DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2021-0694; Project Identifier MCAI-2021-00305-T]
RIN 2120-AA64

Airworthiness Directives; De Havilland Aircraft of Canada Limited
(Type Certificate Previously Held by Bombardier, Inc.) Airplanes

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 De Havilland Aircraft of Canada Limited Model DHC-8-401 and -402
airplanes. This proposed AD was prompted by reports of a possible hard
contact between the #2 top high level sensor (HLS) terminal screw head
and the #6 outer wing fuel access panel stiffener flange. This proposed
AD would require removing and replacing or reworking the #6 outer wing
fuel access panel assembly. 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 8,
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 De
Havilland Aircraft of Canada Limited, Q-Series Technical Help Desk, 123
Garratt Boulevard, Toronto, Ontario M3K 1Y5, Canada; telephone 416-375-
4000; fax 416-375-4539; email thd@dehavilland.com; internet https://
dehavilland.com. You may view this service information at the FAA,
Airworthiness Products Section, Operational Safety Branch, 2200 South
216th St., Des Moines, WA. For information on the availability of this
material at the FAA, call 206-231-3195.

Examining the AD Docket

You may examine the AD docket at https://www.regulations.gov by
searching for and locating Docket No. FAA-2021-0694; 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, any comments
received, and other information. The street address for Docket
Operations is listed above.

FOR FURTHER INFORMATION CONTACT: Thomas Niczky, Aerospace Engineer,
Avionics and Electrical Systems Section, FAA, New York ACO Branch, 1600
Stewart Avenue, Suite 410, Westbury, NY 11590; telephone 516-228-7347;
fax 516-794-5531; email 9-avs-nyaco-cos@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-2021-0694; Project Identifier
MCAI-2021-00305-T" 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 received about this NPRM.

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
Thomas Niczky, Aerospace Engineer, Avionics and Electrical Systems
Section, FAA, New York ACO Branch, 1600 Stewart Avenue, Suite 410,
Westbury, NY 11590; telephone 516-228-7347; fax 516-794-5531; email 9-avs
-nyaco-cos@faa.gov. 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 Civil Aviation (TCCA), which is the aviation
authority for Canada, has issued TCCA AD CF-2021-08, dated March 9,
2021 (TCCA AD CF-2021-08) (also referred to after this as the Mandatory
Continuing Airworthiness Information, or the MCAI), to correct an
unsafe condition for De Havilland Aircraft of Canada Limited Model DHC-
8-401 and -402 airplanes, serial numbers 4001 and 4003 through 4628
inclusive. You may examine the MCAI in the AD docket at https://www.
regulations.gov by searching for and locating Docket No. FAA-2021-0694.

This proposed AD was prompted by the discovery that as a result of
build tolerances, a hard contact could occur between the #2 top HLS
terminal screw head and the #6 outer wing fuel access panel stiffener
flange. The FAA is proposing this AD to address the possibility of
electrical arcing during a lightning strike, which could be a source of
ignition inside the fuel tank. See the MCAI for additional background
information.

Related Service Information Under 1 CFR Part 51

De Havilland Aircraft of Canada Limited has issued Service Bulletin
84-57-35, Revision A, dated February 11, 2021. This service information
describes procedures for replacing or reworking the #6 outer wing fuel
access panel assembly. The rework involves an eddy current or
fluorescent liquid penetrant inspection of the rework area for crack
indications. 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 the ADDRESSES section.

FAA's Determination

This product has been approved by the aviation authority of another
country, and is approved for operation in the United States. Pursuant
to the FAA's bilateral agreement with the State of Design Authority,
the FAA has been notified of the unsafe condition described in the MCAI
and service information referenced above. The FAA is proposing this AD
because the FAA evaluated all the relevant information and determined
the unsafe condition described previously is likely to exist or develop
on other products of the same type design.

Proposed AD Requirements in This NPRM

This proposed AD would require accomplishing the actions specified
in the service information already described.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would
affect 54 airplanes of U.S. registry. For either replacement or repair
of the #6 outer wing fuel access panel, depending on the option
selected by the operator to comply with this proposed AD, the FAA
estimates the following costs:

Estimated Costs

The FAA has included all known costs in its cost estimate.
According to the manufacturer, however, some or all of the costs of
this proposed AD may be covered under warranty, thereby reducing the
cost impact on affected operators.

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) 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 adding the following new airworthiness
directive: