DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2019-0705; Product Identifier 2019-NM-098-AD]
RIN 2120-AA64

Airworthiness Directives; The Boeing Company Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

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

SUMMARY: The FAA is revising an earlier proposal for certain The Boeing
Company Model 737-600, -700, -700C, -800, and -900 series airplanes. This
action revises the notice of proposed rulemaking (NPRM) by revising
certain inspections to provide the correct thickness callouts for the
fuselage skin and bear strap. The FAA is proposing this airworthiness
directive (AD) to address the unsafe condition on these products. Since
these actions would impose an additional burden over that in the NPRM, the
FAA is reopening the comment period to allow the public the chance to
comment on these changes.

DATES: The comment period for the NPRM published in the Federal Register
on October 1, 2019 (84 FR 52047), is reopened. The FAA must receive
comments on this SNPRM by June 15, 2020.

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 https://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 SNPRM, 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, Airworthiness Products Section, Operational Safety
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 https://www.regulations.gov by searching for
and locating Docket No. FAA-2019-0705.

Examining the AD Docket

You may examine the AD docket on the Internet at https://www.regulations.
gov by searching for and locating Docket No. FAA-2019-0705; 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 SNPRM, the regulatory
evaluation, any comments received, and other information. The street
address for Docket Operations is listed above. Comments will be available
in the AD docket shortly after receipt.

FOR FURTHER INFORMATION CONTACT: Michael Bumbaugh, Aerospace Engineer,
Airframe Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des
Moines, WA 98198; phone and fax: 206-231-3522; email: michael.bumbaugh@
faa.gov.

SUPPLEMENTARY INFORMATION:

Comments Invited

The FAA invites 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-2019-0705; Product Identifier
2019-NM-098-AD" at the beginning of your comments. The FAA specifically
invites comments on the overall regulatory, economic, environmental, and
energy aspects of this SNPRM. The FAA will consider all comments received
by the closing date and may amend this SNPRM because of those comments.

The FAA will post all comments, without change, to https://www.regulations
.gov, including any personal information you provide. The FAA will also
post a report summarizing each substantive verbal contact received about
this SNPRM.

Discussion

The FAA issued an 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, and
-900 series airplanes. The NPRM published in the Federal Register on
October 1, 2019 (84 FR 52047). The NPRM was prompted by reports of cracks
in the bear strap between certain stations, sometimes common to fasteners
in the gap cover and emanating from rough sanding marks found on the
surface of the bear strap. The NPRM proposed to require inspections of the
fuselage skin and bear strap at the forward galley door between certain
stations for cracks, and applicable on-condition actions.

Actions Since the NPRM was Issued

Since the FAA issued the NPRM, the FAA has determined that, for certain
inspections specified in the proposed AD, certain thickness callouts for
the fuselage skin and bear strap were incorrect. Therefore, the FAA has
determined the correct thickness callouts must be included in those
inspections.

Comments

The FAA gave the public the opportunity to comment on the NPRM. The
following presents the comments received on the NPRM and the FAA’s
response to each comment.

Effect of Winglets on Accomplishment of the Proposed Actions

Aviation Partners Boeing stated that accomplishing Supplemental Type Cer-
tificate (STC) ST00830SE does not affect the actions specified in the
proposed AD. The FAA concurs with the commenter. The FAA has 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 Include Updated Service Information

Boeing requested that the FAA revise the NPRM to include a later revision
of the service information. Boeing pointed out that the skin and bear
strap thicknesses referenced in Boeing Alert Requirements Bulletin 737
-53A1383 RB, dated May 9, 2019, were incorrectly specified as 0.0710
inches and 0.10 inches respectively, which affects the proper calibration
of the inspection probe. Boeing stated that the correct skin and bear
strap thicknesses should be 0.100 inches and 0.090 inches respectively.
Boeing also mentioned that a new revision to the service information that
corrects the skin and bear strap thicknesses was being coordinated with
the FAA.

The FAA agrees for the reasons provided. Therefore, the FAA has included
Boeing Alert Requirements Bulletin 737-53A1383 RB, Revision 1, dated
February 19, 2020, as the appropriate source of service information for
doing the actions specified in this SNPRM. Additionally, the FAA has also
included paragraph (i) of this SNPRM to allow credit for actions
accomplished before the effective date of this AD, using Boeing Alert
Requirements Bulletin 737-53A1383 RB, dated May 9, 2019, provided that for
airplanes on which Option 2, Condition 4, has been done (no external
repair and have done the external low frequency eddy current (LFEC)
inspection of the forward galley door bear strap and external high
frequency eddy current (HFEC) inspection of the fuselage skin for any
crack), operators also do the external LFEC inspection of the forward
galley door bear strap and external HFEC inspection of the fuselage skin
for any crack identified in accordance with Figure 4 of the Accomplishment
Instructions of Boeing Alert Requirements Bulletin 737-53A1383 RB,
Revision 1, dated February 19, 2020, and do all applicable on-condition
actions.

Request for Credit for Actions Accomplished Prior to the Effective Date

Alaska Airlines (AAL), United Airlines (UAL), and Delta Air Lines (DAL)
requested that the FAA provide credit for accomplishing the actions
specified in paragraph (g) of the proposed AD prior to the effective date
of this AD in accordance with Boeing Alert Requirements Bulletin 737
-53A1383 RB, dated May 9, 2019 (which was referred to as the appropriate
source of information for doing the actions required by paragraph (g) of
the proposed AD).

The FAA acknowledges the commenter’s requests and agrees to clarify. As
previously stated, the FAA has included Boeing Alert Requirements Bulletin
737-53A1383 RB, Revision 1, dated February 19, 2020, as the appropriate
source of service information for doing the actions specified in this
SNPRM. The FAA has also included paragraph (i) of this SNPRM to allow
credit for actions accomplished before the effective date of this SNPRM,
using Boeing Alert Requirements Bulletin 737-53A1383 RB, dated May 9,
2019, provided, for certain airplanes, that certain actions are done.

Request to Exclude a Certain Inspection of Certain Repaired Areas

DAL requested that the proposed AD be revised to exclude an internal sur-
face HFEC inspection in areas that were repaired if the repair met certain
conditions. DAL noted that the design approval holder has specifically
recommended that the surface HFEC inspection not be required if certain
repairs have been accomplished, however, those repairs must have been
installed after the original issue date of Boeing Alert Requirements
Bulletin 737-53A1383 RB and must have been approved by The Boeing Company
Organization Designation Authorization (ODA) via FAA Form 8100-9. DAL
asked that such repairs be approved as AMOCs, regardless of when the
repair was installed.

The FAA agrees to clarify. Paragraph (h)(1) of this AD allows using the
notes and flag notes in Boeing Alert Requirements Bulletin 737-53A1383 RB,
Revision 1, dated February 19, 2020, as written. This means that, for
actions done "after the original issue date of Boeing Alert Requirements
Bulletin 737-53A1383 RB" operators are not required to do the internal
surface HFEC in areas where the repair covers the affected inspection
zone, provided the repair meets the conditions specified in Boeing Alert
Requirements Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020.
Operators do not need to obtain an AMOC to use this provision, provided
the repair meets the conditions specified in Boeing Alert Requirements
Bulletin 737-53A1383 RB, Revision 1, dated February 19, 2020.

However, the FAA notes that this provision does not extend to repairs that
were done before the original issue date of Boeing Alert Requirements
Bulletin 737-53A1383 RB. Under the provisions of paragraph (i) of this AD,
the FAA will consider requests for approval of repairs in this area that
affect compliance with this AD and were done before the original issue
date of Boeing Alert Requirements Bulletin 737-53A1383 RB if sufficient
data are submitted to substantiate that the repair would provide an
acceptable level of safety. The FAA has not changed this SNPRM regarding
this issue.

Request for AMOC for Repairs Accomplished Before Service Information
Publication

Southwest Airlines (SWA) requested that the FAA include previously
accomplished repairs for the crack condition identified in Boeing Alert
Requirements Bulletin 737-53A1383 RB as an approved AMOC, including
repairs accomplished before the original issue date of Boeing Alert
Requirements Bulletin 737-53A1383 RB. SWA mentioned that its fleet has
repaired many crack conditions common to the inspection area specified in
Boeing Alert Requirements Bulletin 737-53A1383 RB, and that most of those
repairs were accomplished before Boeing Alert Requirements Bulletin 737
-53A1383 RB, was released. SWA also pointed out that those repairs were
approved via FAA Form 8100-9.

The FAA disagrees with the commenter’s request. Note (b) to Tables 1 and 2
in Boeing Alert Requirements Bulletin 737-53A1383 RB is intended to
address repairs that were designed as corrective actions to the unsafe
condition addressed in the service information and this AD, are approved
by The Boeing Company ODA, and include a follow-on inspection program. For
this reason, the FAA allows FAA Form 8100-9 for approved repairs that meet
all criteria specified in note (b) to Tables 1 and 2 in Boeing Alert
Requirements Bulletin 737-53A1383 RB to be exempted from the inspections
in those repaired areas, but does not allow just any FAA-approved repair
to be exempted from these required inspections. However, under the
provisions of paragraph (i) of this AD, the FAA will consider requests for
approval of certain repairs in this area that affect compliance with this
AD if sufficient data are submitted to substantiate that the repair would
provide an acceptable level of safety. The FAA has not changed this SNPRM
regarding this issue.

Request to Clarify Acceptable Previous Repairs

Qantas Airways LTD (Qantas) requested that the FAA clarify whether certain
blend repairs would require approval of a new FAA Form 8100-9, to
reauthorize the existing repairs. Qantas pointed out that the criteria for
the general visual inspection is "any repair." Qantas also mentioned that
a blend repair to a small depth may not be detectable with a general
visual inspection (as specified in Boeing Alert Requirements Bulletin 737
-53A1383 RB) because the area is shot or flap peened after blending.

The FAA agrees to clarify. Boeing Alert Requirements Bulletin 737-53A1383
RB specifies certain repairs that do not require additional contact with
The Boeing Company ODA or the FAA. Those certain repairs are specified in
note (a) to Table 1 and notes (a) and (b) to Table 2 of Boeing Alert
Requirements Bulletin 737-53A1383 RB as: fuselage skin blend out within
the 737-600 structural repair manual (SRM) 53-00-01, 737-700 SRM 53-00-01,
737-700CONV SRM 53-00-01, 737-700IGW (BBJ) SRM 53-00-01, 737-800 SRM 53
-00-01, 737-800BCF SRM 53-00-01, or 737-900 SRM 53-00-01 allowable damage.
Any existing repair that is not specified in that section would require
additional contact with The Boeing Company ODA or the FAA. The FAA has not
changed this SNPRM regarding this issue.

Request to Clarify Exception to the Service Information

Qantas requested that the FAA clarify the intent of the exception to the
service information specified in paragraph (h)(2) of the proposed AD.
Qantas mentioned its perception that when Boeing Alert Requirements
Bulletin 737-53A1383 RB, specifies that "It is not required to contact
Boeing," that the NPRM then requires the operator to contact The Boeing
Company ODA.

The FAA agrees to clarify. Boeing Alert Requirements Bulletin 737-53A1383
RB specifies certain conditions, where contact with Boeing is unnecessary.
Whereas, the exception specified in paragraph (h)(2) of this SNPRM, states
that if Boeing Alert Requirements Bulletin 737-53A1383 RB, specifies to
contact Boeing for repair instructions or for alternative inspections,
this SNPRM requires doing the repair, or doing the alternative inspections
and applicable on-condition actions using a method approved as an AMOC.
The exception in paragraph (h)(2) of this AD, therefore, does not affect
the statements in Boeing Alert Requirements Bulletin 737-53A1383 RB, that
specify "It is not required to contact Boeing." The FAA has not changed
this SNPRM regarding this issue.

Request to Allow Alternate Inspection Procedure

Structural Monitoring Systems PLC (SMS) requested that the FAA allow the
use of SMS comparative vacuum monitoring (CVM) structural monitoring
sensors (and a CVM nondestructive testing procedure (NDT)) as an
alternative to the HFEC inspections of the bear strap. SMS also requested
that for the CVM NDT procedure, the FAA set a repetitive inspection
frequency to 18,000 flight cycles to reduce the level of repair burden on
the operator when a crack is discovered. SMS also requested that the CVM
structural monitoring sensors be used to periodically monitor any crack
propagation, using damage tolerant assessment data to determine the point
of reaching the residual strength capability limit, noting that this is a
similar practice to that used on engines. SMS stated that the structural
monitoring sensors are less intrusive, require less time to access, and
take less time to inspect, while providing an equal level of safety to the
proposed HFEC inspection method. SMS further specified that a CVM NDT
inspection method can be applied three times (or more) more frequently
than the proposed HFEC inspection, while still being less time consuming,
because there is no further disassembly/assembly after initial sensor
installation. SMS then mentioned that it (SMS) would perform any specific
evaluation or testing required by the FAA to demonstrate standard 90
percent probability of detection with 95 percent confidence for the
application. SMS mentioned a recent FAA statement acknowledging "that an
aircraft structure which is subject to damage tolerance assessment can be
considered safe while continuing to operate with an existing [undetected]
crack." SMS specified the belief that the direct quote expresses a
philosophy that is supportive of using the CVM structural monitoring
sensors, and would allow operators to operate the aircraft until such time
as the residual strength capability is reached, using an appropriate
inspection interval.

The FAA disagrees with the request to mandate CVM structural monitoring
sensors, a repetitive CVM NDT procedure with an 18,000 flight cycle
compliance time, and periodic monitoring of crack propagation. SMS did not
provide sufficient substantiation to show the effectivity of CVM
technology for this application. Therefore, the FAA cannot specify or
allow that technology and inspection method as an alternative to those
specified in this SNPRM. The FAA has not changed this SNPRM regarding this
issue. Once the final rule is published, any person may request approval
of an alternative method of compliance (AMOC) under the provisions of
paragraph (j) of this AD.

Related Service Information under 1 CFR part 51

The FAA reviewed Boeing Alert Requirements Bulletin 737-53A1383 RB,
Revision 1, dated February 19, 2020. This service information describes
procedures for inspecting for cracks of the fuselage skin and bear strap
at the forward galley door between certain stations, through the use of
two alternative inspection methods: (1) internal and external general
visual inspections and internal surface HFEC inspections, and (2) external
general visual and external eddy current inspections, and applicable on
-condition actions. On-condition actions include inspections for cracks,
HFEC inspections for cracks, LFEC inspections for cracks, and repair,
depending on the inspection method selected. 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

The FAA is proposing this AD because the FAA 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 revisions to the service information described above expand the
scope of the NPRM. As a result, the FAA has determined that it is
necessary to reopen the comment period to provide additional opportunity
for the public to comment on this SNPRM.

Proposed Requirements of this SNPRM

This SNPRM would require accomplishing the actions specified in the
service information described previously. This proposed AD would also
allow credit for airplanes that have done Option 2, Condition 4, as
specified in Boeing Alert Requirements Bulletin 737-53A1383 RB, dated May
9, 2019, provided that those airplanes do additional inspections. For
information on the procedures and compliance times, see this service
information at https://www.regulations.gov by searching for and locating
Docket No. FAA-2019-0705.

Costs of Compliance

The FAA estimates that this proposed AD affects 752 airplanes of U.S.
registry. The FAA estimates the following costs to comply with this
proposed AD:

Estimated costs for required actions: Option 1

Estimated costs for required actions: Option 2

The FAA has received no definitive data that would enable the agency to
provide cost estimates for the on-condition actions specified in this
proposed 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.

The FAA is 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

The FAA 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) Will not affect intrastate aviation in Alaska, and

(3) 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.

§ 39.13 [Amended]

2. The FAA amends § 39.13 by adding the following new airworthiness
directive (AD):