DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2012-0354; Directorate Identifier 2010-SW-104-AD]
RIN 2120-AA64

Airworthiness Directives; Eurocopter France Helicopters

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: We propose to adopt a new airworthiness directive (AD) for all
Eurocopter France (EC) Model SA-365N, SA-365N1, SA-366G1, AS-365N2, AS
365 N3, EC 155B, and EC155B1 helicopters. This proposed AD was prompted
by the discovery of a cracked main rotor mast nut. This condition, if
not corrected, could lead to complete failure of the mast nut,
resulting in failure of the rotor mast and loss of control of the
helicopter. This proposed AD would require replacing the main rotor
mast nut with an airworthy main rotor mast nut. We are proposing this
AD to prevent failure of the main rotor mast and subsequent loss of
control of the helicopter.

DATES: We must receive comments on this proposed AD by June 4, 2012.

ADDRESSES: You may send comments by any of the following methods:

Federal eRulemaking Docket: Go to http://www.regulations.gov. Follow the
online instructions for sending your comments electronically.

Fax: 202-493-2251.

Mail: Send comments to the U.S. Department of
Transportation, Docket Operations, M-30, West Building Ground Floor,
Room W12-140, 1200 New Jersey Avenue SE., Washington, DC 20590-0001.

Hand Delivery: Deliver to the "Mail" address 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 http://www.regulations.gov or in person at the Docket
Operations Office between 9 a.m. and 5 p.m., Monday through Friday,
except Federal holidays. The AD docket contains this proposed AD, the
economic evaluation, any comments received, and other information. The
street address for the Docket Operations Office (telephone 800-647-5527)
is in the ADDRESSES section. Comments will be available in the AD docket
shortly after receipt.

For service information identified in this proposed AD, contact
American Eurocopter Corporation, 2701 N. Forum Drive, Grand Prairie, TX
75052, telephone (972) 641-0000 or (800) 232-0323, fax (972) 641-3775,
or at http://www.eurocopter.com/techpub. You may review a copy of the
referenced service information at the FAA, Office of the Regional
Counsel, Southwest Region, 2601 Meacham Blvd., Room 663, Fort Worth,
Texas 76137.

FOR FURTHER INFORMATION CONTACT: Gary Roach, Aviation Safety Engineer,
Regulations and Policy Group, Rotorcraft Directorate, FAA, 2601 Meacham
Blvd., Fort Worth, TX 76137; telephone (817) 222-5110; email
gary.b.roach@faa.gov.

SUPPLEMENTARY INFORMATION:

Comments Invited

We invite you to participate in this rulemaking by submitting
written comments, data, or views. We also invite comments relating to
the economic, environmental, energy, or federalism impacts that might
result from adopting the proposals in this document. The most helpful
comments reference a specific portion of the proposal, explain the
reason for any recommended change, and include supporting data. To
ensure the docket does not contain duplicate comments, commenters
should send only one copy of written comments, or if comments are filed
electronically, commenters should submit only one time.

We will file in the docket all comments that we receive, as well as
a report summarizing each substantive public contact with FAA personnel
concerning this proposed rulemaking. Before acting on this proposal, we
will consider all comments we receive on or before the closing date for
comments. We will consider comments filed after the comment period has
closed if it is possible to do so without incurring expense or delay.
We may change this proposal in light of the comments we receive.

