Airworthiness Directives; Bell Textron Inc. Helicopters, 80724-80729 [2024-22929]

Agencies

• Federal Aviation Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 89, Number 193 (Friday, October 4, 2024)]
[Rules and Regulations]
[Pages 80724-80729]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-22929]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2024-0768; Project Identifier AD-2022-00504-R; 
Amendment 39-22825; AD 2024-16-19]
RIN 2120-AA64


Airworthiness Directives; Bell Textron Inc. Helicopters

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 Bell Textron Inc. Model 212, 412, 412CF, and 412EP helicopters. 
This AD was prompted by reports of cracked tail boom attachment barrel 
nuts (barrel nuts). This AD requires replacing all steel alloy barrel 
nuts with nickel alloy barrel nuts, replacing or inspecting other tail 
boom attachment point hardware, repetitively inspecting torque, and 
repetitively replacing tail boom attachment bolts (bolts). This AD also 
prohibits installing steel alloy barrel nuts. The FAA is issuing this 
AD to address the unsafe condition on these products.

DATES: This AD is effective November 8, 2024.
    The Director of the Federal Register approved the incorporation by 
reference of certain publications listed in this AD as of November 8, 
2024.

ADDRESSES: 
    AD Docket: You may examine the AD docket at regulations.gov under 
Docket No. FAA-2024-0768; 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 Bell material identified in this AD, contact Bell 
Textron Inc., P.O. Box 482, Fort Worth, TX 76101; phone: (450) 437-2862 
or 1-800-363-8023; fax: (450) 433-0272; email: 
[email protected]; or website: bellflight.com/support/contact-support.
     You may view this material at the FAA, Office of the 
Regional Counsel, Southwest Region, 10101 Hillwood Parkway, Room 6N-
321, Fort Worth, TX 76177. For information on the availability of this 
material at the FAA, call (817) 222-5110. It is also available at 
regulations.gov under Docket No. FAA-2024-0768.

FOR FURTHER INFORMATION CONTACT: Jacob Fitch, Aviation Safety Engineer, 
FAA, 1801 S Airport Road, Wichita, KS 67209; phone: (817) 222-4130; 
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 serial-numbered 
Bell Textron Inc. (Bell) Model 212, 412, 412CF, and 412EP helicopters. 
The NPRM published in the Federal Register on May 8, 2024 (89 FR 
38841). The NPRM was prompted by reports of cracked barrel nuts on 
Model 412EP helicopters. According to Bell, the root cause for cracking 
can vary from corrosion damage, high time in service, or hydrogen 
embrittlement. Barrel nut cracking can also cause loss of torque on the 
associated bolt and subsequent bolt cracking. Due to design 
similarities, Model 212, 412, and 412CF helicopters are also affected.
    In the NPRM, the FAA proposed to require, for certain serial-
numbered Model 212, 412CF, 412, and 412EP helicopters, replacing the 
upper left-hand (LH) steel alloy barrel nut and bolt with a new nickel 
alloy barrel nut, retainer, and bolt. For certain other serial-numbered 
Model 412 and 412EP helicopters, the FAA proposed to require removing 
the upper LH steel alloy barrel nut, inspecting the removed upper LH 
steel alloy barrel nut and replacing it with a nickel alloy barrel nut 
and retainer, and either inspecting or replacing the upper LH bolt. For 
those serial-numbered Model 212, 412, 412CF, and 412EP helicopters, the 
FAA also proposed to require removing the upper right-hand (RH), lower 
LH, and lower RH steel alloy barrel nuts, inspecting those removed 
steel alloy barrel nuts and replacing them with new nickel alloy barrel 
nuts and retainers, and either inspecting or replacing the upper RH, 
lower LH, and lower RH bolts. Thereafter for those helicopters, as well 
as for one additional serial-numbered Model 412/412EP helicopter, the 
FAA proposed to require inspecting the torque applied on each bolt to 
determine if the torque has stabilized and, depending on the results, 
replacing and inspecting certain tail boom attachment point hardware 
and repeating the torque inspections, or applying torque stripes. For 
all applicable helicopters, the FAA proposed to require repetitively 
inspecting the torque applied on each bolt within a longer-term 
compliance time interval and, depending on the results, replacing and 
inspecting certain tail boom attachment point hardware and repeating 
the torque inspections and stabilization, or applying torque stripes. 
Additionally, for all applicable helicopters, within a longer-term 
compliance time interval, the FAA proposed to require repetitively 
replacing the upper LH bolt and inspecting the other three bolts and, 
depending on the results, taking corrective action. Following 
accomplishment of those actions, the FAA proposed to require inspecting 
the torque applied on each bolt to determine if the torque has 
stabilized and, depending on the results, replacing and inspecting 
certain tail boom attachment point hardware and repeating the torque 
inspections, or applying torque stripes. Lastly, the FAA proposed to 
prohibit installing steel alloy barrel nuts on any helicopter. The

[[Page 80725]]

FAA is issuing this AD to address the unsafe condition on these 
products.

Discussion of Final Airworthiness Directive

Comments

    The FAA received comments from Bell requesting changes to the 
Differences Between This Proposed AD and the Service Information 
section in the NPRM (the Differences Between This AD and the Referenced 
Material section in this final rule). The following presents the 
comments received on the NPRM and the FAA's response to each comment.

Request To Change the Torque Inspection Nomenclature

    In the NPRM, the FAA explained that while the service information 
specifies checking torque, the proposed AD would require inspecting the 
torque. Bell requested the FAA change the torque inspection to a torque 
check consistent with the terminology in its manuals and in the service 
information required by this AD.
    The FAA disagrees. The FAA's regulatory definition of 
``maintenance'' includes inspections but does not include checks. In 
certain ADs, the FAA uses the term ``check'' in limited situations when 
allowing a pilot to perform actions as an exception to the FAA's 
standard maintenance regulations. For this AD, the specified torque 
verification requirement is a maintenance action that must be performed 
by persons authorized under 14 CFR 43.3. Accordingly, this AD must use 
the term ``inspection.''

Comments Regarding Torque Below Minimum Allowable Limit

    In the NPRM, the FAA explained that for stabilizing the tail boom 
attachment hardware torque, the service information does not specify 
actions for if the torque on a bolt is below the minimum allowable 
torque, and therefore the proposed AD would require several actions. 
Bell stated that certain actions such as replacing the bolt, inspecting 
the associated barrel but, and repeating the torque inspection, are 
mandated by Bell Alert Service Bulletin (ASB) 412-21-187, Revision A, 
dated February 23, 2022, part II (torque stabilization) and part III 
(repetitive longer-term torque inspection) of ASB 412-21-187, Revision 
A, February 23, 2022.
    The torque stabilization procedures in part II of the Bell service 
bulletins specify corrective action if the torque has not stabilized 
after checking the torque up to three times maximum. However, the 
procedures do not specify any corrective action if the torque is below 
the minimum allowable torque limit as a result of any individual 
instance of a torque stabilization inspection. Similarly, the 
repetitive longer-term torque inspection procedures in part III of the 
Bell service bulletins specify additional actions if the torque is 
below the minimum allowable torque limit as a result of an inspection. 
However, the FAA determined that those part III procedures are somewhat 
vague and may be interpreted in more than one way. Thus, this AD 
contains specific actions for addressing torque below the minimum 
limits. The FAA has clarified this explanation in the Differences 
Between This AD and the Referenced Material section of this final rule.

Comment Regarding the 5,000 Hours Time-in-Service (TIS) or 5 Year 
Required Actions

    In the NPRM, the FAA explained the proposed AD would require 
replacing the upper LH bolt and visually inspecting the upper RH and 
lower bolts within 5,000 hours TIS or 5 years, while the service 
information did not contain those actions. Bell stated that its service 
bulletins specify that the maintenance manual will be revised to 
include those actions. Bell also cited the 5,000 hour/5-year inspection 
in the Bell Model 412/412EP Maintenance Manual, Issue 001, dated May 
31, 2023.
    The FAA has revised the Differences Between This AD and the 
Referenced Material in this final rule to explain that the referenced 
material specifies that the 5,000 hours TIS or 5 year threshold actions 
will be incorporated into the maintenance manual.

Additional Changes Made to This Final Rule

    Since the NPRM published, the FAA determined that paragraph (c) of 
the proposed AD incorrectly included some serial-numbered helicopters 
that are not eligible for an FAA airworthiness certificate. Therefore, 
the FAA has revised the applicability of this AD to remove those 
helicopters. The FAA has also updated the model for serial number 37052 
in paragraph (c)(4) of this AD to Model 412EP, since it is currently 
registered as such.

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 
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.

Material Incorporated by Reference Under 1 CFR Part 51

    The FAA reviewed the following Bell ASBs, each Revision A, and each 
dated February 23, 2022. This material specifies procedures for 
replacing the steel alloy barrel nuts with nickel alloy barrel nuts, 
inspecting and replacing the tail boom attachment hardware, stabilizing 
the tail boom attachment hardware torque, applying torque seals, and 
inspecting the torque.
     ASB 212-21-166 for Model 212 helicopters,
     ASB 412-21-187 for Model 412/412EP helicopters, and
     ASB 412CF-21-72 for Model 412CF helicopters.
    This material 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 Referenced Material

    The referenced material specifies checking torque, whereas this AD 
requires inspecting torque because that action must be accomplished by 
persons authorized under 14 CFR 43.3.
    When stabilizing the tail boom attachment hardware torque, the 
referenced material does not clearly specify actions for each time the 
torque is below the minimum limit during any torque stabilization 
inspection, whereas this AD requires replacing and inspecting certain 
tail boom attachment point hardware, stabilizing the torque of the 
replaced hardware set, and applying a torque stripe.
    This AD requires replacing each upper LH bolt with a new (zero 
total hours TIS) bolt and visually inspecting the upper RH, lower LH, 
and lower RH bolts within a 5,000 hours TIS or 5 year threshold, 
whereas the referenced material states that these actions will be 
incorporated into the maintenance manual.

Costs of Compliance

    The FAA estimates that this AD affects 105 helicopters of U.S. 
registry. Labor rates are estimated at $85 per work-hour. Based on 
these numbers, the FAA estimates the following costs to comply with 
this AD.
    For the initial requirements for certain helicopters, replacing the 
four steel alloy barrel nuts with new nickel alloy barrel nuts, 
inspecting or replacing up to four bolts, inspecting and stabilizing

[[Page 80726]]

the torque, and applying torque stripes will take up to approximately 
8.5 work-hours for an estimated labor cost of up to $723. The parts 
cost for the four new nickel alloy barrel nuts (including retainers) is 
approximately $680. The parts cost for an upper LH bolt is 
approximately $196 and the parts cost for the other bolts is 
approximately $89 per bolt. The parts cost to apply torque stripes is a 
nominal amount. The estimated cost for these actions is up to 
approximately $1,866 per helicopter.
    For all applicable helicopters, inspecting the torque applied on 
each bolt will take approximately 1 work-hour for an estimated cost of 
$85 per helicopter and $8,925 for the U.S. fleet, per inspection cycle.
    For all applicable helicopters, replacing an upper LH bolt, 
stabilizing the torque, and applying a torque stripe will take up to 
approximately 5 work-hours. The parts cost for an upper LH bolt is 
approximately $196 and the parts cost to apply a torque stripe is a 
nominal amount. The estimated cost for these actions is up to 
approximately $621 per helicopter and $65,205 for the U.S. fleet, per 
replacement cycle. Inspecting one of the other bolts, stabilizing the 
torque, and applying a torque stripe will take up to approximately 3.5 
work-hours for an estimated cost of $298 per bolt and $31,290 for the 
U.S. fleet, per inspection cycle. If required, replacing a bolt 
following that inspection will take a minimal amount of additional time 
and a parts cost of approximately $89.
    If required as a result of failing a torque inspection, visually 
inspecting a barrel nut, replacing a bolt, stabilizing the torque, and 
applying a torque stripe will take up to approximately 5.5 work-hours 
per failed hardware set. The parts cost for an upper LH bolt is 
approximately $196 and the parts cost for the other bolts is 
approximately $89 per bolt. The parts cost to apply a torque stripe is 
a nominal amount. The estimated cost for these actions is $664 (upper 
LH bolt) or $557 (other bolts), per failed hardware set. If required, 
replacing a barrel nut following that inspection will take a minimal 
amount of additional time with a parts cost for a barrel nut (including 
retainer) of approximately $173.
    If required as a result of failing a torque stabilization, 
replacing a barrel nut, visually inspecting a bolt, stabilizing the 
torque, and applying a torque stripe will take up to approximately 5.5 
work-hours and the parts cost for a barrel nut (including retainer) is 
approximately $73. The estimated cost for these actions is $541. If 
required, replacing the bolt following that inspection will take a 
minimal amount of additional time with a parts cost for an upper LH 
bolt of approximately $196 and a parts cost for the other bolts of 
approximately $89 per bolt.

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.

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:

2024-16-19 Bell Textron Inc.: Amendment 39-22825; Docket No. FAA-
2024-0768; Project Identifier AD-2022-00504-R.

(a) Effective Date

    This airworthiness directive (AD) is effective November 8, 2024.

(b) Affected ADs

    None.

(c) Applicability

    This AD applies to the Bell Textron Inc. helicopters, 
certificated in any category, that are identified in paragraphs 
(c)(1) through (5) of this AD.
    (1) Model 212 helicopters, serial numbers (S/N) 30501 through 
30603 inclusive, 30611 through 30753 inclusive, 30755 through 30889 
inclusive, 30891 through 30999 inclusive, 31101 through 31162 
inclusive, 31164 through 31311 inclusive, 32101 through 32142 
inclusive, and 35001 through 35103 inclusive;
    (2) Model 412CF helicopters, S/N 46400 through 46499 inclusive;
    (3) Model 412 and 412EP helicopters, S/N 33001 to 33078 
inclusive, 33080 through 33129 inclusive, 33131 through 33138 
inclusive, 33150 through 33213 inclusive, 36001 through 36687 
inclusive, 36689 through 36999 inclusive, 37002 through 37018 
inclusive, 37021 through 37051 inclusive, 38001, and 39101 through 
39103 inclusive;
    (4) Model 412EP helicopter, S/N 37052; and
    (5) Model 412 and 412EP helicopters, S/N 36688, 37019, 37020, 
37053 through 37999 inclusive, 38002 through 38999 inclusive, and 
39104 through 39999 inclusive.

(d) Subject

    Joint Aircraft System Component (JASC) Code: 5302, Rotorcraft 
Tail Boom.

(e) Unsafe Condition

    This AD was prompted by reports of cracked tail boom attachment 
barrel nuts (barrel nuts). The FAA is issuing this AD to address 
fatigue cracking of barrel nuts, damage to the tail boom attachment 
bolts (bolts), and certain bolts remaining in service beyond fatigue 
limits. The unsafe condition, if not addressed, could result in 
increased fatigue loading and subsequent failure of the bolts, which 
could lead to separation of the tail boom from the helicopter and 
subsequent loss of control of the helicopter.

(f) Compliance

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

(g) Required Actions

    (1) Within 300 hours time-in-service (TIS) or 90 days after the 
effective date of this AD, whichever occurs first, accomplish the 
actions required by paragraphs (g)(1)(i)

[[Page 80727]]

through (iv) of this AD, as applicable. For purposes of this AD, the 
word ``new'' is defined as having zero total hours TIS.
    (i) For all helicopters identified in paragraphs (c)(1) and (2) 
of this AD; and for helicopters identified in paragraph (c)(3) of 
this AD that have accumulated 5,000 or more total hours TIS or 5 or 
more years since new, or if the total hours TIS or age of the 
helicopter is unknown, remove the upper left-hand (LH) steel alloy 
barrel nut part number (P/N) NAS577B9A and upper LH bolt from 
service and replace them with a new nickel alloy barrel nut P/N 
NAS577C9A, new retainer P/N NAS578C9A, and a new bolt in accordance 
with the Accomplishment Instructions, part I, paragraphs 4 through 
7, of Bell Alert Service Bulletin 212-21-166, Revision A, dated 
February 23, 2022 (ASB 212-21-166 Rev A), Bell Alert Service 
Bulletin 412CF-21-72, Revision A, dated February 23, 2022 (ASB 
412CF-21-72 Rev A), or Bell Alert Service Bulletin 412-21-187, 
Revision A, dated February 23, 2022 (ASB 412-21-187 Rev A), as 
applicable to your helicopter model, except you are not required to 
discard parts.
    (ii) For helicopters identified in paragraph (c)(3) of this AD 
that have accumulated less than 5,000 total hours TIS and less than 
5 years since new, remove the upper LH steel alloy barrel nut P/N 
NAS577B9A, the upper LH bolt, countersunk washer, and plain washers, 
and visually inspect the removed upper LH steel alloy barrel nut for 
cracking. If there is any cracking in the upper LH steel alloy 
barrel nut, before further flight, remove the upper LH bolt from 
service. If the upper LH bolt was not removed from service as a 
result of the upper LH steel alloy barrel nut inspection, visually 
inspect the upper LH bolt for any corrosion, damaged threads, wear, 
and fatigue cracking. If the upper LH bolt has any corrosion, a 
damaged thread, wear, or fatigue cracking, before further flight, 
remove the upper LH bolt from service. Regardless of the result of 
the upper LH steel alloy barrel nut inspection, remove the upper LH 
steel alloy barrel nut from service and replace it with a new nickel 
alloy barrel nut P/N NAS577C9A and new retainer P/N NAS578C9A. 
Install a new upper LH bolt or reinstall the existing upper LH bolt, 
as applicable, by following the Accomplishment Instructions, part I, 
paragraphs 6 and 7, of ASB 412-21-187 Rev A.
    (iii) For helicopters identified in paragraphs (c)(1) through 
(3) of this AD, remove the upper right-hand (RH) steel alloy barrel 
nut P/N NAS577B8A, the upper RH bolt, countersunk washer, and plain 
washers, and visually inspect the removed upper RH steel alloy 
barrel nut for cracking. If there is any cracking in the upper RH 
steel alloy barrel nut, before further flight, remove the upper RH 
bolt from service. If the upper RH bolt was not removed from service 
as a result of the upper RH steel alloy barrel nut inspection, 
visually inspect the upper RH bolt for any corrosion, damaged 
threads, wear, and fatigue cracking. If the upper RH bolt has any 
corrosion, a damaged thread, wear, or fatigue cracking, before 
further flight, remove the upper RH bolt from service. Regardless of 
the result of the upper RH steel alloy barrel nut inspection, remove 
the upper RH steel alloy barrel nut from service and replace it with 
a new nickel alloy barrel nut P/N NAS577C8A and new retainer P/N 
NAS578C8A. Install a new upper RH bolt or reinstall the existing 
upper RH bolt, as applicable, by following the Accomplishment 
Instructions, part I, paragraphs 11 and 12, of ASB 212-21-166 Rev A, 
ASB 412-21-187 Rev A, or ASB 412CF-21-72 Rev A, as applicable to 
your helicopter model.
    (iv) For helicopters identified in paragraphs (c)(1) through (3) 
of this AD, remove one of the lower steel alloy barrel nuts P/N 
NAS577B6A, its lower bolt, countersunk washer, and plain washers, 
and visually inspect the removed lower steel alloy barrel nut for 
cracking. If there is any cracking in the lower steel alloy barrel 
nut, before further flight, remove the lower bolt from service. If 
the lower bolt was not removed from service as a result of the lower 
steel alloy barrel nut inspection, visually inspect the lower bolt 
for any corrosion, damaged threads, wear, and fatigue cracking. If 
the lower bolt has any corrosion, a damaged thread, wear, or fatigue 
cracking, before further flight, remove the lower bolt from service. 
Regardless of the result of the lower steel alloy barrel nut 
inspection, remove the lower steel alloy barrel nut from service and 
replace it with a new nickel alloy barrel nut P/N NAS577C6A and new 
retainer P/N NAS578C6A. Install a new lower bolt or reinstall the 
existing lower bolt, as applicable, by following the Accomplishment 
Instructions, part I, paragraphs 16 and 17, of ASB 212-21-166 Rev A, 
ASB 412-21-187 Rev A, or ASB 412CF-21-72 Rev A, as applicable to 
your helicopter model. Repeat the actions required by this paragraph 
for the other lower tail boom attachment point.
    (2) For helicopters identified in paragraphs (c)(1) through (3) 
of this AD, after accumulating 1 hour TIS, but not to exceed 5 hours 
TIS after accomplishing the actions required by paragraph (g)(1) of 
this AD, using the torque value information in the Accomplishment 
Instructions, part II, paragraph 1, of ASB 212-21-166 Rev A, ASB 
412-21-187 Rev A, or ASB 412CF-21-72 Rev A, as applicable to your 
helicopter model, inspect the torque applied on each bolt. 
Thereafter, repeat the torque inspection of each bolt after 
accumulating 1 hour TIS, but not to exceed 5 hours TIS, to determine 
if the torque has stabilized. Do not exceed three torque inspections 
total for each bolt and accomplish the actions required by 
paragraphs (g)(2)(i) and (ii) of this AD.
    Note 1 to the introductory text of paragraph (g)(2): This note 
applies to the introductory text of paragraph (g)(2), the 
introductory text of paragraph (g)(2)(i), paragraph (g)(2)(i)(B), 
and paragraph (g)(2)(ii) of this AD. The Accomplishment 
Instructions, part II, paragraph 1, of ASB 212-21-166 Rev A, ASB 
412-21-187 Rev A, and ASB 412CF-21-72 Rev A each refer to part I for 
allowable torque limits; part I of ASB 212-21-166 Rev A, ASB 412-21-
187 Rev A, and ASB 412CF-21-72 Rev A specify the different torque 
limits for the different bolts.
    (i) If the torque on a bolt is below the minimum allowable 
torque limit as a result of any instance of the torque inspection or 
if after three torque inspection attempts, the torque on any bolt 
has not stabilized, before further flight, accomplish the actions 
required by paragraphs (g)(2)(i)(A) and (B) of this AD.
    (A) Remove the hardware set of one failed tail boom attachment 
point (barrel nut, retainer, bolt, countersunk washer, and plain 
washers). Remove the barrel nut and retainer from service as 
applicable to the affected tail boom attachment point. Visually 
inspect the removed bolt for any corrosion, damaged threads, wear, 
and fatigue cracking. If the bolt has any corrosion, a damaged 
thread, wear, or fatigue cracking, before further flight, remove the 
bolt from service.
    (B) Install a new bolt or reinstall the existing bolt, as 
applicable, and a new nickel alloy barrel nut P/N NAS577C9A, 
NAS577C8A, or NAS577C6A, and new retainer P/N NAS578C9A, NAS578C8A, 
or NAS578C6A, with the P/N of the new nickel alloy barrel nut and 
the P/N of the new retainer being as applicable to the affected tail 
boom attachment point by following the Accomplishment Instructions, 
part I, paragraphs 6 and 7, paragraphs 11 and 12, or paragraphs 16 
and 17, of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, or ASB 412CF-
21-72 Rev A, as applicable to your helicopter model and with the 
paragraphs as applicable to that bolt. Repeat the actions required 
by paragraphs (g)(2)(i)(A) and (B) of this AD for each failed tail 
boom attachment point, one hardware set at a time. Then repeat the 
actions required by paragraph (g)(2) of this AD just for each newly 
installed or reinstalled bolt until the torque for all four tail 
boom attachment points stabilizes.
    (ii) If the torque for all four tail boom attachment points has 
stabilized, before further flight, apply a torque stripe to all four 
bolts.
    (3) For the helicopter identified in paragraph (c)(4) of this 
AD, within 5 hours TIS after the effective date of this AD, inspect 
the torque applied on each bolt in accordance with the 
Accomplishment Instructions, part II, paragraphs 1 and 2, of ASB 
412-21-187 Rev A. Thereafter, repeat the torque inspection of each 
bolt after accumulating 1 hour TIS, but not to exceed 5 hours TIS, 
to determine if the torque has stabilized. Do not exceed three 
torque inspections total for each bolt and accomplish the actions 
required by paragraphs (g)(2)(i) and (ii) of this AD.
    Note 2 to paragraph (g)(3): The Accomplishment Instructions, 
part II, paragraph 1, of ASB 412-21-187 Rev A refers to part I for 
allowable torque limits; part I of ASB 412-21-187 Rev A specifies 
the different torque limits for the different bolts.
    (4) For helicopters identified in paragraphs (c)(1) through (4) 
of this AD, within 600 hours TIS or 12 months, whichever occurs 
first after applying torque stripes to all four bolts as required by 
paragraph (g)(2)(ii) of this AD, and thereafter within intervals not 
to exceed 600 hours TIS or 12 months, whichever occurs first; and 
for helicopters identified in paragraph (c)(5) of this AD, within 
600 hours TIS or 12 months after the effective date of this AD, 
whichever occurs first, and thereafter within intervals not to 
exceed 600 hours TIS or 12 months,

[[Page 80728]]

whichever occurs first, using the torque value information in the 
Accomplishment Instructions, part II, paragraph 1, of ASB 212-21-166 
Rev A, ASB 412-21-187 Rev A, or ASB 412CF-21-72 Rev A, as applicable 
to your helicopter model, inspect the torque applied on each bolt. 
If the torque on any bolt is below the minimum allowable torque 
limit, accomplish the actions required by paragraphs (g)(4)(i) and 
(ii) of this AD.
    (i) Before further flight, remove the hardware set of one failed 
tail boom attachment point (barrel nut, retainer, bolt, countersunk 
washer, and plain washers). Visually inspect the removed barrel nut 
for cracking, corrosion, and loss of tare torque. If the barrel nut 
has any cracking, corrosion, or has lost any tare toque, before 
further flight, remove the barrel nut and retainer from service and 
replace them with a new nickel alloy barrel nut P/N NAS577C9A, 
NAS577C8A, or NAS577C6A, and new retainer P/N NAS578C9A, NAS578C8A, 
or NAS578C6A, with the P/N of the new nickel alloy barrel nut and 
the P/N of the new retainer being as applicable to the affected tail 
boom attachment point. Regardless of the result of the barrel nut 
inspection, remove the bolt from service and replace it with a new 
bolt by following the Accomplishment Instructions, part I, 
paragraphs 6 and 7, paragraphs 11 and 12, or paragraphs 16 and 17, 
of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, or ASB 412CF-21-72 
Rev A, as applicable to your helicopter model and with the 
paragraphs as applicable to that bolt. Repeat the actions required 
by this paragraph for each failed tail boom attachment point, one 
hardware set at a time.
    (ii) After accumulating 1 hour TIS, but not to exceed 5 hours 
TIS after accomplishing the actions required by paragraph (g)(4)(i) 
of this AD, using the torque value information in the Accomplishment 
Instructions, part II, paragraph 1, of ASB 212-21-166 Rev A, ASB 
412-21-187 Rev A, or ASB 412CF-21-72 Rev A, as applicable to your 
helicopter model, inspect the torque applied on each newly installed 
bolt. Thereafter, repeat the torque inspection of those bolts after 
accumulating 1 hour TIS, but not to exceed 5 hours TIS, to determine 
if the torque has stabilized. Do not exceed three torque inspections 
total for those bolts and accomplish the actions required by 
paragraphs (g)(2)(i) and (ii) of this AD.
    Note 3 to paragraph (g)(4): The Accomplishment Instructions, 
part II, paragraph 1, of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, 
and ASB 412CF-21-72 Rev A, each refer to part I for allowable torque 
limits; part I of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, and 
ASB 412CF-21-72 Rev A, specify the different torque limits for the 
different bolts.
    (5) Within the compliance times specified in Table 1 to the 
introductory text of paragraph (g)(5) of this AD, accomplish the 
actions required by paragraphs (g)(5)(i) through (iv) of this AD.

Table 1 to the Introductory Text of Paragraph (g)(5)
[GRAPHIC] [TIFF OMITTED] TR04OC24.000

    (i) Remove the upper LH bolt from service and replace it with a 
new upper LH bolt by following the Accomplishment Instructions, part 
I, paragraphs 6 and 7, of ASB 212-21-166 Rev A, ASB 412-21-187 Rev 
A, or ASB 412CF-21-72 Rev A, as applicable to your helicopter model. 
Then accomplish the actions required by paragraph (g)(5)(v) of this 
AD.
    Note 4 to paragraph (g)(5)(i): This note applies to paragraphs 
(g)(5)(i) through (v) of this AD. The Accomplishment Instructions, 
part II, paragraph 1, of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, 
and ASB 412CF-21-72 Rev A, each refer to part I for allowable torque 
limits; part I of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, and 
ASB 412CF-21-72 Rev A, specify the different torque limits for the 
different bolts.
    (ii) With the upper RH bolt removed, visually inspect the upper 
RH bolt for any corrosion, damaged threads, wear, and fatigue 
cracking. If the upper RH bolt has any corrosion, a damaged thread, 
wear, or fatigue cracking, before further flight, remove the upper 
RH bolt from service. Install a new

[[Page 80729]]

upper RH bolt or reinstall the existing upper RH bolt, as 
applicable, by following the Accomplishment Instructions, paragraphs 
11 and 12 of ASB 212-21-166 Rev A, ASB 412-21-187 Rev A, or ASB 
412CF-21-72 Rev A, as applicable to your helicopter model. Then 
accomplish the actions required by paragraph (g)(5)(v) of this AD.
    (iii) With the lower LH bolt removed, visually inspect the lower 
LH bolt for any corrosion, damaged threads, wear, and fatigue 
cracking. If the lower LH bolt has any corrosion, a damaged thread, 
wear, or fatigue cracking, before further flight, remove the lower 
LH bolt from service. Install a new lower LH bolt or reinstall the 
existing lower LH bolt, as applicable, by following the 
Accomplishment Instructions, paragraphs 16 and 17 of ASB 212-21-166 
Rev A, ASB 412-21-187 Rev A, or ASB 412CF-21-72 Rev A, as applicable 
to your helicopter model. Then accomplish the actions required by 
paragraph (g)(5)(v) of this AD.
    (iv) With the lower RH bolt removed, visually inspect the lower 
RH bolt for any corrosion, damaged threads, wear, and fatigue 
cracking. If the lower RH bolt has any corrosion, a damaged thread, 
wear, or fatigue cracking, before further flight, remove the lower 
RH bolt from service. Install a new lower RH bolt or reinstall the 
existing lower RH bolt, as applicable, by following the 
Accomplishment Instructions, paragraphs 16 and 17 of ASB 212-21-166 
Rev A, ASB 412-21-187 Rev A, or ASB 412CF-21-72 Rev A, as applicable 
to your helicopter model. Then accomplish the actions required by 
paragraph (g)(5)(v) of this AD.
    (v) After accumulating 1 hour TIS, but not to exceed 5 hours TIS 
after accomplishing the actions required by paragraph (g)(5)(i), 
(ii), (iii), or (iv) of this AD, using the torque value information 
in the Accomplishment Instructions, part II, paragraph 1, of ASB 
212-21-166 Rev A, ASB 412-21-187 Rev A, or ASB 412CF-21-72 Rev A, as 
applicable to your helicopter model, inspect the torque applied on 
each bolt. Thereafter, repeat the torque inspection of those bolts 
after accumulating 1 hour TIS, but not to exceed 5 hours TIS, to 
determine if the torque has stabilized. Do not exceed three torque 
inspections total for those bolts and accomplish the actions 
required by paragraphs (g)(2)(i) and (ii) of this AD.
    (6) For helicopters identified in paragraph (c) of this AD, as 
of the effective date of this AD, do not install a steel alloy 
barrel nut P/N NAS577B9A, P/N NAS577B8A, or P/N NAS577B6A on any 
helicopter.

(h) Special Flight Permit

    A one-time special flight permit may be issued in accordance 
with 14 CFR 21.197 and 21.199 in order to fly to a maintenance area 
to perform the required actions in this AD.

(i) Alternative Methods of Compliance (AMOCs)

    (1) The Manager, Central Certification 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 Central Certification Branch, 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.

(j) Additional Information

    For more information about this AD, contact Jacob Fitch, 
Aviation Safety Engineer, FAA, 1801 S Airport Road, Wichita, KS 
67209; phone: (817) 222-4130; email: [email protected].

(k) Material Incorporated by Reference

    (1) The Director of the Federal Register approved the 
incorporation by reference of the material listed in this paragraph 
under 5 U.S.C. 552(a) and 1 CFR part 51.
    (2) You must use this material as applicable to do the actions 
required by this AD, unless the AD specifies otherwise.
    (i) Bell Alert Service Bulletin 212-21-166, Revision A, dated 
February 23, 2022.
    (ii) Bell Alert Service Bulletin 412-21-187, Revision A, dated 
February 23, 2022.
    (iii) Bell Alert Service Bulletin 412CF-21-72, Revision A, dated 
February 23, 2022.
    (3) For Bell material identified in this AD, contact Bell 
Textron Inc., P.O. Box 482, Fort Worth, TX 76101; phone: (450) 437-
2862 or 1-800-363-8023; fax: (450) 433-0272; email: 
[email protected]; or website: bellflight.com/support/contact-support.
    (4) You may view this material at the FAA, Office of the 
Regional Counsel, Southwest Region, 10101 Hillwood Parkway, Room 6N-
321, Fort Worth, TX 76177. For information on the availability of 
this material at the FAA, call (817) 222-5110.
    (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 [email protected].

    Issued on September 27, 2024.
Victor Wicklund,
Deputy Director, Compliance & Airworthiness Division, Aircraft 
Certification Service.
[FR Doc. 2024-22929 Filed 10-3-24; 8:45 am]
BILLING CODE 4910-13-P