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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA-2020-0341; Project Identifier 2020-NM-017-AD; Amendment
39-21586; AD 2021-11-24]
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 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 significant changes
made to the airworthiness limitations (AWLs) related to fuel tank
ignition prevention and the nitrogen generation system (NGS). This AD
requires revising the existing maintenance or inspection program, as
applicable, to incorporate the April 2019 or November 2020 revision of
the airworthiness limitations document. The FAA is issuing this AD to
address the unsafe condition on these products.
DATES: This AD is effective July 20, 2021.
The Director of the Federal Register approved the incorporation by
reference of a certain publication listed in this AD as of July 20,
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-2020-0341.
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-
0341; 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: Christopher Baker, Aerospace Engineer,
Propulsion Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des
Moines, WA 98198; phone and fax: 206-231-3552; email:
Christopher.R.Baker@faa.gov.
SUPPLEMENTARY INFORMATION:
Background
The FAA 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 May 6, 2020
(85 FR 26888). The NPRM was prompted by significant changes made to the
AWLs related to fuel tank ignition prevention and the NGS. The NPRM
proposed to require revising the existing maintenance or inspection
program, as applicable, to incorporate the April 2019 revision of the
airworthiness limitations document.
The FAA is issuing 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. In
addition, the FAA is issuing this AD to address the potential loss of
engine fuel suction feed capability, which could result in dual engine
flameouts,
inability to restart engines, and consequent forced landing of the airplane.
Comments
The FAA gave the public the opportunity to participate in
developing this final rule. The following presents the comments
received on the NPRM and the FAA's response to each comment.
Support for the NPRM
The Air Line Pilots Association, International (ALPA), United
Airlines, and an individual stated support for the NPRM.
Request To Delay Issuance of Final Rule
All Nippon Airways (ANA) requested that the FAA delay issuance of
the final rule until Boeing releases the next revision of Boeing 737-
600/700/700C/800/900/900ER Special Compliance Items/Airworthiness
Limitations, D626A001-9-04. The commenter explained that in the current
revision of Boeing 737-600/700/700C/800/900/900ER Special Compliance
Items/Airworthiness Limitations, D626A001-9-04, dated April 2019
(Boeing D626A001-9-04, dated April 2019), for Airworthiness Limitation
(AWL) No. 47-AWL-09, ``Nitrogen Generation System--Oxygen Sensor,''
operators must replace the NGS oxygen sensor with a new oxygen sensor
because installation of an overhauled part is not approved at this
time. The commenter stated that Boeing is working with the FAA to allow
testing of the oxygen sensor using the component maintenance manual,
and on-wing testing using the aircraft maintenance manual, and Boeing
plans to revise AWL No. 47-AWL-09 to allow testing and installation of
an overhauled part. The commenter anticipated that the next revision of
Boeing 737-600/700/700C/800/900/900ER Special Compliance Items/
Airworthiness Limitations, D626A001-9-04, would include the revised AWL
No. 47-AWL-09.
The FAA acknowledges the commenter's request. Since publication of
the NPRM, Boeing has issued Boeing 737-600/700/700C/800/900/900ER
Special Compliance Items/Airworthiness Limitations, D626A001-9-04,
dated November 2020 (Boeing D626A001-9-04, dated November 2020), which
limits the applicability of AWL No. 47-AWL-09 to certain Model 737
airplanes and states that an oxygen sensor can be replaced with a new
oxygen sensor or an oxygen sensor repaired per AWL No. 47-AWL-10
``Nitrogen Generation System--Oxygen Sensor Repair.'' This AD requires
updating the existing maintenance/inspection program to incorporate
Boeing D626A001-9-04, dated April 2019; or Boeing D626A001-9-04, dated
November 2020. In addition, based upon requests from other commenters,
the FAA has extended the initial compliance time for replacement of the
oxygen sensor due to a parts availability issue. The FAA has revised
the grace period for the initial ALI task in paragraph (g)(13) of this
AD from 12 months to 36 months. This extended grace period will still
provide an acceptable level of safety.
Request To Extend the Compliance Time
Air China, ANA, China Eastern Airlines (CEA), Delta Air lines
(DAL), Japan Airlines (JAL), Okay Airlines (OKY), Southwest Airlines
(SWA), and Turkish Airlines (THY) requested that the initial compliance
time for the replacement of the oxygen sensor as specified in paragraph
(g)(13) of the proposed AD be extended because of a parts availability
issue. The commenters contacted Boeing and determined that there would
be a shortage of parts, which would prevent them from complying with
the proposed requirement specified in paragraph (g)(13) of the proposed
AD within the compliance time specified in the proposed AD.
The FAA agrees with the commenters' requests based on the
information provided by the commenters. The FAA contacted Boeing and
confirmed that there is a parts availability issue, which could create
an undue burden on operators because it could prevent them from
complying with the requirement specified in paragraph (g)(13) of this
AD, subsequently grounding the affected airplanes. The FAA has revised
the initial compliance time in paragraph (g)(13) of this AD from 12
months to 36 months.
Request To Add an Off-Wing Inspection for AWL No. 47-AWL-09
SWA requested that the FAA consider coordinating this AD with
Boeing to allow for an off-wing inspection of the oxygen sensor, and
repair if necessary, as opposed to a mandated time-limited replacement.
SWA stated that this would mitigate the parts availability impact
across the industry as well the cost of complying with AWL No. 47-AWL-09.
The FAA agrees that an off-wing inspection would reduce the burden
on operators. This AD allows operators to optionally incorporate Boeing
D626A001-9-04, dated November 2020, which includes an off-wing
inspection as specified in AWL No. 47-AWL-10. Boeing modified the
requirement of AWL No. 47-AWL-09 to allow the use of repaired parts and
added AWL No. 47-AWL-10 to describe the requirements for the method of
inspection/repair in Boeing D626A001-9-04, dated November 2020. This AD
still requires operators to use Boeing D626A001-9-04, dated April 2019,
but provides an option for operators to incorporate Boeing D626A001-9-
04, dated November 2020, into their maintenance program. In addition,
the FAA has determined that an on-wing inspection is currently being
developed by Boeing and that subject on-wing inspection is expected to
be implemented in a future revision of the Boeing D626A001-9-04
document. Under the provisions of paragraph (k) of this AD, the FAA
will consider requests for approval of an alternative method of
compliance (AMOC) if sufficient data are submitted to substantiate that
the change would provide an acceptable level of safety.
Request To Clarify the Applicability of a Certain AWL Item
CEA, DAL, JAL, OKY, Ryan Air, and THY requested clarification of
the applicability specified in AWL No. 47-AWL-09, which addresses
replacement of the oxygen sensor in the NGS. The commenters noted that
in Boeing D626A001-9-04, dated April 2019, the other AWLs specific to
the NGS show the airplane applicability in terms of the airplanes that
have the NGS installed, or incorporation of the actions in Boeing
Service Bulletin 737-47-1002 or Boeing Service Bulletin 737-47-1003.
The commenters noted that all airplanes on the U.S. registry are
required to have the NGS system installed, but the commenters expected
the applicability of AWL No. 47-AWL-09 to be similar to the other AWLs
included in Boeing D626A001-9-04, dated April 2019. In addition, OKY
noted that the applicability in AWL No. 47-AWL-09 was listed as all
airplanes, but in Boeing Fleet Team Digest Document 737NG-FTD-47-19003,
created on May 8, 2020, the applicability is Model 737NG airplanes
delivered after June 2019 or modified with a new, improved ASM (air
separation module) using the procedures in Boeing Service Bulletin 737-
47-1015.
DAL and the other commenters explained that they contacted Boeing
regarding this applicability issue. The commenters stated that Boeing
confirmed that the applicability specified in AWL No. 47-AWL-09 is incorrect
and
Boeing advised that in the next revision of Boeing D626A001-9-04, dated
April 2019,
the applicability specified in AWL No. 47-AWL-09 will be updated to include
airplanes having L/Ns 1820, 1831, 2517, 2620, and subsequent, and all
airplanes that have incorporated the actions specified in Boeing
Service Bulletin 737-47-1003. Several of the commenters stated that
paragraph (g)(13) of the proposed AD should include additional text to
clarify the applicability of AWL No. 47-AWL-09. The commenters stated
that by incorporating this information into the final rule, the FAA
would prevent the need for operators to apply for an AMOC in the
future.
The FAA acknowledges the commenters' requests. As mentioned
previously, Boeing has published Boeing D626A001-9-04, dated November
2020, and in this revision the applicability specified in AWL No. 47-
AWL-09 was updated and limited to specify only airplanes having L/Ns
1820, 1831, 2517, 2620, and subsequent, and all airplanes that have
incorporated the actions specified in Boeing Service Bulletin 737-47-
1003. The FAA has changed the AD to allow the use of Boeing D626A001-9-
04, dated November 2020, which correctly identifies the applicability
for AWL No. 47-AWL-09.
Request To Clarify the Unsafe Condition
Boeing, DAL, and CEA requested clarification of the unsafe
condition specified in the Discussion section of the NPRM and paragraph
(e) of the proposed AD. The commenters remarked that the wording
implied that increased flammability in the center fuel tank leads to
fuel tank explosion. The commenters explained that increased
flammability alone does not lead to a fuel tank explosion; there must
also be a concurrent ignition source in the center fuel tank. The
commenters suggested that it would be more accurate to state that the
increased flammability combined with an ignition source could lead to
a
fuel tank explosion.
In addition, the commenters requested that the unsafe condition be
revised to address the potential loss of engine fuel suction feed
capability. The commenters pointed out that paragraph (g)(14) of the
proposed AD specified AWL No. 28-AWL-101, ``Engine Fuel Suction Feed
Operational Test,'' which would be required to protect the airplane
from engine flameout during suction feed operations. The commenters
observed that this proposed action is not associated with the
prevention of fuel tank ignition.
The FAA agrees with the commenters' requests based on the reasons
provided by the commenters. The FAA has revised the Background section
in this final rule and paragraph (e) of this AD accordingly.
Request To Account for Indirect Costs
ANA, CEA, DAL, OKY, SWA, and THY expressed concern regarding the
indirect financial burden associated with accomplishing the actual on-
wing work resulting from the maintenance program or inspection program
changes that would be required by the proposed AD. DAL specifically
noted that accomplishment of the oxygen sensor replacement specified in
AWL No. 47-AWL-09, would require replacement of approximately 130
oxygen sensors with new oxygen sensors, and based on price quotes from
the manufacturer of the oxygen sensors, it would cost an additional
$7,000,000 over the estimated $7,560 per operator specified in the
Costs of Compliance section of the NPRM. DAL stated that once all
airplanes have reached the threshold for replacing the oxygen sensor
the recurring cost would be approximately $2,000,000 per year for this
task.
The FAA disagrees with changing the cost of compliance information
for this AD. The cost information provided in this AD describes only
the direct costs of the specific actions required by this AD. The FAA
recognizes that, in doing the actions required by an AD, operators
might incur incidental costs in addition to the direct costs. The
extended compliance time previously mentioned could alleviate some of
these indirect costs, as they would be spread out over 36 months
instead of occurring within 12 months. Also, Boeing D626A001-9-04,
dated November 2020, was revised to allow operators to use a repaired
oxygen sensor in AWL No. 47-AWL-09 and added AWL No. 47-AWL-10 to
describe the requirements for the method of inspection/repair. As
identified above in a previous comment, operators now have the option
to incorporate Boeing D626A001-9-04, dated November 2020, into their
maintenance and inspection program, thereby reducing the financial
impact of these requirements. The AD has not been changed in this
regard.
Request for Clarification of Compliance Time Interval Units
DAL and CEA requested that the FAA explain why paragraph (g) of the
proposed AD expressed compliance time intervals in terms of months when
Boeing D626A001-9-04, dated April 2019, specifies these intervals in
terms of years. The commenter mentioned it was unclear if an AMOC would
be required if an operator incorporated the compliance intervals in
years, as specified in Boeing D626A001-9-04, dated April 2019, instead
of months, as specified in the proposed AD.
The FAA disagrees that there is a difference in the calculated
compliance times described by the commenters. The FAA uses compliance
times defined in months for required AD actions. Operators have the
capability of converting years to months when comparing the compliance
times of required AD actions and the times specified in a
manufacturer's document. The FAA has determined that operators should
not be confused when these conversions take place and an operator does
not need to request an AMOC. Regardless of how an operator records the
compliance time, within 36 months or within 3 years after the effective
date of this AD, the compliance times in this AD, Boeing D626A001-9-04,
dated April 2019, and Boeing D626A001-9-04, dated November 2020, end at
the same time. The FAA has not changed this AD in regard to this issue.
Request To Include Additional Affected AD in Paragraph (b) of Proposed
AD
DAL and CEA requested that AD 2018-20-13, Amendment 39-19447 (83 FR
52305, October 17, 2018) (AD 2018-20-13), be included in the list of
affected ADs in paragraph (b) of the proposed AD. DAL and CEA noted
that paragraphs (i)(1)(i) through (iii) of AD 2018-20-13 require
incorporation of AWL Nos. 28-AWL-21, 28-AWL-22, and 28-AWL-24 that are
included in Boeing 737-600/700/700C/800/900/900ER Special Compliance
Items/Airworthiness Limitations, D626A001-9-04, dated June 2018, into
an operator's maintenance or inspection program as applicable. DAL and
CEA suggested that only the latter revision of these AWLs that are
included in Boeing D626A001-9-04, dated April 2019, should be mandated.
DAL and CEA stated that the requirements of paragraphs (i)(1)(i)
through (iii) of AD 2018-20-13 should be terminated when the
requirements of the proposed AD become effective.
The FAA agrees with the commenter's request; paragraph (b) of this
AD has been revised to include AD 2018-20-13 in paragraph (b)(6) of
this AD, and the subsequent paragraph has been redesignated as
paragraph (b)(7) of this AD. In addition, this AD has been revised to
include a new paragraph (j)(6) of this AD to terminate the requirements
specified in paragraphs (i)(1)(i) through (iii) of AD 2018-20-13, and
the
subsequent paragraph has been redesignated as paragraph (j)(7) of this
AD.
Request To Change the Subject in Paragraph (d) of the Proposed AD
DAL and CEA requested that the Subject in paragraph (d) of the
proposed AD be changed from Air Transport Association (ATA) of America
Code 71, Powerplant, to ATA Code 28, Fuel. DAL and CEA noted that the
unsafe condition specified in the proposed AD is associated with
ignition sources in the fuel tanks and flammability exposure of the
center fuel tank. The fuel system is the subject of ATA Code 28.
Previously issued ADs identified in paragraph (b) of the proposed AD,
which are similar to the proposed AD, have specified ATA Code 28 as the
subject in paragraph (d).
The FAA agrees with the commenter's request based on the reasons
provided by the commenter. Paragraph (d) of this AD has been changed to
ATA Code 28, Fuel.
Effects of Winglets on Accomplishment of the Proposed Actions
Aviation Partners Boeing stated that the installation of blended or
split scimitar winglets per Supplemental Type Certificated (STC)
ST008300SE does not affect compliance with the proposed actions.
The FAA agrees that STC ST008300SE does not affect compliance with
the actions required by this AD. The FAA has not changed this AD in
this regard.
Reduction of Applicable Airplanes Since NPRM Was Issued
The FAA has updated the applicability, paragraph (c) of this AD, to
remove airplanes that were delivered with Boeing 737-600/700/700C/800/
900/900ER Special Compliance Items/Airworthiness Limitations, D626A001-
9-04, dated April 2019, thereby reducing the scope of the affected
airplanes in this final rule.
Conclusion
The FAA reviewed the relevant data, considered the comments
received, and determined that air safety and the public interest
require adopting this final rule with the changes described previously
and 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.
The FAA also determined that these changes will not increase the
economic burden on any operator or increase the scope of this final
rule.
Related Service Information Under 1 CFR Part 51
The FAA reviewed Boeing 737-600/700/700C/800/900/900ER Special
Compliance Items/Airworthiness Limitations, D626A001-9-04, dated April
2019; and Boeing 737-600/700/700C/800/900/900ER Special Compliance
Items/Airworthiness Limitations, D626A001-9-04, dated November 2020.
This service information describes AWLs that include airworthiness
limitation instructions (ALIs) and critical design configuration
control limitations (CDCCLs) tasks related to fuel tank ignition
prevention and the NGS. 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.
Differences Between This AD and the Service Information
The ``Description'' column of AWL No. 28-AWL-20 identifies certain
operational tests. However, the operational test for left center tank
fuel boost pump relay R54 and right center tank fuel boost pump relay
R55 is not required for airplanes on which the actions specified in
paragraph (g)(2)(ii) of AD 2011-20-07, Amendment 39-16818 (76 FR 60710,
September 30, 2011), have been done, or airplanes that have installed
STC ST02076LA.
Paragraph (g) of this AD requires operators to revise their
existing 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 D626A001-9-04, dated November 2020. Paragraph (h) of this AD
allows certain changes to be made to the requirements specified in AWL
No. 28-AWL-05 as an option.
Costs of Compliance
The FAA estimates that this AD affects 2,057 airplanes of U.S.
registry. The FAA estimates the following costs to comply with this AD:
The FAA determined that revising the existing maintenance or
inspection program takes an average of 90 work-hours per operator,
although the agency recognizes that this number may vary from operator
to operator. In the past, the FAA estimated that this action takes 1
work-hour per airplane. Since operators incorporate maintenance or
inspection program changes for their affected fleet(s), the FAA
determined that a per-operator estimate is more accurate than a per-
airplane estimate. Therefore, the FAA estimates the average total cost
per operator to be $7,650 (90 work-hours x $85 per work-hour).
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
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
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:
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