Airworthiness Directives; Bell Textron Inc., Helicopters, 38841-38846 [2024-09573]

Agencies

• Federal Aviation Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 89, Number 90 (Wednesday, May 8, 2024)]
[Proposed Rules]
[Pages 38841-38846]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-09573]


========================================================================
Proposed Rules
                                                Federal Register
________________________________________________________________________

This section of the FEDERAL REGISTER contains notices to the public of 
the proposed issuance of rules and regulations. The purpose of these 
notices is to give interested persons an opportunity to participate in 
the rule making prior to the adoption of the final rules.

========================================================================


Federal Register / Vol. 89, No. 90 / Wednesday, May 8, 2024 / 
Proposed Rules

[[Page 38841]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2024-0768; Project Identifier AD-2022-00504-R]
RIN 2120-AA64


Airworthiness Directives; Bell Textron Inc., Helicopters

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 Bell Textron Inc., Model 212, 412, 412CF, and 412EP 
helicopters. This proposed AD was prompted by reports of cracked tail 
boom attachment barrel nuts (barrel nuts). This proposed AD would 
require replacing all steel alloy barrel nuts with nickel alloy barrel 
nuts and, replacing or inspecting other tail boom attachment point 
hardware and depending on the results, replacing hardware, stabilizing 
torque, and applying torque stripes. This proposed AD would also 
require repetitively inspecting torque and, depending on the results, 
corrective action. This proposed AD would require repetitively 
replacing the upper left-hand (LH) tail boom attachment bolt (bolt) and 
repetitively inspecting the other tail boom attachment point bolts. 
Lastly, this proposed AD would prohibit installing steel alloy barrel 
nuts. 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 June 24, 
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-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 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 
Bell Textron, Inc., P.O. Box 482, Fort Worth, TX 76101, United States; 
phone (450) 437-2862 or 1-800-363-8023; fax (450) 433-0272; email: 
[email protected]; website: bellflight.com/support/contact-support.
     You may view this service information 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.

FOR FURTHER INFORMATION CONTACT: Jacob Fitch, Aviation Safety Engineer, 
FAA, 1801 S Airport Road, Wichita, KS 67209; telephone (817) 222-4130; 
email [email protected].

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-2024-0768; Project Identifier 
AD-2022-00504-R'' 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 Jacob 
Fitch, Aviation Safety Engineer, FAA, 1801 S Airport Road, Wichita, KS 
67209; telephone (817) 222-4130; email [email protected]. Any 
commentary that the FAA receives which is not specifically designated 
as CBI will be placed in the public docket for this rulemaking.

Background

    The FAA received reports of cracked barrel nuts involving Model 
412EP helicopters. According to Bell Textron Inc., 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 by the same unsafe condition. This 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.

FAA's Determination

    The FAA is issuing this NPRM after determining that the unsafe 
condition described previously is likely to exist or

[[Page 38842]]

develop on other products of these same type designs.

Related Service Information Under 1 CFR Part 51

    The FAA reviewed the following Bell alert service bulletins (ASBs), 
each Revision A, and each dated February 23, 2022. This service 
information 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 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, for certain serial-numbered Bell 
Textron Inc., Model 212, 412CF, 412, and 412EP helicopters, removing 
the upper LH steel alloy barrel nut and bolt from service and replacing 
them with a new nickel alloy barrel nut, retainer, and bolt. For 
certain other serial-numbered Bell Textron Inc., Model 412 and 412EP 
helicopters, this proposed AD would require removing the upper LH steel 
alloy barrel nut from service, visually inspecting the removed upper LH 
steel alloy barrel nut and replacing it with a nickel alloy barrel nut 
and retainer, and either visually inspecting or replacing the upper LH 
bolt. For those serial-numbered Bell Textron Inc., Model 212, 412, 
412CF, and 412EP helicopters, this proposed AD would also require 
removing the upper right-hand (RH), lower LH, and lower RH steel alloy 
barrel nuts, visually inspecting those removed steel alloy barrel nuts, 
and replacing them with new nickel alloy barrel nuts and retainers, and 
either visually 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, this proposed AD 
would 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, this proposed AD would 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, this proposed AD 
would require repetitively replacing the upper LH bolt within a longer-
term compliance time interval by requiring removal of it from service 
and replacing it with a new upper LH bolt. This proposed AD would also 
require, for all applicable helicopters, visually inspecting the other 
three bolts within a longer-term compliance time interval and, 
depending on the results, corrective action. Following accomplishment 
of those actions, this proposed AD would 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, this proposed AD would prohibit installing steel alloy 
barrel nuts on any helicopter.

Differences Between This Proposed AD and the Service Information

    The service information specifies checking torque, whereas this 
proposed AD would require 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 
service information does not specify what to do if the torque on a bolt 
is below the minimum allowable torque limit, whereas this proposed AD 
would require replacing and inspecting certain tail boom attachment 
point hardware, stabilizing the torque of the replaced hardware set, 
and applying a torque stripe.
    This proposed AD would require replacing each upper LH bolt with a 
new (zero total hours time-in-service (TIS)) bolt within a 5,000 hours 
TIS or 5 year threshold, whereas the service information does not 
specify that action. This proposed AD would also require visually 
inspecting the upper RH, lower LH, and lower RH bolts within a 5,000 
hours TIS or 5 year threshold, whereas the service information does not 
specify those actions.

Costs of Compliance

    The FAA estimates that this AD, if adopted as proposed, would 
affect 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 proposed 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 
the torque, and applying torque stripes would 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) 
would be approximately $680. The parts cost for an upper LH bolt would 
be approximately $196 and the parts cost for the other bolts would be 
approximately $89 per bolt. The parts cost to apply torque stripes 
would be a nominal amount. The estimated cost for these actions would 
be up to approximately $1,866 per helicopter.
    For all applicable helicopters, inspecting the torque applied on 
each bolt would 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 would take up to 
approximately 5 work-hours. The parts cost for an upper LH bolt would 
be approximately $196 and the parts cost to apply a torque stripe would 
be a nominal amount. The estimated cost for these actions would be 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 would take up to approximately 
3.5 work-hours for an estimated cost of $298 per other bolt and $31,290 
for the U.S. fleet, per inspection cycle. If required, replacing a bolt 
following that inspection would take a minimal amount of additional 
time and the parts cost would be 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 would take up to approximately 5.5 work-hours 
per failed hardware set. The parts cost for an upper LH bolt would be 
approximately $196 and the parts cost for the other bolts would be 
approximately $89 per bolt. The parts cost to apply a torque stripe 
would be a nominal amount. The estimated cost for these actions would 
be $664 (upper

[[Page 38843]]

LH bolt) or $557 (other bolts), per failed hardware set. If required, 
replacing a barrel nut following that inspection would take a minimal 
amount of additional time and the parts cost for a barrel nut 
(including retainer) would be 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 would take up to approximately 5.5 
work-hours and the parts cost for a barrel nut (including retainer) 
would be approximately $73. The estimated cost for these actions would 
be $541. If required, replacing the bolt following that inspection 
would take a minimal amount of additional time and the parts cost for 
an upper LH bolt would be approximately $196 and the parts cost for the 
other bolts would be 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

    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

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:

Bell Textron Inc.: Docket No. FAA-2024-0768; Project Identifier AD-
2022-00504-R.

(a) Comments Due Date

    The FAA must receive comments on this airworthiness directive 
(AD) by June 24, 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 
30999 inclusive, 31101 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 33213 
inclusive, 34001 through 34036 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 412 and 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) 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 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

[[Page 38844]]

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, 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

[[Page 38845]]

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)

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[GRAPHIC] [TIFF OMITTED] TP08MY24.007

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    (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 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.

[[Page 38846]]

(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 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.

(j) Related Information

    For more information about this AD, contact Jacob Fitch, 
Aviation Safety Engineer, FAA, 1801 S Airport Road, Wichita, KS 
67209; telephone (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 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) 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 service information identified in this AD, contact Bell 
Textron, Inc., P.O. Box 482, Fort Worth, TX 76101, United States; 
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 service information 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 that is 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 March 22, 2024.
Victor Wicklund,
Deputy Director, Compliance & Airworthiness Division, Aircraft 
Certification Service.
[FR Doc. 2024-09573 Filed 5-1-24; 4:15 pm]
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