/inspection 
table, which could be used for airplanes having over 30,000 flight 
cycles.
    We agree partially with the commenter's request. As stated 
previously under ``Request to Extend Certain Compliance Times,'' we 
have changed the compliance time in the AD to allow for better 
maintenance scheduling for operators. However, in order for operators 
to accomplish an inspection that is not specified in the AD, they must 
request and receive approval of an alternative method of compliance 
(AMOC) in accordance with paragraph (m) of this AD. This is necessary 
so that we can make a specific determination that an alternative 
inspection does or does not address the identified unsafe condition. 
If, after reviewing the changes included in this AD, SWA still wants to 
pursue the alternative inspection proposal, it can request an AMOC.

Request To Change Paragraph (f) of This AD

    Boeing asks that the second sentence in paragraph (f) of the NPRM 
be changed to eliminate the reference to ``part number (P/N) 65C7021.'' 
Boeing reiterated the wording in that sentence and suggested it be 
changed to read, ``Subject support brackets are attached to the frame 
with two rivets.'' Boeing states that this change is required because 
the P/N may not be visible or even exist on the bracket, but the 
brackets can be easily identified by the number of fasteners attaching 
them to the frame. The structural detail of concern in the referenced 
service bulletin is the two fastener attachments. There are some air 
conditioning brackets (not having P/N 65C7021-( )) attached to the 
frame with three or more fasteners, but there is no known cracking at 
these locations.
    We agree with the commenter's request for the reasons provided by 
the commenter. We have changed paragraph (f) of this AD accordingly.

Request To Clarify Which Frames Require Inspection

    ATA, on behalf of Alaska Airlines, requests clarification of 
inspection requirements. Alaska states that the NPRM is not clear on 
the inspection requirements for the subject frames, and asks that 
clarification be provided in the final rule. Alaska also asks if 
access/identification of the brackets at the frame locations specified 
in the referenced service bulletin is required.
    In addition, Alaska asks for clarification of the requirements for 
the optional preventive modification specified in paragraph (i) of the 
NPRM. Alaska states that the frames that do not require inspection may 
have two rivet attachments.
    We agree that clarification is needed for the reason provided by 
the commenter. The frames between stations 360 and 907 that have a 
support bracket with a two-rivet configuration attached need to be 
identified and inspected. The specific bracket does not need to be 
identified by part number. Inspection of the frames at stations 540, 
663.75, 685, and 727 is not necessary. In addition, inspection of the 
frames at stations 616 and 601 on Model 737-200/-300/-400/-500 
airplanes and the frames at stations 578 and 601 on Model 737-400 
airplanes is not necessary. These frames are not susceptible to 
cracking at the bracket attachment. The optional preventive 
modification is not necessary for frames not susceptible to cracking. 
We have revised paragraph (f) of this AD to clarify the frames that do 
require an inspection. The change for paragraph (f) of this AD also 
clarifies the provision for the optional preventive modification as 
specified in paragraph (i) of this AD.

Request To Include Previously Repaired Frames

    United Airlines (UAL) states that neither the referenced service 
bulletin nor the NPRM addresses the disposition of a frame that has 
been repaired previously per the structural repair manual (SRM). UAL 
adds that inspection requirements are included in the service bulletin, 
but the corrective action necessary for cracking found during an 
inspection of a frame repaired

[[Page 254]]

previously per the SRM is not included. In addition, an option to 
install a new repair on a frame that was repaired previously per the 
SRM in order to end the repetitive inspection requirement is not 
included.
    We agree partially with the commenter. We infer that the commenter 
wants further instruction on corrective action for discrepancies found 
in previously repaired frames and an option to install a new repair on 
those frames. We understand that installation of the generic frame 
repairs described in the SRM may vary extensively, depending on the 
original damage being repaired; however, guidelines do not exist to 
allow evaluation of these frame repairs for appropriate follow-on 
action. We agree that guidelines could be created that would allow the 
operator to evaluate the frame repair that is installed currently for 
appropriate follow-on actions. Such guidelines could be evaluated for 
issuance of an AMOC. Operators may request approval of an AMOC for 
repairs that are not identified in this AD under the provisions of 
paragraph (m)(1) of this AD. We have made no change to the AD in this 
regard.

Request for Credit for Previously Accomplished Actions

    ATA, on behalf of Delta Airlines (DAL), states that on August 20, 
2002, Boeing issued All Operator Message M-7200-02-01292. The message 
specifies accomplishing medium frequency eddy current inspections of 
affected brackets for airplanes with less than 30,000 total flight 
cycles, or within 5,000 flight cycles after issuance of the message, 
whichever occurred later. The inspections are to be repeated every 
6,000 flight cycles (except where repairs or modifications were 
installed). The message also describes typical repairs and a 
terminating modification. DAL adds that neither the NPRM or the 
referenced service bulletin refer to the message or to the inspections 
and repairs accomplished per the message. DAL notes that this is a 
serious omission, as operators have been accomplishing inspections and 
repairs per the message during the twenty-eight months between issuance 
of the message and issuance of the referenced service bulletin. DAL 
states that credit for inspection/repairs and modifications 
accomplished in accordance with the message should be given in the AD.
    We agree with the commenter's request for the reasons provided. We 
have reviewed Boeing Communication M-7200-02-01292, dated August 20, 
2002, and find that the procedures therein are essentially the same as 
the procedures specified in the referenced service bulletin. Therefore, 
we have added a new paragraph (j) to the AD, and re-identified 
subsequent paragraphs, to give credit for actions accomplished before 
the effective date of this AD per the Boeing communication. The Boeing 
communication does not specify any post repair or modification 
inspection, therefore, operators are still required to accomplish those 
actions required by paragraph (k) of this AD.

Request To Increase Work Hours

    KLM, and ATA, on behalf of UAL and U.S. Airways, ask that the work 
hours included in the Costs of Compliance section of the NPRM be 
increased.
    UAL states that there is an enormous amount of open-up required to 
do the inspection that is not taken into account in the Costs of 
Compliance section of the NPRM.
    US Airways states that the cost section does not accurately reflect 
the actual cost of the NPRM to the airline industry. U.S. Airways notes 
that the frames between station 360 and station 907 are affected by the 
subject inspection and encompass essentially all of section 43 and 
section 46 of the airplane. Passenger seats, passenger service units, 
overhead bins, and sidewall liners must be removed to accommodate the 
inspection. This excessive teardown of the interior passenger cabin 
will add considerable downtime to this inspection. These interior 
passenger cabin items are not routinely removed at the intervals 
required by the initial inspection, nor the repeat inspection intervals 
(6,000 flight cycles), identified by the NPRM. Additionally, the Costs 
of Compliance section does not reflect an accurate time required to 
perform repairs should any cracks be found. U.S. Airways requests that 
the Costs of Compliance section be revised to accurately reflect the 
impact this NPRM would have on the industry by including factors for 
interior tear down and assembly for the initial and repeat inspections, 
plus a more accurate downtime cost incurred to accomplish repairs.
    KLM states that the work hours specified for the preventive 
modification and repair specified in the Costs of Compliance section 
are conservative. The estimated costs are based upon the inspection 
itself, while all activities to gain access to the support brackets are 
not taken into account. KLM adds that the work hours required to gain 
access in accordance with the referenced service bulletin are 
conservative when taking into account that passenger seats, service 
units, overhead stowage bins, and sidewall lining need to be removed. 
KLM requests that a more realistic number of work hours be specified in 
the Costs of Compliance section.
    We do not agree with the commenters' requests. The cost information 
below describes only the direct costs of the specific actions required 
by this AD. Based on the best data available, the manufacturer provided 
the number of work hours (2 work hours per frame) necessary to do the 
required actions. This number represents the time necessary to perform 
only the actions actually required by this AD. We recognize that, in 
doing the actions required by an AD, operators may incur incidental 
costs in addition to the direct costs. The cost analysis in AD 
rulemaking actions, however, typically does not include incidental 
costs such as the time required to gain access and close up, time 
necessary for planning, or time necessitated by other administrative 
actions. Those incidental costs, which may vary significantly among 
operators, are almost impossible to calculate. We have not changed the 
AD in this regard.
    We do not agree that the on-condition costs specified in the NPRM 
for time required to perform repairs if any cracks are found is 
inaccurate. As we noted above, the information provided by the 
manufacturer is the latest information we have, and that information 
has been used as the time required to perform repairs. We have not 
changed the AD in this regard.

Conclusion

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

Costs of Compliance

    There are about 2,131 airplanes of the affected design in the 
worldwide fleet. This AD affects about 938 airplanes of U.S. registry. 
The inspection to identify subject support brackets, and subsequent 
MFEC and HFEC inspections take about 2 work hours per frame, with 
approximately 32 to 45 frames to be inspected per airplane, at an 
average labor rate of $65 per work hour. Based on these figures, the 
estimated cost of the AD for U.S. operators is between $3,902,080 and 
$5,487,300, or between $4,160 and $5,850 per airplane.

[[Page 255]]

    The following table provides the estimated costs for U.S. operators 
to comply with the inspections of each frame for cracking, the 
preventive modification, and the repair specified in this AD, at an 
average labor rate of $65 per work hour. Note that the estimated cost 
specified in the table is per frame, not per airplane, as it is unknown 
how many frames on each airplane will have a subject bracket installed.

                      Estimated On-Condition Costs
------------------------------------------------------------------------
                                                               Cost per
            Action              Work hours       Parts          frame
------------------------------------------------------------------------
Preventive modification......            4  Operator-               $260
                                             provided.
Repair.......................            6  $608...........          998
------------------------------------------------------------------------

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 and placed it in the AD docket. 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 Federal Aviation Administration (FAA) amends Sec.  39.13 by 
adding the following new airworthiness directive (AD):

2006-26-09 Boeing: Amendment 39-14867. Docket No. FAA-2005-22629; 
Directorate Identifier 2005-NM-089-AD.

Effective Date

    (a) This AD becomes effective February 8, 2007.

Affected ADs

    (b) None.

Applicability

    (c) This AD applies to Boeing Model 737-200, -300, -400, and -
500 series airplanes; certificated in any category; as identified in 
Boeing Special Attention Service Bulletin 737-53-1216, Revision 1, 
dated June 8, 2006.

Unsafe Condition

    (d) This AD results from numerous reports indicating that frame 
cracks have been found at the attachment holes for support brackets 
for the air conditioning outlet extrusion. We are issuing this AD to 
detect and correct such cracking, which, if the cracking were to 
continue to grow, could result in a severed frame. A severed frame, 
combined with existing multi-site damage at the stringer 10 lap 
splice, could result in rapid 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.

Inspection to Determine Subject Support Brackets

    (f) Perform a one-time general visual inspection of the frames 
between station 360 and station 907 to identify the support brackets 
for the air conditioning outlet extrusion attached with a two-rivet 
configuration, in accordance with Part I of the Accomplishment 
Instructions of Boeing Special Attention Service Bulletin 737-53-
1216, Revision 1, dated June 8, 2006. Do this inspection at the 
applicable time specified in paragraph 1.E., ``Compliance,'' of the 
service bulletin, except, where the service bulletin specifies a 
compliance time after the issuance of the service bulletin, this AD 
requires compliance within the specified compliance time after the 
effective date of this AD.

Repetitive Inspections for Cracking

    (g) For each frame with a subject support bracket identified 
during the inspection in accordance with paragraph (f) of this AD: 
Perform a medium-frequency eddy current inspection for cracking of 
the frame around the attachment rivets of the support bracket, and a 
high-frequency eddy current inspection for cracking of the frame 
adjacent to the inboard fastener hole, by doing all the actions 
specified in and in accordance with Part I of the Accomplishment 
Instructions of Boeing Special Attention Service Bulletin 737-53-
1216, Revision 1, dated June 8, 2006, except for paragraph 3.B.2. of 
Part I (which was already done in accordance with paragraph (f) of 
this AD). Do the initial inspections at the applicable time 
specified in paragraph 1.E., ``Compliance,'' of the service 
bulletin, except, where the service bulletin specifies a compliance 
time after the issuance of the service bulletin, this AD requires 
compliance within the specified compliance time after the effective 
date of this AD. If no cracking is found, repeat the inspections 
thereafter at intervals not to exceed the repeat interval specified 
in paragraph 1.E., ``Compliance,'' of the service bulletin, until 
paragraph (h) or (i) of this AD is done.

Repair

    (h) For any frame in which cracking is found during any 
inspection required by paragraph (g) of this AD: Before further 
flight, repair the cracking by doing all applicable actions in 
accordance with Part III of the Accomplishment Instructions of 
Boeing Special Attention Service Bulletin 737-53-1216, Revision 1, 
dated June 8, 2006. Then, do paragraph (k) of this AD, at the time 
specified in that paragraph. Doing this repair ends the repetitive 
inspections required by

[[Page 256]]

paragraph (g) of this AD for each modified frame.

Optional Preventive Modification

    (i) For any frame on which a support bracket for the air 
conditioning outlet extrusion attached with a two-rivet 
configuration is installed: Doing all actions associated with the 
preventive modification in accordance with Part II of the 
Accomplishment Instructions of Boeing Special Attention Service 
Bulletin 737-53-1216, Revision 1, dated June 8, 2006, ends the 
repetitive inspections required by paragraph (g) of this AD for each 
modified frame. Do the requirements of paragraph (k) of this AD on 
each modified frame at the time specified in that paragraph.

Actions Accomplished According to Related Service Information

    (j) Actions accomplished before the effective date of this AD 
according to Boeing Communication M-7200-02-01292, dated August 20, 
2002; are considered acceptable for compliance with the 
corresponding actions specified in paragraphs (f), (g), (h), and (i) 
of this AD, as applicable.

Post-Modification/Repair Inspections

    (k) For each frame repaired or modified in accordance with 
paragraph (h), (i), or (j) of this AD, as applicable: Within 24,000 
flight cycles after doing the modification/repair, but after a 
minimum of 18,000 flight cycles after doing the modification/repair, 
do one-time detailed inspections for cracking of the repaired/
modified frame, air conditioning attach brackets, and stringer 
clips, by doing all actions in accordance with Part IV of the 
Accomplishment Instructions of Boeing Special Attention Service 
Bulletin 737-53-1216, Revision 1, dated June 8, 2006. If any 
cracking is found during the post-modification/repair inspections, 
before further flight, repair the cracking using a method approved 
in accordance with paragraph (m) of this AD.

Actions Accomplished Previously

    (l) Inspections/modifications/repairs done before the effective 
date of this AD in accordance with Boeing Special Attention Service 
Bulletin 737-53-1216, dated January 27, 2005, are acceptable for 
compliance with the corresponding actions required by this AD.

Alternative Methods of Compliance (AMOCs)

    (m)(1) The Manager, Seattle Aircraft Certification Office (ACO), 
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 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.
    (3) Before using any AMOC approved in accordance with 14 CFR 
39.19 on any airplane to which the AMOC applies, notify the 
appropriate principal inspector in the FAA Flight Standards 
Certificate Holding District Office.

Material Incorporated by Reference

    (n) You must use Boeing Special Attention Service Bulletin 737-
53-1216, Revision 1, dated June 8, 2006, 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 
https://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 https://
www.archives.gov/federal_register/code_of_federal_
regulations/ibr_locations.html.

    Issued in Renton, Washington, on December 21, 2006.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. E6-22462 Filed 1-3-07; 8:45 am]
BILLING CODE 4910-13-P