DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2023-0933; Project Identifier MCAI-2022-00554-T;
Amendment 39-22666; AD 2024-02-02]
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: Final rule.

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SUMMARY: The FAA is adopting a new airworthiness directive (AD) for
certain De Havilland Aircraft of Canada Limited Model DHC-8-401 and -
402 airplanes. This AD was prompted by reports that the saddle washer
(radius filler) for the front and rear spar joints may have been
incorrectly manufactured for several years. This AD requires inspecting
the horizontal stabilizer to vertical joint for gaps and bending of the
saddle washer and adjacent washers, and replacing parts if necessary.
The FAA is issuing this AD to address the unsafe condition on these
products.

DATES: This AD is effective March 21, 2024.
The Director of the Federal Register approved the incorporation by
reference of a certain publication listed in this AD as of March 21,
2024.

ADDRESSES:
AD Docket: You may examine the AD docket at regulations.gov under
Docket No. FAA-2023-0933; 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, the mandatory continuing airworthiness
information (MCAI), 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.
Material Incorporated by Reference:
For service information identified in this final rule,
contact De Havilland Aircraft of Canada Limited, Dash 8 Series Customer
Response Centre, 5800 Explorer Drive, Mississauga, Ontario, L4W 5K9,
Canada; telephone 855-310-1013 or 647-277-5820; email
thd@dehavilland.com; website dehavilland.com.
You may view this service information at the FAA,
Airworthiness Products Section, Operational Safety Branch, 2200 South
216th Street, Des Moines, WA. For information on the availability of
this material at the FAA, call 206-231-3195. It is also available at
regulations.gov under Docket No. FAA-2023-0933.

FOR FURTHER INFORMATION CONTACT: Yaser Osman, Aviation Safety Engineer,
FAA, 1600 Stewart Avenue, Suite 410, Westbury, NY 11590; telephone 516-
228-7300; email 9-avs-nyaco-cos@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 certain De Havilland
Aircraft of Canada Limited Model DHC-8-401 and -402 airplanes. The NPRM
published in the Federal Register on April 19, 2023 (88 FR 24144). The
NPRM was prompted by AD CF-2022-21, dated April 21, 2022, issued by
Transport Canada, which is the aviation authority for Canada (referred
to after this as the MCAI). The MCAI states that certain saddle washers
for the front and rear spar joint may have been incorrectly
manufactured for several years. Non-conforming saddle washers could
potentially become deformed when installed, and lead to gaps at the
horizontal stabilizer to vertical stabilizer joint, that would result
in reduction of the pre-load at the joint.
In the NPRM, the FAA proposed to require inspecting the horizontal
stabilizer to vertical joint for gaps and bending of the saddle washer
and adjacent washers, and replacing parts if necessary. The FAA is
issuing this AD to address gapping and bending of the saddle washer
that could have the potential to reduce the life of the bolt, which in
turn could affect the structural integrity of the horizontal stabilizer
to vertical stabilizer joint.
You may examine the MCAI in the AD docket at regulations.gov under
Docket No. FAA-2023-0933.

Discussion of Final Airworthiness Directive

Comments

The FAA received a comment from the Air Line Pilots Association,
International (ALPA). ALPA supported the NPRM without change.
The FAA received additional comments from De Havilland Aircraft of
Canada Limited. The following presents the comments received on the
NPRM and the FAA's response to each comment.

Request To Refer to New Service Information

De Havilland Aircraft of Canada Limited requested that the FAA
revise the proposed AD to refer to De Havilland Aircraft of Canada
Limited Service Bulletin 84-55-12, Revision B, dated April 20, 2023. De
Havilland Aircraft of Canada Limited noted that the service information
had been updated since the NPRM was released.
The FAA agrees with the request. De Havilland Aircraft of Canada
Limited Service Bulletin 84-55-12, Revision B, dated April 20, 2023,
provides clarity on service information that may be used to do rework
if there are gaps in the new radius fillers (saddle washers), and
specifies an additional radius filler part number. The FAA has revised
this AD to refer to De Havilland Aircraft of Canada Limited Service
Bulletin 84-55-12, Revision B, dated April 20, 2023. The FAA has also
revised paragraph (i) of this AD to provide credit for De Havilland
Aircraft of Canada Limited Service Bulletin 84-55-12, Revision A, dated
February 16, 2022.

Request To Revise Corrective Actions

De Havilland Aircraft of Canada Limited requested that the FAA
revise paragraph (h) of the proposed AD. The
commenter stated that De Havilland Aircraft of Canada Limited Service
Bulletin 84-55-12, Revision B, dated April 20, 2023, includes
instructions for reworking the new radius fillers that exhibit fouling
conditions (gapping), and that the proposed AD should be amended to
explain this.
The FAA agrees to clarify. Paragraph (h) of this AD requires
corrective actions (parts replacements) in accordance with Section
3.B., Part B, of the Accomplishment Instructions of De Havilland
Aircraft of Canada Limited Service Bulletin 84-55-12, Revision B, dated
April 20, 2023. The rework the commenter mentioned is part of Section
3.B., Part B, and is specified as part of the corrective actions if
gapping is found after replacement of the radius filler. Therefore,
that step is included as part of the requirements of paragraph (h) of
this AD.

Request To Correct the Number of U.S. Registered Airplanes

De Havilland Aircraft of Canada Limited requested that the FAA
revise the cost of compliance section to correct the number of affected
airplanes. The commenter stated that the number of aircraft on the U.S.
registry is 49, not 400 as stated in the NPRM.
The FAA agrees that the number of U.S. registered airplanes is less
than that specified in the NPRM. After reviewing the FAA registry, the
FAA has determined the correct number of affected airplanes is 54. The
FAA has revised the Costs of Compliance section accordingly.

Conclusion

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 this State of Design Authority, it
has notified the FAA of the unsafe condition described in the MCAI
referenced above. The FAA reviewed the relevant data, considered the
comments received, and determined that air safety requires adopting
this AD as proposed. Accordingly, the FAA is issuing this AD to address
the unsafe condition on this product. Except for minor editorial
changes, and any other 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 De Havilland Aircraft of Canada Limited Service
Bulletin 84-55-12, Revision B, dated April 20, 2023. This service
information specifies procedures for a detailed visual inspection of
the front and rear spar joints for signs of gapping or bending of the
radius filler and/or adjacent washers, and depending on the inspection
results, replacement of the saddle washer, adjacent washers, bolt, and
barrel nut.
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.

Costs of Compliance

The FAA estimates that this AD affects 54 airplanes of U.S.
registry. The FAA estimates the following costs to comply with this AD:

Estimated Costs for Required Actions

The FAA estimates the following costs to do any necessary on-
condition action that would be required based on the results of any
required actions. The FAA has no way of determining the number of
aircraft that might need this on-condition action:

Estimated Costs of On-Condition Actions

The FAA has included all known costs in its cost estimate.
According to the manufacturer, however, some or all of the costs of
this 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

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: