[Federal Register Volume 90, Number 159 (Wednesday, August 20, 2025)]
[Rules and Regulations]
[Pages 40529-40531]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2025-15839]
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Rules and Regulations
Federal Register
________________________________________________________________________
This section of the FEDERAL REGISTER contains regulatory documents
having general applicability and legal effect, most of which are keyed
to and codified in the Code of Federal Regulations, which is published
under 50 titles pursuant to 44 U.S.C. 1510.
The Code of Federal Regulations is sold by the Superintendent of Documents.
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Federal Register / Vol. 90, No. 159 / Wednesday, August 20, 2025 /
Rules and Regulations
[[Page 40529]]
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA-2024-2555; Project Identifier AD-2024-00214-R;
Amendment 39-23089; AD 2025-15-02]
RIN 2120-AA64
Airworthiness Directives; Siam Hiller Holdings, Inc.
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 Siam Hiller Holdings, Inc. (Siam Hiller), Model UH-12E (Army
OH-23G and H-23F) and UH-12E-L helicopters. This AD was prompted by
reports of cracks found in a main rotor (M/R) transmission drive shaft
(drive shaft). This AD requires inspecting certain M/R drive shafts for
a crack, prohibits installing certain M/R drive shafts unless the
inspection is done, and prohibits using certain paint strippers. The
FAA is issuing this AD to address the unsafe condition on these
products.
DATES: This AD is effective September 24, 2025.
ADDRESSES:
AD Docket: You may examine the AD docket at regulations.gov under
Docket No. FAA-2024-2555; or in person at Docket Operations between 9
a.m. and 5 p.m., Monday through Friday, except Federal holidays. The AD
docket contains this final rule, any comments received, and other
information. The address for Docket Operations is U.S. Department of
Transportation, Docket Operations, M-30, West Building Ground Floor,
Room W12-140, 1200 New Jersey Avenue SE, Washington, DC 20590.
FOR FURTHER INFORMATION CONTACT: Eduardo Orozco-Duran, Aviation Safety
Engineer, FAA, 3960 Paramount Boulevard, Lakewood, CA 90712; phone:
(562) 627-5264; 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 Siam Hiller
Model UH-12E (Army OH-23G and H-23F) and UH-12E-L helicopters. The NPRM
was published in the Federal Register on January 14, 2025 (90 FR
03046). The NPRM was prompted by reports of two cracks in an M/R drive
shaft that were found during an inspection involving a Siam Hiller
Model UH-12E helicopter. In the NPRM, the FAA proposed to require
inspecting certain M/R drive shafts for a crack, prohibit installing
certain M/R drive shafts unless the inspection is done, and prohibit
using certain paint strippers. The FAA is issuing this AD to address
non-conforming parts and the use of improper paint stripper; and to
detect cracking of the M/R drive shaft. The unsafe condition, if not
addressed, could result in separation of the M/R drive shaft and M/R
blades from the helicopter and consequent loss of control of the
helicopter.
Discussion of Final Airworthiness Directive
Comments
The FAA received comments from Summit Helicopters, Inc (Summit
Helicopters). The following presents the comments received on the NPRM
and the FAA's response to each comment.
Request To Extend Compliance Times
Summit Helicopters stated the compliance time proposed in the NPRM
would create significant economic impact for their company and is
requesting an additional time margin to be added for the required
inspections. The commenter stated that the time required to perform
these inspections, as proposed in the NPRM, is significantly short of
the actual time it would take to perform these inspections. Summit
Helicopters requested to be able to delay inspection until November
2025 or extend compliance to the next scheduled overhaul inspection.
Additionally, the commenter provided a detailed explanation of the
actions that would be required to comply with the actions of the AD.
The FAA agrees to revise the initial compliance time to be within 4
years of the effective date of this AD or at the next M/R transmission
assembly overhaul inspection after the effective date of this AD,
whichever comes first.
Request To Revise Cost
Summit Helicopters stated that the cost of the actions proposed in
the NPRM did not include the costs of baking, shipping, and other
precondition tasks such as the removal, reinstallation, and reassembly
of the M/R drive shaft. Summit Helicopters requested changes to the
cost of compliance to include the above costs. Summit Helicopters
commented that the removal and reinstallation process would take at
least an additional 11.5 hours. In addition, Summit Helicopters has
also commented that, based on operator experience, the labor work-hours
required to strip, bake, inspect, prime, and paint will take
approximately 6.5 hours instead of 5 hours.
The FAA partially agrees. The FAA disagrees with providing cost
information for shipping, handling, and transportation, or pre-
condition tasks such as removal, reinstallation, and reassembly. The
cost information specified in the proposed AD describes only the direct
costs of the specific actions required by this AD. Based on the best
data available, the manufacturer provided the number of work-hours
necessary to do the required actions. This number represents the time
necessary to perform only the actions actually required by this AD. The
FAA recognizes that, in doing the actions required by an AD, operators
might incur incidental costs in addition to the direct costs. The cost
analysis in AD rulemaking actions, however, typically does not include
incidental costs such as the time necessary for planning or time
necessitated by other administrative actions. Those incidental costs
might vary significantly among operators. In addition, the total amount
of work-hours will only account for the total work-hours for the
corrective actions and not the 11.5 work-hours required for pre-
condition tasks and the 24 work-hours associated with relief baking
span time. As stated previously, it is also important to note that
special
[[Page 40530]]
flight permits are allowed in the AD, therefore operators are allowed
to transport their helicopters to any repair facility to have these
actions performed. However, the FAA agrees to update the cost of
compliance to reflect an accurate estimate due to Summit Helicopter
experience of work-hours required to perform corrective actions to
paint strip, relief bake, inspect, prime and paint. The FAA also
accepts the provided estimate as our initial analysis did not consider
the availability of outsized ovens and will assume that it is $1,850
for each shaft. Therefore, the FAA is updating the cost to be up to
$1,850 based on the size of the oven and increasing the total work-
hours from 5 work-hours to 6.5 work-hours.
Request To Remove the Requirement To Use Certain Materials
Summit Helicopters requested that the FAA provide additional
specifications that meet the requirements of paint strippers with
specifications TT-R-248B and TT-R-2918A Type I. The commenter stated
that during its initial search, it was difficult to find paint stripper
with specifications TT-R-248B and TT-R-2918A Type I. Summit Helicopters
suggested replacing the requirement for the use of the specified paint
stripper with one more readily available.
The FAA disagrees with Summit Helicopters' request to provide
additional specifications that meet the need for non-embrittling paint
stripper, other than a paint stripper with specifications TT-R-248B or
TT-R-2918A Type I because certain paint strippers used in aviation
maintenance can pose risks to aircraft materials and structural
integrity. Additionally, the FAA provides maintenance and safety
guidelines for aircraft paint removal processes to prevent structural
damage and ensure airworthiness, which can be found in documents such
as Federal Specification TT-R-248B or TT-R-2918A Type I. Operators that
prefer to accomplish this action by means other than those specified in
this AD may submit an alternative method of compliance, as indicated in
paragraph (i) of this final rule. However, the FAA did revise the
reference to the paint stripper specifications in paragraphs (g)(1) and
(h)(2) of this AD to remove the revision letter from the number, in an
effort to improve search results for operators.
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
any 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.
Costs of Compliance
The FAA estimates that this AD affects 110 helicopters of U.S.
registry. Labor costs are estimated at $85 per hour. Based on these
numbers, the FAA estimates the following costs to comply with this AD.
Removing the coatings, hydrogen embrittlement relief baking, and
magnetic particle inspecting the M/R drive shaft takes 6.5 work-hours
and parts cost up to $1,850 for an estimated cost of $2,402.50 per
helicopter and $264,275 for the U.S. fleet. If required, replacing the
M/R drive shaft takes 5 work-hours and parts cost $15,000 for an
estimated cost of $15,425 per helicopter.
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:
2025-15-02 Siam Hillar Holdings, Inc.: Amendment 39-23089; Docket
No. FAA-2024-2555; Project Identifier AD-2024-00214-R.
(a) Effective Date
This airworthiness directive (AD) is effective September 24,
2025.
(b) Affected ADs
None.
(c) Applicability
This AD Applies to Siam Hiller Holdings, Inc., Model UH-12E
(Army OH-23G and H-23F) and UH-12E-L helicopters, certificated in
any category, with a main rotor (M/R) transmission drive shaft
(drive shaft) having part number (P/N) 23600 installed.
Note 1 to paragraph (c): Hiller Aircraft Corporation Main Rotor
Transmission Assembly Overhaul Manual, Manual 63-20, for UH-12E
Series Helicopters, accepted May 6, 2015, contains additional
information pertaining to inspecting the M/R drive shaft and refers
to an M/R drive shaft as a transmission M/R mast and M/R drive
shaft, interchangeably.
(d) Subject
Joint Aircraft System Component (JASC) Code 6230, Main Rotor
Mast/Swashplate.
(e) Unsafe Condition
This AD was prompted by reports of cracks in the M/R drive
shaft. The FAA is issuing this AD to address non-conforming parts
and the use of improper paint stripper; and to detect cracking of
the M/R drive shaft. The unsafe condition, if not addressed, could
result in separation of the M/R drive shaft and M/R blades from the
helicopter and consequent loss of control of the helicopter.
[[Page 40531]]
(f) Compliance
Comply with this AD within the compliance times specified,
unless already done.
(g) Required Actions
At the next overhaul inspection of the M/R transmission assembly
or within 4 years after the effective date of this AD, whichever
comes first, with the M/R drive shaft removed, inspect the M/R drive
shaft by accomplishing the actions required by paragraphs (g)(1)
through (3) of this AD.
(1) Remove all coatings from all surfaces of the M/R drive shaft
by using paint stripper TT-R-248 or TT-R-2918 Type I.
(2) Hydrogen embrittlement relief bake the M/R drive shaft for
24 hours minimum at 375 [deg]F 25 [deg]F.
(3) Magnetic particle inspect all surfaces of the M/R drive
shaft for a crack. If there is a crack, before further flight,
remove the M/R drive shaft from service and install an airworthy M/R
drive shaft.
Note 2 to paragraph (g): Hiller Aircraft Corporation Main Rotor
Transmission Assembly Overhaul Manual, Manual 63-20, for UH-12E
Series Helicopters, accepted May 6, 2015, contains additional
information pertaining to inspecting the M/R drive shaft, applying
appropriate coatings to the M/R drive shaft, and returning the
helicopter to service.
(h) Parts Installation Limitations
(1) As of the effective date of this AD, do not install an M/R
drive shaft having P/N 23600 on any helicopter unless the actions
required by paragraphs (g)(1) through (3) of this AD have been
accomplished.
(2) As of the effective date of this AD, do not use any paint
stripper other than TT-R-248 or TT-R-2918 Type I to remove coatings
from all areas of the M/R drive shaft.
(i) Alternative Methods of Compliance (AMOCs)
(1) The Manager, West 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 West Certification Branch, send it to
the attention of the person identified in paragraph (j)(1) of this
AD and email 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
(1) For more information about this AD, contact Eduardo Orozco-
Duran, Aviation Safety Engineer, FAA, 3960 Paramount Boulevard,
Lakewood, CA 90712; phone: (562) 627-5264; email: [email protected].
(2) For Hiller Aircraft Corporation material identified in this
AD that is not incorporated by reference, contact Hiller Aircraft
Corporation, 925 M Street, Firebaugh, CA 93622; phone: (559) 659-
5959; or website: hilleraircraftcorporation.com/.
(k) Material Incorporated by Reference
None.
Issued on August 15, 2025.
Steven W. Thompson,
Acting Deputy Director, Compliance & Airworthiness Division, Aircraft
Certification Service.
[FR Doc. 2025-15839 Filed 8-19-25; 8:45 am]
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