DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2021-0728; Project Identifier MCAI-2020-00656-R;
Amendment 39-21867; AD 2021-26-08]
RIN 2120-AA64

Airworthiness Directives; Bell Textron Canada Limited 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 Canada Limited Model 206, 206A, 206A-1, 206B,
206B-1, 206L, 206L-1, 206L-3, and 206L-4 helicopters. This AD was
prompted by reports of cracked or missing nuts on the tail rotor drive
shaft (TRDS) disc pack (Thomas) couplings. This AD requires removing
certain nuts from service, installing newly designed nuts, and applying
a specific torque and a torque stripe to each newly installed nut. This
AD then requires, after the installation of each newly designed nut,
inspecting the torque and, depending on the inspection results, either
applying a torque stripe or performing further inspections and removing
certain parts from service. Finally, this AD prohibits installing any
affected nut on any TRDS Thomas coupling. The FAA is issuing this AD to
address the unsafe condition on these products.

DATES: This AD is effective January 27, 2022.

The Director of the Federal Register approved the incorporation by
reference of certain documents listed in this AD as of January 27, 2022.

ADDRESSES: For service information identified in this final rule,
contact Bell Textron Canada Limited, 12,800 Rue de l'Avenir, Mirabel,
Quebec J7J 1R4, Canada; telephone 1-450-437-2862 or 1-800-363-8023; fax
1-450-433-0272; email productsupport@bellflight.com; or at
https://www.bellflight.com/support/contact-support. You may view the referenced
service information at the FAA, Office of the Regional Counsel,
Southwest Region, 10101 Hillwood Pkwy., Room 6N-321, Fort Worth, TX
76177. For information on the availability of this material at the FAA,
call (817) 222-5110. Service information that is incorporated by
reference is also available at https://www.regulations.gov by searching
for and locating Docket No. FAA-2021-0728.

Examining the AD Docket

You may examine the AD docket at https://www.regulations.gov by
searching for and locating Docket No. FAA-2021-0728; 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, the
Transport Canada AD, any comments received, and other information. The
street address for Docket Operations is U.S. Department of
Transportation, Docket Operations, M-30, West Building Ground Floor,
Room W12-140, 1200 New Jersey Avenue SE, Washington, DC 20590.

FOR FURTHER INFORMATION CONTACT: Matt Fuller, AD Program Manager,
General Aviation & Rotorcraft Unit, Airworthiness Products Section,
Operational Safety Branch, FAA, 10101 Hillwood Pkwy., Fort Worth, TX
76177; telephone (817) 222-5110; email matthew.fuller@faa.gov.

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 Bell Textron Canada
Limited Model 206, 206A, 206A-1, 206B, 206B-1, 206L, 206L-1, 206L-3,
and 206L-4 helicopters with nut part number (P/N) MS21042L4 or P/N
MS21042L5 installed on the TRDS Thomas couplings. The NPRM published in
the Federal Register on September 14, 2021 (86 FR 51038). In the NPRM,
the FAA proposed to require, within 600 hours time-in-service (TIS)
after the effective date of this AD, removing each affected nut from
service, installing a newly designed nut, and applying a specific
torque and a torque stripe to each newly installed nut. The NPRM also
proposed to require, within 25 hours TIS after installation of each
newly designed nut, inspecting the torque of each nut, and depending on
the results of the inspection, further inspections and removing certain
parts from service. Finally, the NPRM proposed to prohibit installing
any affected nut on any TRDS Thomas coupling.

The NPRM was prompted by a series of ADs issued by Transport
Canada, which is the aviation authority for Canada. Initially,
Transport Canada issued Canadian AD CF-2019-34, dated September 25,
2019 (Transport Canada AD CF-2019-34), to correct an unsafe condition
for Bell Helicopter Textron Canada Limited (now Bell Textron Canada
Limited) Model 206, 206A, 206A-1, 206B, 206B-1, 206L, 206L-1, 206L-3,
and 206L-4 helicopters, all serial numbers. Transport Canada AD
CF-2019-34 advised of reports of cracked or missing nuts at the TRDS
Thomas couplings, which could have been caused by improper torque or
hydrogen embrittlement. This condition, if not addressed, could result
in loss of the tail rotor and subsequent loss of control of the
helicopter.

After Transport Canada issued Transport Canada AD CF-2019-34, it
was determined that helicopters modified in accordance with
Supplemental Type Certificate (STC) SH2750NM or Transport Canada STC
SH99-202, were not able to comply with Transport Canada AD CF-2019-34.
Accordingly, Transport Canada issued AD CF-2020-15, dated May 13, 2020
(Transport Canada AD CF-2020-15) which supersedes Transport Canada AD
CF-2019-34, and contains a new requirement for helicopters with STC
SH2750NM or Transport Canada STC SH99-202 installed or models that have
been modified per Bell Service Instruction BHT-206-SI-2052, Revision 1,
dated October 14, 2010 (BHT-206-SI-2052). Transport Canada advises for
certain model helicopters, the newly designed nuts cannot be installed
because STC SH2750NM and Transport Canada STC SH99-202 install a pulley
at the Thomas coupling location causing insufficient clearance.
Transport Canada further advises for certain model helicopters with STC
SH2750NM or Transport Canada STC SH99-202 installed, different part-
numbered nuts may be installed which were not identified in the
applicable service information and are now required to be replaced with
a new part-numbered nut that is not vulnerable to the unsafe condition.
Accordingly, Air Comm Corporation, the STC holder for STC SH2750NM,
issued new service information to address these additional issues and
provide newly developed instructions which apply to certain model
helicopters with STC SH2750NM or Transport Canada STC SH99-202
installed.

Additionally, Transport Canada advises that BHT-206-SI-2052, which
is optional, specifies procedures for Model 206L-1 and 206L-3
helicopters to upgrade the airframe and systems and also includes
installation of the Model 206L-4 TRDS Thomas coupling. According to
Transport Canada, models that have incorporated BHT-206-SI-2052, with
STC SH2750NM or Transport Canada STC SH99-202 installed, will have the
Model 206L-4 helicopter pulley configuration and are subject to the Air
Comm Corporation service information.

Accordingly, Transport Canada AD CF-2020-15 requires the
replacement of the affected nuts with the newly designed nuts at each
TRDS Thomas coupling.

Discussion of Final Airworthiness Directive

Comments

The FAA received comments from one commenter; Bell. Bell
recommended certain changes pertaining to the torque limits applied to
each newly installed nut and the time for performing the torque
recheck. The following presents the comments received on the NPRM and
the FAA's response to each comment.

Bell commented that the NPRM calls for an initial torque of 50 in/
lb to each nut, whereas the Bell maintenance manual requires an initial
torque of 50-70 in/lb to each nut. Additionally, Bell explained that,
as per its Standards Practice Manual (BHT-ALL-SPM) Chapter 2, tare
torque must also be taken into consideration for self-locking hardware
and that the total assembly torque is the measured tare torque plus the
standard torque or specified torque. Bell requested that the
installation torque in the AD be revised to read 50-70 in/lb.

The FAA agrees that in this instance the maximum initial torque
limit and the tare torque should be consistent with Bell's maintenance
manuals and has revised this AD accordingly.

Bell also commented that the NPRM calls for the torque recheck to
be performed within 25 hours, whereas its maintenance manual requires
the torque recheck between 10-25 hours. Bell recommended that the
torque recheck be done within 25 hours TIS. The FAA agrees with the
comment but no changes to this AD were necessary.

Conclusion

These helicopters have been approved by the aviation authority of
Canada and are approved for operation in the United States. Pursuant to
the FAA's bilateral agreement with Canada, Transport Canada, its
technical representative, has notified the FAA of the unsafe condition
described in its AD. The FAA reviewed the relevant data, considered the
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 helicopters. However, after the NPRM was
published, the FAA discovered that costs were inadvertently excluded in
the NPRM; those costs, which are nominal, are included in this final
rule. Except for minor editorial changes, the change to the costs of
compliance, and any other changes described previously, this AD is
adopted as proposed in the NPRM. None of the changes will significantly
increase the economic burden on any operator.

Related Service Information Under 1 CFR Part 51

The FAA reviewed Bell Alert Service Bulletin 206-19-136, dated
August 27, 2019 for FAA-certificated Model 206, 206A-series, and 206B-
series helicopters and non FAA-certificated Model TH-67 helicopters and
Bell Alert Service Bulletin 206L-19-181, Revision A, dated August 29,
2019 for Model 206L, 206L-1, 206L-3, and 206L-4 helicopters. This
service information specifies procedures for replacing the affected
nuts with the newly designed corrosion-resistant nuts.

This service information is reasonably available because the
interested parties have access to it through their normal course of
business or by the means identified in the ADDRESSES section.

Other Related Service Information

The FAA reviewed Air Comm Corporation Service Bulletin SB 206EC-
092619, Revision NC, dated September 26, 2019, which also specifies
procedures for replacing the affected nuts with the newly designed
corrosion-resistant nuts, but explains that affected helicopters
equipped with Air Comm Corporation air conditioning systems installed
under STC SH2750NM use the affected nut to attach a pulley onto the
TRDS, which causes clearance issues for the nuts to be installed at the
coupling. Therefore, this service bulletin specifies replacing the nut
with a lower profile nut.

The FAA also reviewed BHT-206-SI-2052. This service information
specifies procedures to upgrade Model 206L-1 and 206L-3 helicopters to
allow operations at an increased internal gross weight.

Differences Between This AD and the Transport Canada AD

Transport Canada AD CF-2020-15 requires compliance within 600 hours
air time or within the next 24-months, whichever occurs first, whereas
this AD requires compliance within 600 hours TIS and an additional
inspection within 25 hours TIS after installation of certain nuts.

Costs of Compliance

The FAA estimates that this AD affects 1,439 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.

Replacing each affected nut with the newly designed nut and
applying torque and a torque stripe will take about 4 work-hours, and
parts will cost about $75 for an estimated cost of $415 per nut
replacement and $597,185 per nut replacement for the U.S. fleet.

Checking the torque, and if applicable, applying a torque stripe,
will take a minimal amount of time and have a nominal parts cost. If
required, inspecting each TRDS Thomas coupling, and each bolt, nut, and
washer for elongated holes and fretting on the fasteners will take
about 0.5 work-hour for an estimated cost of $43 per inspection.
Replacing each TRDS Thomas coupling will take about 4 work-hours, and
parts will cost about $4,000 for an estimated cost of $4,340 per TRDS
Thomas coupling replacement. Replacing each nut will take about 4 work-
hours, and parts will cost about $75 for an estimated cost of $415 per
nut replacement. Replacing a bolt or washer will take a minimal amount
of time and parts will cost a nominal amount.

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

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]

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