DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2017-0814; Product Identifier 2017-NM-066-AD]
RIN 2120-AA64

Airworthiness Directives; The Boeing Company Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: We propose to adopt a new airworthiness directive (AD) for
certain The Boeing Company Model 737-600, -700, -700C, -800, -900, and
-900ER series airplanes. This proposed AD was prompted by significant
changes made to the airworthiness limitations (AWL) related to fuel
tank ignition prevention and the nitrogen generation system. This
proposed AD would require revision of the maintenance or inspection
program, as applicable, to include the latest revision of the AWLs. We
are proposing this AD to address the unsafe condition on these
products.

DATES: We must receive comments on this proposed AD by November 16, 2017.

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: Deliver to Mail address above between 9
a.m. and 5 p.m., Monday through Friday, except Federal holidays.

For service information identified in this NPRM, contact Boeing
Commercial Airplanes, Attention: Contractual & Data Services (C&DS),
2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-5600;
telephone 562-797-1717; Internet https://www.myboeingfleet.com. You may
view this service information at the FAA, Transport Standards Branch,
1601 Lind Avenue SW., Renton, WA. For information on the availability
of this material at the FAA, call 425-227-1221.

Examining the AD Docket

You may examine the AD docket on the Internet at http://www.regulations.
gov by searching for and locating Docket No. FAA-2017-
0814; 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 NPRM, 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: Tak Kobayashi, Aerospace Engineer,
Propulsion Section, FAA, Seattle ACO Branch, 1601 Lind Avenue SW.,
Renton, WA 98057-3356; phone: 425-917-6499; fax: 425-917-6590; email:
takahisa.kobayashi@faa.gov.

SUPPLEMENTARY INFORMATION:

Comments Invited

We invite you to send any written relevant data, views, or
arguments about this proposal. Send your comments to an address listed
under the ADDRESSES section. Include "Docket No. FAA-2017-0814;
Product Identifier 2017-NM-066-AD" at the beginning of your comments.
We specifically invite comments on the overall regulatory, economic,
environmental, and energy aspects of this NPRM. We will consider all
comments received by the closing date and may amend this NPRM 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 NPRM.

Discussion

The FAA has examined the underlying safety issues involved in fuel
tank explosions on several large transport airplanes, including the
adequacy of existing regulations, the service history of airplanes
subject to those regulations, and existing maintenance practices for
fuel tank systems. As a result of those findings, we issued a final
rule titled "Transport Airplane Fuel Tank System Design Review,
Flammability Reduction and Maintenance and Inspection Requirements"
(66 FR 23086, May 7, 2001). In addition to new airworthiness standards
for transport airplanes and new maintenance requirements, that rule
included Amendment 21-78, which established Special Federal Aviation
Regulation No. 88 ("SFAR 88") at 14 CFR part 21. Subsequently, SFAR
88 was amended by: Amendment 21-82 (67 FR 57490, September 10, 2002;
corrected at 67 FR 70809, November 26, 2002) and Amendment 21-83 (67 FR
72830, December 9, 2002; corrected at 68 FR 37735, June 25, 2003, to
change "21-82" to "21-83").

Among other actions, SFAR 88 requires certain type design (i.e.,
type certificate (TC) and supplemental type certificate (STC)) holders
to substantiate that their fuel tank systems can prevent ignition
sources in the fuel tanks. This requirement applies to type design
holders for large turbine-powered transport airplanes and for
subsequent modifications to those airplanes. It requires them to
perform design reviews and to develop design changes and maintenance
procedures if their designs do not meet the new fuel tank safety
standards. As explained in the preamble to the final rule published on
May 7, 2001, we intended to adopt airworthiness directives to mandate
any changes found necessary to address unsafe conditions identified as
a result of these reviews.

In evaluating these design reviews, we have established four
criteria intended to define the unsafe conditions associated with fuel
tank systems that require corrective actions. The percentage of
operating time during which fuel tanks are exposed to flammable
conditions is one of these criteria. The other three criteria address
the failure types under evaluation: Single failures, single failures in
combination with another latent condition(s), and in-service failure experience.
For all four criteria, the evaluations included consideration of previous actions
taken that may mitigate the need for further action.

We issued AD 2008-10-10 R1, Amendment 39-16164 (75 FR 1529, January
12, 2010) ("AD 2008-10-10 R1"), which applies to certain The Boeing
Company Model 737-600, -700, -700C, -800, and -900 series airplanes. AD
2008-10-10 R1 requires incorporation of fuel system AWLs and also
requires an initial inspection to phase in certain repetitive
inspections, and repair if necessary. The fuel system AWLs were
developed to satisfy SFAR 88 requirements and included in the
Airworthiness Limitations Section (ALS) of the manufacturer's
Instructions for Continued Airworthiness. Since we issued AD 2008-10-10
R1, the ALS has been significantly revised by the manufacturer to
correct technical and editorial errors and also to add new
requirements. Those changes affect the fuel system and nitrogen
generation system AWLs. We have determined that the specific revisions
of the ALS mandated by AD 2008-10-10 R1, and the revisions of the ALS
that have been delivered with airplanes as part of the type design and
airworthiness certificate, on or after March 31, 2006 (see paragraph
(c), "Applicability," of AD 2008-10-10 R1, which applied to airplanes
with an original standard airworthiness certificate or original export
certificate of airworthiness issued before March 31, 2006), are
inadequate to provide information necessary to maintain critical design
features and perform inspections.

We propose to adopt this new AD to require revising the maintenance
or inspection program, as applicable, to incorporate the AWLs provided
in Boeing 737-600/700/700C/800/900/900ER Special Compliance Items/
Airworthiness Limitations, dated January 2017 (the latest revision of
the ALS). We are proposing this AD to prevent the potential for
ignition sources inside the fuel tanks and also to prevent increasing
the flammability exposure of the center fuel tank caused by latent
failures, alterations, repairs, or maintenance actions, which could
result in a fuel tank explosion and consequent loss of an airplane.

We have determined that accomplishing the revision required by
paragraph (g) of this proposed AD would terminate the following
requirements for that airplane:

All requirements of AD 2008-10-10 R1.

The revision required by paragraphs (h) and (h)(1) of AD
2008-06-03, Amendment 39-15415 (73 FR 13081, March 12, 2008).

The revision required by paragraph (g) of AD 2008-17-15,
Amendment 39-15653 (73 FR 50714, August 28, 2008).

The revision required by paragraph (k) of AD 2011-18-03,
Amendment 39-16785 (76 FR 53317, August 26, 2011).

All requirements of AD 2013-15-17, Amendment 39-17533 (78
FR 52838, August 27, 2013).

Airworthiness Limitations Based on Type Design

The FAA recently became aware of an issue related to the
applicability of ADs that require incorporation of the Airworthiness
Limitations section (ALS) of the Instructions for Continued
Airworthiness (ICA) into an operator's maintenance or inspection
program.

U.S. operators must operate their airplanes in an airworthy
condition, in accordance with 14 CFR 91.7(a). Included in this
obligation is the requirement to perform any maintenance or inspections
specified in the ALS, and in accordance with the ALS as specified in 14
CFR 43.16 and 91.403(c), unless an alternative has been approved by the
FAA.

When a type certificate is issued for a type design, the specific
ALS, including its revision level, is part of that type design, as
specified in 14 CFR 21.31(c).

The sum effect of these operational and maintenance requirements is
an obligation to comply with the ALS revision defined in the type
design referenced in the manufacturer's conformity statement. This
obligation may introduce a conflict with an AD if the AD requires a
specific ALS revision for new airplanes that are delivered with a later
ALS revision as part of their type design.

The FAA has approved alternative methods of compliance (AMOCs) that
allow operators to incorporate the most recent ALS revision into their
maintenance/inspection programs, in lieu of the ALS revision required
by the AD. This enables the operator to comply with both the AD and the
type design.

However, compliance with AMOCs is normally optional, and we
recently became aware that some operators choose to retain the AD-
mandated ALS revision in their fleet-wide maintenance/inspection
programs, including those for new airplanes delivered with later ALS
revisions, to help standardize the maintenance of the fleet. To ensure
that operators comply with the applicable ALS revision for newly
delivered airplanes containing a later revision than that specified in
an AD, we plan to mandate the latest ALS revision as of the effective
date of an AD, if we are to mandate a specific ALS revision, and limit
the applicability to those airplanes delivered on or before the
effective date of that AD.

This proposed AD therefore mandates the latest ALS revision as of
the effective date of the AD for Model 737-600, -700, -700C, -800, -
900, and -900ER series airplanes with an original certificate of
airworthiness or original export certificate of airworthiness that was
issued on or before the effective date of the AD. Operators of
airplanes with an original certificate of airworthiness or original
export certificate of airworthiness issued after that date must comply
with the airworthiness limitations specified as part of the approved
type design.

Related Service Information Under 1 CFR Part 51

We reviewed Boeing 737-600/700/700C/800/900/900ER Special
Compliance Items/Airworthiness Limitations, D626A001-9-04, dated
January 2017. This service information describes AWLs that include
airworthiness limitation instructions (ALI) and critical design
configuration control limitations (CDCCL) tasks related to fuel tank
ignition prevention and the nitrogen generation system. This service
information is reasonably available because the interested parties have
access to it through their normal course of business or by the means
identified in the ADDRESSES section.

FAA's Determination

We are proposing this AD 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.

Proposed AD Requirements

This proposed AD would require revisions to certain operator
maintenance documents to include new actions (e.g., inspections) and
CDCCLs. Compliance with these actions and CDCCLs is required by 14 CFR
91.403(c). For airplanes that have been previously modified, altered,
or repaired in the areas addressed by this proposed AD, the operator
may not be able to accomplish the actions described in the revisions.
In this situation, to comply with 14 CFR 91.403(c), the operator must
request approval for an alternative method of compliance according to
paragraph (k) of this proposed AD. The request should include a
description of changes to the required inspections that will ensure the
continued operational safety of the airplane.

Notwithstanding any other maintenance or operational requirements,
components that have been identified as airworthy or installed on the
affected airplanes before accomplishing the revision of the airplane
maintenance or inspection program specified in this proposed AD do not
need to be reworked in accordance with the latest revision of the
CDCCLs specified by this proposed AD for incorporation. However, once
the airplane maintenance or inspection program has been revised as
required by this proposed AD, future maintenance actions on these
components must be done in accordance with the CDCCLs specified by this
proposed AD.

Differences With the Service Information

The "description" column of AWL No. 28-AWL-20 identifies certain
operational tests. However, airplanes on which the actions specified in
paragraph (g)(2)(ii) of AD 2011-20-07 have been done are not required
to do the operational test for left center tank fuel boost pump relay
R54 and right center tank fuel boost pump relay R55.

Paragraph (g) of this proposed AD would require operators to revise
their maintenance or inspection program by incorporating, in part, AWL
No. 28-AWL-05, "Wire Separation Requirements for New Wiring Installed
in Proximity to Wiring That Goes Into the Fuel Tanks" in Boeing 737-
600/700/700C/800/900/900ER Special Compliance Items/Airworthiness
Limitations, D626A001-9-04, dated January 2017. Paragraph (h) of this
proposed AD would allow certain changes to be made to the requirements
specified in AWL No. 28-AWL-05 as an option.

Clarification of the Service Information

The "applicability" column of AWL No. 28-AWL-19 identifies
affected airplanes. For airplanes on which the actions specified in
paragraph (s) of AD 2011-18-03 have been done, incorporation of Boeing
Service Bulletin 737-28A1206 is not required. Therefore, those
airplanes are not affected by AWL No. 28-AWL-19 and are not required to
do the functional test.

The "applicability" column of AWL No. 28-AWL-23 identifies
affected airplanes. For airplanes on which the actions specified in
paragraph (s) of AD 2011-18-03 have been done, incorporation of Boeing
Service Bulletin 737-28A1248 is not required. Therefore, those
airplanes are not affected by AWL No. 28-AWL-23 and are not required to
do the functional test.

Alternative Methods of Compliance (AMOC) Previously Approved for
Compliance With AD 2008-10-10 R1

The FAA has previously issued AMOC approvals for compliance with
paragraph (g)(3) of AD 2008-10-10 R1 to allow operators to incorporate
alternative versions of AWL No. 28-AWL-05. AWL No. 28-AWL-05 includes
the requirements for new wiring introduced by any alterations or
changes to the type design, including STC modifications, in proximity
to wiring that penetrates the fuel tank wall. Certain STCs that
introduced new wiring near the fuel quantity indicating system (FQIS)
wiring utilized design features that were different from the critical
design features for fuel tank ignition prevention specified in the AD-
mandated version of AWL No. 28-AWL-05. For those STCs, we have approved
alternative versions of AWL No. 28-AWL-05 that specified critical
design features associated with STC modifications. We have determined
that certain critical design features specified in the AMOC-approved
versions of AWL No. 28-AWL-05 are not acceptable to meet the intent of
this AWL. Therefore, this proposed AD does not allow credit for AMOCs
previously approved under AD 2008-10-10 R1. However, based on our
assessment of critical design features, we have provided an optional
action under paragraph (h) of this proposed AD to allow certain changes
to be made to the requirements specified in AWL No. 28-AWL-05. Under
this optional action, certain critical design features we have
previously approved and consider to be acceptable can be specified in
AWL No. 28-AWL-05.

The requirements for new wiring versus existing wiring are
specified in AWL No. 28-AWL-05. Based on these requirements, any STC
modifications that are installed after the incorporation of AWL No. 28-
AWL-05 (version required by paragraph (g) of this AD) must comply with
AWL No. 28-AWL-05, including any mandatory rework, or the operator must
request approval of an AMOC according to paragraph (k) of this proposed
AD. Any STC modifications that are installed prior to the incorporation
of AWL No. 28-AWL-05 (version required by paragraph (g) of this AD) are
not required to be reworked for compliance with the new wiring
requirements of AWL No. 28-AWL-05, except that future repair and
replacement of existing wiring must follow AWL No. 28-AWL-05.

Costs of Compliance

We estimate that this proposed AD affects 1,417 airplanes of U.S.
registry. We estimate the following costs to comply with this proposed
AD:

Estimated Costs
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Action Labor cost Parts cost Cost per product Cost on U.S. operators
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Revising the maintenance or inspection program 1 work-hour x $85 per hour = $85 $0 $85 $120,445
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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.

This proposed AD is issued in accordance with authority delegated
by the Executive Director, Aircraft Certification Service, as
authorized by FAA Order 8000.51C. In accordance with that order,
issuance of ADs is normally a function of the Compliance and
Airworthiness Division, but during this transition period, the
Executive Director has delegated the authority to
issue ADs applicable to transport category airplanes to the Director of
the System Oversight Division.

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):