86080 Federal Register / Vol. 88, No. 237 / Tuesday, December 12, 2023 / Proposed Rules 

(2) Service information identified in this 

AD that is not incorporated by reference is 

available at the addresses specified in 

paragraphs (o)(3) and (4) of this AD. 

(o) Material Incorporated by Reference 

(1) The Director of the Federal Register 

approved the incorporation by reference 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 

737–34A3572 RB, dated October 15, 2020. 

(ii) Boeing Alert Requirements Bulletin 

737–34A3573 RB, dated August 5, 2020. 

(iii) Boeing Alert Requirements Bulletin 

777–34A0385 RB, Revision 1, dated March 8, 

2021. 

(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 material at the 

National Archives and Records 

Administration (NARA). For information on 

the availability of this material at NARA, 

visit www.archives.gov/federal-register/cfr/ 

ibr-locations or email fr.inspection@nara.gov. 

Issued on October 4, 2023. 

Victor Wicklund, 

Deputy Director, Compliance & Airworthiness 

Division, Aircraft Certification Service. 

[FR Doc. 2023–24306 Filed 12–11–23; 8:45 am] 

BILLING CODE 4910–13–P 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 39 

[Docket No. FAA–2023–2235; Project 

Identifier AD–2023–01009–T] 

RIN 2120–AA64 

Airworthiness Directives; The Boeing 

Company Airplanes 

AGENCY: Federal Aviation 

Administration (FAA), DOT. 

ACTION: Notice of proposed rulemaking 

(NPRM). 

SUMMARY: The FAA proposes to adopt a 

new airworthiness directive (AD) for 

certain The Boeing Company Model 

737–600, –700, –700C, –800, –900, and 

–900ER series airplanes. This proposed 

AD was prompted by two engine fan 

blade-out (FBO) events that resulted in 

the separation of engine inlet cowl and 

fan cowl parts from the airplane 

damaging the fuselage, which caused 

loss of pressurization and subsequent 

emergency descent. The FBO events 

also resulted in cracks in the primary 

exhaust nozzle, potentially resulting in 

the departure of the primary exhaust 

nozzle and damaging a stabilizer or 

striking the fuselage and window. This 

proposed AD would require an 

inspection or maintenance records 

check to determine if the primary 

exhaust nozzle has an affected part 

number and, for affected primary 

exhaust nozzles, an installation of 

bridge brackets onto the primary 

exhaust nozzle, or as an option, an 

installation of a serviceable primary 

exhaust nozzle. This proposed AD 

would also require revising the existing 

maintenance or inspection program, as 

applicable, to incorporate new 

airworthiness limitations. The FAA is 

proposing this AD to address the unsafe 

condition on these products. 

DATES: The FAA must receive comments 

on this proposed AD by January 26, 

2024. 

ADDRESSES: You may send comments, 

using the procedures found in 14 CFR 

11.43 and 11.45, by any of the following 

methods: 

• Federal eRulemaking Portal: Go to 

regulations.gov. Follow the instructions 

for submitting comments. 

• Fax: 202–493–2251. 

• Mail: U.S. Department of 

Transportation, Docket Operations, M– 

30, West Building Ground Floor, Room 

W12–140, 1200 New Jersey Avenue SE, 

Washington, DC 20590. 

• Hand Delivery: Deliver to Mail 

address above between 9 a.m. and 5 

p.m., Monday through Friday, except 

Federal holidays. 

AD Docket: You may examine the AD 

docket at regulations.gov under Docket 

No. FAA–2023–2235; 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 NPRM, any comments 

received, and other information. The 

street address for Docket Operations is 

listed above. 

Material Incorporated by Reference: 

• For service information identified 

in this NPRM, 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 by searching for and 

locating Docket No. FAA–2023–2235. 

FOR FURTHER INFORMATION CONTACT: Luis 

Cortez-Muniz, Aviation Safety Engineer, 

FAA, 2200 South 216th St., Des Moines, 

WA 98198; telephone: 206–231–3958; 

email: luis.a.cortez-muniz@faa.gov. 

SUPPLEMENTARY INFORMATION: 

Comments Invited 

The FAA invites you to send any 

written relevant data, views, or 

arguments about this proposal. Send 

your comments to an address listed 

under ADDRESSES. Include ‘‘Docket No. 

FAA–2023–2235; Project Identifier AD– 

2023–01009–T’’ at the beginning of your 

comments. The most helpful comments 

reference a specific portion of the 

proposal, explain the reason for any 

recommended change, and include 

supporting data. The FAA will consider 

all comments received by the closing 

date and may amend this proposal 

because of those comments. 

Except for Confidential Business 

Information (CBI) as described in the 

following paragraph, and other 

information as described in 14 CFR 

11.35, the FAA will post all comments 

received, without change, to 

regulations.gov, including any personal 

information you provide. The agency 

will also post a report summarizing each 

substantive verbal contact received 

about this NPRM. 

Confidential Business Information 

CBI is commercial or financial 

information that is both customarily and 

actually treated as private by its owner. 

Under the Freedom of Information Act 

(FOIA) (5 U.S.C. 552), CBI is exempt 

from public disclosure. If your 

comments responsive to this NPRM 

contain commercial or financial 

information that is customarily treated 

as private, that you actually treat as 

private, and that is relevant or 

responsive to this NPRM, it is important 

that you clearly designate the submitted 

comments as CBI. Please mark each 

page of your submission containing CBI 

as ‘‘PROPIN.’’ The FAA will treat such 

marked submissions as confidential 

under the FOIA, and they will not be 

placed in the public docket of this 

NPRM. Submissions containing CBI 

should be sent to Luis Cortez-Muniz, 

Aviation Safety Engineer, FAA, 2200 

South 216th St., Des Moines, WA 98198; 

telephone: 206–231–3958; email: 

luis.a.cortez-muniz@faa.gov. Any 

commentary that the FAA receives that 


ddrumheller on DSK120RN23PROD with PROPOSALS1
Federal Register / Vol. 88, No. 237 / Tuesday, December 12, 2023 / Proposed Rules 86081 

is not specifically designated as CBI will 

be placed in the public docket for this 

rulemaking. 

Background 

The FAA received two reports of 

engine events that resulted in the 

separation of engine inlet cowl and fan 

cowl parts from the airplane. One event 

occurred in August 2016 on a Boeing 

Model 737–700 series airplane powered 

by a CFM56–7B engine. The left engine 

failed due to the FBO but the airplane 

landed successfully. The second event 

occurred on April 17, 2018, on a Boeing 

Model 737–700 series airplane powered 

by a CFM56–7B engine. In that event, an 

FBO occurrence resulted in the release 

of fan cowl parts and the engine cowling 

departing the airplane. The fan cowl 

parts damaged the fuselage, which 

caused loss of pressurization and 

subsequent emergency descent. 

Although the airplane landed safely, 

there was one passenger fatality. In that 

event, the suspected cause of the FBO 

occurrence was a low-cycle fatigue 

crack in the dovetail of fan blade 

number 13 of engine number 1. The 

broken fan blade hit the engine fan case 

at a critical location causing a 

significant impulse, displacement, and 

imbalance of the fan rotor effecting the 

structural integrity of the engine 

cowling. 

In response to these events, the FAA 

issued two AD actions for the CFM 

International S.A. (CFM) Model 

CFM56–7B engines. The FAA issued 

emergency AD 2018–09–51, 

Amendment 39–19287 (83 FR 23794, 

May 23, 2018) (AD 2018–09–51), which 

requires a one-time ultrasonic 

inspection of the concave and convex 

sides of the fan blade dovetail. The FAA 

also issued AD 2018–26–01, 

Amendment 39–19531 (83 FR 66090, 

December 26, 2018) (AD 2018–26–01), 

which requires initial and repetitive 

inspections of the concave and convex 

sides of the fan blade dovetail to detect 

cracking and replacement of any blades 

found. The FAA issued AD 2018–09–51 

to address fan blade failure due to 

cracking, which could result in an 

engine in-flight shutdown (IFSD), 

uncontained release of debris, damage 

to the engine, damage to the airplane, 

and possible airplane decompression. 

The FAA issued AD 2018–26–01 to 

address failure of the fan blade, which 

could result in the engine inlet cowl 

disintegrating and debris penetrating the 

fuselage, causing a loss of 

pressurization, and prompting an 

emergency descent. 

Since AD 2018–09–51 and AD 2018– 

26–01 were issued, the FAA has 

determined further rulemaking is 

necessary to reduce the probability of 

unsecured nacelle components, should 

an engine fan blade failure occur. As 

evidenced by Exemption No. 19212, 

dated July 13, 2022 (Docket No. FAA– 

2023–2235), Boeing developed 

modifications to the inlet cowl, fan 

cowl, and exhaust nozzle that must be 

accomplished prior to July 31, 2028. 

Boeing petitioned and the FAA later 

agreed to amend Exemption No. 19212 

to 19212A, which added a requirement 

that solutions to address potential 

maintenance errors must be 

incorporated prior to December 31, 

2029. However, to implement these 

design changes, the FAA must issue 

rulemaking to address the unsafe 

condition. 

This proposed AD would address the 

unsafe condition related to the primary 

exhaust nozzle that was also a result of 

the FBO events. During an FBO event, 

primary exhaust nozzles that are not 

strengthened could depart the engine, 

potentially damaging a stabilizer or 

striking the fuselage and window. This 

condition, if not addressed, could result 

in loss of control of the airplane, or in 

a rapid decompression and hazard to 

window-seated passengers aft of the 

wing. 

FAA’s Determination 

The FAA is issuing this NPRM after 

determining that the unsafe condition 

described previously is likely to exist or 

develop on other products of the same 

type design. 

Related Service Information Under 1 

CFR Part 51 

The FAA reviewed Boeing Special 

Attention Requirements Bulletin 737– 

78–1106 RB, dated September 1, 2023. 

This service information specifies 

procedures for a maintenance records 

check, or an inspection of the engine to 

identify if the engine has a primary 

exhaust nozzle with an affected part 

number. For affected primary exhaust 

nozzles, the service information 

specifies procedures for installing 

bridge brackets onto the primary 

exhaust nozzle, or as an option, 

installing a serviceable exhaust nozzle 

onto the engine. 

The service information also requires 

revision of the operator’s maintenance 

or inspection program, as applicable, by 

incorporating certain airworthiness 

limitations (AWLs). 

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. 

Proposed AD Requirements in This 

NPRM 

This proposed AD would require 

accomplishing the actions specified in 

the service information already 

described, except as discussed under 

‘‘Differences Between this Proposed AD 

and the Service Information’’ and except 

for any differences identified as 

exceptions in the regulatory text of this 

proposed AD. For information on the 

procedures and compliance times, see 

this service information at 

regulations.gov under Docket No. FAA– 

2023–2235. 

This proposed AD would require 

revisions to certain operator 

maintenance documents to include new 

airworthiness limitations. Compliance 

with these limitations is required by 14 

CFR 91.403(c). For airplanes that have 

been previously modified, altered, or 

repaired in the areas addressed by this 

proposed AD, the operator may not be 

able to accomplish the actions described 

in the revisions. In this situation, to 

comply with 14 CFR 91.403(c), the 

operator must request approval for an 

alternative method of compliance 

according to paragraph (j) of this 

proposed AD. 

Differences Between This Proposed AD 

and the Service Information 

The Effectivity of Boeing Special 

Attention Requirements Bulletin 737– 

78–1106 RB inadvertently excluded 

Boeing Model 737–600, –700, –700C, 

–800, –900, and –900ER series airplanes 

having line numbers 1245, 1614, 1810, 

1839, 1885, 1934, 1979, 1991, 2080, 

2157, 2232, 2531, 2822, 3071, 3189, and 

3319. Those airplanes are affected by 

the identified unsafe condition; for 

those airplanes, this proposed AD 

would require accomplishment of the 

applicable actions specified in Boeing 

Special Attention Requirements Bulletin 

737–78–1106 RB, September 1, 2023. 

The FAA has confirmed with Boeing 

that the Accomplishment Instructions of 

Boeing Special Attention Requirements 

Bulletin 737–78–1106 RB, September 1, 

2023, are applicable to the expanded 

group of airplanes. 

Boeing Special Attention 

Requirements Bulletin 737–78–1106 RB, 

dated September 1, 2023, identifies 

‘‘System Airworthiness Limitation NO. 

2—Fan Blade Out Conditions,’’ and 

‘‘System Airworthiness Limitation NO. 

3—Fan Blade Out Conditions’’ as the 

airworthiness limitations that must be 

incorporated. In addition to those 

limitations, the FAA has determined 

that ‘‘System Airworthiness Limitation 

NO. 4—Engine Nacelle Maintenance 

Errors’’ must also be incorporated as 


ddrumheller on DSK120RN23PROD with PROPOSALS1
86082 Federal Register / Vol. 88, No. 237 / Tuesday, December 12, 2023 / Proposed Rules 

specified in paragraph (h) of this 

proposed AD. System Airworthiness 

Limitation NO. 4 specifically provides 

the limitation that mandates solutions to 

maintenance errors that must be 

accomplished prior to December 31, 

2029, as required by Exemption No. 

19212A. 

Costs of Compliance 

The FAA estimates that this AD, if 

adopted as proposed, would affect 1,215 

airplanes of U.S. registry. The FAA 

estimates the following costs to comply 

with this proposed AD: 

ESTIMATED COSTS

Action Labor cost Parts cost Cost per product Cost on U.S. operators 

Inspect for affected part numbers or maintenance records 

check.

2 work-hours × $85 per hour = 

$170.

$0 ............................ $170 ........................ $206,550. 

Bridge bracket installation * ........ Up 23 work-hours × $85 per 

hour = $1,955.

Up $63,200 ............. Up to $65,155 ......... Up to $79,163,325 **. 

* The option to install a serviceable primary exhaust nozzle would cost up to $65,155 per product. 

** Not all airplanes will have an affected primary exhaust nozzle so the fleet cost will be significantly lower. 

The FAA has determined that revising 

the existing maintenance or inspection 

program takes an average of 90 workhours 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 agency 

estimates the average total cost per 

operator to be $7,650 (90 work-hours × 

$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 

The FAA determined that this 

proposed AD would not have federalism 

implications under Executive Order 

13132. This proposed AD would not 

have a substantial direct effect on the 

States, on the relationship between the 

national Government and the States, or 

on the distribution of power and 

responsibilities among the various 

levels of government. 

For the reasons discussed above, I 

certify this proposed regulation: 

(1) Is not a ‘‘significant regulatory 

action’’ under Executive Order 12866, 

(2) Would not affect intrastate 

aviation in Alaska, and 

(3) Would not have a significant 

economic impact, positive or negative, 

on a substantial number of small entities 

under the criteria of the Regulatory 

Flexibility Act. 

List of Subjects in 14 CFR Part 39 

Air transportation, Aircraft, Aviation 

safety, Incorporation by reference, 

Safety. 

The Proposed Amendment 

Accordingly, under the authority 

delegated to me by the Administrator, 

the FAA proposes to amend 14 CFR part 

39 as follows: 

PART 39—AIRWORTHINESS 

DIRECTIVES 

■ 1. The authority citation for part 39 

continues to read as follows: 

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

§ 39.13 [Amended] 

■ 2. The FAA amends § 39.13 by adding 

the following new airworthiness 

directive: 

The Boeing Company: Docket No. FAA– 

2023–2235; Project Identifier AD–2023– 

01009–T. 

(a) Comments Due Date 

The FAA must receive comments on this 

airworthiness directive (AD) by January 26, 

2024. 

(b) Affected ADs 

None. 

(c) Applicability 

This AD applies to The Boeing Company 

Model 737–600, –700, –700C, –800, –900, 

and –900ER series airplanes specified in 

paragraphs (c)(1) and (2) of this AD, 

certificated in any category. 

(1) Airplanes identified in Boeing Special 

Attention Requirements Bulletin 737–78– 

1106 RB, dated September 1, 2023. 

(2) Airplanes having line numbers 1245, 

1614, 1810, 1839, 1885, 1934, 1979, 1991, 

2080, 2157, 2232, 2531, 2822, 3071, 3189, 

and 3319. 

(d) Subject 

Air Transport Association (ATA) of 

America Code 78, Exhaust. 

(e) Unsafe Condition 

This AD was prompted by two engine fan 

blade-out (FBO) events that resulted in the 

separation of engine inlet cowl and fan cowl 

parts from the airplane damaging the 

fuselage, which caused loss of pressurization 

and subsequent emergency descent. The FBO 

events also resulted in cracks in the primary 

exhaust nozzle, which could result in the 

departure of the primary exhaust nozzle. The 

FAA is issuing this AD to address primary 

exhaust nozzles that are not strengthened, 

which during an FBO event, could depart the 

engine, potentially damaging a stabilizer or 

striking the fuselage and window. The unsafe 

condition, if not addressed, could result in 

loss of control of the airplane, or in a rapid 

decompression and hazard to window-seated 

passengers aft of the wing. 

(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 Special 

Attention Requirements Bulletin 737–78– 

1106 RB, dated September 1, 2023, do all 

applicable actions identified in, and in 

accordance with, the Accomplishment 

Instructions of Boeing Special Attention 

Requirements Bulletin 737–78–1106 RB, 

dated September 1, 2023. 

Note 1 to paragraph (g): Guidance for 

accomplishing the actions required by this 

AD can be found in Boeing Special Attention 

Service Bulletin 737–78–1106, dated 

September 1, 2023, which is referred to in 

Boeing Special Attention Requirements 


ddrumheller on DSK120RN23PROD with PROPOSALS1
Federal Register / Vol. 88, No. 237 / Tuesday, December 12, 2023 / Proposed Rules 86083 

Bulletin 737–78–1106 RB, dated September 

1, 2023. 

(h) Exceptions to Service Information 

Specifications 

Where Tables 1 and 2 of Boeing Special 

Attention Requirements Bulletin 737–78– 

1106 RB specify incorporating 737–600/700/ 

700C/800/900/900ER Airworthiness 

Limitations (AWLs) document D626A001–9– 

01 ‘‘System Airworthiness Limitation NO. 

2—Fan Blade Out Conditions,’’ and ‘‘System 

Airworthiness Limitation NO. 3—Fan Blade 

Out Conditions’’ into the operators’ 

maintenance program, this AD requires 

revising the existing maintenance or 

inspection program, as applicable, by 

incorporating the information specified in 

Figure 1 to the introductory text of paragraph 

(h) of this AD into the airworthiness 

limitations within 90 days after the effective 

date of this AD, or before further flight after 

accomplishing any of the actions specified in 

paragraphs (h)(1) through (3) of this AD, 

whichever occurs first. 

Figure 1 to the Introductory Text of 

Paragraph (h)—System Airworthiness 

Limitations 

(1) The Condition 1, (Option 1) or 

Condition 3 (Option 1) actions specified in 

Boeing Special Attention Requirements 

Bulletin 737–78–1106 RB, dated September 

1, 2023. 

(2) The Condition 1, (Option 2) or 

Condition 3 (Option 2) action specified in 

Boeing Special Attention Requirements 

Bulletin 737–78–1106 RB, dated September 

1, 2023. 

(3) The determination that the primary 

exhaust nozzles are not affected as specified 

in Condition 2 or Condition 4 of Boeing 

Special Attention Requirements Bulletin 

737–78–1106 RB, dated September 1, 2023. 

(i) No Alternative Actions 

After the existing maintenance or 

inspection program has been revised as 

required by paragraph (h) of this AD, no 

alternative actions may be used unless the 

actions are approved as an alternative 

method of compliance (AMOC) in 

accordance with the procedures specified in 

paragraph (j) of this AD. 

(j) Alternative Methods of Compliance 

(AMOCs) 

(1) The Manager, AIR–520, Continued 

Operational Safety 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 (k) of this AD. 

Information may be emailed to: 9-ANMSeattle-ACO-AMOC-Requests@faa.gov. 

(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, AIR–520, Continued Operational 

Safety 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 

For more information about this AD, 

contact Luis Cortez-Muniz, Aviation Safety 

Engineer, FAA, 2200 South 216th St., Des 

Moines, WA 98198; telephone: 206–231– 

3958; email: luis.a.cortez-muniz@faa.gov. 

(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 Special Attention Requirements 

Bulletin 737–78–1106 RB, dated September 

1, 2023. 

(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; website 

myboeingfleet.com. 

