DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2015-8133; Directorate Identifier 2015-NM-101-AD;
Amendment 39-18631; AD 2016-18-01]
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 adopting a new airworthiness directive (AD) for certain
The Boeing Company Model 737-600, -700, -700C, -800, -900, and -900ER
series airplanes. This AD was prompted by reports of heavy corrosion
and chrome damage on the forward and aft trunnion pin assemblies of the
right and left main landing gears (MLGs). This AD requires repetitive
lubrication of the forward and aft trunnion pin assemblies of the right
and left MLGs; repetitive inspections of these assemblies for corrosion
and chrome damage, and related investigative and corrective actions if
necessary; and installation of new or modified trunnion pin assembly
components, which will terminate the repetitive lubrication and
repetitive inspections. We are issuing this AD to detect and correct
heavy corrosion and chrome damage on the forward and aft trunnion pin
assemblies of the right and left MLGs, which could result in cracking
of these assemblies and collapse of the MLGs.

DATES: This AD is effective October 5, 2016.
The Director of the Federal Register approved the incorporation by
reference of a certain publication listed in this AD as of October 5,
2016.

ADDRESSES: For service information identified in this final rule,
contact Boeing Commercial Airplanes, Attention: Data & Services
Management, P.O. Box 3707, MC 2H-65, Seattle, WA 98124-2207; telephone
206-544-5000, extension 1; fax 206-766-5680; Internet https://www.
myboeingfleet.com. You may view this referenced service information
at the FAA, Transport Airplane Directorate, 1601 Lind Avenue SW.,
Renton, WA. For information on the availability of this material at the
FAA, call 425-227-1221. It is also available on the Internet at http://www.
regulations.gov by searching for and locating Docket No. FAA-2015-8133.

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-2015-
8133; 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 AD, the regulatory evaluation, any comments received, and
other information. The address for the Docket Office (phone: 800-647-
5527) is Docket Management Facility, 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 Branch, ANM-120S, FAA Seattle Aircraft Certification Office,
1601 Lind Avenue SW., Renton, WA 98057-3356; phone: 425-917-6450; fax:
425-917-6590; email: alan.pohl@faa.gov.

SUPPLEMENTARY INFORMATION:

Discussion

We issued a notice of proposed rulemaking (NPRM) to amend 14 CFR
part 39 by adding an AD that would apply to certain The Boeing Company
Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes.
The NPRM published in the Federal Register on December 31, 2015 (80 FR
81795) (``the NPRM''). The NPRM was prompted by reports of heavy
corrosion and chrome damage on the forward and aft trunnion pin
assemblies of the right and left MLGs. The NPRM proposed to require
repetitive lubrication of the forward and aft trunnion pin assemblies
of the right and left MLGs; repetitive inspections of these assemblies
for corrosion and chrome damage, and related investigative and
corrective actions if necessary; and installation of new or modified
trunnion pin assembly components, which would terminate the repetitive
lubrication and repetitive inspections. We are issuing this AD to
detect and correct heavy corrosion and chrome damage on the forward and
aft trunnion pin assemblies of the right and left MLGs, which could
result in cracking of these assemblies and collapse of the MLGs.

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 stated that it concurs with the contents of the NPRM.

Effect of Winglets on Accomplishment of the Proposed Actions

Aviation Partners Boeing stated that accomplishing Supplemental
Type Certificate (STC) ST00830SE does not affect the accomplishment of
the actions specified in the NPRM.
We concur with the commenter. We have redesignated paragraph (c) of
the proposed AD as paragraph (c)(1) and added new paragraph (c)(2) in
this AD to state that installation of STC ST00830SE does not affect the
ability to accomplish the actions required by this final rule.
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 for Clarification of Requirements

Delta Airlines (DAL) requested an explanation of how the
requirements are different between AD 2014-08-11, Amendment 39-17835
(79 FR 23903, April 29, 2014) (``AD 2014-08-11'') and the NPRM. DAL
noted that the requirements of AD 2014-08-11 include an inspection for
discrepancies of the transition radius of the MLG forward trunnion
pins, and corrective actions if necessary. DAL elaborated that this
inspection is for finish damage (scrapes through primer), signs of
corrosion, pitting, and scratches in the base metal of that area. DAL
pointed out that the NPRM requires a general visual inspection of the
MLG forward trunnion pin assembly for signs of corrosion or chrome
plating damage, and if either condition is found, a detailed inspection
of the forward trunnion pin assembly is required. DAL mentioned that
the detailed inspection requires verification that a new seal and
retainer configuration is installed, and if the overhaul limits exceed
what is specified in the component maintenance manual, replacement of
the forward trunnion pin assembly is necessary. DAL reasoned that the
forward trunnion pin inspections required by AD 2014-08-11 should be
superseded by the proposed forward trunnion pin inspections in the
NPRM. DAL stated that the detailed inspection proposed in the NPRM has
additional corrective actions if any loose or missing chrome plating is
found, beyond what is required in AD 2014-08-11. DAL also conveyed that
the inspections for signs of corrosion are the same in the NPRM and AD
2014-08-11.
We agree to provide clarification regarding how the requirements
are different between the requirements in the proposed AD and the
requirements mandated by AD 2014-08-11. The applicability of the
proposed AD includes certain The Boeing Company Model 737-600, -700, -
700C, -800, -900, and -900ER series airplanes, line numbers 1 through
3526 inclusive. The applicability of AD 2014-08-11 includes certain The
Boeing Company Model 737-600, -700, -700C, -800, -900, and -900ER
series airplanes, line numbers 1423 through 3526 inclusive. Although
certain airplane line numbers are included in the applicability of both
the proposed AD and AD 2014-08-11, the issues addressed by the NPRM and
AD 2014-08-11 are not the same. Furthermore, the inspection
instructions in the service information required for accomplishing the
actions in the proposed AD are different from the inspection
instructions in the service information required by AD 2014-08-11. The
inspections in the proposed AD focus on chrome damage and corrosion on
the shank of the forward trunnion pins, and the inspections required by
AD 2014-08-11 focus on finish scratches and corrosion in the transition
radius of the forward trunnion pins. We have not changed this AD
regarding this issue.
In addition, we note that the service information required to do
the actions required by AD 2014-08-11 (which cites Boeing Special
Attention Service Bulletin 737-32-1402, Revision 1, dated February 7,
2013), includes a recommendation by Boeing that operators accomplish
the specified actions concurrently with the actions specified in Boeing
Special Attention Service Bulletin 737-32-1448 (Boeing Special
Attention Service Bulletin 737-32-1448, Revision 1, dated May 29, 2015,
is the appropriate source of service information for accomplishing the
actions required by this AD).

Likewise, Boeing Special Attention Service Bulletin 737-32-1448,
Revision 1, dated May 29, 2015, includes a recommendation by Boeing
that operators accomplish the specified actions concurrently with the
actions specified in Boeing Special Attention Service Bulletin 737-32-
1402.

Request for Clarification of Lube Fittings Location

DAL requested clarification regarding the location of the lube
fittings for the forward and aft MLG trunnion pin assemblies in
paragraph (g) of the NPRM. DAL commented that the NPRM stated to do the
repetitive lubrication in accordance with Work Package 1 of the
Accomplishment Instructions of Boeing Special Attention Service
Bulletin 737-32-1448, Revision 1, dated May 29, 2015. DAL noted that
Work Package 1 of the Accomplishment Instructions of Boeing Special
Attention Service Bulletin 737-32-1448, Revision 1, dated May 29, 2015,
refers to section 12-21-11 of the Boeing 737-600/700/800/900 Aircraft
Maintenance Manual (AMM) as an accepted procedure for the repetitive
lubrication of the MLG trunnion pin assemblies. DAL stated that section
12-21-11 of the AMM specifically identifies the locations of the
trunnion bearing housing and the aft trunnion bearing, but does not
specifically identify the locations of the two lube fittings for the
forward and aft trunnion pins.
We agree with the commenter that the two lube fittings for the
forward and aft trunnion pins are not specifically mentioned in section
12-21-11 of the Boeing 737-600/700/800/900 AMM. These locations are
identified as Item [6], ``Outer Cylinder,'' on page 307 of the AMM.
However, there are only three lube fittings associated with Item [6],
so it is possible to determine which two fittings are to be used for
lubricating the forward and aft trunnion pins. We consulted with Boeing
and confirmed that the two lube fittings are located on the bottom of
the outer cylinder trunnion, directly under the pins. We have not
changed this AD regarding this issue.

Request for Clarification of Corrective Actions in Paragraph (h) of the
Proposed AD

DAL requested clarification of certain corrective actions in
paragraph (h) of the proposed AD. DAL asked if an operator can replace
an affected trunnion pin assembly instead of overhauling it. DAL
pointed out that neither the NPRM nor Boeing Special Attention Service
Bulletin 737-32-1448, Revision 1, dated May 29, 2015, specify the part
number of the replacement trunnion pin assembly. DAL asked if an
operator can replace an affected pin assembly with any properly
approved pin assembly using the Boeing 737 Aircraft Illustrated Parts
Catalog, Boeing Drawing 161A0002, ``Boeing Model 737-NG Main Landing
Gear Component Interchangeability List,'' or a similar document.
We agree with the commenter's request for clarification. Operators
may elect to replace a trunnion pin assembly with a serviceable unit in
lieu of performing an overhaul. However, operators should be aware that
some of the existing trunnion pin assemblies require modification.
Figures 9, 11, and 12 of Boeing Special Attention Service Bulletin 737-
32-1448, Revision 1, dated May 29, 2015, provide instructions for
modifying certain pin assemblies. Note (c) in each of these figures
refers to paragraph 2.C.3., ``Parts Modified and Reidentified,'' of
Boeing Special Attention Service Bulletin 737-32-1448, Revision 1,
dated May 29, 2015, which shows the existing and modified part numbers.
For use of other part numbers, such as those identified in the Boeing
737 Aircraft Illustrated Parts Catalog or Boeing Drawing 161A0002,
``Boeing Model 737-NG Main Landing Gear Component Interchangeability
List,'' operators may request an alternative method of compliance in
accordance with the procedures specified in paragraph (m) of this AD.
We have not changed this AD regarding this issue.

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 correcting 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 Special Attention Service Bulletin 737-32-1448,
Revision 1, dated May 29, 2015. The service information describes
procedures for lubricating the forward and aft trunnion pin assemblies
on the left and right MLGs, inspecting the forward and aft trunnion pin
assemblies for corrosion or damage, and performing corrective actions.
In addition, the service information describes procedures for
installing a new forward trunnion pin housing assembly, seal, and
retainer configuration. 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 1,023 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.

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

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 adding the following new airworthiness
directive (AD):