DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2020-0692; Project Identifier MCAI-2019-00140-E]
RIN 2120-AA64

Airworthiness Directives; Pratt & Whitney Canada Corp. Turboprop Engines

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: The FAA proposes to adopt a new airworthiness directive (AD)
for all Pratt & Whitney Canada Corp. PT6A-34, -34B, -34AG, -114, and -
114A model turboprop engines. This proposed AD was prompted by several
reports of low-time fractures of compressor turbine (CT) blades
resulting in loss of power or in-flight shutdown of the engine. This
proposed AD would require replacement of certain CT vanes. This
proposed AD would also require removal from service of certain CT
blades when these blades have been operated with certain CT vanes. 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 October 1, 2020.

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 https://www.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.

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-2020-
0692; 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, the mandatory continuing airworthiness information (MCAI),
any comments received, and other information. The street address for
Docket Operations is listed above. Comments will be available in the AD
docket shortly after receipt.

FOR FURTHER INFORMATION CONTACT: Barbara Caufield, Aerospace Engineer,
ECO Branch, FAA, 1200 District Avenue, Burlington, MA 01803; phone:
781-238-7146; fax: 781-238-7199; email: barbara.caufield@faa.gov.

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 the ADDRESSES section. Include "Docket No. FAA-2020-0692;
Project Identifier MCAI-2019-00140-E" 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 NPRM 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
https://www.regulations.gov, including any personal information you
provide. The agency will also post a report summarizing each
substantive verbal contact we received about this proposal.

Confidential Business Information

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 Barbara Caufield, Aerospace Engineer, ECO Branch,
FAA, 1200 District Avenue, Burlington, MA 01803. Any commentary that
the FAA receives which is not specifically designated as CBI will be
placed in the public docket for this rulemaking.

Background

Transport Canada, which is the aviation authority for Canada, has
issued Canada AD CF 2019-30R1, dated December 17, 2019 (referred to
after this as "the MCAI"), to address the unsafe condition on these
products. The MCAI states:

There have been several reported events of low time CT blade
fractures resulting in power loss/In-flight shutdown (IFSD) on post
P&WC Service Bulletin (SB) 1669 configured PT6A-114 engines,
featuring new CMSX-6 CT blades. In addition, relatively low time
failures of Non-P&WC CT blades have also been reported on PT6A-34
and -114 series engines.

In service data shows that these low time failures were reported
on engines that had CT vanes installed that were repaired in
accordance with repair specification number STI 72-50-254 held by
Southwest Turbine Inc. (STI). Most of the affected engines are
installed on single-engine powered aeroplanes and some events have
resulted in the loss of the aeroplane and fatalities.

Dimensional checks and operational testing of the subject STI
repaired CT vane removed from an incident engine, revealed that it
did not conform to the engine manufacturer's CT vane type design
criteria. The noted variations and features in the STI repaired CT
vane can cause airflow distortion and subsequent aerofoil excitation
of the CT blades resulting in High Cycle Fatigue (HCF) failure of
the CT blades. Test data indicates that the stress levels induced in
CT blades by the adverse effect of subject airflow distortion
exceeds the design requirements for CMSX-6 CT blades.

An IFSD or loss of power on a single-engine powered aeroplane
under certain conditions can lead to an unsafe condition as seen in
some past events. AD CF-2019-30 was issued on 19 August 2019 to
address the potential hazard of power loss/IFSD as a result of CT
blade failures on engines with CT vanes installed that were repaired
in accordance with repair specification number STI 72-50-254.

This AD revision, CF-2019-30R1, is issued to update the
background information and to clarify the affected P&WC CT blade
Part Numbers (P/Ns).

You may obtain further information by examining the MCAI in the AD
docket on the internet at https://www.regulations.gov by searching for
and locating Docket No. FAA-2020-0692.

FAA's Determination

This product has been approved by the aviation authority of Canada
and is approved for operation in the United States. Pursuant to our
bilateral agreement with Canada, they have notified us of the unsafe
condition described in the MCAI and service information referenced
above. The FAA is issuing this NPRM because we evaluated all the
relevant information provided by Transport Canada and determined the
unsafe condition described previously is likely to exist or develop in
other products of the same type design.

Proposed AD Requirements

This proposed AD would require replacement of certain CT vanes.
This proposed AD would also require removal from service of certain CT
blades when these blades have been operated with certain CT vanes.

Costs of Compliance

The FAA estimates that this proposed AD affects 907 engines
installed on airplanes of U.S. registry. The FAA estimates that 63
engines will need to replace the CT vanes and CT blades.
The FAA estimates the following costs to comply with this proposed
AD:

Estimated Costs

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) 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 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

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 (AD):