DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2021-0546; Project Identifier MCAI-2021-00387-P]
RIN 2120-AA64

Airworthiness Directives; Hoffmann GmbH & Co. KG Propellers

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: The FAA proposes to supersede Airworthiness Directive (AD)
2020-25-05, which applies to all Hoffmann GmbH & Co. KG (Hoffmann)
model HO-V 72 propellers. AD 2020-25-05 requires amending the existing
aircraft flight manual (AFM) with abnormal propeller vibration
instructions. AD 2020-25-05 also requires visual inspection and non-
destructive test (NDT) inspection of the propeller hub and, depending
on the results of the inspections, replacement of the propeller hub
with a part eligible for installation. AD 2020-25-05 also requires
replacement of the propeller hub before exceeding 30 years since the
date of manufacture. Since the FAA issued AD 2020-25-05, analyses of
the inspection results showed that the 30-year life limit of the
propeller hub is no longer needed. This proposed AD would retain
certain requirements of AD 2020-25-05 and remove the 30-year life limit
of the propeller hub. 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 August 20,
2021.

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.

For service information identified in this NPRM, contact Hoffmann
GmbH & Co. KG, Kupferlingstrasse 9, 83022, Rosenheim, Germany;
phone: +49 0 8031 1878 0; email: info@hoffmann-prop.com; website:
https://hoffmann-prop.com. You may view this service information at the
FAA, Airworthiness Products Section, Operational Safety Branch, 1200
District Avenue, Burlington, MA 01803. For information on the
availability of this material at the FAA, call (781) 238-7759.

Examining the AD Docket

You may examine the AD docket at https://www.regulations.gov by
searching for and locating Docket No. FAA-2021-0546; 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.

FOR FURTHER INFORMATION CONTACT: Michael Schwetz, Aviation Safety
Engineer, Boston ACO Branch, FAA, 1200 District Avenue, Burlington, MA
01803; phone: (781) 238-7761; fax: (781) 238-7199; email:
michael.schwetz@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 ADDRESSES. Include "Docket No. FAA-2021-0546; Project Identifier
MCAI-2021-00387-P" 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
the proposal 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 receive about this proposed AD.

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
Michael Schwetz, Aviation Safety Engineer, Boston ACO 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

The FAA issued AD 2020-25-05, Amendment 39-21347 (85 FR 78702,
December 7, 2020), (AD 2020-25-05), for all Hoffmann model HO-V 72
propellers. AD 2020-25-05 was prompted by reports of cracks at
different positions on two affected propeller hubs. AD 2020-25-05
requires amending the existing AFM with abnormal propeller vibration
instructions. AD 2020-25-05 also requires visual inspection and NDT
inspection of the propeller hub and, depending on the results of the
inspections, replacement of the propeller hub with a part eligible for
installation. AD 2020-25-05 also requires replacement of the propeller
hub before exceeding 30 years since the date of manufacture or within
30 days after the effective date of AD 2020-25-05, whichever occurs
later. The agency issued AD 2020-25-05 to prevent failure of the
propeller hub.

Actions Since AD 2020-25-05 Was Issued

Since the FAA issued AD 2020-25-05, the European Union Aviation
Safety Agency (EASA), which is the Technical Agent for the Member
States of the European Community, has issued EASA AD 2020-0226R1, dated
March 31, 2021 (referred to after this as "the MCAI"), to address the
unsafe condition on these products. The MCAI states:

Cracks have been reported at different positions on two affected
parts, both installed on Slingsby T67 "Firefly" aeroplanes. One
crack was found during scheduled inspection, the other crack during
an unscheduled inspection after abnormal vibrations occurred. Both
cases are under investigation by Hoffmann Propeller.

This condition, if not detected and corrected, could lead to in-
flight propeller detachment, possibly resulting in damage to the
airplane and/or injury to persons on the ground.

To address this potential unsafe condition, Hoffmann issued the
SB, providing applicable instructions.

For the reasons described above, EASA issued Emergency AD 2020-
0226-E to require inspections of affected parts and, depending on
findings, replacement, and introduces a life limit for affected
parts. That [EASA] AD also required, for certain aeroplanes,
amendment of the applicable Aircraft Flight Manual (AFM).

Since that [EASA] AD was issued, recent analyses of inspection
results showed that the life limit of 30 years is no longer
necessary and Hoffmann Propeller issued Revision D of the SB
accordingly.

This [EASA] AD is revised to delete the life limit and to
introduce a clarification for corrective action(s) during overhaul
in paragraph (6) [of EASA AD].

You may obtain further information by examining the MCAI in the AD
docket at https://www.regulations.gov by searching for and locating
Docket No. FAA-2021-0546.

In addition, Hoffmann issued Service Bulletin SB E53, Rev. D, dated
February 18, 2021, to no longer specify that the propeller hub be
replaced before exceeding 30 years since the date of manufacture.

FAA's Determination

This product has been approved by EASA and is approved for
operation in the United States. Pursuant to the FAA's bilateral
agreement with the European Community, EASA has notified the FAA of the
unsafe condition described in the MCAI and service information. The FAA
is issuing this NPRM because the agency evaluated all the relevant
information provided by EASA and determined the unsafe condition
described previously is likely to exist or develop in other products of
the same type design.

Related Service Information Under 1 CFR Part 51

The FAA reviewed Hoffmann Propeller GmbH & Co. KG Service Bulletin
SB E53, Rev. D, dated February 18, 2021. This service information
specifies procedures for visual and NDT inspections of the propeller
hub for cracks. 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.

Proposed AD Requirements in This NPRM

This proposed AD would retain certain requirements of AD 2020-25-
05. This proposed AD would no longer require that the propeller hub be
replaced before exceeding 30 years since the date of manufacture or
within 30 days after the effective date of AD 2020-25-05.

Differences Between the Proposed AD and MCAI or Service Information

EASA AD 2020-0226R1, dated March 31, 2021, applies to Hoffmann HO-V
72 propellers with propeller hub HO-V 72 ( ) ( )-( )-( ) that have been
used or are expected to be used for aerobatic maneuvers. This proposed
AD applies to all Hoffmann model HO-V 72 propellers regardless of their
use.

Hoffmann Propeller GmbH & Co. KG Service Bulletin SB E53, Rev. D,
dated February 18, 2021, specifies that operators must send any
propeller found with a crack to Hoffmann for investigation. The service
bulletin also specifies that operators must report any propeller with
cracked hubs to Hoffmann. This proposed AD does not mandate sending the
propeller or information to Hoffmann.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would
affect 35 propellers installed on airplanes of U.S. registry.

The FAA estimates the following costs to comply with this proposed AD:

Estimated Costs

The FAA estimates the following costs to do any necessary
replacement that would be required based on the results of the proposed
inspection. The agency has no way of determining the number of aircraft
that might need this replacement:

On-Condition 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 be-
cause it addresses an unsafe condition that is likely to exist or develop
on products identified in this rulemaking action.

Regulatory Findings

The FAA has 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 that the proposed
regulation:

(1) Is not a "significant regulatory action" under Executive
Order 12866,

(2) Would not affect intrastate aviation in Alaska, and

(3) Would 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:

a. Removing Airworthiness Directive AD 2020-25-05, Amendment 39-21347
(85 FR 78702, December 7, 2020); and

b. Adding the following new airworthiness directive: