[Federal Register Volume 86, Number 65 (Wednesday, April 7, 2021)]
[Rules and Regulations]
[Pages 17899-17902]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2021-07034]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2020-0848; Product Identifier 2020-NM-088-AD; Amendment 
39-21486; AD 2021-07-09]
RIN 2120-AA64


Airworthiness Directives; The Boeing Company Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: The FAA is superseding Airworthiness Directive (AD) 2007-07-
03, which applied to certain The Boeing Company Model 747-100, 747-
100B, 747-100B SUD, 747-200B, 747-200C, 747-200F, 747-300, 747-400, 
747-400D, 747-400F, 747SR, and 747SP series airplanes. AD 2007-07-03 
required repetitive tests to detect hot air leaking from the trim air 
diffuser ducts or sidewall riser duct assemblies (collectively referred 
to as TADDs), related investigative actions, and corrective actions if 
necessary. AD 2007-07-03 also provided an optional terminating action 
for the repetitive tests. This AD requires repetitive inspections of 
all TADD material for damage and applicable on-condition actions. This 
AD was prompted by reports that high temperature composite material 
TADDs installed as specified in AD 2007-07-03 have also failed. The FAA 
is issuing this AD to address the unsafe condition on these products.

DATES: This AD is effective May 12, 2021.
    The Director of the Federal Register approved the incorporation by 
reference of a certain publication listed in this AD as of May 12, 
2021.

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; telephone 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-2020-0848.

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-2020-
0848; 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, any comments received, and other information. The 
address for Docket Operations 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: Nicole S. Tsang, Aerospace Engineer, 
Cabin Safety and Environmental Systems Section, FAA, Seattle ACO 
Branch, 2200 South 216th St., Des Moines, WA 98198; phone and fax: 206-
231-3959; email: [email protected].

SUPPLEMENTARY INFORMATION: 

Discussion

    The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 
CFR part 39 to supersede AD 2007-07-03, Amendment 39-15003 (72 FR 
14395, March 28, 2007) (AD 2007-07-03). AD 2007-07-03 applied to 
certain The Boeing Company Model 747-100, 747-100B, 747-100B SUD, 747-
200B, 747-200C, 747-200F, 747-300, 747-400, 747-400D, 747-400F, 747SR, 
and 747SP series airplanes. The NPRM published in the Federal Register 
on September 22, 2020 (85 FR 59451). The NPRM was prompted by reports 
of sealant deteriorating on the outside of the center wing fuel tank 
and analysis showing that sealant may deteriorate inside the tank due 
to excess heat from TADDs. The NPRM was also prompted by reports 
indicating that the high temperature composite material TADDs installed 
as specified in AD 2007-07-03 have also failed. The NPRM proposed to 
require repetitive inspections of all TADD material for damage and 
applicable on-condition actions. The FAA is issuing this AD to address 
potential hot air leakage from original fiberglass fabric material or 
high temperature composite material TADDs that can cause damage to the 
center wing fuel tank secondary fuel barrier coating and primary 
sealant, which can cause fuel leakage into an ignition zone, possibly 
resulting in a fire or explosion.

Comments

    The FAA 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

    Air Line Pilots Association, International (ALPA), Boeing, and 
Jesse Addo expressed support for the NPRM.

Requests To Extend Compliance Times for Initial and Repetitive 
Inspections

    Cathay Pacific Airways Limited (CPA), Lufthansa German Airlines 
(Lufthansa), and SFN requested that the compliance time for the initial 
and repetitive inspection be extended. Lufthansa suggested that an 
interval of 11,000 flight hour (FH) would still provide a sufficient 
level of safety based on its fleet reliability data. Lufthansa stated 
that the proposed interval is not comprehensible based on its data and 
would result in an extension of each A-check by 200 percent of normal 
and generate a very high economic impact. SFN agreed with Lufthansa's 
analysis and requested an interval of 10,000 FH to coincide with the C-
check, because doing the inspection at the 1,200 FH

[[Page 17900]]

interval would require the inspection be done at each A-check (1,000 
FH). SFN comments that this would be problematic for two reasons: It 
would generate a very high economic impact, and it would result in a 
higher frequency of floor panel removal/installation that would 
increase the risk of wire damage over the center fuel tank. CPA 
requested that the compliance time for the initial inspection be 
extended. CPA asserted that the replacement of the TADDs at the initial 
inspection, to extend the next inspection to 16,000 FH, would not be 
possible due to availability of spare TADDs and base maintenance 
scheduling. CPA also noted that the 1,200 FH repetitive inspection 
interval will impose a huge burden on essential cargo operations. The 
commenters noted that the inspections were not suitable for the line 
maintenance environment due to the extensive access portion of the 
inspection.
    The FAA disagrees with the requests. In developing an appropriate 
compliance time, the FAA considered the safety implications, parts 
availability, normal maintenance schedules, and the manufacturer's 
recommendations, and determined that the 1,200 FH compliance time would 
allow for an adequate level of safety. After initial installation of 
high temperature TADDs, operators may avoid repeat inspections at 1,200 
FH intervals by installing new high temperature TADDs at each 16,000 FH 
interval, without an alternative method of compliance (AMOC) or 
additional rulemaking, as long as required actions are completed at 
that interval. However, under the provisions of paragraph (h) of this 
AD, the FAA will consider requests for approval of an extension of the 
compliance time if sufficient data are submitted to substantiate that 
the extension would provide an acceptable level of safety. 
Additionally, as noted in the NPRM, the FAA considers this AD interim 
action. The manufacturer is currently developing a modification. Once 
the modification is developed, approved, and available, the FAA might 
consider additional rulemaking. We have not changed this AD with regard 
to this request.

Request To Allow AMOC for Access and Inspection

    KLM Royal Dutch Airlines (KLM) requested that the NPRM be revised 
to allow an AMOC to use holes at certain locations in the floor for 
access and a borescope for the inspection. KLM outlined a method for 
accessing the inspection area more quickly and with less disruption 
using borescopes and examination holes in the floor panels, if Boeing 
modified the panels. KLM noted that currently more than 38 work hours 
are required to remove and replace floor panels--a huge effort for a 5-
hour inspection that is repeated frequently. KLM recalled that a 
similar inspection using access holes and borescopes was used in the 
1980s to inspect the floors under toilets.
    The FAA disagrees with the need for an alternate inspection method. 
Note that this AD does not mandate how to access the inspection site, 
it only mandates a detailed inspection of the affected parts. However, 
the FAA is not aware of Boeing developing any new design for the floor 
panels that includes pluggable holes. As noted, this AD is considered 
interim action and if any new design is developed, the FAA might 
consider further rulemaking. This AD has not been changed with regard 
to this request.

Request To Simplify Language in NPRM

    One commenter requested that the NPRM be written in language more 
understandable to the average person to help clarify the unsafe 
condition. The commenter stated that the SUMMARY section may be unclear 
and confusing and argued that it is the FAA's duty to present the 
issues pertaining to TADDs in a more comprehensible way in order to 
emphasize the importance and urgency of the identified unsafe 
condition. The commenter asserted that the FAA does not clearly explain 
why hot air leakage from the TADDs as a result of hot trim air causing 
the material properties to degrade is potentially dangerous or creates 
an unsafe condition. Therefore, the commenter stated that the FAA 
should describe in more detail the dangers and unsafe conditions the 
TADDs, especially the high temperature composite material TADDs, 
present. The commenter further argued that the FAA should better break 
down the focal component of the proposed and former rules, which is the 
TADD, and do it while making the terms and concepts understandable to 
the layperson.
    The FAA disagrees with changing the nature of the language in this 
final rule. The FAA strives to follow guidelines as outlined in FAA 
Order 1000.36, FAA Writing Standards,\1\ as well as using plain 
language principles \2\ to draft regulations, but a certain level of 
subject matter knowledge is assumed on the part of the reader. As noted 
by the commenter, ADs are written for the owners and operators of the 
affected airplanes, for the purpose of increasing aviation safety. 
Therefore, it is important that the content of an AD is written for the 
understanding of those individuals required to comply with the 
requirements of the AD.
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    \1\ FAA Order 1000.36, FAA Writing Standards, dated March 31, 
2003 (https://rgl.faa.gov/Regulatory_and_Guidance_Library/
rgOrders.nsf/0/880c01691d0546c386256cfc005ec613/$FILE/
Order_1000.36.pdf).
    \2\ Plain Writing Act of 2010 (https://www.plainlanguage.gov/).
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    It is also important to note that information that is appropriate 
for inclusion in the SUMMARY section of a rule is driven by the Office 
of the Federal Register (OFR).\3\ Additional detail may not be added to 
the SUMMARY. Additional detail in the Discussion is also unnecessary. 
The unsafe condition was clearly stated in the proposed AD to be damage 
to the center wing fuel tank secondary fuel barrier coating and primary 
sealant, which can cause fuel leakage into an ignition zone, possibly 
resulting in a fire or explosion--caused by potential hot air leakage 
from original fiberglass fabric material or high temperature composite 
material TADDs.
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    \3\ This information may be found in the OFR's Document Drafting 
Handbook (https://www.archives.gov/files/federal-register/write/handbook/ddh.pdf).
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    We have not changed this AD in this regard.

Request To Clarify Necessity for Supersedure of AD 2007-07-03

    A commenter also requested that the NPRM be revised to clearly 
state why it is necessary to supersede AD 2007-07-03, given the high 
labor costs of performing the newly required actions.
    The FAA agrees to clarify the need to supersede AD 2007-07-03. The 
FAA issues ADs, including any necessary supersedures, whenever there is 
an unsafe condition that must be addressed. As described under the 
section, ``Actions Since AD 2007-07-03 Was Issued,'' operators reported 
that high temperature composite material TADDs installed as specified 
in AD 2007-07-03 have also failed. Further inspection showed that the 
high temperature composite material TADDs were ruptured, with damaged 
insulation in poor condition. Analysis showed that hot trim air was 
causing material properties degradation of both the original fiberglass 
fabric material and high temperature composite material TADDs, which 
potentially causes hot air leakage from the TADD(s). Since the unsafe 
condition has been reported even with AD 2007-07-03 in effect, the FAA 
has determined that it is necessary to issue this AD, which supersedes 
AD 2007-07-03, to adequately address

[[Page 17901]]

possible hot air leaks that can damage the secondary fuel barrier of 
the center wing fuel tank. As noted in this final rule, a damaged fuel 
barrier could allow fuel to leak into an area where it may cause a fire 
or explosion. The FAA has not changed this AD with regard to this 
request.

Conclusion

    The FAA reviewed the relevant data, considered the comments 
received, and determined that air safety and the public interest 
require adopting this AD as proposed, except for minor editorial 
changes. The FAA has 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.

Related Service Information Under 1 CFR Part 51

    The FAA reviewed Boeing Alert Requirements Bulletin 747-21A2577 RB, 
dated February 18, 2020. The service information describes procedures 
for repetitive detailed inspections of TADDs made of original 
fiberglass fabric material and high temperature composite material for 
damage and applicable on-condition actions. On-condition actions 
include TADD replacement, detailed inspection of the center wing tank 
secondary fuel barrier and the center wing tank primary sealant for 
damage, a measurement of the electrical conductivity change of the 
upper skin of the center wing tank for indications of damage, other 
replacement as applicable, and repair. 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.

Interim Action

    The FAA considers this AD interim action. The manufacturer is 
currently developing a modification that will address the unsafe 
condition identified in this AD. Once this modification is developed, 
approved, and available, the FAA might consider additional rulemaking.

Costs of Compliance

    The FAA estimates that this AD affects 188 airplanes of U.S. 
registry. The FAA estimates the following costs to comply with this AD:

                                      Estimated Costs for Required Actions
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                                                                                                 Cost on U.S.
             Action                     Labor cost          Parts cost     Cost per  product       operators
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Repetitive inspections.........  Up to 44 work-hours x                $0  Up to $3,740 per    Up to $703,120 per
                                  $85 per hour = Up to                     inspection cycle.   inspection cycle.
                                  $3,740 per inspection
                                  cycle.
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    The FAA has received no definitive data that would enable providing 
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.
    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 has 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) 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.

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

0
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]

0
2. The FAA amends Sec.  39.13 by:
0
a. Removing Airworthiness Directive (AD) 2007-07-03, Amendment 39-15003 
(72 FR 14395, March 28, 2007), and
0
b. Adding the following new AD:

2021-07-09 The Boeing Company: Amendment 39-21486; Docket No. FAA-
2020-0848; Product Identifier 2020-NM-088-AD.

(a) Effective Date

    This airworthiness directive (AD) is effective May 12, 2021.

(b) Affected ADs

    This AD replaces AD 2007-07-03, Amendment 39-15003 (72 FR 14395, 
March 28, 2007).

(c) Applicability

    This AD applies to all The Boeing Company Model 747-100, 747-
100B, 747-100B SUD, 747-200B, 747-200C, 747-200F, 747-300, 747-400, 
747-400D, 747-400F, 747SR, and 747SP series airplanes, certificated 
in any category.

(d) Subject

    Air Transport Association (ATA) of America Code 21, Air 
conditioning.

(e) Unsafe Condition

    This AD was prompted by reports of sealant deteriorating on the 
outside of the center wing fuel tank and analysis showing that 
sealant may deteriorate inside the tank due to excess heat from 
leaking trim air diffuser ducts or sidewall riser duct assemblies 
(collectively referred to as TADDs). This AD was also prompted by 
reports indicating that the high temperature composite material 
TADDs installed as

[[Page 17902]]

specified in AD 2007-07-03 have also failed. The FAA is issuing this 
AD to address potential hot air leakage from original fiberglass 
fabric material or high temperature composite material TADDs that 
can cause damage to the center wing fuel tank secondary fuel barrier 
coating and primary sealant, which can cause fuel leakage into an 
ignition zone, possibly resulting in a fire or explosion.

(f) Compliance

    Comply with this AD within the compliance times specified, 
unless already done.

(g) Required Actions

    Except as specified by paragraph (h) of this AD: At the 
applicable times specified in the ``Compliance,'' paragraph of 
Boeing Alert Requirements Bulletin 747-21A2577 RB, dated February 
18, 2020, do all applicable actions identified in, and in accordance 
with, the Accomplishment Instructions of Boeing Alert Requirements 
Bulletin 747-21A2577 RB, dated February 18, 2020.
    Note 1 to paragraph (g): Guidance for accomplishing the actions 
required by this AD can be found in Boeing Alert Service Bulletin 
747-21A2577, dated February 18, 2020, which is referred to in Boeing 
Alert Requirements Bulletin 747-21A2577 RB, dated February 18, 2020.

(h) Exceptions to Service Information Specifications

    (1) Where Boeing Alert Requirements Bulletin 747-21A2577 RB, 
dated February 18, 2020, uses the phrase ``the original issue date 
of Requirements Bulletin 747-21A2577 RB,'' this AD requires using 
``the effective date of this AD.''
    (2) Where Boeing Alert Requirements Bulletin 747-21A2577 RB, 
dated February 18, 2020, specifies contacting Boeing for repair 
instructions: This AD requires doing the repair before further 
flight using a method approved in accordance with the procedures 
specified in paragraph (j) of this AD.

(i) Parts Installation Prohibition

    As of the effective date of this AD, no person may install an 
original fiberglass fabric material TADD assembly, having a part 
number listed in Appendix A of Boeing Alert Requirements Bulletin 
747-21A2577 RB, dated February 18, 2020, on any airplane.

(j) Alternative Methods of Compliance (AMOCs)

    (1) The Manager, Seattle ACO Branch, FAA, has the authority to 
approve AMOCs for this AD, if requested using the procedures found 
in 14 CFR 39.19. In accordance with 14 CFR 39.19, send your request 
to your principal inspector or local Flight Standards District 
Office, as appropriate. If sending information directly to the 
manager of the certification office, send it to the attention of the 
person identified in paragraph (k)(1) of this AD. Information may be 
emailed to: [email protected].
    (2) Before using any approved AMOC, notify your appropriate 
principal inspector, or lacking a principal inspector, the manager 
of the local flight standards district office/certificate holding 
district office.
    (3) An AMOC that provides an acceptable level of safety may be 
used for any repair, modification, or alteration required by this AD 
if it is approved by The Boeing Company Organization Designation 
Authorization (ODA) that has been authorized by the Manager, Seattle 
ACO Branch, FAA, to make those findings. To be approved, the repair 
method, modification deviation, or alteration deviation must meet 
the certification basis of the airplane, and the approval must 
specifically refer to this AD.

 (k) Related Information

    (1) For more information about this AD, contact Nicole S. Tsang, 
Aerospace Engineer, Cabin Safety and Environmental Systems Section, 
FAA, Seattle ACO Branch, 2200 South 216th St., Des Moines, WA 98198; 
phone and fax: 206-231-3959; email: [email protected].
    (2) Service information identified in this AD that is not 
incorporated by reference is available at the addresses specified in 
paragraphs (l)(3) and (4) of this AD.

(l) Material Incorporated by Reference

    (1) The Director of the Federal Register approved the 
incorporation by reference (IBR) of the service information listed 
in this paragraph under 5 U.S.C. 552(a) and 1 CFR part 51.
    (2) You must use this service information as applicable to do 
the actions required by this AD, unless the AD specifies otherwise.
    (i) Boeing Alert Requirements Bulletin 747-21A2577 RB, dated 
February 18, 2020.
    (ii) [Reserved]
    (3) For service information identified in this AD, 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.
    (4) 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.
    (5) You may view this service information that is incorporated 
by reference at the National Archives and Records Administration 
(NARA). For information on the availability of this material at 
NARA, email [email protected], or go to: https://www.archives.gov/federal-register/cfr/ibr-locations.html.

    Issued on March 22, 2021.
Lance T. Gant,
Director, Compliance & Airworthiness Division, Aircraft Certification 
Service.
[FR Doc. 2021-07034 Filed 4-6-21; 8:45 am]
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