[Federal Register Volume 88, Number 65 (Wednesday, April 5, 2023)]
[Rules and Regulations]
[Pages 20070-20073]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-07034]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2022-1063; Project Identifier AD-2021-01339-T; 
Amendment 39-22375; AD 2023-05-06]
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 737-8, 737-9, and 737-8200 airplanes. 
This AD was prompted by a determination that new airworthiness 
limitations are necessary to require periodic replacement; or testing, 
and replacement if necessary; of the oxygen sensor of the nitrogen 
generation system (NGS). This AD requires revising the existing 
maintenance or inspection program, as applicable, to incorporate the 
new airworthiness limitations. The FAA is issuing this AD to address 
the unsafe condition on these products.

DATES: This AD is effective May 10, 2023.
    The Director of the Federal Register approved the incorporation by 
reference of certain publications listed in this AD as of May 10, 2023.

ADDRESSES: 
    AD Docket: You may examine the AD docket at regulations.gov under 
Docket No. FAA-2022-1063; 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.
    Material Incorporated by Reference:
     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; website 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 at 
regulations.gov under Docket No. FAA-2022-1063.

FOR FURTHER INFORMATION CONTACT: Sam Dorsey, Aerospace Engineer, 
Propulsion Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des 
Moines, WA 98198; phone and fax: 206-231-3415; email: 
[email protected].

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 737-8, 737-9, and 737-8200 airplanes. The NPRM published 
in the Federal Register on November 28, 2022 (87 FR 72902). The NPRM 
was prompted by a determination that a new airworthiness limitation is 
necessary to require periodic replacement of the oxygen sensor of the 
NGS. In the NPRM, the FAA proposed to require revising the existing 
maintenance or inspection program, as applicable, to incorporate the 
new airworthiness limitation. The FAA is issuing this AD to prevent 
increasing the flammability exposure of the center fuel tank, which 
together with an ignition source in the fuel tank, could lead to a fuel 
tank explosion and consequent loss of the airplane.

Discussion of Final Airworthiness Directive

Comments

    The FAA received comments from the Air Line Pilots Association, 
International (ALPA) and an individual who supported the NPRM without 
change.
    The FAA received additional comments from four commenters, 
including Boeing, American Airlines, SIA Engineering Company, and 
United Airlines (United). The following presents the comments received 
on the NPRM and the FAA's response to each comment.

Request To Refer to Latest Service Information

    Boeing and United requested that the proposed AD be revised to 
specify compliance with Boeing 737-7/8/8200/9/10 Special Compliance 
Items/Airworthiness Limitations, D626A011-9-04, dated May 2022, instead 
of Boeing 737-7/8/8200/9/10 Special Compliance Items/Airworthiness 
Limitations, D626A011-9-04, dated January 2019. Boeing noted that 
Boeing 737-7/8/8200/9/10 Special Compliance Items/Airworthiness 
Limitations, D626A011-9-04, dated May 2022 includes a revision to 47-
AWL-09 and the addition of new airworthiness limitation 47-AWL-10 
(which is a Critical Design Configuration Control Limitation (CDCCL) 
that specifies procedures for oxygen sensor repairs). Boeing added that 
the revision to 47-AWL-09 provides additional options for operators 
beyond replacing the oxygen sensor with a new oxygen sensor. Those 
options include testing the installed NGS oxygen sensor using a 
functional check described in the Airplane Maintenance Manual (AMM) 
(and replacing if necessary), and replacing the oxygen sensor with an 
NGS oxygen sensor repaired as specified in 47-AWL-10. United noted that 
these changes provide operators with benefits necessary for the 
efficient accomplishment of task 47-AWL-09.
    The FAA partially agrees with the commenters' requests. Boeing 737-
7/8/8200/9/10 Special Compliance Items/Airworthiness Limitations, 
D626A011-9-04, dated May 2022, provides options that are relieving, but 
also includes a new CDCCL requirement that was not included in the 
proposed AD. The FAA has therefore revised this AD to require 
incorporating the information specified in AWL No. 47-AWL-09, 
``Nitrogen Generation System--Oxygen Sensor,'' of Boeing 737-7/8/8200/
9/10 Special Compliance Items/Airworthiness Limitations, D626A011-9-04, 
dated

[[Page 20071]]

January 2019; or the information specified in 47-AWL-09 and 47-AWL-10 
of Boeing 737-7/8/8200/9/10 Special Compliance Items/Airworthiness 
Limitations, D626A011-9-04, dated May 2022.

Request To Refer to Latest Service Information

    American Airlines requested that the FAA add a provision to 
accomplish the oxygen sensor replacement with a repaired or overhauled 
sensor instead of a brand new sensor. The commenter noted that this 
provision would ease the burden on operators by not requiring them to 
scrap used sensors and buy new ones. American Airlines added that the 
737NG fleet has a similar AWL requirement, with a provision that a 
repaired sensor may be installed.
    The FAA agrees with the commenter's request. As noted previously, 
this AD has been revised to allow incorporating the information in 
Boeing 737-7/8/8200/9/10 Special Compliance Items/Airworthiness 
Limitations, D626A011-9-04, dated May 2022, which includes provisions 
for replacing the oxygen sensor with a repaired oxygen sensor or 
testing the oxygen sensor, and replacing if necessary.

Request To Clarify Applicability

    SIA Engineering Company asked that the FAA confirm the commenter's 
understanding of paragraph (c) of the proposed AD. SIA Engineering 
Company requested confirmation that the proposed AD does not affect The 
Boeing Company Model 737-8, 737-9, and 737-8200 airplanes having 
original airworthiness certificate or original export certificate of 
airworthiness issued on or before April 1, 2021, and with a line number 
not identified in paragraph (c)(2) of the proposed AD.
    The FAA agrees to clarify. This AD applies to The Boeing Company 
Model 737-8, 737-9, and 737-8200 airplanes having original 
airworthiness certificate or original export certificate of 
airworthiness issued on or before April 1, 2021, and it also applies to 
The Boeing Company Model 737-8, 737-9, and 737-8200 airplanes with a 
line number specified in paragraph (c)(2) of this AD. This AD does not 
apply to any airplanes not specified in paragraph (c)(1) or (2) of this 
AD.

Request To Revise a Sentence in the Background

    Boeing requested that the FAA revise a sentence in the Background 
section. In the NPRM the sentence reads ``Degraded performance by the 
sensor could result in the [air separation module] ASM failing to 
produce nitrogen-enriched air, and the fuel tank becoming more 
flammable due to excessive oxygen-enriched air.'' Boeing stated that 
this sentence is inaccurate because it implies a causality between a 
failing oxygen sensor and a degrading ASM, when there is none. Boeing 
added that the sentence further implies that the oxygen enriched air 
(OEA) is redirected to the fuel tanks if the ASMs start going bad. 
Boeing stated that the sentence should state: ``Degraded oxygen sensor 
performance could result in the system failing to detect when the ASM 
performance degrades below the acceptable threshold for nitrogen-
enriched air, and the fuel tank becoming more flammable due to 
receiving poor-quality nitrogen-enriched air.''
    The FAA agrees that there is no causality between the degraded 
performance of the oxygen sensor and failure of ASM. Degradation of the 
oxygen sensor performance does not directly result in the ASM failing 
to produce nitrogen-enriched air, but rather it would result in a 
failure to detect the condition of the ASM not performing at a required 
level. However, the sentence in question from the Background section of 
the NPRM will not be carried over to this final rule. Therefore, the 
FAA has not changed this AD regarding this issue.

Request To Include Cost for Replacement Sensor

    United requested that the NPRM be revised to include the cost of a 
replacement NGS oxygen sensor and its availability.
    The FAA disagrees with the commenter's request. This AD does not 
require compliance with the maintenance actions specified in the AWL 
items. Instead, this AD requires operators to revise their existing 
maintenance or inspection program, as applicable, to incorporate the 
new airworthiness limitations. Compliance with any airworthiness 
limitation is required by 14 CFR 91.403(c). Therefore, compliance with 
the AWLs is not a requirement of this AD, and including the cost of a 
replacement part would be inappropriate. The FAA has not changed this 
AD regarding this issue.

Conclusion

    The FAA reviewed the relevant data, considered any comments 
received, and determined that air safety requires adopting this AD as 
proposed. Accordingly, the FAA is issuing this AD to address the unsafe 
condition on these products. Except for minor editorial changes, and 
any other changes described previously, this AD is adopted as proposed 
in the NPRM. None of the changes will increase the economic burden on 
any operator.

Related Service Information Under 1 CFR Part 51

    The FAA reviewed Boeing 737-7/8/8200/9/10 Special Compliance Items/
Airworthiness Limitations, D626A011-9-04, dated January 2019. This 
service information describes, among other airworthiness limitations 
(AWLs), airworthiness limitation instruction (ALI) AWL No. 47-AWL-09, 
``Nitrogen Generation System--Oxygen Sensor,'' for replacing oxygen 
sensors.
    The FAA also reviewed Boeing 737-7/8/8200/9/10 Special Compliance 
Items/Airworthiness Limitations, D626A011-9-04, dated May 2022. This 
service information describes, among other AWLs, ALI AWL No. 47-AWL-09, 
``Nitrogen Generation System (NGS)--Oxygen Sensor,'' for replacement; 
or testing, and replacement if necessary; of the oxygen sensor of the 
nitrogen generation system (NGS), and AWL No. 47-AWL-10, ``Nitrogen 
Generation System (NGS)--Oxygen Sensor Repair,'' for repairing oxygen 
sensors.
    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 ADDRESSES.

Costs of Compliance

    The FAA estimates that this AD affects 62 airplanes of U.S. 
registry. The FAA estimates the following costs to comply with this AD:
    The FAA has 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. Since operators incorporate maintenance or inspection 
program changes for their affected fleet(s), the FAA has 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 workhour).

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

[[Page 20072]]

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.

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 adding the following new airworthiness 
directive:

2023-05-06 The Boeing Company: Amendment 39-22375; Docket No. FAA-
2022-1063; Project Identifier AD-2021-01339-T.

(a) Effective Date

    This airworthiness directive (AD) is effective May 10, 2023.

(b) Affected ADs

    None

(c) Applicability

    This AD applies to The Boeing Company Model 737-8, 737-9, and 
737-8200 airplanes, certificated in any category, identified in 
paragraphs (c)(1) and (2) of this AD.
    (1) Airplanes with an original airworthiness certificate or 
original export certificate of airworthiness issued on or before 
April 1, 2021.
    (2) Airplanes with line numbers 7668, 7678, and 7915.

(d) Subject

    Air Transport Association (ATA) of America Code 28, Fuel.

(e) Unsafe Condition

    This AD was prompted by significant changes made to 
airworthiness limitations (AWLs) related to the nitrogen generation 
system (NGS). The FAA is issuing this AD to prevent increasing the 
flammability exposure of the center fuel tank, which together with 
an ignition source in the fuel tank, could lead to a fuel tank 
explosion and consequent loss of the airplane.

(f) Compliance

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

(g) Maintenance or Inspection Program Revision

    Within 60 days after the effective date of this AD, revise the 
existing maintenance or inspection program, as applicable, to 
incorporate the information specified in AWL No. 47-AWL-09, 
``Nitrogen Generation System--Oxygen Sensor,'' of Boeing 737-7/8/
8200/9/10 Special Compliance Items/Airworthiness Limitations, 
D626A011-9-04, dated January 2019; or the information specified in 
AWL No. 47-AWL-09, ``Nitrogen Generation System (NGS)--Oxygen 
Sensor,'' and AWL No. 47-AWL-10, ``Nitrogen Generation System 
(NGS)--Oxygen Sensor Repair,'' of Boeing 737-7/8/8200/9/10 Special 
Compliance Items/Airworthiness Limitations, D626A011-9-04, dated May 
2022. The initial compliance time for accomplishing task AWL No. 47-
AWL-09 is: Within 18,000 flight hours after the date of issuance of 
the original airworthiness certificate or the original export 
certificate of airworthiness, within 18,000 flight hours after the 
most recent replacement or test was performed as specified in AWL 
No. 47-AWL-09, or within 12 months after the effective date of this 
AD, whichever is latest.

(h) No Alternative Actions, Intervals, or Critical Design Configuration 
Control Limitations (CDCCLs)

    After the existing maintenance or inspection program has been 
revised as required by paragraph (g) of this AD, no alternative 
actions (e.g., inspections), intervals, or CDCCLs may be used unless 
the actions, intervals, and CDCCLs are approved as an alternative 
method of compliance (AMOC) in accordance with the procedures 
specified in paragraph (i) of this AD.

(i) 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 responsible Flight Standards 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 (j) 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 responsible Flight Standards 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.

(j) Additional Information

    For more information about this AD, contact Sam Dorsey, 
Aerospace Engineer, Propulsion Section, FAA, Seattle ACO Branch, 
2200 South 216th St., Des Moines, WA 98198; phone and fax: 206-231-
3415; email: [email protected].

(k) 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 737-7/8/8200/9/10 Special Compliance Items/
Airworthiness Limitations, D626A011-9-04, dated January 2019.
    (ii) Boeing 737-7/8/8200/9/10 Special Compliance Items/
Airworthiness Limitations, D626A011-9-04, dated May 2022.
    (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; website 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 protected], or go to: www.archives.gov/federal-register/cfr/ibr-locations.html.


[[Page 20073]]


    Issued on March 5, 2023.
Christina Underwood,
Acting Director, Compliance & Airworthiness Division, Aircraft 
Certification Service.
[FR Doc. 2023-07034 Filed 4-4-23; 8:45 am]
BILLING CODE 4910-13-P