[Federal Register Volume 86, Number 74 (Tuesday, April 20, 2021)]
[Rules and Regulations]
[Pages 20445-20448]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2021-08058]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2019-1071; Project Identifier AD-2019-NM-165-AD; 
Amendment 39-21494; AD 2021-07-17]
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 all 
The Boeing Company Model 737-900ER series airplanes. This AD was 
prompted by reports of significant corrosion of electrical connectors 
located in the main landing gear (MLG) wheel well. This AD requires 
repetitive records checks to determine exposure to certain deicing 
fluids or repetitive inspections for corrosion of the electrical 
connectors, and corrective actions if necessary. The FAA is issuing 
this AD to address the unsafe condition on these products.

DATES: This AD is effective May 25, 2021.
    The Director of the Federal Register approved the incorporation by 
reference of a certain publication listed in this AD as of May 25, 
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-2019-1071.

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-
1071; 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: Julio C. Alvarez, Aerospace Engineer, 
Systems and Equipment Section, FAA, Seattle ACO Branch, 2200 South 
216th St., Des Moines, WA 98198; phone and fax: 206-231-3657; 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 all The Boeing Company 
Model 737-900ER series airplanes. The NPRM published in the Federal 
Register on January 10, 2020 (85 FR 1290). The NPRM was prompted by 
reports of significant corrosion of electrical connectors located in 
the MLG wheel well. The NPRM proposed to require repetitive records 
checks to determine exposure to certain deicing fluids or repetitive 
inspections for corrosion of the electrical connectors, and corrective 
actions if necessary.
    The FAA is issuing this AD to address corrosion and subsequent 
moisture ingress that may lead to electrical shorting of the connectors 
and incorrect functioning of critical systems necessary for safe flight 
and landing.

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

    Air Line Pilots Association, International (ALPA) and two other 
commenters supported the NPRM.

Request To Revise Resistance Values

    Boeing requested that Boeing Alert Service Bulletin 737-24A1148, 
Revision 1, dated July 10, 2003, which incorrectly specified a maximum 
electrical bonding resistance of 5 milliohms for aluminum and 10 
milliohms for stainless steel, be replaced with Boeing Alert Service 
Bulletin 737-24A1148, Revision 2, dated September 14, 2020, which 
updates the maximum allowable resistance values to 3 milliohms for both 
aluminum and stainless steel, per AWL No. 28-AWL-04, as identified in 
Subsection G of Boeing Temporary Revision (TR) 09-020, dated March 
2008, to the Boeing 737-600/700/800/900 Maintenance Planning Document 
(MPD), D626A001-Certification Maintenance Requirements (CMR), Revision 
March 2008. Boeing also advised that operators who have incorporated 
Boeing Alert Service Bulletin 737-24A1148, Revision 1, dated July 10, 
2003, should restore the fuel quantity indicating system (FQIS) 
aluminum and stainless steel connectors to a maximum resistance of 3 
milliohms at the next inspection interval per Boeing Alert Service 
Bulletin 737-24A1148, Revision 2, dated September 14, 2020. Boeing 
observed that the maximum allowable resistance values of 5 milliohms 
(aluminum) and 10 milliohms (stainless steel) specified in Boeing Alert 
Service Bulletin 737-24A1148, Revision 1, dated July 10, 2003, are 
greater than the values specified in AWL No. 28-AWL-04, and that the 
proposed AD is in conflict with

[[Page 20446]]

AD 2008-10-10 R1, Amendment 39-16164 (75 FR 1529, January 12, 2010) (AD 
2008-10-10 R1), and AD 2018-20-24, Amendment 39-19458 (83 FR 51815, 
October 15, 2018) (AD 2018-20-24), both of which reference AWL No. 28-
AWL-04. ADs 2008-10-10 and 2018-20-24 currently require revising the 
Airworthiness Limitations (AWLs) section of the Instructions for 
Continued Airworthiness by incorporating new limitations for fuel tank 
systems to satisfy Special Federal Aviation Regulation No. 88 (in 14 
CFR part 21) for FQIS connectors in unpressurized area. The critical 
design configuration control limitations (CDCCLs) require that if the 
FQIS connector D4850 is disturbed or repaired, the electrical bonding 
resistance value from the backshell to the structure must be 3 
milliohms or less.
    The FAA agrees with the request to require the revised service 
information, which updates the maximum allowable resistance values to 3 
milliohms. These values are consistent with AD 2008-10-10 R1 and AD 
2018-20-24 and SFAR No. 88 requirements. The FAA has revised paragraph 
(g)(2) of this AD to specify Boeing Alert Service Bulletin 737-24A1148, 
Revision 2, dated September 14, 2020, and has also updated the 
``Related Service Information under CFR part 51'' paragraph in this 
final rule.

Request To Specify Initial Compliance Time

    Delta Air Lines (DAL) suggested that paragraph (g) specify the 
compliance time as within 24 months of issuance of the original 
certificate of airworthiness or 12 months after the effective date of 
this AD, whichever comes later. DAL noted that newer airplanes having 
accumulated less than 24 months since the issuance of the original 
certificate of airworthiness should not require inspection prior to the 
accumulation of 24 months since the issuance of the original 
certificate of airworthiness, because these aircraft were in a known 
corrosion-free condition upon completion of production. This condition, 
DAL asserted, is equivalent to an aircraft that has just been inspected 
as required by this AD. DAL maintained that because the repeat interval 
after initial inspection given in the proposed rule is 24 months, an 
equivalent level of safety would be provided if the initial inspection 
were accomplished within 24 months of delivery or 12 months after the 
effective date of this AD, whichever occurs later.
    The FAA agrees with the request. An affected airplane that has just 
received an original airworthiness certificate or original export 
certificate of airworthiness is in a condition equivalent to that of 
completing the repetitive inspection; therefore, conducting an initial 
inspection within 24 months is appropriate to address the concern of 
the AD for that airplane. The initial compliance time specified in 
paragraph (g) of this AD has been changed to include this information.

Request To Modify Compliance Times

    DAL suggested that paragraph (g)(2) of the proposed AD be changed 
to add a new paragraph (g)(2)(iv) specifying ``If connectors or 
contacts show signs of corrosion or connector resistance measurements 
are greater than the specified milliohm limit given in Boeing Alert 
Service Bulletin 737-24A1148, Revision 1, accomplish appropriate 
corrective action(s) prior to further flight in accordance with Boeing 
Alert Service Bulletin 737-24A1148, Revision 1.'' DAL observed that the 
applicable times specified in paragraphs (g)(2)(i) through (iii) of the 
proposed AD are specific to corrosion of the backshells, and that the 
proposed AD does not clearly define corrective actions for the 
connectors and contacts, which would also be inspected in paragraph 
(g)(2) of the proposed AD. DAL contended that the intended action of 
the proposed AD is for discrepant connectors and contacts to have 
corrective action accomplished prior to further flight.
    The FAA disagrees with the request to modify paragraph (g)(2) of 
this AD. The service information adequately specifies when to perform 
corrective actions for connectors and contacts. The FAA has not changed 
this AD with regard to this request.

Request To Address Discrepancies in NPRM

    DAL noted the following discrepancies with Boeing Alert Service 
Bulletin 737-24A1148, Revision 1, dated July 10, 2003: The Work 
Instructions, paragraph 3.B of the Accomplishment Instructions, 
indicate that the accomplishment instructions are divided into two 
parts; however, they are actually divided into three parts. Also, part 
3 of the Work Instructions does not give the instruction to remove 
electrical power from the airplane, yet Figure 5, Step 10, of the ASB 
instructs to restore electrical power. DAL noted that if electrical 
power was not removed, it cannot be restored. The FAA infers a request 
to address the discrepancies in the proposed AD.
    The FAA agrees with addressing the stated discrepancies in this AD. 
The 57 discrepancies have been rectified in Boeing Alert Service 
Bulletin 737-24A1148, Revision 2, dated September 14, 2020, and this AD 
has been changed to reference that revision.

Request To Include AMOC Notices

    DAL requested that the proposed AD be revised to include references 
to two FAA-approved AMOCs to the mandated service information: AMOC 
Notice 737-24A1148-AMOC-01, dated May 06, 2013, and FAA AMOC Letter 
130S- 09-9, dated April 28, 2009. DAL observed that the AMOCs are 
applicable service documentation that should be specifically included 
in the final rule to facilitate operators in correctly incorporating 
the requirements of the final rule.
    The FAA partially agrees with the request. To facilitate operators 
in correctly incorporating the requirements of the final rule, 
paragraph (i)(4) of this AD has been changed to include reference to 
FAA AMOC Letter 130S-09-9, dated April 28, 2009. However, Boeing AMOC 
Notice 737-24A1148-AMOC-01, dated May 6, 2013, has been incorporated 
into the revised service bulletin that is mandated by this AD and 
therefore is not included in paragraph (i)(4) of this AD.

Request To Give Credit for Previous Actions

    United Airlines (UAL) generally supported the NPRM and requested 
that credit be given for actions previously accomplished in their 
maintenance inspection program per their publication EA 2400-01516, 
addressing Boeing Alert Service Bulletin 737-24A1148, Revision 1, dated 
July 10, 2003. UAL stated it has incorporated inspections of its 737-
900ER fleet starting May 2010, using their publication EA 2400-01516.
    The FAA agrees that operators should get credit for performing 
actions of Boeing Alert Service Bulletin 737-24A1148, Revision 1, dated 
July 10, 2003, referenced in the NPRM. As stated previously, this final 
rule has been revised to refer to the latest service bulletin, Boeing 
Alert Service Bulletin 737-24A1148, Revision 2, dated September 14, 
2020, which contains updated service information to address the unsafe 
condition. Operators who previously performed the work before the 
effective date of this AD using Boeing Alert Service Bulletin 737-
24A1148, dated December 6, 2001, or Revision 1, dated July 10, 2003, 
may receive credit for accomplishment of the initial detailed 
inspection specified in paragraph (g)(2) of this AD; however, the 
updated FQIS connector D4850 resistance values must be used at the

[[Page 20447]]

next repetitive inspection interval, in accordance with Boeing Alert 
Service Bulletin 737-24A1148, Revision 2, dated September 14, 2020. The 
FAA has added paragraph (h) of this AD to provide credit for Boeing 
Alert Service Bulletin 737-24A1148, dated December 6, 2001, and Boeing 
Alert Service Bulletin 737-24A1148, Revision 1, dated July 10, 2003.

Effect of Winglets on Accomplishment of the Proposed Actions

    Aviation Partners Boeing stated that the installation of winglets 
per Supplemental Type Certificate STC ST00830SE does not affect the 
accomplishment of the manufacturer's service instructions. Blended 
winglets are part of the production type certificate for the 737-900ER 
and are not an STC installation.
    The FAA agrees with the commenter that STC ST00830SE does not 
affect the accomplishment of the manufacturer's service instructions. 
Therefore, the installation of STC ST00830SE does not affect the 
ability to accomplish the actions required by this AD. The FAA has not 
changed this AD as a result of this comment.

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 Alert Service Bulletin 737-24A1148, 
Revision 2, dated September 14, 2020. This service information 
describes procedures for repetitive records checks to determine 
exposure to certain deicing fluids or repetitive inspections for 
corrosion of the electrical connectors, and corrective actions if 
necessary. This service information is reasonably available because the 
interested parties have access to it through their normal course of 
business or by the means identified in the ADDRESSES section.

Costs of Compliance

    The FAA estimates that this AD affects 346 airplanes of U.S. 
registry. The FAA estimates the following costs to comply with this AD:

                                                 Estimated Costs
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                                                                                                 Cost on U.S.
             Action                     Labor cost          Parts cost     Cost per product        operators
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Repetitive records check.......  1 work-hour x $85 per                $0  $85 per inspection  Up to $29,410 per
                                  hour = $85 per                           cycle.              inspection cycle.
                                  inspection cycle.
Repetitive detailed inspection.  3 work-hours x $85 per               $0  $255 per            Up to $88,230 per
                                  hour = $255 per                          inspection cycle.   inspection cycle.
                                  inspection cycle.
----------------------------------------------------------------------------------------------------------------

    The FAA estimates the following costs to do any necessary repairs 
or replacements that would be required based on the results of the 
inspection. The FAA has no way of determining the number of aircraft 
that might need these repairs or replacements:

                                               On-Condition Costs
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              Action                       Labor cost                Parts cost             Cost per product
----------------------------------------------------------------------------------------------------------------
Cleaning or replacement..........  Up to 5 work-hours x $85   Up to $831..............  Up to $1,256.
                                    per hour = Up to $425.
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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

0
1. The authority citation for part 39 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701.

[[Page 20448]]

Sec.  39.13  [Amended]

0
2. The FAA amends Sec.  39.13 by adding the following new airworthiness 
directive:

2021-07-17 The Boeing Company: Amendment 39-21494 ; Docket No. FAA-
2019-1071; Product Identifier 2019-NM-165-AD.

(a) Effective Date

    This airworthiness directive (AD) is effective May 25, 2021.

(b) Affected ADs

    None.

(c) Applicability

    This AD applies to all The Boeing Company Model 737-900ER series 
airplanes, certificated in any category.

(d) Subject

    Air Transport Association (ATA) of America Code 24, Electrical 
power.

(e) Unsafe Condition

    This AD was prompted by reports of significant corrosion of 
electrical connectors located in the main landing gear (MLG) wheel 
well. The FAA is issuing this AD to address corrosion and subsequent 
moisture ingress that may lead to electrical shorting of the 
connectors and incorrect functioning of critical systems necessary 
for safe flight and landing.

(f) Compliance

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

(g) Required Actions

    Within 24 months after the date of issuance of the original 
airworthiness certificate or the date of issuance of the original 
export certificate of airworthiness or 12 months after the effective 
date of this AD, whichever is later: Do the actions required by 
paragraph (g)(1) or (2) of this AD.
    (1) Determine airplane exposure to runway deicing fluids 
containing potassium formate or potassium acetate by reviewing 
airport data on the types of components in the deicing fluid used at 
airports that support airplane operations.
    (i) If the airplane has not been exposed: Repeat the 
requirements specified in paragraph (g)(1) of this AD thereafter at 
intervals not to exceed 24 months.
    (ii) If the airplane has been exposed: Within 90 days after that 
determination is made, do the inspection required by paragraph 
(g)(2) of this AD. Repeat the inspection thereafter at intervals not 
to exceed 24 months.
    (2) Do a detailed inspection of the electrical connectors, 
including the contacts and backshells of the line replaceable unit 
(LRU) in the wheel well of the MLG, for corrosion in accordance with 
the Accomplishment Instructions of Boeing Alert Service Bulletin 
737-24A1148, Revision 2, dated September 14, 2020. Perform 
applicable corrective actions at the applicable times, as specified 
in paragraphs (g)(2)(i) through (iii) of this AD, in accordance with 
the Accomplishment Instructions of Boeing Alert Service Bulletin 
737-24A1148, Revision 2, dated September 14, 2020. Repeat the 
inspection thereafter at intervals not to exceed 24 months. For the 
purposes of this AD, a detailed inspection is defined as an 
intensive visual examination of a specific structural area, system, 
installation, or assembly to detect damage, failure, or 
irregularity. Available lighting is normally supplemented with a 
direct source of good lighting at intensity deemed appropriate by 
the inspector. Inspection aids such as mirror, magnifying lenses, 
etc., may be used. Surface cleaning and elaborate access procedures 
may be required.
    (i) If the total backshell surface area corrosion is 10 percent 
or less, clean the backshell(s) before further flight.
    (ii) If the total backshell surface area corrosion is greater 
than 10 percent but less than 20 percent, replace the connectors and 
backshells within 30 days after the detailed inspection.
    (iii) If the total backshell surface area corrosion is 20 
percent or more, replace the connectors and backshells before 
further flight.

(h) Credit for Previous Actions

    This paragraph provides credit for the initial detailed 
inspection and applicable corrective actions specified in paragraph 
(g)(2) of this AD, if those actions were performed before the 
effective date of this AD using Boeing Alert Service Bulletin 737-
24A1148, dated December 6, 2001, or Boeing Alert Service Bulletin 
737-24A1148, Revision 1, dated July 10, 2003.

(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 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 (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 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.
    (4) FAA AMOC Letter 130S-09-9, dated April 28, 2009, and AMOCs 
approved previously for AD 2005-18-23, Amendment 39-14264 (70 FR 
54253, September 14, 2005), are approved as AMOCs for the 
corresponding provisions of this AD.

(j) Related Information

    For more information about this AD, contact Julio C. Alvarez, 
Aerospace Engineer, Systems and Equipment Section, FAA, Seattle ACO 
Branch, 2200 South 216th St., Des Moines, WA 98198; phone and fax: 
206-231-3657; 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 Alert Service Bulletin 737-24A1148, Revision 2, dated 
September 14, 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 29, 2021.
Lance T. Gant,
Director, Compliance & Airworthiness Division, Aircraft Certification 
Service.
[FR Doc. 2021-08058 Filed 4-19-21; 8:45 am]
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