DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2018-0409; Product Identifier 2017-NM-120-AD; Amendment
39-19559; AD 2019-03-07]
RIN 2120-AA64

Airworthiness Directives; The Boeing Company Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: We are superseding Airworthiness Directive (AD) 2017-16-05,
which applied to certain The Boeing Company Model 737-600, -700, -700C,
-800, -900, and -900ER series airplanes. AD 2017-16-05 required a one-
time detailed visual inspection for discrepancies in the Krueger flap
bullnose attachment hardware, and related investigative and corrective
actions if necessary. This AD adds airplanes and an additional
inspection to determine if any Krueger flap no. 1, 2, 3, or 4 has been
replaced, and related investigative and corrective actions. Since this
is a rotable parts issue, the applicability of this AD has been
expanded beyond the airplanes listed in the related service bulletin to
include all airplanes on which a Krueger flap bullnose may be
installed. This AD was prompted by a report of a Krueger flap bullnose
departing an airplane during taxi, which caused damage to the wing
structure and thrust reverser, and a report of a missing no. 2 Krueger
flap bullnose hinge bolt from an airplane that was not included in the
effectivity of AD 2017-16-05. We are issuing this AD to address the
unsafe condition on these products.

DATES: This AD is effective March 29, 2019.
The Director of the Federal Register approved the incorporation by
reference of a certain publication listed in this AD as of March 29,
2019.

ADDRESSES: For service information identified in this final rule,
contact Boeing Commercial Airplanes, Attention: Contractual & Data
Services (C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA
90740-5600; phone: 562-797-1717; internet: https://www.myboeingfleet.com.
You may view this service information at the
FAA, Transport Standards Branch, 2200 South 216th St., Des Moines, WA.
For information on the availability of this material at the FAA, call
206-231-3195. It is also available on the internet at http://www.regulations.gov
by searching for and locating Docket No. FAA-2018-0409.

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-2018-
0409; or in person at Docket Operations between 9 a.m. and 5 p.m.,
Monday through Friday, except Federal holidays. The AD docket contains
this final rule, the regulatory evaluation, any comments received, and
other information. The address for Docket Operations (phone: 800-647-
5527) is U.S. Department of Transportation, Docket Operations, M-30,
West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue SE,
Washington, DC 20590.

FOR FURTHER INFORMATION CONTACT: Alan Pohl, Aerospace Engineer,
Airframe Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des
Moines, WA 98198; phone and fax: 206-231-3527; email:
alan.pohl@faa.gov.

SUPPLEMENTARY INFORMATION:

Discussion

We issued a notice of proposed rulemaking (NPRM) to amend 14 CFR
part 39 to supersede AD 2017-16-05, Amendment 39-18982 (82 FR39344,
August 18, 2017) (``AD 2017-16-05''). AD 2017-16-05 applied to certain
The Boeing Company Model 737-600, -700, -700C, -800, -900, and -900ER
series airplanes. The NPRM published in the Federal Register on May 15,
2018 (83 FR22420). The NPRM was prompted by a report of a Krueger flap
bullnose departing an airplane during taxi, which caused damage to the
wing structure and thrust reverser, and a report of a missing no. 2
Krueger flap bullnose hinge bolt from an airplane that was not included
in the effectivity of AD 2017-16-05. The NPRM proposed to continue to
require a one-time detailed visual inspection for discrepancies in the
Krueger flap bullnose attachment hardware, and related investigative
and corrective actions, if necessary. The NPRM also proposed to add
airplanes and an additional inspection to determine if any Krueger flap
no. 1, 2, 3, or 4 has been replaced, and related investigative and
corrective actions. Since this is a rotable parts issue, the
applicability of this AD has been expanded beyond the airplanes listed
in the related service bulletin to include all airplanes on which a
Krueger flap bullnose may be installed. We are issuing this AD to
address missing Krueger flap bullnose hardware. Such missing hardware
could result in the Krueger flap bullnose departing the airplane during
flight, which could damage empennage structure and lead to the
inability to maintain continued safe flight and landing.

Comments

We gave the public the opportunity to participate in developing
this AD. The following presents the comments received on the NPRM and
the FAA's response to each comment.

Support for the NPRM

Boeing concurred with the content of the NPRM. Delta Air Lines
(DAL) and American Airlines (AAL) concurred with the intent of the
NPRM.

Effect of Winglets on Accomplishment of the Proposed Actions

Aviation Partners Boeing stated that accomplishing the Supplemental
Type Certificate (STC) ST00830SE does not affect the actions specified
in the NPRM.
We concur with the commenter. We have redesignated paragraph (c) of
the proposed AD as paragraph (c)(1) of this AD and added paragraph
(c)(2) to this AD to state that installation of STC ST00830SE does not
affect the ability to accomplish the actions required by this AD.
Therefore, for airplanes on which STC ST00830SE is installed, a
``change in product'' alternative method of compliance (AMOC) approval
request is not necessary to comply with the requirements of 14 CFR
39.17.

Request To Remove Airplanes From the Applicability

All Nippon Airways (ANA) requested that we remove the airplanes
identified in paragraph (c)(3) of the proposed AD. ANA stated that
those airplanes are not required to do the actions specified in
paragraph (g) of the proposed AD.
We disagree with the request. Although the airplanes identified in
paragraph (c)(1)(iii) of this AD (paragraph (c)(3) of the proposed AD)
are not required to do the actions specified in paragraph (g) of this
AD, those airplanes must still comply with the parts installation
limitation specified in paragraph (i) of this AD. We have not changed
this AD in this regard.

Request for a Different Method of Compliance

DAL requested that we include an option in paragraph (i) of the
proposed AD to install the Krueger flap before accomplishing the
required actions. DAL mentioned that it has updated its manuals to
inspect after installation on the airplane, not prior to installation.
We agree that clarification is necessary. The required inspection
of the Krueger flap bullnose can only be accomplished after
installation on the Krueger flap assembly, either prior to or after
installation on the airplane. We have revised paragraph (i) to specify
that the actions required by paragraph (g) of this AD must be
accomplished after installation but prior to further flight.

Request To Clarify Which Krueger Flaps Are Affected

DAL and AAL requested that we clarify paragraph (i) of the proposed
AD to specify affected Krueger flap(s) and Krueger flap bullnose(s).
DAL stated that not all four positions need to be inspected, only the
Krueger flap(s) and Krueger flap bullnose(s) being installed. AAL
suggested that we reword paragraph (i) of the proposed AD to improve
clarity.
We agree with the request because it is not necessary to perform
the actions specified in paragraph (i) of this AD on all four Krueger
flap(s) or Krueger flap bullnose(s). Only the Krueger flap(s) or
Krueger flap bullnose(s) being installed must be inspected. We have
revised paragraph (i) of this AD to specify: ``These actions are
required only for the Krueger flap(s) or Krueger flap bullnose(s) being
installed.''

Conclusion

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

Related Service Information Under 1 CFR Part 51

We reviewed Boeing Alert Service Bulletin 737-57A1327, Revision 2,
dated July 25, 2017. This service information describes procedures for
a one-time detailed visual inspection for discrepancies in the Krueger
flap bullnose attachment hardware, and related investigative and
corrective actions; and an inspection to determine if any Krueger flap
no. 1, 2, 3, or 4 has been replaced, and related investigative and
corrective actions. 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.

Costs of Compliance

We estimate that this AD affects 1,814 airplanes of U.S. registry.
We estimate the following costs to comply with this AD:


Estimated Costs

We have received no definitive data that would enable us to provide
cost estimates for the on-condition actions specified in this AD.
According to the manufacturer, some of the costs of this AD may be
covered under warranty, thereby reducing the cost impact on affected
individuals. We do not control warranty coverage for affected
individuals. As a result, we have included all available 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.
This 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 and
associated appliances to the Director of the System Oversight Division.

Regulatory Findings

We have determined that this AD will not have federalism
implications under Executive Order 13132. This AD will not have a
substantial direct effect on the States, on the relationship between
the national government and the States, or on the distribution of power
and responsibilities among the various levels of government.
For the reasons discussed above, I certify that this AD:
(1) Is not a ``significant regulatory action'' under Executive
Order 12866,
(2) Is not a ``significant rule'' under DOT Regulatory Policies and
Procedures (44 FR 11034, February 26, 1979),
(3) Will not affect intrastate aviation in Alaska, and
(4) Will not have a significant economic impact, positive or
negative, on a substantial number of small entities under the criteria
of the Regulatory Flexibility Act.

List of Subjects in 14 CFR Part 39

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

Adoption of the Amendment

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

PART 39--AIRWORTHINESS DIRECTIVES

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

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

Sec. 39.13 [Amended]

2. The FAA amends Sec. 39.13 by removing Airworthiness Directive (AD)
2017-16-05, Amendment 39-18982 (82 FR 39344, August 18, 2017), and
adding the following new AD: