DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2020-0975; Project Identifier 2020-NM-061-AD; Amendment
39-21566; AD 2021-11-04]
RIN 2120-AA64

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

AGENCY: Federal Aviation Administration (FAA), Department of
Transportation (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-8-400, -401,
and -402 airplanes. This AD was prompted by a report of main landing
gear (MLG) retractions after striking an obstacle or severe wheel
imbalance after a tire failure. This AD requires inspections for
correct height of the lock link over-center stop pin and for correct
gaps of the left-hand and right-hand MLG downlock proximity sensors,
replacement of the shim if necessary, corrective actions, and
installation of a new, improved proximity sensor electronic unit (PSEU)
with software changes. The FAA is issuing this AD to address the unsafe
condition on these products.

DATES: This AD is effective July 9, 2021.
The Director of the Federal Register approved the incorporation by
reference of certain publications listed in this AD as of July 9, 2021.

ADDRESSES: For service information identified in this final rule,
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. It is also
available on the internet at https://www.regulations.gov by searching
for and locating Docket No. FAA-2020-0975.

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-
0975; 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, 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.

FOR FURTHER INFORMATION CONTACT: Darren Gassetto, Aerospace Engineer,
Mechanical Systems and Administrative Services Section, FAA, New York
ACO Branch, 1600 Stewart Avenue, Suite 410, Westbury, NY 11590;
telephone 516-228-7323; fax 516-794-5531; email 9-avs-nyacocos@faa.gov.

SUPPLEMENTARY INFORMATION:

Background

Transport Canada Civil Aviation (TCCA), which is the aviation
authority for Canada, has issued TCCA AD CF-2016-31R1, dated March 24,
2017 (TCCA AD CF-2016-31R1) (also referred to as the Mandatory
Continuing Airworthiness Information, or the MCAI), to correct an
unsafe condition for certain De Havilland Aircraft of Canada Limited
Model DHC-8-400, -401, and -402 airplanes. You may examine the MCAI in
the AD docket on the internet at https://www.regulations.gov by
searching for and locating Docket No. FAA-2020-0975.
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-8-400, -401, and -402 airplanes.
The NPRM published in the Federal Register on November 2, 2020 (85 FR
69276). The NPRM was prompted by a report of MLG retractions after
striking an obstacle or severe wheel imbalance after a tire failure.
The NPRM proposed to require inspections for correct height of the lock
link over-center stop pin and for correct gaps of the left-hand and
right-hand MLG downlock proximity sensors, replacement of the shim if
necessary, corrective actions, and installation of a new improved PSEU
with software changes. The FAA is issuing this AD to address loss of
MLG downlock signal caused by the vibrations from those events, which
leads to de-energizing the MLG solenoid sequence valve (SSV) and
subsequent removal of hydraulic pressure from the MLG downlock
actuator. Loss of the hydraulic pressure in the downlock actuator,
combined with the vibrations, can cause the stabilizer brace to unlock
and the MLG to subsequently retract. See the MCAI for additional
background information.

Comments

The FAA gave the public the opportunity to participate in
developing this final rule. The following presents the comments
received on the NPRM and the FAA's response to each comment.

Request To Exclude Certain Steps of the Accomplishment Instructions of
Service Information

Horizon Air requested that paragraphs (g), (h), and (i) of the
proposed AD be revised to require only paragraph 3.B. of the
Accomplishment Instructions of the service bulletins referenced in
those paragraphs. Horizon Air stated that the Job Set-up section
(paragraph 3.A.) of the Accomplishment Instructions do not directly
address the unsafe condition. Horizon Air also asserted that retaining
the Job Set-up sections restricts an operator's ability to do other
maintenance in conjunction with the required service bulletins.
The FAA disagrees with the request to exclude paragraph 3.A., Job
Set-up, of the Accomplishment Instructions from this AD's requirements. The Job
Set-up sections of the required service bulletins include specific
procedures for the electrical power and proper configurations of the
nose landing gear (NLG) and MLG, which are necessary for accomplishing
the applicable corrective actions on the PSEUs and proximity detectors
and to prevent possible damage to that equipment. Requiring the Job
Set-up instructions should not, in general, restrict the ability to
schedule other maintenance actions in conjunction with the required
actions. The FAA has not changed this AD in this regard.

Request To Allow Use of Alternative Service Information When Installing
a Certain Part

Horizon Air requested that paragraph (i) of the proposed AD be
revised to also allow installation of PSEU part number (P/N) 30145-0602
in accordance with Bombardier Service Bulletin 84-32-143, Revision B,
dated November 16, 2016. Horizon Air pointed out that both documents
stated that operators may receive a PSEU with P/N 30145-0601 or 30145-
0602. Further, Horizon Air noted that PSEU P/N 30145-0602 is ``two-way
interchangeable'' with P/N 30145-0601, and that the installation
instructions are the same in both service bulletins.
The FAA disagrees with the request to revise paragraph (i) of this
AD. The FAA agrees that the service information does state a two-way
interchangeability of PSEU P/N 30145-0601 with PSEU P/N 30145-0602 and
that operators may receive either PSEU P/N due to component
availability. However, the service information also states that those
in receipt of a PSEU must declare the appropriate service information
specific to the PSEU P/N. In addition, while most of the Accomplishment
Instructions between Bombardier Service Bulletin 84-32-143, Revision B,
dated November 16, 2016, and Bombardier Service Bulletin 84-32-149,
dated November 16, 2016, are the same, they are not identical.
Therefore, recording compliance with another service bulletin would not
be in compliance with the applicable corrective actions for the PSEU P/
N. The FAA has not changed the AD in this regard.

Conclusion

The FAA reviewed the relevant data, considered the comments
received, and determined that air safety and the public interest
require adopting this final rule as proposed, except for minor
editorial changes. The FAA has determined that these minor changes:
Are consistent with the intent that was proposed in the
NPRM for addressing the unsafe condition; and
Do not add any additional burden upon the public than was
already proposed in the NPRM.

Related Service Information Under 1 CFR Part 51

De Havilland Aircraft of Canada Limited has issued Bombardier
Service Bulletin 84-32-140, Revision B, dated January 30, 2018. This
service information describes set-up procedures for proper
configuration of the MLG prior to performing subsequent procedures for
inspections for correct height of the lock link over-center stop pin
and for correct gaps of the left-hand and right-hand MLG downlock
proximity sensors, and replacement of the shim.
De Havilland Aircraft of Canada Limited has also issued Bombardier
Service Bulletin 84-32-143, Revision B, dated November 16, 2016, which
describes procedures for installation of a new, improved PSEU, P/N
30145-0601, with software changes.
De Havilland Aircraft of Canada Limited has also issued Bombardier
Service Bulletin 84-32-149, dated November 16, 2016, which describes
procedures for installation of a new, improved PSEU, P/N 30145-0602,
with software changes.
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 57 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 actions 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 these on-condition actions:

Estimated Costs of On-Condition Actions

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.

Adoption of 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: