DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. FAA-2017-0052; Product Identifier 2016-SW-081-AD; Amendment
39-21024; AD 2020-02-11]
Airworthiness Directives; Bell Helicopter Textron Inc. Helicopters
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final rule.
SUMMARY: The FAA is superseding Airworthiness Directive (AD) 2015-04-04
for Bell Helicopter Textron Inc. (Bell) Model 412 and 412EP
helicopters. AD 2015-04-04 required revising the Rotorcraft Flight
Manual (RFM) for your helicopter and installing a placard to limit
flights to visual flight rules (VFR) and prohibit night operations
because of failing inverters. This AD requires replacing the affected
inverter with a new inverter. This AD was prompted by numerous failures
of inverters. The FAA is issuing this AD to address the unsafe
condition on these products.
DATES: This AD is effective March 17, 2020.
ADDRESSES: For service information identified in this final rule,
contact Bell Helicopter Textron, Inc., P.O. Box 482, Fort Worth, TX
76101; telephone 817-280-3391; fax 817-280-6466; or at https://www.
bellcustomer.com. You may view this service information at the FAA,
Office of the Regional Counsel, Southwest Region, 10101 Hillwood Pkwy.,
Room 6N-321, Fort Worth, TX 76177.
Examining the AD Docket
You may examine the AD docket on the internet at https://www.regulations.
gov by searching for and locating Docket No. FAA-2017-
0052; 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 AD, the economic evaluation, any comments received, and other
information. The address for Docket Operations is Docket Operations,
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: Tim Beauregard, Aviation Safety
Engineer, DSCO Branch, AIR-7J0, FAA, 10101 Hillwood Pkwy., Fort Worth,
TX 76177; telephone 817-222-5190; email firstname.lastname@example.org.
The FAA issued a notice of proposed rulemaking (NPRM) to amend 14
CFR part 39 to supersede AD 2015-04-04, Amendment 39-18106 (80 FR 9594,
February 24, 2015) (``AD 2015-04-04''). AD 2015-04-04 applied to Bell
Model 412 and 412EP helicopters with a static inverter part number (P/
N) 412-375-079-101 or 412-375-079-103 with a serial number 29145 or
higher installed. The NPRM published in the Federal Register on August
2, 2018 (83 FR 37764). The NPRM was prompted by numerous failures of
inverters and a newly introduced improved inverter, which corrects the
unsafe condition. Bell determined the root causes of the failures were
an external connector that caused a short circuit inside inverter P/N
412-375-079-101 and components chafing because of variations in the
assembly process and packaging tolerances for inverter P/N 412-375-079-
103. Bell introduced an improved inverter, P/N 412-375-079-105, and
retrofit kits to replace inverter P/N 412-375-079-101 or 412-375-079-
103 on helicopters with serial numbers 33001 or higher. These
replacements and repairs correct the unsafe condition by providing 450
voltage amperes (VA) of total power instead of 500 VA, thereby reducing
the input power to the inverter. The NPRM proposed to require these
repairs and replacements. The FAA is issuing this AD to address the
unsafe condition on these products.
After the NPRM was published, The FAA received comments from two
commenters, Bell and Leonardo Helicopters. The following presents the
comments received on the NPRM, and the FAA's response to each comment.
Request: Bell and Leonardo Helicopters requested clarification as
to why the FAA did not indicate that the NPRM applied to helicopters
with static inverters that had a serial number 29145 or higher in the
NPRM's Applicability section. Leonardo Helicopters stated no evidence
exists that static inverters with a serial number lower than 29145 have
the unsafe condition described in the NPRM.
FAA Response: The FAA agrees and has revised this AD to specify
that this AD only applies to static inverters with serial numbers 29145
Request: Bell requested the FAA allow inverter P/N 412-375-079-103
450 VA or P/N 412-375-079-101 450 VA to be replaced by inverter P/N
412-075-158-101 250 VA if the Electrical Load Analysis (ELA)
requirements are met per Bell Alert Service Bulletin 412-16-171, dated
March 22, 2016 (ASB 412-16-171).
FAA Response: The FAA disagrees. ASB 412-16-171 does not have a
standard listed for how to conduct the ELA or the margins that may be
acceptable. Therefore, the FAA could not legally enforce such a
Request: Bell requested the FAA either increase the 25 hours time-
in-service (TIS) compliance time or add an alternate compliance date
because no additional failures have occurred since ASB 412-16-171 was
FAA Response: The FAA disagrees. ASB 412-16-171 set a compliance
time no later than January 1, 2017. The FAA believes that 25 hours TIS
is appropriate given that three years have passed between the deadline
in ASB 412-16-171 and the publication of this final rule.
Request: Bell requested that the FAA correct an error in the NPRM.
The NPRM stated that Bell introduced a new inverter and recommended
repairs that ``correct the unsafe condition by providing 250 VA of
total power instead of 500 VA, thereby reducing the input power to the
inverter.'' Bell stated that ``250 VA'' should be changed to ``450
FAA Response: The FAA agrees and has revised this AD to include the
Request: Bell stated that Bell Alert Service Bulletin 412-13-156,
dated April 25, 2013 (ASB 412-13-156) related to P/N 412-375-079-101 only
that inverter P/N 412-375-079-103 would eventually replace inverter P/N
412-375-079-101 but was not part of ASB 412-13-156's method of
compliance. Bell stated the NPRM did not match the ASB.
FAA Response: The FAA disagrees because ASB 412-13-156's method of
compliance appears to include replacing inverter P/N 412-375-079-101
with inverter P/N 412-375-079-103. Paragraph 9 of ASB 412-13-156
states, ``Remove the affected inverter and replace with inverter P/N
Request: Bell requested that the FAA add more information in the
Discussion paragraph regarding an alternative method of compliance
(AMOC) issued to AD 2015-04-04. Bell requested this information should
include Bell Alert Service Bulletin 412-15-164, dated March 13, 2015
(ASB 412-15-164), which was issued to notify individuals that an AMOC
to AD 2015-04-04, was available. Bell ASB 412-15-164 specifies the FAA-
approved AMOC, which allows instrument flight rules (IFR) and night
operations provided the helicopter is flown by two pilots.
FAA Response: The FAA agrees and has revised the information in the
Related Service Information section.
Request: Bell requested the FAA clarify a statement in the NPRM
that Bell notified the FAA that ASB 412-16-171 contained errors in the
serial numbers listed in Part B.
FAA Response: The FAA agrees. The FAA noticed an error in the
serial numbers listed in ASB 412-16-171, Part B, and reached out to
Bell for clarification. The FAA received an email from Bell dated
August 29, 2017, confirming the existence of an error. The email from
Bell stated: ``There is an error in Part B. According to the
`Helicopters Affected' block, helicopters 36696 through 36999 and 37013
through subsequent have the intent of the bulletin accomplished prior
to delivery therefore, Part B should read: Part B is applicable to
helicopters 36248 through 36695 and 37002 through 37012.''
The FAA has reviewed the relevant information and determined that
an unsafe condition exists and is likely to exist or develop on other
helicopters of these same type designs and that air safety and the
public interest require adopting the AD requirements as proposed with
the changes described previously. These changes are consistent with the
intent of the proposals in the NPRM and will not increase the economic
burden on any operator nor increase the scope of the AD.
Related Service Information
The FAA reviewed Bell ASB 412-15-164, which specifies an AMOC
approved by the FAA for AD 2015-04-04. Instead of the flight
limitations mandated by AD 2015-04-04, ASB 412-15-164 limits allow
operation under IFR and night operations with two pilots.
The FAA reviewed Bell ASB 412-16-171, which specifies replacing
certain serial-numbered inverters P/N 412-375-079-101 and 412-375-079-
103 with inverter P/N 412-375-079-105 as a direct replacement or with
retrofit kit. Bell specifies that completing the actions specified by
the ASB constitute terminating action for Bell ASB 412-15-164.
The FAA also reviewed Bell Service Instruction for Inverter
Retrofit Kit BHT-412-SI-93, dated February 15, 2016, which provides
instructions for installing retrofit kit P/N 412-704-058-103.
Costs of Compliance
The FAA estimates that this AD affects 73 helicopters of U.S.
Registry. The FAA estimates that operators may incur the following
costs in order to comply with this AD. Labor costs are estimated at $85
Installing an inverter or retrofit kit requires about 3 work-hours
and parts cost about $15,749, for an estimated cost of $16,004 per
helicopter and $1,168,292 for the U.S. fleet.
Differences Between This AD and the Service Information
Bell ASB 412-16-171 requires compliance no later than January 1,
2017, while this AD requires compliance within 25 hours TIS. Bell ASB
412-16-171 makes an ELA a determining factor for corrective actions.
This proposed AD makes no such requirement. Bell ASB 412-16-171
provides instructions for helicopters with serial numbers 36649, 36658,
36659, 36673, 36681 through 36684, 36686, 36688, 36690, 36692, 36694,
and 36696 through 36704, and this AD does not. Bell has notified the
FAA of errors in the S/Ns listed for Part B of ASB 412-16-171.
Accordingly, this AD is only applicable to those serial-numbered
helicopters subject to the unsafe condition.
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.
The FAA has determined that 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
(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.
The FAA prepared an economic evaluation of the estimated costs to
comply with this AD and placed it in the AD docket.
List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by
Adoption of 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 removing Airworthiness Directive (AD)
2015-04-04, Amendment 39-18106 (80 FR 9594, February 24, 2015), and
adding the following new AD: