DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2012-0268; Directorate Identifier 2011-NM-129-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.

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

SUMMARY: We are revising an earlier proposed airworthiness directive
(AD) for certain The Boeing Company Model 737-600, -700, -700C, -800,
-900 and -900ER series airplanes. That NPRM proposed to require
inspecting for a serial number that starts with the letters "SAIC'' on
the left- and right-side horizontal stabilizer identification plate; a
detailed inspection for correct bolt protrusion and chamfer of the
termination fitting bolts of the horizontal stabilizer rear spar, if
necessary; inspecting to determine if certain bolts are installed, if
necessary; and doing related investigative and corrective actions if
necessary. That NPRM was prompted by reports of incorrectly installed
bolts common to the rear spar termination fitting on the horizontal
stabilizer. This action revises that NPRM by adding airplanes to the
applicability. We are proposing this supplemental NPRM to prevent loss
of structural integrity of the horizontal stabilizer attachment and
loss of control of the airplane. Since these actions impose an
additional burden over that proposed in the 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 April 22, 2013.

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, 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: Nancy Marsh, Aerospace Engineer,
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office
(ACO), 1601 Lind Avenue SW., Renton, Washington 98057-3356; phone: 425-
917-6440; fax: 425-917-6590; email: nancy.marsh@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-2012-0268;
Directorate Identifier 2011-NM-129-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 The Boeing Company Model 737-600, -700, -700C,
-800, and -900 series airplanes. That NPRM published in the Federal
Register on March 20, 2012 (77 FR 16188). That NPRM proposed to require
inspecting for a serial number that starts with the letters "SAIC'' on
the left- and right-side horizontal stabilizer identification plate; a
detailed inspection for correct bolt protrusion and chamfer of the
termination fitting bolts of the horizontal stabilizer rear spar, if
necessary; inspecting to determine if certain bolts are installed, if
necessary; and doing related investigative and corrective actions if
necessary.

Actions Since Previous NPRM (77 FR 16188, March 20, 2012) Was Issued

Since we issued the previous NPRM (77 FR 16188, March 20, 2012), we
have determined that horizontal stabilizers are frequently rotated on
the fleet and could be installed on any Model 737-600, -700, -700C,
-800, and -900 airplane, including airplanes outside the applicability
of the NPRM. Therefore, we have determined that the identified unsafe
condition may exist on all Model 737-600, -700, -700C, -800, -900, and
-900ER series airplanes.

Comments

We gave the public the opportunity to comment on the previous NPRM
(77 FR 16188, March 20, 2012). The following presents the comments
received on the NPRM and the FAA's response to each comment.

Support for the Previous NPRM (77 FR 16188, March 20, 2012)

United Airlines stated it supports the previous NPRM (77 FR 16188,
March 20, 2012).

Request To Revise Applicability

Southwest Airlines (Southwest) requested that we revise the
applicability of the previous NPRM (77 FR 16188, March 20, 2012).
Southwest suggested revising the applicability of the NPRM to identify
serial numbers of the affected horizontal stabilizers, or to open the
applicability of the NPRM to all airplanes, since the applicability
listed in the previous NPRM and the effectivity of the service
information do not account for horizontal stabilizers interchanged
between airplanes.

We agree with the commenter's request for the reasons described in
"Actions Since Previous NPRM (77 FR 16188, March 20, 2012) was
Issued.'' We have revised paragraph (c) of this supplemental NPRM to
include all The Boeing Company Model 737-600, -700, -700C, -800, -900,
and -900ER series airplanes, because the horizontal stabilizers can be
rotated among airplanes. This change has been coordinated with Boeing.

We also have added new paragraph (k) to this supplemental NPRM (and
re-identified subsequent paragraphs) to prohibit installation of a
horizontal stabilizer on any airplane included in the applicability of
this AD unless the horizontal stabilizer has been inspected and
applicable corrective actions have been done and no incorrect bolt
protrusion and no incorrect chamfer of the termination fitting
fasteners have been found.

Request To Improve Inspection Procedures

Southwest and TUIfly Fluggesellschaft mbH requested we revise the
previous NPRM (77 FR 16188, March 20, 2012) to permit operators to
demonstrate compliance for inspecting the horizontal stabilizer to
determine the serial number by means of a review of the manufacturer's
delivery documentation for the accomplishment of Boeing Service
Bulletin 737-55-1090, dated March 30, 2011. TUIfly Fluggesellschaft
said that the delivery paperwork received with the airplane includes
the serial number of the stabilizers installed on the airplane at the
time of delivery.

We agree that the manufacturer's delivery documentation identifies
the serial number of the horizontal stabilizer assembly installed on
the airplane at the time of delivery. However, as discussed in the
previous comment, horizontal stabilizers are rotable parts, so in
addition to the delivery records, the airplane maintenance records must
also be used to positively identify the current stabilizer installed on
the airplane. We have added wording to paragraph (g) of this
supplemental NPRM to state that a review of manufacturer delivery and
operator maintenance records is acceptable if that review conclusively
determines the serial number of the horizontal stabilizer.

STC Winglet Comment

Aviation Partners Boeing stated that the installation of winglets
per Supplemental Type Certificate (STC) ST00830SE does not affect
accomplishment of the proposed requirements.

We have added paragraph (c)(2) to this supplemental NPRM to state
that installation of STC ST00830SE (http://rgl.faa.gov/Regulatory_and_Guidance_Library/
rgstc.nsf/0/408E012E008616A7862578880060456C?OpenDocument&Highlight=st00830se)
does not affect the ability to accomplish the actions proposed by this
supplemental NPRM. Therefore, for airplanes on which STC ST00830SE is
installed, a "change in product'' alternative method of compliance
(AMOC) approval request is not necessary to comply with the
requirements of Section 39.17 of the Federal Aviation Regulations (14
CFR 39.17). For all other AMOC requests, the operator must request
approval of an AMOC in accordance with the procedures specified in
paragraph (l) of this supplemental NPRM.

Request To Revise Applicability To Include Bolt Type BACB30XL

American Airlines (American) requested that the inspections and
corrective actions specified in Boeing Service Bulletin 737-55-1090,
dated March 30, 2011, be used to address the inspections and corrective
actions for the alternative bolt type part number (P/N) BACB30XL that
may be installed at the same locations as bolt type P/N BACB30US14K()
or BACB30US16K(). American indicated the existing service information
does not provide corrective actions for the alternative bolt type P/N
BACB30XL that may be installed in the locations requiring bolt
inspection.

We disagree with the request because Boeing Service Bulletin 737-
55-1090, dated March 30, 2011, provides specific inspection criteria
and measurements that are applicable only to the bolt type P/N
BACB30US. Those criteria cannot be directly applied to the alternative
bolt types. The manufacturer plans to revise that service bulletin to
include corrective actions for the alternative bolt type P/N BACB30XL.
We will review the service bulletin and may approve the revised service
instructions as an AMOC to the AD, when the revised service bulletin is
available. We have not changed the supplemental NPRM in this regard.

Request To Allow Alternative Service Information

Oman Air (Oman) requested that credit for prior accomplishment of
Boeing Service Letters 737-SL-55-027, dated April 12, 2007, and 737-SL-
55-028, dated April 26, 2007, be given as an alternative to the
accomplishment of the inspections and corrective actions specified in
Boeing Service Bulletin 737-55-1090, dated March 30, 2011, which are
required by paragraphs (g), (h), and (k) of the previous NPRM (77 FR
16188, March 20, 2012).

We disagree. Boeing Service Letter 737-SL-55-027, dated April 12,
2007, and Boeing Service Letter 737-SL-55-028, dated April 26, 2007,
were published prior to the identification of the safety issues created
by the missing washers. Although these service letters provide
instructions for the replacement of any missing washers, they do not
address the potential durability issues created by the unclamped joint
that are addressed by the repetitive inspections of the structure, as
specified in Boeing Service Bulletin 737-55-1090, dated March 30, 2011.
The commenter did not provide any data to substantiate the durability
of the corrective actions specified in those service letters. This
proposal could be considered if data were provided to substantiate the
request, using the procedures defined in paragraph (l) of this
supplemental NPRM for requesting approval of an AMOC. We have not
changed the supplemental NPRM in this regard.

Revision to Service Bulletin

The Boeing Company (Boeing) stated it will revise Boeing Service
Bulletin 737-55-1090, dated March 30, 2011, to instruct operators to
inspect for bolt types other than BACB30US, to provide repair methods
for bolt configurations other than BACB30US, and to revise Figure 1 of
that service bulletin to correctly identify the serial number location
in lieu of the part number location.

Boeing did not request a specific change to the previous NPRM (77
FR 16188, March 20, 2012). We already specified the correct location of
the serial number in paragraph (j) of the previous NPRM. We also
already specified that an inspection for bolt types other than part
number BACB30US14K() or BACB30US16K() is required for paragraph (g) of
the previous 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 these
same type designs. Certain changes described above expand the scope of
the original NPRM (77 FR 16188, March 20, 2012). 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 inspecting for a serial number
that starts with the letters "SAIC'' on the left- and right-side
horizontal stabilizer identification plate; a detailed inspection for
correct bolt protrusion and chamfer of the termination fitting bolts of
the horizontal stabilizer rear spar, if necessary; inspecting to
determine if certain bolts are installed, if necessary; and doing
related investigative and corrective actions if necessary.

Costs of Compliance

We estimate that this proposed AD affects 1,147 airplanes of U.S. registry.

We estimate the following costs to comply with this proposed AD:

Estimated Costs

We have received no definitive data that would enable us to provide
a cost estimate for the on-condition actions (contacting Boeing and
repairing cracks or damage) specified in this supplemental NPRM.

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

Authority for This Rulemaking

Title 49 of the United States Code specifies the FAA's authority to
issue rules on aviation safety. Subtitle I, section 106, describes the
authority of the FAA Administrator. "Subtitle VII: Aviation Programs''
describes in more detail the scope of the Agency's authority.

We are issuing this rulemaking under the authority described in
Subtitle VII, Part A, Subpart III, Section 44701: "General
requirements.'' Under that section, Congress charges the FAA with
promoting safe flight of civil aircraft in air commerce by prescribing
regulations for practices, methods, and procedures the Administrator
finds necessary for safety in air commerce. This regulation is within
the scope of that authority because it addresses an unsafe condition
that is likely to exist or develop on products identified in this
rulemaking action.

Regulatory Findings

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 this 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 adding the following new airworthiness
directive (AD):