Discussion

The European Aviation Safety Agency (EASA), which is the Technical
Agent for the Member States of the European Union, has issued AD No.:
2006-0368R1, dated December 2, 2010, and corrected December 8, 2010 (AD
2006-0368R1), to correct an unsafe condition for the EC Model SA 365 N,
SA 365 N1, AS 365 N2, AS 365 N3, SA 366 G1, EC 155 B, and EC 155 B1
helicopters. EASA advises that a cracked (partially failed) main rotor
mast nut was discovered during a complete overhaul of a main rotor
mast. The start of the crack was related to circular scoring found in
the nut threads. EASA states that this condition, if not corrected,
"could lead to complete failure of the mast nut, possibly resulting in
failure of the rotor mast and consequent loss of control of the
helicopter." To address this unsafe condition, EASA issued Emergency
AD 2006-0368-E, dated December 6, 2006 (AD 2006-0368-E), to require
repetitive inspections of the mast nut, and replacement of the nut if
cracked. Since issuance of AD 2006-0368-E, EC has developed
modification (MOD) 0762C42 to improve the strength of the mast nut by
changing its material. Replacing mast nut part number (P/N) 360A31-
1020-20 with mast nut P/N 365A31-2060-20 or 365A31-2060-21 (as
applicable to helicopter type) "constitutes an optional terminating
action" for the repetitive inspection requirements. For this reason,
EASA issued AD 2006-0368R1 "to inform which helicopters remain subject
to inspections and replacement requirements" of the AD.

FAA's Determination

We are proposing this AD because we evaluated all known relevant
information and determined that an unsafe condition exists and is
likely to exist or develop on other products of these same type
designs.

Related Service Information

We reviewed EC Alert Service Bulletin (ASB) No. 62.00.23, Revision
1, for Model SA-365N, SA-365N1, AS-365N2, and AS 365 N3 helicopters; EC
ASB 62.12, Revision 1, for Model SA-366G1 helicopters; and EC ASB
62A014, Revision 1, for Model EC 155B and EC155B1 helicopters, all
dated Oct 27, 2010. The ASBs contain procedures for repetitively
inspecting the mast nut for a crack or failure. The ASBs remove any
helicopter with MOD 0762C42 incorporated from the applicability of the
ASB. EASA classified this ASB as mandatory and issued AD 2006-0368R1 to
ensure the continued airworthiness of these helicopters.

Proposed AD Requirements

This proposed AD would require, for EC Model SA-365N, SA-365N1,
SA366G1, AS-365N2, AS 365 N3, EC 155B, and EC155B1 helicopters,
certificated in any category, with a mast nut P/N 360A31-1020-20
installed:

For EC Models SA-365N, SA-365N1, AS-365N2, and AS 365 N3,
prior to accumulating 1,650 hours time-in-service (TIS) or within the
next 50 hours TIS, whichever occurs later, remove mast nut P/N 360A31-
1020-20 and replace with an airworthy mast nut of a different P/N.

For EC Model SA-366G1, prior to accumulating 990 hours TIS
or within the next 30 hours TIS, whichever occurs later, remove mast
nut P/N 360A31-1020-20 and replace with an airworthy mast nut of a
different P/N.

For EC Models EC 155B and EC155B1, prior to accumulating
660 hours TIS or within the next 50 hours TIS, whichever occurs later,
remove mast nut P/N 360A31-1020-20 and replace with an airworthy mast
nut of a different P/N.

Differences Between This Proposed AD and the EASA AD

The EASA AD allows for either inspecting the mast nut at regular
intervals or replacing the mast nut, while the proposed AD requires
replacing the mast nut. The EASA AD uses flight hours of the main rotor
mast assembly, while the proposed AD uses TIS of the helicopter.

Costs of Compliance

We estimate that this proposed AD affects 30 helicopters of U.S.
registry. We estimate that replacing the mast nut with an airworthy
mast nut would require 32 work-hours, at an average labor cost of $85
per work-hour. Parts would cost about $3,100. Based on these costs, we
estimate a total cost per helicopter of $5,820, and a total cost for
the U.S. operator fleet of $174,600.

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.

We are 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

We 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, I certify this proposed regulation:

1. Is not a "significant regulatory action" under Executive Order
12866;

2. Is not a "significant rule" under the DOT Regulatory Policies
and Procedures (44 FR 11034, February 26, 1979);

3. Will not affect intrastate aviation in Alaska to the extent that
it justifies making a regulatory distinction; and

4. 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.

We prepared an economic evaluation of the estimated costs to comply
with this proposed AD and placed it in the AD docket.

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):