(4) You may view this service information 

at the FAA, Airworthiness Products Section, 

Operational Safety Branch, 2200 South 216th 


ddrumheller on DSK120RN23PROD with PROPOSALS1EP12DE23.000</GPH>

SYSTD.i AIRWORTHINESS LIMITATION No_ 2 

·FAN BLADE OUT CONDITIONS 

. .\ll aircraft must instill the following modillcations: ( I) engine inlets 'I.Vith new spacer. design and 

increased fast~ capability (2) fan cowls ,1-ith new :radial restraint fitting hooks, new radial restraint 

clips, and :m extemal doublec at the starter vent (3) fan cow1· support beam fastener changes (except for 

737-000ER mcraft,. because the fan cowl ·support be.im fastener ch:mges are already incorporated). All 

aircraft that have not :inroqlorated these modmcations cannot operate past July 31, 2028 unless upgraded 

to new hardware that is :fully compliant to §§25.90l(c) and AppendbtK15.LI to Part 25_ Boe:ing will 

release all senrice data to allow retrofit ofbardw,1re updates to the CFMS&-7B nacel]e prior to that date 

SYSTEM AIRWORTHINESS LTh-:ITfATION No. 3 

FAN BLWE OUT CONDITIONS 

· All aircraft delivered without the Perfomlance Improvement Package {PW) must·instill engine exhaust· 

nozzle structural stiffening elements.. All ainnft that have hot :incoqiorated these modmcations cannot 

operate past.July :31, 2028 unless upgraded to new hanhvare that JS fully compliant to §§25.90 l(t) and 

Appendix K15 :1:1 to Part 25. Boeing \\ill release all service data to all<t.v retrofit of hardware updates·to 

the Cflvfio-7B nacelle prior to that date. 

SYSTEMAIR.WORTHINESS LTh.IlTATIONNo_ 4 

.ENGINE NACELLE l\fAINTENA.NCE·ERRORS 

All aircraft must incorporate solutions to address potential maintenance errors, e"g:, the failure to 

completely latch the fan cowl or the fan cowl integrated drive generator {IDG) door .. .\ll aircraft that have 

not incorporated changes to become :fully compliant with §§15.901(c)andAppendix K15.1.1 toPart25 

cannot be operated past Decemb« 31, 2029_ 
86084 Federal Register / Vol. 88, No. 237 / Tuesday, December 12, 2023 / Proposed Rules 

St., Des Moines, WA. For information on the 

availability of this material at the FAA, call 

206–231–3195. 

(5) You may view this material at the 

National Archives and Records 

Administration (NARA). For information on 

the availability of this material at NARA, 

visit www.archives.gov/federal-register/cfr/ 

ibr-locations or email fr.inspection@nara.gov. 

Issued on December 1, 2023. 

Victor Wicklund, 

Deputy Director, Compliance & Airworthiness 

Division, Aircraft Certification Service. 

[FR Doc. 2023–27101 Filed 12–11–23; 8:45 am] 

BILLING CODE 4910–13–P 

DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

14 CFR Part 39 

[Docket No. FAA–2023–2236; Project 

Identifier AD–2023–00962–T] 

RIN 2120–AA64 

Airworthiness Directives; The Boeing 

Company Airplanes 

AGENCY: Federal Aviation 

Administration (FAA), DOT. 

ACTION: Notice of proposed rulemaking 

(NPRM). 

SUMMARY: The FAA proposes to adopt a 

new airworthiness directive (AD) for all 

The Boeing Company Model 737–600, 

–700, –700C, –800, –900, and –900ER 

series airplanes. This proposed AD was 

prompted by two engine fan blade-out 

(FBO) events that resulted in the 

separation of engine inlet cowl and fan 

cowl parts from the airplane. In one 

event, fan cowl parts damaged the 

fuselage, which caused loss of 

pressurization and subsequent 

emergency descent. This proposed AD 

would require replacing specified inlet 

cowl aft bulkhead fasteners for certain 

airplanes; for certain other airplanes, 

inspecting the inlet cowl aft bulkhead 

fastener and replacing the fasteners if 

rivets are found, and, for all airplanes, 

replacement of the crushable spacers 

used in the attachment of the inlet cowl 

to the engine fan case; or as an option, 

installing a serviceable inlet cowl. This 

proposed AD would also require 

revising the existing maintenance or 

inspection program, as applicable, to 

incorporate new airworthiness 

limitations. The FAA is proposing this 

AD to address the unsafe condition on 

these products. 

DATES: The FAA must receive comments 

on this proposed AD by January 26, 

2024. 

ADDRESSES: You may send comments, 

using the procedures found in 14 CFR 

11.43 and 11.45, by any of the following 

methods: 

• Federal eRulemaking Portal: Go to 

regulations.gov. Follow the instructions 

for submitting comments. 

• Fax: 202–493–2251. 

• Mail: U.S. Department of 

Transportation, Docket Operations, M– 

30, West Building Ground Floor, Room 

W12–140, 1200 New Jersey Avenue SE, 

Washington, DC 20590. 

• Hand Delivery: Deliver to Mail 

address above between 9 a.m. and 5 

p.m., Monday through Friday, except 

Federal holidays. 

AD Docket: You may examine the AD 

docket at regulations.gov under Docket 

No. FAA–2023–2236; 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 NPRM, any comments 

received, and other information. The 

street address for Docket Operations is 

listed above. 

Material Incorporated by Reference: 

• For service information identified 

in this NPRM, 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 by searching for and 

locating Docket No. FAA–2023–2236. 

FOR FURTHER INFORMATION CONTACT: Luis 

Cortez-Muniz, Aviation Safety Engineer, 

FAA, 2200 South 216th St., Des Moines, 

WA 98198; telephone 206–231–3958; 

email: luis.a.cortez-muniz@faa.gov. 

SUPPLEMENTARY INFORMATION: 

Comments Invited 

The FAA invites you to send any 

written relevant data, views, or 

arguments about this proposal. Send 

your comments to an address listed 

under ADDRESSES. Include ‘‘Docket No. 

FAA–2023–2236; Project Identifier AD– 

2023–00962–T’’ at the beginning of your 

comments. The most helpful comments 

reference a specific portion of the 

proposal, explain the reason for any 

recommended change, and include 

supporting data. The FAA will consider 

all comments received by the closing 

date and may amend this proposal 

because of those comments. 

Except for Confidential Business 

Information (CBI) as described in the 

following paragraph, and other 

information as described in 14 CFR 

11.35, the FAA will post all comments 

received, without change, to 

regulations.gov, including any personal 

information you provide. The agency 

will also post a report summarizing each 

substantive verbal contact received 

about this NPRM. 

Confidential Business Information 

CBI is commercial or financial 

information that is both customarily and 

actually treated as private by its owner. 

Under the Freedom of Information Act 

(FOIA) (5 U.S.C. 552), CBI is exempt 

from public disclosure. If your 

comments responsive to this NPRM 

contain commercial or financial 

information that is customarily treated 

as private, that you actually treat as 

private, and that is relevant or 

responsive to this NPRM, it is important 

that you clearly designate the submitted 

comments as CBI. Please mark each 

page of your submission containing CBI 

as ‘‘PROPIN.’’ The FAA will treat such 

marked submissions as confidential 

under the FOIA, and they will not be 

placed in the public docket of this 

NPRM. Submissions containing CBI 

should be sent to Luis Cortez-Muniz, 

Aviation Safety Engineer, FAA, 2200 

South 216th St., Des Moines, WA 98198; 

telephone 206–231–3958; email: 

luis.a.cortez-muniz@faa.gov. Any 

commentary that the FAA receives that 

is not specifically designated as CBI will 

be placed in the public docket for this 

rulemaking. 

Background 

The FAA received two reports of 

engine events that resulted in the 

separation of engine inlet cowl and fan 

cowl parts from the airplane. One event 

occurred in August 2016 on a Boeing 

Model 737–700 series airplane powered 

by a CFM56–7B engine. The left engine 

failed due to the FBO but the airplane 

landed successfully. The second event 

occurred on April 17, 2018, on a Boeing 

Model 737–700 series airplane powered 

by a CFM56–7B engine. In that event, an 

FBO occurrence resulted in the release 

of fan cowl parts and the engine cowling 

departing the airplane. The fan cowl 

parts damaged the fuselage, which 

caused loss of pressurization and 

subsequent emergency descent. 

Although the airplane landed safely, 

there was one passenger fatality. In that 

event, the suspected cause of the FBO 

occurrence was a low-cycle fatigue 

crack in the dovetail of fan blade 

number 13 of engine number 1. The 

broken fan blade hit the engine fan case 

at a critical location causing a 

significant impulse, displacement, and 


ddrumheller on DSK120RN23PROD with PROPOSALS1