DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2021-0573; Project Identifier 2018-CE-046-AD; Amendment
39-21822; AD 2021-24-01]
RIN 2120-AA64

Airworthiness Directives; Pilatus Aircraft Ltd. Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: The FAA is adopting a new airworthiness directive (AD) for
Pilatus Aircraft Ltd. (Pilatus) Model PC-12/45, PC-12/47, and PC-12/47E
airplanes with Supplemental Type Certificate (STC) SA00634DE installed.
This AD was prompted by a report of strake attachment brackets and the
fuselage frame failing at the upper most bracket attachment location.
This AD requires inspecting the strake, attachment brackets,
surrounding structure, and bolts and replacing components and repairing
damage if necessary. The FAA is issuing this AD to address the unsafe
condition on these products.

DATES: This AD is effective January 13, 2022.
The Director of the Federal Register approved the incorporation by
reference of a certain publication listed in this AD as of January 13,
2022.

ADDRESSES: For service information identified in this final rule,
contact Pilatus Business Aircraft Ltd., Customer Support Department,
12300 Pilatus Way, Broomfield, CO 80021; phone: (866) 721-2435; fax:
(303) 465-9099; email: productsupport@pilbal.com. You may view this
service information at the FAA, Airworthiness Products Section,
Operational Safety Branch, 901 Locust, Kansas City, MO 64106. For
information on the availability of this material at the FAA, call (816)
329-4148. It is also available at https://www.regulations.gov by
searching for and locating Docket No. FAA-2021-0573.

Examining the AD Docket

You may examine the AD docket at https://www.regulations.gov by
searching for and locating Docket No. FAA-2021-0573; 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: Richard R. Thomas, Aviation Safety
Engineer, Denver ACO Branch, FAA, 26805 E 68th Avenue, Denver, CO
80249; phone: (303) 342-1080; fax: (303) 342-1088; email: 9-Denver-
Aircraft-Cert@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 Pilatus Aircraft Ltd.
Model PC-12/45, PC-12/47, and PC-12/47E airplanes with STC SA00634DE
installed. The NPRM published in the Federal Register on July 22, 2021
(86 FR 38613). The NPRM was prompted by a report of strake attachment
brackets and the fuselage frame failing at the upper most bracket
attachment location. In the NPRM, the FAA proposed to require
inspecting the strake, attachment brackets, and bolts for movement and
damage, both internal and external, and replacing components and
repairing damage if necessary. The FAA is issuing this AD to prevent
buffeting of the strakes. This condition, if not addressed, could
result in airplane flutter and reduced lateral stability, which may
lead to loss of control of the airplane.

Discussion of Final Airworthiness Directive

Comments

The FAA received no comments on the NPRM or on the determination of
the costs.

Differences Between the NPRM and the Final Rule

The FAA has clarified the wording of the required inspections in
paragraph (g) of this AD. This is not a substantive change.

Conclusion

The FAA reviewed the relevant data 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
the changes described previously, this AD is adopted as proposed in the
NPRM. None of the changes will increase the economic burden on any
operator.

Related Service Information Under 1 CFR Part 51

The FAA reviewed Pilatus Service Bulletin PC-12 Series, Report
Number 12-1700-64-0000, Revision B, dated August 10, 2018 (Pilatus
Report 12-1700-64-0000B), which contains procedures for inspection of
all fuselage strake attachment bolts and the surrounding structure.
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.

Differences Between This AD and the Service Information

Pilatus Report 12-1700-64-0000B specifies a one-time inspection
within 10 flight hours of issuance of the service bulletin and
recommends repeat inspections without specifying an inspection
interval. This AD requires repeating the inspection every 150 flight
hours. Pilatus Report 12-1700-64-0000B specifies contacting Pilatus for
further instructions. This AD requires using an FAA-approved repair
method. Pilatus Report 12-1700-64-0000B applies to Pilatus PC-12
aircraft serial numbers 190 to 1575. This AD applies to all Pilatus
Aircraft Ltd. Models PC-12/45, PC-12/47, and PC-12/47E airplanes,
regardless of serial number, if STC SA00634DE is installed.

Interim Action

The FAA considers this AD an interim action. Pilatus is working on
a modification with the intent of minimizing, if not eliminating, the
buffeting of the strakes. Once this action is developed, approved, and
available, the FAA may consider additional rulemaking.

Costs of Compliance

The FAA estimates that this AD affects 30 airplanes of U.S.
registry.
The FAA estimates the following costs to comply with this AD:

Estimated Costs

The extent of damage found during the proposed inspections may vary
considerably from airplane to airplane. The FAA has no way of knowing
how many airplanes may have damage or the extent of damage each
airplane may have.

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: