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[Federal Register Volume 77, Number 196 (Wednesday, October 10, 2012)]
[Proposed Rules]
[Pages 61550-61559]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2012-24805]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2011-0155; Directorate Identifier 2009-NM-141-AD]
RIN 2120-AA64

Airworthiness Directives; The Boeing Company Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Supplemental notice of proposed rulemaking (NPRM); reopening of 
comment period.

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SUMMARY: We are revising an earlier proposed airworthiness directive 
(AD) for certain Model 737-200, -200C, -300, -400, and -500 series 
airplanes. That proposed AD would have superseded an existing AD that 
applies to certain The Boeing Company Model 737-200, -200C, -300, -400, 
and -500 series airplanes. The existing AD currently requires 
repetitive inspections to find fatigue cracking of certain upper and 
lower skin panels of the fuselage, and follow-on and corrective actions 
if necessary. The existing AD also includes a terminating action for 
the repetitive inspections of certain modified or repaired areas only. 
That NPRM proposed to add new inspections for cracking of the fuselage 
skin along certain chem-milled lines, and corrective actions if 
necessary. That NPRM also proposed to reduce certain thresholds and 
intervals required by the existing AD. This action revises that NPRM by 
reducing the proposed repetitive inspection intervals. We are proposing 
this supplemental NPRM to detect and correct fatigue cracking of the 
skin panels, which could result in sudden fracture and failure of the 
skin panels of the fuselage, and consequent rapid decompression of the 
airplane. Since these actions impose an additional burden over that 
proposed in the previous NPRM, we are reopening the comment period to 
allow the public the chance to comment on these proposed changes.

DATES: We must receive comments on this supplemental NPRM by November 
26, 2012.

ADDRESSES: You may send comments, using the procedures found in 14 CFR 
11.43 and 11.45, by any of the following methods:
     Federal eRulemaking Portal: Go to http://www.regulations.gov. Follow the instructions for submitting comments.
     Fax: 202-493-2251.
     Mail: U.S. Department of Transportation, Docket 
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New 
Jersey Avenue SE., Washington, DC 20590.
     Hand Delivery: U.S. Department of Transportation, Docket 
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New 
Jersey Avenue SE., Washington, DC 20590, between 9 a.m. and 5 p.m., 
Monday through Friday, except Federal holidays.
    For service information identified in this proposed AD, contact 
Boeing Commercial Airplanes, Attention: Data & Services Management, 
P.O. Box 3707,

[[Page 61551]]

MC 2H-65, Seattle, Washington 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, 
Washington. 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 proposed AD, the regulatory 
evaluation, any comments received, and other information. The street 
address for the Docket Office (phone: 800-647-5527) is in the ADDRESSES 
section. Comments will be available in the AD docket shortly after 
receipt.

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; phone: 425-917-
6447; fax: 425-917-6590; email: wayne.lockett@faa.gov.

SUPPLEMENTARY INFORMATION:

Comments Invited

    We invite you to send any written relevant data, views, or 
arguments about this proposed AD. Send your comments to an address 
listed under the ADDRESSES section. Include ``Docket No. FAA-2011-0155; 
Directorate Identifier 2009-NM-141-AD'' at the beginning of your 
comments. We specifically invite comments on the overall regulatory, 
economic, environmental, and energy aspects of this proposed AD. We 
will consider all comments received by the closing date and may amend 
this proposed AD because of those comments.
    We will post all comments we receive, without change, to http://www.regulations.gov, including any personal information you provide. We 
will also post a report summarizing each substantive verbal contact we 
receive about this proposed AD.

Discussion

    We issued an NPRM to amend 14 CFR part 39 to include an AD that 
would apply to certain Model 737-200, -200C, -300, -400, and -500 
series airplanes. That NPRM published in the Federal Register on March 
8, 2011 (76 FR 12619). That NPRM proposed to supersede AD 2004-18-06, 
Amendment 39-13784 (69 FR 54206, September 8, 2004), to continue to 
require repetitive inspections to find fatigue cracking of certain 
upper and lower skin panels of the fuselage, and follow-on and 
corrective actions if necessary. That NPRM also included a terminating 
action for the repetitive inspections of certain modified or repaired 
areas only. That NPRM proposed to add new inspections for cracking of 
the fuselage skin along certain chem-milled lines, and corrective 
actions if necessary. That NPRM also proposed to reduce certain 
thresholds and intervals required by the existing AD. That NPRM 
resulted from reports indicating new findings of cracks were found 
along the edges of the chem-milled pockets in the upper skin at certain 
stringers.

Actions Since Previous NPRM Was Issued

    Since we issued the previous NPRM (76 FR 12619, March 8, 2011), 
extensive continued evaluation of the chem-mill step cracking has been 
done, which resulted in a determination that the repetitive inspection 
intervals and the compliance time for the inspections of the crown area 
and other known areas of fuselage skin cracking must be reduced in 
order to adequately address the identified unsafe condition.

Comments

    We gave the public the opportunity to comment on the previous NPRM 
(76 FR 12619, March 8, 2011). The following presents the comments 
received on the previous NPRM and the FAA's response to each comment.

Supportive Comments

    The National Transportation Safety Board and Jonathan W. Ketron 
support the content of the previous NPRM (76 FR 12619, March 8, 2011).

Request To Supersede AD 2003-14-06, Amendment 39-13225 (68 FR 42956, 
July 21, 2003)

    Alaska Airlines (ASA) asked that we change the previous NPRM (76 FR 
12619, March 8, 2011) to also supersede AD 2003-14-06, Amendment 39-
13225 (68 FR 42956, July 21, 2003). ASA explained that paragraph (g) of 
AD 2004-18-06, Amendment 39-13784 (69 FR 54206, September 8, 2004), 
allows accomplishing one-time internal inspections in accordance with 
paragraph (b) or paragraph (c) of AD 2003-14-06 in order to terminate 
the repetitive inspections required by paragraph (a) of AD 2004-18-06 
(paragraph (g) of the previous NPRM). ASA added that the previous NPRM 
restates these required external inspections. ASA noted that AD 2003-
14-06 was initially released to address inadequate phosphoric anodizing 
of the skin panels, leading to disbonding of internal doublers. ASA 
stated further that subsequent events showed that fatigue cracking of 
chem-milled skins cannot be solely attributed to improper anodizing or 
disbonded doublers. ASA added that the previous NPRM does not clearly 
address the requirements in AD 2003-14-06, which will remain in effect 
until after the final rule is released.
    We do not agree to supersede AD 2003-14-06, Amendment 39-13255 (68 
FR 42956, July 21, 2003). The one-time internal inspection in that AD 
is required for safety and is not related to the chem-milled step 
cracking addressed by this supplemental NPRM. In addition, the one-time 
inspection required by AD 2003-14-06 only terminates the external eddy 
current inspections required by paragraph (a) of AD 2004-18-06, 
Amendment 39-13784 (69 FR 54206, September 8, 2004), which is restated 
in paragraph (g) of this supplemental NPRM. All external detailed 
inspections are still required by paragraph (g) of this supplemental 
NPRM. We have made no change to this supplemental NPRM in this regard.

Request for Clarification of Language in Paragraphs (g) and (h) of the 
Previous NPRM (76 FR 12619, March 8, 2011)

    Boeing requested that paragraphs (g) and (h) of the previous NPRM 
(76 FR 12619, March 8, 2011) be revised to better distinguish between 
existing and new requirements. Specifically, Boeing stated that the 
language used in paragraphs (g) and (h) of the previous NPRM could be 
interpreted to mean that using Boeing Alert Service Bulletin 737-
53A1210, Revision 3, dated July 16, 2009, is optional for accomplishing 
the required actions at the inspection thresholds and intervals 
required by AD 2004-18-06, Amendment 39-13784 (69 FR 54206, September 
8, 2004). Boeing requested clarification of the wording to indicate 
that the inspection, methods, thresholds, and ``repeats'' in accordance 
with Revision 3 of this service bulletin are now required.
    We agree that clarification is necessary. Boeing Alert Service 
Bulletin 737-53A1210, Revision 3, dated July 16, 2009, can be used for 
accomplishing the required actions in AD 2004-18-06, Amendment 39-13784 
(69 FR 54206, September 8, 2004). However, it is not required to use 
Revision 3 of this service bulletin to accomplish the requirements of 
the existing AD; rather, it is required to use that revision for the 
new actions

[[Page 61552]]

required by paragraphs (p), (q), and (s) of this supplemental NPRM.
    Consequently, we have revised paragraphs (g) and (h) of this 
supplemental NPRM to remove the sentence beginning ``As of the 
effective date of this AD * * *'' to clarify that using Boeing Alert 
Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009, is not 
required for accomplishing the requirements of the existing AD.

Request To Change ``Internal'' Detailed Inspection to ``External'' 
Detailed Inspection

    Boeing asked that we change the ``internal'' detailed inspection 
specified in paragraph (h)(1) of the previous NPRM (76 FR 12619, March 
8, 2011) to an ``external'' detailed inspection. Boeing stated that 
this is a typographical error because it is a restatement of the 
requirements of AD 2004-18-06, Amendment 39-13784 (69 FR 54206, 
September 8, 2004).
    We agree that the reference to an ``internal'' detailed inspection 
is a typographical error. We have changed paragraph (h)(1) of this 
supplemental NPRM to specify an ``external'' detailed inspection.

Request To Remove a Paragraph Reference

    Boeing asked that we remove the reference to ``paragraph (m)'' in 
the third sentence of paragraph (g) of the previous NPRM (76 FR 12619, 
March 8, 2011). Boeing stated that paragraph (m) of the previous NPRM 
addresses disbond inspections, which should not terminate the detailed 
or eddy current inspection, as specified.
    We find that clarification is necessary. Paragraph (m) of this 
supplemental NPRM states that accomplishing the optional terminating 
action ``before the effective date of this AD'' terminates the eddy 
current inspections required by paragraph (g) of this supplemental 
NPRM. In addition, paragraph (m) of this supplemental NPRM states that 
the detailed inspections specified in paragraph (g) of this 
supplemental NPRM are not terminated. Paragraph (m) of this 
supplemental NPRM states further that, ``as of the effective date of 
this AD,'' the optional terminating action does not terminate the 
repetitive eddy current inspections required by paragraph (g) of this 
supplemental NPRM.
    We find it necessary to retain the reference to paragraph (m) of 
this supplemental NPRM in paragraph (g) to indicate that accomplishing 
the terminating action in paragraph (m) of this supplemental NPRM 
``before the effective date of this AD'' terminates the eddy current 
inspections required by paragraph (g) of this supplemental NPRM. 
However, we have revised paragraph (m) of this supplemental NPRM to 
indicate that neither detailed nor eddy current inspections can be 
terminated by accomplishing the optional terminating action ``on or 
after the effective date of this AD.''

Request To Clarify Terminating Action

    Boeing asked that the preventative modification language specified 
in paragraph (w) of the previous NPRM (76 FR 12619, March 8, 2011) be 
clarified to specify that doing the modification terminates only the 
repetitive inspections of the chem-milled steps common to stringer 12. 
Boeing stated that Note (c) of Table 2, paragraph 1.E., ``Compliance,'' 
of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 
16, 2009, specifies that accomplishing the preventative modification 
only terminates the inspections at stringer 12. Boeing added that there 
have been post-modification cracks reported at the chem-milled steps 
common to stringer 10, even though the modification doubler covers the 
area. Boeing noted that the internal modification doubler does not span 
the stringer 10 or stringer 13 chem-milled steps by three rows of 
fasteners; therefore, inspections should continue at those locations 
even though the modification doubler is common to them.
    We agree that clarification is necessary. Doing the preventive 
modification of the chem-milled areas in the skin at stringer 12, as 
specified in Part 7 of the Accomplishment Instructions of Boeing Alert 
Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009, ends the 
repetitive inspections for the modified areas common to stringer 12 
only. Cracking of the chem-milled steps has been found at locations 
where doublers do not extend a minimum of three fastener rows beyond 
the chem-milled step. We have changed paragraph (w) of this 
supplemental NPRM accordingly.

Requests To Revise Certain Compliance Times

    Boeing asked that the compliance time specified in paragraph (p)(1) 
of the previous NPRM (76 FR 12619, March 8, 2011) be changed. Boeing 
stated that it is unclear why airplanes that have accomplished 
paragraphs (i), (j)(1)(ii), (k), (l), or (m) of the previous NPRM 
(which are repairs and disbond inspections) must be inspected within 
1,800 flight cycles after the effective date of the AD. Boeing added 
that airplanes identified in paragraph (p)(2) of the previous NPRM that 
have not accomplished those paragraphs are allowed to wait until 4,500 
flight cycles after the last inspection, or 1,800 flight cycles after 
the effective date of the AD, whichever is later. Boeing questioned why 
the airplanes on which repairs have not been installed or a disbond 
inspection has not been accomplished have a different compliance time 
than airplanes that do have these repairs and inspections. Boeing noted 
that by using ``whichever occurs later'' in paragraph (p)(2) of the 
previous NPRM, an operator may accumulate up to 6,299 flight cycles 
(4,499 + 1,800) between inspections that were previously required at 
4,500-flight-cycle intervals in accordance with AD 2004-18-06, 
Amendment 39-13784 (69 FR 54206, September 8, 2004).
    We agree that the compliance times required by paragraph (p) of 
this supplemental NPRM should be clarified. After further review of the 
new inspection requirements in paragraph (p) of this supplemental NPRM, 
we have determined that those inspections are not related to existing 
installed repairs or the disbond inspection. The compliance times 
should not be based on local repairs that may be installed on the 
airplanes. For areas that have repairs installed in accordance with 
paragraphs (i), (j)(1)(ii), (k), (l), and (m) of this AD, the 
inspection is already terminated for these areas only. Therefore, we 
have deleted paragraphs (p)(1) and (p)(2) of the previous NPRM (76 FR 
12619, March 8, 2011), and included the following reduced compliance 
time in paragraph (p) of this supplemental NPRM: ``Within 4,500 flight 
cycles after doing the most recent inspection required by paragraph (g) 
of this AD, or within 1,800 flight cycles after the effective date of 
this AD, whichever is earlier.''
    Boeing also asked that the compliance time specified in paragraph 
(s) of the previous NPRM (76 FR 12619, March 8, 2011) be changed. 
Boeing stated that the repetitive interval should be changed to 1,800 
flight cycles for inspections in areas of known cracking in the lower 
lobe and Section 41, and when both eddy current and detailed 
inspections are required, in accordance with Part 4 of the 
Accomplishment Instructions of Boeing Alert Service Bulletin 737-
53A1210, Revision 3, dated July 16, 2009.
    Boeing also noted that for inspections in areas with no known 
cracking, the threshold should be at the latest of 35,000 total flight 
cycles, or at the earliest of 4,500 flight cycles from the release of 
Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16,

[[Page 61553]]

2009, or 9,000 flight cycles after the previous inspection. Boeing 
stated that, based on additional crack growth data, the repetitive 
inspections in areas of known cracking should be reduced to 1,800 
flight cycles. Boeing added that the inspection threshold should be at 
the latest of 35,000 total flight cycles, or at the earliest of 1,800 
flight cycles from the release of that service bulletin or 4,500 flight 
cycles after the previous inspection. Boeing concluded that in areas of 
no known cracking, the inspections are in place to monitor for new 
cracking; therefore, the repetitive inspection intervals can be 
extended.
    We agree that the compliance times should be changed based on the 
data provided by the manufacturer. We have moved the compliance times 
for the initial and repetitive inspections identified in paragraph (s) 
of the previous NPRM (76 FR 12619, March 8, 2011) to paragraphs (s)(1) 
and (s)(2) of this supplemental NPRM. We also reduced the repetitive 
inspection interval for known cracking in paragraph (s)(2) of this 
supplemental NPRM to 1,800 flight cycles.
    Boeing also asked that the compliance times and repetitive 
intervals specified in paragraphs (t), (u)(1), and (u)(2) of the 
previous NPRM (76 FR 12619, March 8, 2011) be changed. Boeing requested 
that all compliance times (initial and repetitive) that specify 4,500 
flight cycles be changed to 1,800 flight cycles. Boeing stated that the 
window belt skin area is equivalent to the crown skin area, and the 
initial threshold and repetitive interval should be the same as 
required for the crown area.
    We agree that the compliance times should be changed based on the 
information provided. We have changed the compliance times and 
repetitive intervals in paragraphs (t), (u)(1), and (u)(2) of this 
supplemental NPRM accordingly.

Request To Provide Certain Clarifications

    Southwest Airlines (SWA) asked that we change paragraph (h) of the 
previous NPRM (76 FR 12619, March 8, 2011) to provide clarification 
whether the inspections identified in Figures 26, 27, and 31 of Boeing 
Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009, 
are required. SWA asked whether an eddy current or external detailed 
inspection is necessary for certain locations if those inspection 
figures are required. SWA stated that paragraph (h) of the previous 
NPRM specifies an external detailed inspection of the lower lobe area 
and Section 41 of the fuselage, in accordance with Part 4 of the 
Accomplishment Instructions of that service bulletin. SWA added that 
Part 4 also specifies eddy current inspections every 1,800 flight 
cycles.
    We agree that clarification is necessary. The subject inspections 
identified in Figures 26, 27, and 31 of Boeing Alert Service Bulletin 
737-53A1210, Revision 3, dated July 16, 2009, are specified in this 
supplemental NPRM; however, the inspections in those figures are 
required by paragraph (s), not paragraph (h), of this supplemental 
NPRM. No change to either paragraph (h) or (s) of this supplemental 
NPRM is necessary.
    SWA also asked how paragraphs (s) and (u) of the previous NPRM (76 
FR 12619, March 8, 2011) are related, and if paragraph (u) of the 
previous NPRM applies to airplane groups 4, 11, and 16. SWA noted that 
the inspections identified in paragraph (s) of the previous NPRM are 
applicable to Groups 1 through 21 and are done in accordance with Part 
4 of Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 
16, 2009; except as required by paragraph (u) of the previous NPRM. SWA 
also noted that the inspections identified in paragraph (u) of the 
previous NPRM are applicable to Groups 3, 5, 9, 10, 12, 14, 15, 17, 18, 
19, 20, and 21, and are done in accordance with Part 2 of Boeing Alert 
Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009. SWA 
stated that it is unsure how Part 2 and Part 4 are related. SWA added 
that Part 2 addresses Groups 4, 11, and 16; however, those groups are 
not specified in paragraph (u) of the previous NPRM.
    We agree that clarification is necessary because the exception in 
paragraph (s) of the previous NPRM (76 FR 12619, March 8, 2011) is a 
typographical error and should have identified paragraph (x) instead of 
paragraph (u) of the previous NPRM. We have changed paragraph (s) of 
this supplemental NPRM accordingly, which also addresses the 
commenter's concern about Groups 4, 11, and 16.

Request To Exclude Certain Inspection Areas

    SWA asked that, to avoid mandating additional inspections in the 
previous NPRM (76 FR 12619, March 8, 2011), we exclude the inspection 
areas identified in AD 2009-21-01, Amendment 39-16038 (74 FR 52395, 
October 13, 2009). SWA stated that the inspection threshold and 
repetitive intervals required by AD 2009-21-01 are more restrictive for 
certain areas of the lower lobe skins than those in the previous NPRM.
    We agree that the inspection threshold and repetitive intervals 
required by AD 2009-21-01, Amendment 39-16038 (74 FR 52395, October 13, 
2009), are more restrictive for certain areas. Therefore, we have added 
a new paragraph (y)(5) to this supplemental NPRM (and reidentified 
subsequent paragraphs) to specify that inspections and corrective 
actions required by paragraph (g) of AD 2009-21-01 meet the 
corresponding provisions of paragraph (s) of this supplemental NPRM.

Request To Require Eddy Current Inspections Only

    SWA asked that only nondestructive inspections (NDI) be used in 
areas where the previous NPRM (76 FR 12619, March 8, 2011) requires 
both external detailed and eddy current inspections every 1,800 flight 
cycles. SWA stated that paragraph (f) of AD 2008-19-03, Amendment 39-
15670 (73 FR 56958, October 1, 2008), requires repetitive inspections 
along the chem-milled steps at stringers S-1 and S-2R, between STA 400 
and STA 460. SWA added that for line numbers 1001 through 2552, the 
operator has the option of accomplishing repetitive external detailed 
inspections every 2,300 flight cycles, or NDI every 4,500 flight 
cycles. SWA noted that the previous NPRM reduces the repetitive 
inspection interval specified in Tables 1 through 5 of paragraph 1.E., 
``Compliance,'' of Boeing Alert Service Bulletin 737-53A1210, Revision 
3, dated July 16, 2009, from 4,500 flight cycles to 1,800 flight 
cycles. SWA made its request due to this reduced inspection interval.
    We do not agree that only NDI can be used where both external 
detailed and eddy current inspections are required. The overall safety 
concern related to Model 737 fuselage skin panels addressed in this 
supplemental NPRM is mitigated by using detailed inspections in 
conjunction with eddy current inspections. We have made no change to 
the supplemental NPRM in this regard.

Request To Use Ultrasonic Phased Array (UTPA) Inspection

    SWA asked that it be allowed to use a UTPA inspection to inspect 
areas where the previous NPRM (76 FR 12619, March 8, 2011) requires 
external NDI methods. SWA stated Boeing confirmed that it is 
satisfactory to inspect areas covered by the dorsal fin by internally 
using the UTPA inspection in lieu of the NDI methods, using information 
in the nondestructive test manual, in lieu of the external NDI methods.

[[Page 61554]]

    We agree that a UTPA inspection might be able to be used instead of 
the external NDI method. However, we do not agree to include the UTPA 
inspection in this supplemental NPRM because we cannot include 
individual operators' methods of compliance. Under the provisions of 
paragraph (y) of this supplemental NPRM, we will consider requests for 
approval of a change to the inspection type if sufficient data are 
submitted to substantiate that the inspection would provide an 
acceptable level of safety. We have made no change to the supplemental 
NPRM in this regard.

Request To Allow a General Visual Inspection (GVI) Instead of Detailed 
Inspection

    SWA and British Airways asked that we allow a GVI in lieu of the 
detailed inspection specified in paragraphs (p) and (q) of the previous 
NPRM (76 FR 12619, March 8, 2011). SWA stated that both paragraphs 
specify doing external detailed and eddy current inspections of the 
crown area and other known areas of fuselage skin cracking in 
accordance with Part 1 of the Accomplishment Instructions of Boeing 
Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009. 
SWA noted that Part 1 provides doing a GVI with a reduced inspection 
interval of 1,000 flight cycles in non-lap splice areas as an 
alternative to the detailed inspection. SWA and British Airways stated 
that the previous NPRM does not identify the reference in Note (b) of 
Table 1 of paragraph 1.E., ``Compliance,'' of that service bulletin, 
which allows performing a GVI at a reduced inspection interval in lieu 
of the detailed inspection in areas away from the lapjoints. SWA also 
asked if the GVI applies to Figures 32 through 37 of this service 
bulletin.
    We agree with the commenters' requests because we have determined 
that doing the GVI at a reduced inspection interval provides an 
acceptable level of safety. In addition, the GVI does apply to Figures 
32 through 37 of Boeing Alert Service Bulletin 737-53A1210, Revision 3, 
dated July 16, 2009, because the figures are part of the Accomplishment 
Instructions, which is the part of the service bulletin referred to in 
the requirements. We have revised paragraphs (p), (q), and (s) of this 
supplemental NPRM to allow this option.

Request To Allow Use of Corrosion Inhibiting Compound

    US Airways asked that we allow the use of an alternative corrosion 
inhibiting compound (CIC) during repairs. US Airways stated that 
paragraphs (u) and (w) of the previous NPRM (76 FR 12619, March 8, 
2011) refer to Parts 7 and 8 of the Accomplishment Instructions of 
Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 
2009; Parts 7 and 8 refer to Figures 10 and 24, respectively. US 
Airways added that the figures specify applying CIC BMS 3-23, Type 2, 
when completing repairs. US Airways noted that Boeing has approved 
newer CIC BMS 3-35, which is compatible with CIC BMS 3-23, and is 
identified in the applicable corrosion prevention manual. US Airways 
added that Boeing does not plan to add CIC BMS 3-35 to its FAA-approved 
repair documents. US Airways stated that adding this to the previous 
NPRM would avoid requests for approval of AMOCs.
    We agree that CIC BMS 3-35 can be used as an alternative to CIC BMS 
3-23. CIC BMS 3-35 has been qualified and approved as an AMOC for other 
repair situations that specify CIC BMS 3-23. We have added a new 
statement to paragraphs (u) and (w) of this supplemental NPRM to 
include the option of using CIC BMS 3-35 as an equivalent CIC.

Changes to Supplemental NPRM

    The exception in paragraph (o) of this supplemental NPRM was 
included in the requirements of AD 2004-18-06, Amendment 39-13784 (69 
FR 54206, September 8, 2004); however, it was inadvertently removed 
from the proposed requirements in the previous NPRM (76 FR 12619, March 
8, 2011). We have included the exception in paragraphs (g) and (h) of 
this supplemental NPRM.
    We have removed the reference to the Boeing 737 Non-Destructive 
Test Manual specified in paragraph (o) of this supplemental NPRM; the 
inspection identified in that paragraph may be done using Boeing Alert 
Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009.
    We have removed the definition of a ``detailed inspection'' in Note 
1 of the previous NPRM (76 FR 12619, March 8, 2011) from this 
supplemental NPRM. That definition is provided in Boeing Alert Service 
Bulletin 737-53A1210, Revision 3, dated July 16, 2009.
    Due to a typographical error in paragraph (w) of the previous NPRM 
(76 FR 12619, March 8, 2011), we have changed the reference in 
paragraph (w) of this supplemental NPRM to paragraph (u), instead of 
paragraph (p) or (q), respectively.
    We have revised the optional repair method specified in paragraph 
(k) of this supplemental NPRM to remove the reference to repairing any 
cracking per the applicable structural repair manual (SRM) identified 
in Table 1 of the previous NPRM (76 FR 12619, March 8, 2011). Instead, 
we have added a statement to paragraph (k) of this supplemental NPRM to 
specify that guidance on repairing any cracking can be found in the 
applicable SRM identified in paragraphs (k)(1) through (k)(4) of this 
supplemental NPRM.

FAA's Determination

    We are proposing this supplemental NPRM because we evaluated all 
the relevant information and determined the unsafe condition described 
previously is likely to exist or develop in other products of the same 
type design. Certain changes described above expand the scope of the 
previous NPRM (76 FR 12619, March 8, 2011). As a result, we have 
determined that it is necessary to reopen the comment period to provide 
additional opportunity for the public to comment on this supplemental 
NPRM.

Proposed Requirements of the Supplemental NPRM

    This supplemental NPRM would require the actions proposed in the 
previous NPRM (76 FR 12619, March 8, 2011). However, this supplemental 
NPRM reduces the proposed repetitive inspection intervals and the 
compliance time for the inspections of the crown area and other known 
areas of fuselage skin cracking in the previous NPRM (76 FR 12619, 
March 8, 2011).

Costs of Compliance

    There are about 903 airplanes of U.S. registry affected by AD 2004-
18-06, Amendment 39-13784 (69 FR 54206, September 8, 2004).
    The inspections of the crown area that are required by AD 2004-18-
06, Amendment 39-13784 (69 FR 54206, September 8, 2004), take about 94 
work hours per airplane to accomplish, at an average labor rate of $85 
per work hour. Based on these figures, the estimated cost of the 
currently required inspections is $7,990 per airplane, per inspection 
cycle.
    The inspections of the lower lobe area that are required by AD 
2004-18-06, Amendment 39-13784 (69 FR 54206, September 8, 2004), take 
about 96 work hours per airplane to accomplish, at an average labor 
rate of $85 per work hour. Based on these figures, the estimated cost 
of the currently required inspections is $8,160 per airplane, per 
inspection cycle.

[[Page 61555]]

    Should an operator elect to install the preventive modification 
specified in AD 2004-18-06, Amendment 39-13784 (69 FR 54206, September 
8, 2004), it will take about 108 work hours per airplane to accomplish, 
at an average labor rate of $85 per work hour. Based on these figures, 
the estimated cost of the modification is $9,180 per airplane.
    The new proposed inspections would affect about 701 airplanes of 
U.S. registry.
    The new proposed inspections would take about 27 work hours per 
airplane, at an average labor rate of $85 per work hour. Based on these 
figures, the estimated cost of the new actions specified in this 
proposed AD for U.S. operators is $1,608,795, or $2,295 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

    We determined that this proposed AD would not have federalism 
implications under Executive Order 13132. This proposed AD would not 
have a substantial direct effect on the States, on the relationship 
between the national Government and the States, or on the distribution 
of power and responsibilities among the various levels of government.
    For the reasons discussed above, I certify that the proposed 
regulation:
    (1) Is not a ``significant regulatory action'' under Executive 
Order 12866,
    (2) Is not a ``significant rule'' under the DOT Regulatory Policies 
and Procedures (44 FR 11034, February 26, 1979),
    (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.

The Proposed Amendment

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

PART 39--AIRWORTHINESS DIRECTIVES

    1. The authority citation for part 39 continues to read as follows:

    Authority:  49 U.S.C. 106(g), 40113, 44701.

Sec.  39.13  [Amended]

    2. The FAA amends Sec.  39.13 by removing AD 2004-18-06, Amendment 
39-13784 (69 FR 54206, September 8, 2004), and adding the following new 
AD:

The Boeing Company: Docket No. FAA-2011-0155; Directorate Identifier 
2009-NM-141-AD.

(a) Comments Due Date

    We must receive comments by November 26, 2012.

(b) Affected ADs

    (1) This AD supersedes AD 2004-18-06, Amendment 39-13784 (69 FR 
54206, September 8, 2004).
    (2) AD 2002-07-08, Amendment 39-12702 (67 FR 17917, April 12, 
2002); and AD 2003-14-06, Amendment 39-13225 (68 FR 42956, July 21, 
2003); and AD 2009-21-01, Amendment 39-16038 (74 FR 52395, October 
13, 2009); affect this AD.

(c) Applicability

    This AD applies to The Boeing Company Model 737-200, -200C, -
300, -400, and -500 series airplanes, certificated in any category, 
as listed in Boeing Alert Service Bulletin 737-53A1210, Revision 3, 
dated July 16, 2009.

(d) Subject

    Joint Aircraft System Component (JASC)/Air Transport Association 
(ATA) of America Code 53, Fuselage.

(e) Unsafe Condition

    This AD was prompted by new findings of vertical cracks along 
chem-milled steps adjacent to the butt joints. We are issuing this 
AD to detect and correct fatigue cracking of the skin panels, which 
could result in sudden fracture and failure of the skin panels of 
the fuselage, and consequent rapid decompression of the airplane.

(f) Compliance

    Comply with this AD within the compliance times specified, 
unless already done.

(g) Retained External Detailed and Eddy Current Inspections

    This paragraph restates the requirements of paragraph (a) of AD 
2004-18-06, Amendment 39-13784 (69 FR 54206, September 8, 2004) with 
revised service information. For Groups 1 through 5 airplanes 
identified in Boeing Alert Service Bulletin 737-53A1210, Revision 1, 
dated October 25, 2001: Before the accumulation of 35,000 total 
flight cycles, or within 4,500 flight cycles after October 13, 2004 
(the effective date of AD 2004-18-06), whichever is later, do 
external detailed and eddy current inspections of the crown area and 
other known areas of fuselage skin cracking, in accordance with Part 
1 and Figure 1 of the Work Instructions of Boeing Alert Service 
Bulletin 737-53A1210, Revision 1, dated October 25, 2001; or in 
accordance with Part 1 of the Accomplishment Instructions of Boeing 
Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009; 
except as provided by paragraph (o) of this AD. Repeat the external 
detailed and eddy current inspections at intervals not to exceed 
4,500 flight cycles until paragraph (i), (j)(1)(ii), (k), (l), or 
(m) of this AD has been done, as applicable. Although paragraph 1.D. 
of Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated 
October 25, 2001, references a reporting requirement, such reporting 
is not required by this AD. Accomplishing the actions required by 
paragraph (p) or (q) of this AD ends the repetitive requirements in 
this paragraph.

(h) Retained External Detailed Inspection With Reduced Compliance Time

    This paragraph restates the requirements of paragraph (b) of AD 
2004-18-06, Amendment 39-13784 (69 FR 54206, September 8, 2004) with 
revised service information. For all airplanes identified in Boeing 
Alert Service Bulletin 737-53A1210, Revision 1, dated October 25, 
2001, do an external detailed inspection of the lower lobe area and 
section 41 of the fuselage for cracking, in accordance with Part 2 
and Figure 2 of the Work Instructions of Boeing Alert Service 
Bulletin 737-53A1210, Revision 1, dated October 25, 2001; or in 
accordance with Part 4 of the Accomplishment Instructions of Boeing 
Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009; 
except as provided by paragraph (o) of this AD. At the earlier of 
the times specified in paragraphs (h)(1) and (h)(2) of this AD, do 
the inspection specified in this paragraph, and repeat the 
inspection thereafter at intervals not to exceed 4,500 flight cycles 
until paragraph (j)(2) or paragraph (k), as applicable, of this AD 
has been done. Accomplishing the actions required by paragraph (s) 
of this AD ends the requirements in this paragraph.
    (1) Within 9,000 flight cycles after doing the most recent 
external detailed inspection.
    (2) Within 4,500 flight cycles after October 13, 2004 (the 
effective date of AD 2004-18-06, Amendment 39-13784 (69 FR 54206, 
September 8, 2004)), or before the accumulation of 40,000 total 
flight cycles, whichever occurs later.

[[Page 61556]]

(i) Retained Preventive Modification at Stringer 12

    This paragraph restates the requirements of paragraph (c) of AD 
2004-18-06, Amendment 39-13784 (69 FR 54206, September 8, 2004) with 
revised service information. For Groups 3 and 5 airplanes identified 
in Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated 
October 25, 2001: If no cracking is found during any inspection 
required by paragraph (g) of this AD, doing the preventive 
modification of the chem-milled pockets in the upper skin as 
specified in Part 5 of the Work Instructions of Boeing Alert Service 
Bulletin 737-53A1210, Revision 1, dated October 25, 2001; or as 
specified in Part 7 of the Work Instructions of Boeing Alert Service 
Bulletin 737-53A1210, Revision 3, dated July 16, 2009, except as 
required by paragraph (x) of this AD; ends the repetitive external 
detailed and eddy current inspections required by paragraph (g) of 
this AD for the modified area only. As of the effective date of this 
AD, use only Boeing Alert Service Bulletin 737-53A1210, Revision 3, 
dated July 16, 2009.

(j) Retained Corrective Actions

    This paragraph restates the requirements of paragraph (d) of AD 
2004-18-06, Amendment 39-13784 (69 FR 54206, September 8, 2004), 
with revised service information. If any cracking is found during 
any inspection required by paragraph (g), (h), (p), (q), or (s) of 
this AD, before further flight, do the actions specified in 
paragraphs (j)(1) and (j)(2) of this AD, as applicable, in 
accordance with the Work Instructions of Boeing Alert Service 
Bulletin 737-53A1210, Revision 1, dated October 25, 2001; or in 
accordance with the Work Instructions of Boeing Alert Service 
Bulletin 737-53A1210, Revision 3, dated July 16, 2009. As of the 
effective date of this AD, use only Boeing Alert Service Bulletin 
737-53A1210, Revision 3, dated July 16, 2009. Where Boeing Alert 
Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001; or 
Revision 3, dated July 16, 2009; specify to contact Boeing for 
repair instructions, before further flight, repair in accordance 
with a method approved by the Manager, Seattle Aircraft 
Certification Office (ACO), FAA; or in accordance with data meeting 
the type certification basis of the airplane if it is approved by 
the Boeing Commercial Airplanes Organization Designation 
Authorization (ODA) or any other person 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.
    (1) Except as provided by paragraph (k) of this AD, for cracking 
of the crown area, do the repair specified in either paragraph 
(j)(1)(i) or (j)(1)(ii) of this AD.
    (i) Do a time-limited repair in accordance with Part 4 of the 
Work Instructions of Boeing Alert Service Bulletin 737-53A1210, 
Revision 1, dated October 25, 2001; or in accordance with Part 6 of 
the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, 
Revision 3, dated July 16, 2009, except as required by paragraph (x) 
of this AD, then do the actions required by paragraph (l) of this AD 
at the times specified in that paragraph.
    (ii) Do a permanent repair in accordance with Part 3 of the Work 
Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 
1, dated October 25, 2001; or in accordance with Part 5 of the Work 
Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 
3, dated July 16, 2009. Installation of a permanent repair ends the 
repetitive inspections required by paragraph (g) of this AD for the 
repaired area only. Installation of the lap joint repair specified 
in paragraph (g) of AD 2002-07-08, Amendment 39-12702 (67 FR 17917, 
April 12, 2002), is considered acceptable for compliance with the 
corresponding permanent repair specified in this paragraph for the 
repaired areas only.
    (2) Except as provided by paragraph (k) of this AD, for cracking 
of the lower lobe area and Section 41, repair in accordance with 
Part 2 of the Work Instructions of Boeing Alert Service Bulletin 
737-53A1210, Revision 1, dated October 25, 2001; or in accordance 
with paragraph (j)(2)(i) or (j)(2)(ii) of this AD. Accomplishment of 
this repair ends the repetitive inspections required by paragraph 
(h) of this AD for the repaired area only. As of the effective date 
of this, do the repair specified in paragraph (j)(2)(i) or 
(j)(2)(ii) of this AD.
    (i) Do a time-limited repair in accordance with Part 6 of the 
Work Instructions of Boeing Alert Service Bulletin 737-53A1210, 
Revision 3, dated July 16, 2009, except as required by paragraph (x) 
of this AD, then do the actions required by paragraph (l) of this AD 
at the times specified in that paragraph.
    (ii) Do a permanent repair in accordance with Part 5 of the 
Accomplishment Instructions of Boeing Alert Service Bulletin 737-
53A1210, Revision 3, dated July 16, 2009.

(k) Retained Optional Repair Method

    This paragraph restates the requirements of paragraph (e) of AD 
2004-18-06, Amendment 39-13784 (69 FR 54206, September 8, 2004) with 
revised service information. For cracking in any area specified in 
paragraphs (j)(1) and (j)(2) of this AD within the limitations of 
the applicable structural repair manual (SRM) specified in 
paragraphs (k)(1) through (k)(4) of this AD, repair any cracks, in 
accordance with a method approved by the Manager, Seattle ACO; or in 
accordance with data meeting the type certification basis of the 
airplane if it is approved by the Boeing Commercial Airplanes ODA or 
any other person 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. Accomplishment of the applicable 
repair terminates the repetitive inspections required by paragraphs 
(g) and (h) of this AD for the repaired area only. Guidance on 
repairing the cracking can be found in the applicable SRM specified 
in paragraphs (k)(1) through (k)(4) of this AD.
    (1) For Model 737-100, -200 series airplanes, Subject 53-30-3, 
Figure 48, of Boeing 737-100/-200 SRM D6-15565, Revision 102, dated 
September 10, 2010.
    (2) For Model 737-300 series airplanes, Subject 53-00-01, Figure 
229, of Boeing 737-300 SRM D6-37635, Revision 92, dated November 10, 
2010.
    (3) For Model 737-400 series airplanes, Subject 53-00-01, Figure 
231, of Boeing 737-400 SRM, D6-38246, Revision 75, dated November 
10, 2010.
    (4) For Model 737-500 series airplanes, Subject 53-00-01, Figure 
229, of Boeing 737-500 SRM, D6-38441, Revision 70, dated November 
10, 2010.

(l) Retained Follow-on and Corrective Actions

    This paragraph restates the requirements of paragraph (f) of AD 
2004-18-06, Amendment 39-13784 (69 FR 54206, September 8, 2004) with 
revised service information. If a time-limited repair is done, as 
specified in paragraph (j)(1)(i) or (j)(2)(i) of this AD: Do the 
actions specified in paragraphs (l)(1), (l)(2), and (l)(3) of this 
AD, at the times specified in paragraphs (l)(1), (l)(2), and (l)(3) 
of this AD, in accordance with the Work Instructions of Boeing Alert 
Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001; or 
in accordance with the Work Instructions of Boeing Alert Service 
Bulletin 737-53A1210, Revision 3, dated July 16, 2009.
    (1) Within 3,000 flight cycles after doing the repair: Do the 
actions specified in paragraph (l)(1)(i) or (l)(1)(ii) of this AD. 
Then repeat the applicable inspection specified in paragraph 
(l)(1)(i) or (l)(1)(ii) of this AD at intervals not to exceed 3,000 
flight cycles until permanent rivets are installed in the repaired 
area, which ends the repetitive inspections for this paragraph. As 
of the effective date of this AD, do only the inspections specified 
in paragraph (l)(1)(ii) of this AD.
    (i) For repairs done before the effective date of this AD: Do a 
detailed inspection of the repaired area for loose fasteners in 
accordance with Part 4 of the Work Instructions of Boeing Alert 
Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001, or 
do the actions specified in paragraph (l)(1)(ii) of this AD. If any 
loose fastener is found, before further flight, replace with a new 
fastener, in accordance with the Work Instructions of Boeing Alert 
Service Bulletin 737-53A1210, Revision 1, dated October 25, 2001.
    (ii) For repairs done after the effective date of this AD: Do a 
detailed inspection of the repaired area for loose, damaged, and 
missing fasteners, in accordance with Part 6 of the Work 
Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 
3, dated July 16, 2009. If any loose, missing, or damaged fastener 
is found, before further flight, replace with a new fastener, in 
accordance with Boeing Alert Service Bulletin 737-53A1210, Revision 
3, dated July 16, 2009.
    (2) At the applicable time specified in paragraph (l)(2)(i) and 
(l)(2)(ii) of this AD: Do inspections of the repaired area for 
cracking in accordance with Part 4 of the Work Instructions of 
Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 
25, 2001; or in accordance with Part 6 of the Work Instructions of 
Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July

[[Page 61557]]

16, 2009. If any cracking is found, before further flight, repair in 
accordance with a method approved by the Manager, Seattle ACO, or in 
accordance with data meeting the type certification basis of the 
airplane if it is approved by the Boeing Commercial Airplanes ODA or 
any other person 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.
    (i) For repairs done before the effective date of this AD: 
Within 4,000 flight cycles after doing the repair, do the 
inspections.
    (ii) For repairs done on or after the effective date of this AD: 
Within 3,000 flight cycles after doing the repair, do the 
inspections.
    (3) At the earlier of the times specified in paragraphs 
(l)(3)(i) and (l)(3)(ii) of this AD: Make the repair permanent in 
accordance with Part 4 and Figure 20 of the Work Instructions of 
Boeing Alert Service Bulletin 737-53A1210, Revision 1, dated October 
25, 2001, or do the permanent repair, in accordance with Part 5 of 
the Work Instructions of Boeing Alert Service Bulletin 737-53A1210, 
Revision 3, dated July 16, 2009, which ends the repetitive 
inspections for the repaired area only. As of the effective date of 
this AD, only Boeing Alert Service Bulletin 737-53A1210, Revision 3, 
dated July 16, 2009, can be used to make the repair permanent.
    (i) Within 10,000 flight cycles after doing the repair in 
accordance with Boeing Alert Service Bulletin 737-53A1210, Revision 
1, dated October 25, 2001.
    (ii) At the later of the times specified in paragraphs 
(l)(3)(ii)(A) and (l)(3)(ii)(B) of this AD.
    (A) Within 6,000 flight cycles after doing the repair.
    (B) Within 1,000 flight cycles after the effective date of this 
AD.

(m) Retained Optional Terminating Action for Repetitive Eddy Current 
Inspections

    This paragraph restates the requirements of paragraph (g) of AD 
2004-18-06, Amendment 39-13784 (69 FR 54206, September 8, 2004) with 
revised service information. Accomplishment of paragraph (b) or (c), 
as applicable, of AD 2003-14-06, Amendment 39-13225 (68 FR 42956, 
July 21, 2003), before the effective date of this AD ends the 
repetitive eddy current inspections required by paragraph (g) of 
this AD for that skin panel only; however, the repetitive external 
detailed inspections required by paragraph (g) of this AD are still 
required for all areas. Accomplishing paragraph (b) or (c), as 
applicable, of AD 2003-14-06, on or after the effective date of this 
AD, does not end either the repetitive detailed or eddy current 
inspections required by paragraph (g) of this AD.

(n) Retained Credit for Previous Actions

    This paragraph restates the requirements of paragraph (h) of AD 
2004-18-06, Amendment 39-13784 (69 FR 54206, September 8, 2004). 
Inspections, repairs, and preventive modifications done before 
October 13, 2004 (the effective date of AD 2004-18-06), in 
accordance with Boeing Alert Service Bulletin 737-53A1210, dated 
December 14, 2000, are acceptable for compliance with the 
corresponding actions required by paragraphs (g), (h), (i), (j), 
(k), and (l) of this AD.

(o) Retained Exception to Service Bulletin Procedures

    This paragraph restates the requirements of paragraph (i) of AD 
2004-18-06, Amendment 39-13784 (69 FR 54206, September 8, 2004) with 
revised service information. For airplanes subject to the 
requirements of paragraphs (g) and (h) of this AD: Inspections 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 chem-
milled step. If an external doubler covers the chem-milled step, but 
does not span it by a minimum of 3 rows of fasteners above and 
below, in lieu of requesting approval for an alternative method of 
compliance (AMOC), one option to comply with the inspection 
requirement of paragraphs (g) and (h) of this AD is to inspect all 
chem-milled steps covered by the repair in accordance with the Work 
Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 
3, dated July 16, 2009.

(p) New Requirements of This AD: Repetitive External Detailed and Eddy 
Current Inspections of the Crown Area and Other Known Areas of Fuselage 
Skin Cracking, and Corrective Actions

    For Groups 1 through 5 and Groups 9 through 21 airplanes 
identified in Boeing Alert Service Bulletin 737-53A1210, Revision 3, 
dated July 16, 2009, on which the inspections required by paragraph 
(g) of this AD have been done before the effective date of this AD: 
Within 4,500 flight cycles after doing the most recent inspection 
required by paragraph (g) of this AD, or within 1,800 flight cycles 
after the effective date of this AD, whichever is earlier; do 
external detailed and eddy current inspections of the crown area and 
other known areas of the fuselage skin cracking, in accordance with 
Part 1 of the Accomplishment Instructions of Boeing Alert Service 
Bulletin 737-53A1210, Revision 3, dated July 16, 2009; except as 
provided by paragraph (o) of this AD. Repeat the external detailed 
and eddy current inspections thereafter at intervals not to exceed 
1,800 flight cycles. Accomplishing the inspections required by this 
paragraph ends the repetitive inspections required by paragraph (g) 
of this AD. Before further flight, do all applicable corrective 
actions as specified in paragraph (j) of this AD. For the locations 
specified in Boeing Alert Service Bulletin 737-53A1210, Revision 3, 
dated July 16, 2009; in lieu of doing detailed inspections, 
operators may do general visual inspections, provided that the 
general visual inspections are done at intervals not to exceed 1,000 
flight cycles.

(q) New Requirements of This AD: Repetitive External Detailed and Eddy 
Current Inspections of the Crown Area and Other Known Areas of Fuselage 
Skin Cracking, and Corrective Actions

    For Groups 1 through 5 and 9 through 21 airplanes identified in 
Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 
16, 2009; on which the inspections required by paragraph (g) of this 
AD have not been done before the effective date of this AD: Before 
the accumulation of 28,000 total flight cycles, or within 1,800 
flight cycles after the effective date of this AD, whichever is 
later, do external detailed and eddy current inspections of the 
crown area and other known areas of fuselage skin cracking, in 
accordance with Part 1 of the Accomplishment Instructions of Boeing 
Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009, 
except as provided by paragraph (o) of this AD. Repeat the external 
detailed and eddy current inspections thereafter at intervals not to 
exceed 1,800 flight cycles. Accomplishing the inspections required 
by this paragraph ends the repetitive inspections required by 
paragraph (g) of this AD. Before further flight, do all applicable 
corrective actions as specified in paragraph (j) of this AD. For the 
locations specified in Boeing Alert Service Bulletin 737-53A1210, 
Revision 3, dated July 16, 2009; in lieu of doing detailed 
inspections, operators may do general visual inspections, provided 
that the general visual inspections are done at intervals not to 
exceed 1,000 flight cycles.

(r) New Requirements of This AD: Repetitive External Detailed and Eddy 
Current Inspections of the Fuselage Skin Along the Chem-Milled Steps of 
the Butt Joints, and Corrective Actions

    For Group 1 through 5, and 9 through 21 airplanes identified in 
Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 
16, 2009: At the later of the times specified in paragraphs (r)(1) 
and (r)(2) of this AD, do external detailed and eddy current 
inspections for vertical cracks in the fuselage skin along the chem-
milled steps of the butt joints, in accordance with Part 3 of the 
Accomplishment Instructions of Boeing Alert Service Bulletin 737-
53A1210, Revision 3, dated July 16, 2009. Repeat the inspections 
thereafter at intervals not to exceed 1,800 flight cycles or 1,800 
flight hours, whichever occurs first. If any cracking is found, 
before further flight, repair in accordance with Part 5 of the 
Accomplishment Instructions of Boeing Alert Service Bulletin 737-
53A1210, Revision 3, dated July 16, 2009. Doing the repair 
terminates the repetitive inspections specified in this paragraph 
for the repaired area only.
    (1) Before the accumulation of 55,000 total flight cycles or 
55,000 total flight hours, whichever occurs first.
    (2) Within 1,800 flight cycles or 1,800 flight hours after the 
effective date of this AD, whichever occurs first.

(s) New Requirements of This AD: Repetitive Detailed and Eddy Current 
Inspections Along the Chem-Milled Lines of the Fuselage Skin of the 
Lower Lobe Area and Section 41, and Corrective Actions

    For Groups 1 through 21 airplanes identified in Boeing Alert 
Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009: At 
the applicable time specified in paragraph (s)(1) or (s)(2) of this 
AD, do external detailed and eddy current inspections, as 
applicable, for horizontal

[[Page 61558]]

cracks along the chem-milled lines of the fuselage skin of the lower 
lobe area and section 41, in accordance with Part 4 of the 
Accomplishment Instructions of Boeing Alert Service Bulletin 737-
53A1210, Revision 3, dated July 16, 2009; except as required by 
paragraph (x) of this AD. Repeat the inspections thereafter at 
intervals not to exceed 1,800 flight cycles. Accomplishing the 
inspections required by this paragraph ends the repetitive 
inspections required by paragraph (h) of this AD. Before further 
flight, do all applicable corrective actions as specified in 
paragraph (j) of this AD. For the locations specified in Boeing 
Alert Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009; 
in lieu of doing detailed inspections, operators may do general 
visual inspections, provided that the general visual inspections are 
done at intervals not to exceed 1,000 flight cycles.
    (1) In areas of no known cracking where only a detailed 
inspection is accomplished: Do the inspection at the later of the 
times specified in paragraphs (s)(1)(i) and (s)(1)(ii) of this AD.
    (i) Before the accumulation of 35,000 total flight cycles.
    (ii) Within 9,000 flight cycles after the most recent inspection 
required by paragraph (h) of this AD, or within 1,800 flight cycles 
after the effective date of this AD, whichever is earlier.
    (2) In areas of known cracking where both a detailed and eddy 
current inspection is accomplished: Do the inspection at the latest 
of the times specified in paragraphs (s)(2)(i) and (s)(2)(ii) of 
this AD.
    (i) Before the accumulation of 35,000 total flight cycles.
    (ii) Within 4,500 flight cycles after the most recent inspection 
required by paragraph (h) of this AD, or within 1,800 flight cycles 
after the effective date of this AD, whichever is earlier.

(t) New Requirements of This AD: Repetitive External Detailed and Eddy 
Current Inspections Along the Chem-Milled Lines of the Fuselage Skin of 
the Window Belt Area, and Corrective Actions

    For Groups 4, 11, and 16 airplanes identified in Boeing Alert 
Service Bulletin 737-53A1210, Revision 3, dated July 16, 2009: 
Before the accumulation of 25,000 total flight cycles or within 
1,800 flight cycles after the effective date of this AD, whichever 
is later, do external detailed and eddy current inspections for 
horizontal cracks along the chem-milled lines of the fuselage skin 
of the fuselage window belt area, in accordance with Part 2 of the 
Accomplishment Instructions of Boeing Alert Service Bulletin 737-
53A1210, Revision 3, dated July 16, 2009. Repeat the inspections 
thereafter at intervals not to exceed 1,800 flight cycles. If any 
cracking is found, before further flight, repair using a method 
approved in accordance with paragraph (y) of this AD. Doing the 
repair terminates the repetitive inspections specified in this 
paragraph for the repaired area only.

(u) New Requirements of This AD: Repetitive External Detailed and Eddy 
Current Inspections Along the Chem-Milled Lines of the Fuselage Skin of 
the Fuselage Window Belt Area, and Corrective Actions

    For Groups 3, 5, 9, 10, 12, 14, 15, 17, 18, 19, 20, and 21 
airplanes identified in Boeing Alert Service Bulletin 737-53A1210, 
Revision 3, dated July 16, 2009: Do the actions specified in 
paragraph (u)(1) or (u)(2) of this AD, as applicable. Part 7 (Figure 
10) of the Accomplishment Instructions of Boeing Alert Service 
Bulletin 737-53A1210, Revision 3, dated July 16, 2009, specifies 
applying corrosion inhibiting compound (CIC) BMS 3-23 to the 
surfaces of the repaired area. As an option to using CIC BMS 3-23, 
operators may use CIC BMS 3-35, which is equivalent to CIC BMS 3-23.
    (1) For airplanes on which the inspections required by paragraph 
(g) of this AD have been done before the effective date of this AD: 
Within 4,500 flight cycles after doing the most recent inspection 
required by paragraph (g) of this AD, or within 1,800 flight cycles 
after the effective date of this AD, whichever is earlier, do 
external detailed and eddy current inspections for horizontal cracks 
along the chem-milled lines of the fuselage skin of the fuselage 
window belt area, in accordance with Part 2 of the Accomplishment 
Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 
3, dated July 16, 2009. Repeat the inspections thereafter at 
intervals not to exceed 1,800 flight cycles. If any cracking is 
found, before further flight, repair in accordance with Part 8 of 
the Accomplishment Instructions of Boeing Alert Service Bulletin 
737-53A1210, Revision 3, dated July 16, 2009, except as required by 
paragraph (x) of this AD.
    (2) For airplanes on which the inspections required by paragraph 
(g) of this AD have not been done before the effective date of this 
AD: Before the accumulation of 25,000 total flight cycles or within 
1,800 flight cycles after the effective date of this AD, whichever 
is later, do external detailed and eddy current inspections for 
horizontal cracks along the chem-milled lines of the fuselage skin 
of the fuselage window belt area, in accordance with Part 2 of the 
Accomplishment Instructions of Boeing Alert Service Bulletin 737-
53A1210, Revision 3, dated July 16, 2009. Repeat the inspections 
thereafter at intervals not to exceed 1,800 flight cycles. If any 
cracking is found, before further flight, repair in accordance with 
Part 8 of the Accomplishment Instructions of Boeing Alert Service 
Bulletin 737-53A1210, Revision 3, dated July 16, 2009, except as 
required by paragraph (x) of this AD.

(v) New Optional Repair

    For airplanes on which cracking is found during any inspection 
required by paragraph (p), (q), (r), or (s) of this AD, as 
applicable, doing the repair of the chem-milled area in the skin, as 
specified in Part 5 or Part 6 of the Accomplishment Instructions of 
Boeing Alert Service Bulletin 737-53A1210, Revision 3, dated July 
16, 2009, ends the repetitive external detailed and eddy current 
inspections required by paragraph (p), (q), (r), or (s) of this AD, 
as applicable, for the repaired area only.
    Note 1 to paragraph (v) of this AD: Part 8 of the Accomplishment 
Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 
3, dated July 16, 2009, specifies a post-repair inspection of the 
skin chem-milled crack repair at stringer 12; that inspection is not 
required by this AD. The damage tolerance inspections specified in 
Table 7 of paragraph 1.E., ``Compliance,'' of Boeing Alert Service 
Bulletin 737-53A1210, Revision 3, dated July 16, 2009, may be used 
in support of compliance with section 121.1109(c)(2) or 
129.109(c)(2) of the Code of Federal Regulations (14 CFR 
121.1109(c)(2) or 14 CFR 129.109(c)(2)).

(w) New Optional Preventive Modification at Stringer 12

    For airplanes on which no cracking is found during any 
inspection required by paragraph (u) of this AD, doing the 
preventive modification of the chem-milled areas in the skin at 
stringer 12, as specified in Part 7 of the Accomplishment 
Instructions of Boeing Alert Service Bulletin 737-53A1210, Revision 
3, dated July 16, 2009, except as required by paragraph (x) of this 
AD, ends the repetitive external detailed and eddy current 
inspections required by paragraph (u) of this AD, for the modified 
areas common to stringer 12 only. Part 7 (Figure 10) of the 
Accomplishment Instructions of Boeing Alert Service Bulletin 737-
53A1210, Revision 3, dated July 16, 2009, specifies applying CIC BMS 
3-23 to the surfaces of the repaired area. As an option to using CIC 
BMS 3-23, operators may use CIC BMS 3-35, which is equivalent to CIC 
BMS 3-23.

(x) Exception to Service Information

    Where Boeing Alert Service Bulletin 737-53A1210, Revision 3, 
dated July 16, 2009, specifies to contact Boeing for repair 
instructions, before further flight, repair using a method approved 
in accordance with paragraph (y) of this AD.

(y) Alternative Methods of Compliance (AMOCs)

    (1) The Manager, Seattle ACO, FAA, has the authority to approve 
AMOCs for this AD, if requested using the procedures found in 14 CFR 
39.19. In accordance with 14 CFR 39.19, send your request to your 
principal inspector or local Flight Standards District Office, as 
appropriate. If sending information directly to the manager of the 
ACO, send it to the attention of the person identified in the 
Related Information section of this AD. Information may be emailed 
to: 9-ANM-Seattle-ACO-AMOC-Requests@faa.gov.
    (2) Before using any approved AMOC, notify your appropriate 
principal inspector, or lacking a principal inspector, the manager 
of the local flight standards district office/certificate holding 
district office.
    (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 the 
Boeing Commercial Airplanes ODA that 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.

[[Page 61559]]

    (4) AMOCs approved previously in accordance with AD 2004-18-06, 
Amendment 39-13784 (69 FR 54206, September 8, 2004), are approved as 
AMOCs for the corresponding provisions of this AD.
    (5) Inspections and corrective actions required by paragraph (g) 
of AD 2009-21-01, Amendment 39-16038 (74 FR 52395, October 13, 
2009), are approved as AMOCs for the corresponding provisions of 
paragraph (s) of this AD; but only for the areas of the lower lobe 
skin identified in AD 2009-21-01.

(z) Related Information

    (1) For more information about this AD, contact Wayne Lockett, 
Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft 
Certification Office, 1601 Lind Avenue SW., Renton, Washington 
98057-3356; phone: 425-917-6447; fax: 425-917-6590; email: 
wayne.lockett@faa.gov.
    (2) For service information identified in this AD, contact 
Boeing Commercial Airplanes, Attention: Data & Services Management, 
P.O. Box 3707, MC 2H-65, Seattle, Washington 98124-2207; telephone 
206-544-5000, extension 1; fax 206-766-5680; Internet https://www.myboeingfleet.com.
    (3) You may review copies of the referenced service information 
at the FAA, Transport Airplane Directorate, 1601 Lind Avenue SW., 
Renton, Washington. For information on the availability of this 
material at the FAA, call 425-227-1221.

    Issued in Renton, Washington, on September 28, 2012.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 2012-24805 Filed 10-9-12; 8:45 am]
BILLING CODE 4910-13-P
```