DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2024-1692; Project Identifier MCAI-2024-00050-T;
Amendment 39-22878; AD 2024-22-07]
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 a report of an in-flight event
where isolation valve caution messages were received. This AD requires
inspecting the fuse/shuttle valve serial numbers, and replacing certain
fuse/shuttle valves, as specified in a Transport Canada AD, which is
incorporated by reference (IBR). The FAA is issuing this AD to address
the unsafe condition on these products.

DATES: This AD is effective December 31, 2024.

The Director of the Federal Register approved the incorporation by
reference of a certain publication listed in this AD as of December 31, 2024.

ADDRESSES:

AD Docket: You may examine the AD docket at regulations.gov under
Docket No. FAA-2024-1692; 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 Transport Canada material identified in this AD,
contact Transport Canada, Transport Canada National Aircraft
Certification, 159 Cleopatra Drive, Nepean, Ontario K1A 0N5, Canada;
telephone 888-663-3639; email TC.AirworthinessDirectives-
Consignesdenavigabilite.TC@tc.gc.ca. You may find this material on the
Transport Canada website at tc.canada.ca/en/aviation.

You may view this material 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 at regulations.gov under
Docket No. FAA-2024-1692.

FOR FURTHER INFORMATION CONTACT: Gabriel Kim, 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 June 21, 2024 (89 FR 51988). The
NPRM was prompted by AD CF-2024-01, dated January 11, 2024, issued by
Transport Canada, which is the aviation authority for Canada (Transport
Canada AD CF-2024-01) (also referred to as the MCAI). The MCAI states
that an in-service event was reported where the crew received a number
two isolation valve (ISO #2) caution message followed by a number one
isolation valve (ISO #1) caution message. The landing gear was extended
via an alternate extension system as the crew prepared for landing.
Upon landing, the crew used the emergency brake to stop the airplane.
The airplane stopped safely within the runway limits.

Subsequent maintenance activity discovered an external leak from
the main landing gear (MLG) brake assembly, and it was found that the
fuse/shuttle valve assembly did not function properly. Further
investigation revealed that the fuse/shuttle valve assembly failure
resulted from a factory assembly error, which occurred on a limited
number of fuse/shuttle valves.

The assembly error can cause valve deformation leading to premature
wear, and eventually fuse/shuttle valve failure. This condition, if not
corrected, could result in the loss of powered landing gear extension/
retraction, outboard and inboard spoilers, nose wheel steering, and
normal braking, and possibly a runway excursion.

In the NPRM, the FAA proposed to require inspecting the fuse/
shuttle valve serial numbers, and replacing certain fuse/shuttle
valves, as specified in Transport Canada AD CF-2024-01. The FAA is
issuing this AD to address the unsafe condition on these products.

You may examine the MCAI in the AD docket at regulations.gov under
Docket No. FAA-2024-1692.

Discussion of Final Airworthiness Directive

Comments

The FAA received a comment from Air Line Pilots Association,
International (ALPA). The following presents the comment received on
the NPRM and the FAA's response to the comment.

Request To Reduce Compliance Time

ALPA stated the compliance time of 8,000 flight hours or 48 months
whichever occurs first after the effective date of the proposed AD is
excessive for such unsafe condition, that could result in the loss of
powered landing gear extension/retraction, outboard and inboard
spoilers, nose wheel steering, normal braking, and possibly a runway
excursion. The FAA infers that ALPA is requesting the FAA reduce the
compliance time.

The FAA does not agree with the request. The FAA has determined
that Transport Canada's compliance time calculation is adequate. The
low probability of a critical event is due to the single occurrence and
high flight hours. In addition, multiple isolation valves can
effectively mitigate hydraulic fluid leaks. After considering all the
available information, the FAA has determined that the compliance time,
as proposed, represents an appropriate interval of time in which the
required actions can be performed in a timely manner within the
affected fleet, while still maintaining an adequate level of safety.
Additionally, the FAA notes that there has been only one event of an
in-service aircraft, and in that event, the aircraft landed safely.
With only one event and the high amount of flight hours in the fleet,
the probability of the unsafe condition occurring is low. It is possible that all
the systems listed in this AD could fail simultaneously; however, that is unlikely.
Aircraft hydraulic systems typically have an isolation valve, which in
this case was activated and annunciated. The isolation valve was
effective, and although hydraulic fluid leaked, the hydraulic pressure
remained at normal levels. This AD has not been changed regarding this request.

Clarification of Unsafe Condition

Paragraph (e) of the proposed AD states the FAA is issuing this AD
to address certain fuse/shuttle valves. The FAA has revised paragraph
(e) of this AD to state the FAA is issuing this AD to address failure
of certain fuse/shuttle valves to clarify it is the failure of the
fuse/shuttle valves that could lead to the unsafe condition.

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
comment 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 the change described previously, this AD is adopted as proposed in
the NPRM. None of the changes will increase the economic burden on any
operator.

Material Incorporated by Reference Under 1 CFR Part 51

Transport Canada AD CF-2024-01 specifies procedures for inspecting
the fuse/shuttle valve serial numbers, and if any fuse/shuttle valve
assemblies with the listed serial numbers are found, replacing the
affected fuse/shuttle valves.

This material is reasonably available because the interested
parties have access to it through their normal course of business or by
the means identified in ADDRESSES section.

Costs of Compliance

The FAA estimates 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 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 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: