DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2021-0960; Project Identifier 2019-CE-021-AD]
RIN 2120-AA64

Airworthiness Directives; Viking Air Limited (Type Certificate
Previously Held by Bombardier, Inc., de Havilland, Inc.) Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: The FAA proposes to supersede Airworthiness Directive (AD) 80-
13-10, AD 80-13-12 R1, and AD 2008-03-01, which apply to certain de
Havilland (type certificate now held by Viking Air Limited) Model DHC-
6-1, DHC-6-100, DHC-6-200, and DHC-6-300 airplanes. AD 80-13-10
requires repetitively inspecting the main landing gear (MLG) legs for
cracks and corrosion. AD 80-13-12 R1 requires repetitively inspecting
each engine nacelle lower longeron for cracks and buckling. AD 2008-03-
01 requires incorporating inspections, modifications, and life limits
of certain structural components into the aircraft maintenance program.
Since the FAA issued those ADs, new and more restrictive airworthiness
limitations have been issued for certain structural components. This
proposed AD would require incorporating into maintenance records new or
revised life limits, modification limits, and inspection or overhaul
intervals. 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 December
23, 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 Viking Air
Limited Technical Support, 1959 De Havilland Way, Sidney, British
Columbia, Canada, V8L 5V5; phone: (North America) (800) 663-8444; fax:
(250) 656-0673; email: technical.support@vikingair.com; website:
https://www.vikingair.com/support/service-bulletins. You may view this
service information at the Airworthiness Products Section, Operational
Safety Branch, FAA, 901 Locust, Kansas City, MO 64106. For information
on the availability of this material at the FAA, call (816) 329-4148.

Examining the AD Docket

You may examine the AD docket at https://www.regulations.gov by
searching for and locating Docket No. FAA-2021-0960; 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, the MCAI,
any comments received, and other information. The street address for
Docket Operations is listed above.

FOR FURTHER INFORMATION CONTACT: Aziz Ahmed, Aviation Safety Engineer,
New York ACO Branch, FAA, 1600 Stewart Avenue, Suite 410, Westbury, NY
11590; phone: (516) 228-7329; fax: (516) 794-5531; email:
aziz.ahmed@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 the ADDRESSES section. Include ``Docket No. FAA-2021-0960;
Project Identifier 2019-CE-021-AD'' 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 proposed AD.

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 Aziz
Ahmed, Aviation Safety Engineer, New York ACO Branch, FAA, 1600 Stewart
Avenue, Suite 410, Westbury, NY 11590. Any commentary that the FAA
receives which is not specifically designated as CBI will be placed in
the public docket for this rulemaking.

Background

The FAA issued AD 80-13-10, Amendment 39-3812 (45 FR 43155, June
26, 1980) (AD 80-13-10) for de Havilland (type certificate now held by
Viking Air Limited) Model ``DHC-6 type'' airplanes with certain MLG
legs. AD 80-13-10 was prompted by several incidents involving collapse
of the MLG. AD 80-13-10 requires repetitively inspecting the weld
juncture at the Y-joint of the MLG legs for cracks and corrosion. The
FAA issued AD 80-13-10 to prevent failure of the MLG legs at the Y-
joint weld, which could result in wing damage during taxiing
operations.
The FAA issued AD 80-13-12 R1, Amendment 39-4135 (46 FR 31251, June
15, 1981) (AD 80-13-12 R1) for certain serial-numbered de Havilland
(now Viking Air Limited) Model ``DHC-6 type'' airplanes with
intermediate or high floatation tires, skis, or floats. AD 80-13-12 R1
was prompted by reports of cracks or buckling on the engine nacelle
lower longerons. AD 80-13-12 R1 requires repetitively inspecting each
engine nacelle lower longeron for cracks and buckling. The FAA issued
AD 80-13-12 R1 to prevent possible failure of the engine nacelle lower
longerons due to cracking or buckling.
The FAA issued AD 2008-03-01, Amendment 39-15350 (73 FR 5729,
January 31, 2008) (AD 2008-03-01), for all Viking Air Limited Model
DHC-6-1, DHC-6-100, DHC-6-200, and DHC-6-300 airplanes. AD 2008-03-01
was prompted by structural evaluations of the DHC-6 series airplanes
that showed the service life limits and inspection schedules needed to
be revised. AD 2008-03-01 was based on Canadian AD CF-2000-14, dated
May 25, 2000 (AD CF-2000-14), issued by Transport Canada, which is the
aviation authority for Canada. AD 2008-03-01 requires incorporating the
inspections, modifications, and life limits (retirement) of certain
structural components, as contained in Revision 5 of the DHC-6 Product
Support Manual (PSM) 1-6-11, into the aircraft maintenance program. The
FAA issued AD 2008-03-01 to maintain the structural integrity of the
airplane.

Actions Since AD 2008-03-01 Was Issued

Since the FAA issued AD 2008-03-01, Transport Canada has superseded
AD CF-2000-14 and issued Canadian AD CF-2019-02, dated January 9, 2019
(referred to after this as ``the MCAI''). The MCAI applies to all
Viking Air Limited (formerly de Havilland) Model DHC-6 series 1, DHC-6
series 100, DHC-6 series 110, DHC-6 series 200, DHC-6 series 210, DHC-6
series 300, DHC-6 series 310, DHC-6 series 320, and DHC-6 series 400
airplanes. The MCAI states:

The airworthiness limitations for DHC-6 aeroplanes are defined
and published in the Viking Air Ltd. (Viking) Airframe Airworthiness
Limitations Manual, Product Support Manual (PSM) 1-6-11, approved by
Transport Canada. The instructions contained in PSM 1-6-11 have been
identified as mandatory actions for continued airworthiness. Failure
to comply with those instructions could result in an unsafe
condition.
Viking Air Ltd. published Revision 9 of PSM 1-6-11 earlier in
2018. Revision 9 of PSM 1-6-11, dated 30 April 2018, includes some
new and/or more restrictive limitations than those contained in
Revision 5. For the reason described above, this [Transport Canada]
AD requires implementation of the actions specified in PSM 1-6-11
Revision 9.
The compliance requirements for several of the tasks in PSM 1-6-
11 were previously a range of flight hours and flight cycles. With
Revision 9 of PSM 1-6-11, the range-based requirements have been
changed to specific flight hours and flight cycle limits. This
[Transport Canada] AD provides a phase-in allowance for those
limitations so that operators will have the opportunity to schedule
the modifications and inspections required by the limitations. The
phase-in allowances are intended to mitigate the impact of changing
from compliance ranges to compliance limits for aeroplanes that are
approaching or have exceeded the limits on the effective date of the
[Transport Canada] AD.
Revision 9 of PSM 1-6-11 also includes some airworthiness
limitations that were previously contained in service bulletins (SB)
or other PSMs. Some of those limitations were mandated by [Transport
Canada] ADs, specifically AD CF-80-06, CF-81-07R4 and CF-95-12.
Because the affected limitations will now be controlled in PSM 1-6-
11, the above mentioned [Transport Canada] ADs are superseded by
this [Transport Canada] AD.
The following are new tasks in PSM 1-6-11 Revision 9:
1. Task 27-007 Replacement of flight control pulleys at Fuselage
Station (FS) 270.
2. Tasks 32-001 and 32-002 Overhaul of main landing gear leg.
There is an associated requirement to ensure that each affected part
has been assigned a unique serial number.
3. Task 53-006 Inspection of the skin flange of machined frame
at FS 239.
4. Tasks 54-003 to 54-010 Inspection of nacelle longerons.
5. Tasks 57-039 to 57-041 Inspection for wing upper skin
disbond.
Task 27-004 Replacement of flight control cables after spillage
of corrosive materials in PSM 1-6-11 was limited to landplane
configurations in previous revisions of PSM 1-6-11 but is now
applicable to all configurations.
The intent of the word ``airframe'' in PSM 1-6-11 Revision 9 is
to include fuselage, nacelles, struts, interiors, cowlings,
fairings, airfoils, landing gear and their controls. The airframe
life limitation in PSM 1-6-11 Revision 9 is not intended to apply to
components such as those in the fuel, electrical and hydraulic
systems that are occasionally transferred from one aeroplane to
another and may be salvaged from an aeroplane that is retired from
service for use on an in-service aeroplane. PSM 1-6-13 defines
current airworthiness limitations for DHC-6 avionics that are not
addressed in this [Transport Canada] AD.

Model DHC-6-400 airplanes were type certificated after AD CF-2000-
14 was issued and are subject to the same unsafe condition. You may
examine the MCAI in the AD docket at https://www.regulations.gov by
searching for and locating Docket No. FAA-2021-0960.

Related Service Information Under 1 CFR Part 51

The FAA reviewed DHC-6 Twin Otter PSM 1-6-11, Airframe
Airworthiness Limitations Manual, Revision 9, dated April 30, 2018. The
service information contains airworthiness limitations for certain
structural components. 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 this State of Design Authority, it
has notified the FAA of the unsafe condition described in the MCAI and
service information referenced above. The FAA is issuing this NPRM
after determining the unsafe condition described previously is likely
to exist or develop on other products of the same type design.

Proposed AD Requirements

This proposed AD would require incorporating into maintenance
records new or revised life limits, modification limits, and inspection
or overhaul intervals. This proposed AD would also allow a ``phase-in''
compliance period for the initial completion of certain tasks.

ADs Mandating Airworthiness Limitations

The FAA has previously mandated airworthiness limitations by
issuing ADs that require revising the airworthiness limitation section
(ALS) of the existing maintenance manual or instructions for continued
airworthiness to incorporate new or revised inspections and life
limits. This proposed AD, however, would require incorporating new or
revised inspections and life limits into the maintenance records
required by 14 CFR 91.417(a)(2) or 135.439(a)(2) for your airplane. The
FAA does not intend this as a substantive change. Requiring
incorporation of the new ALS requirements into the maintenance records,
rather than requiring individual repetitive inspections and
replacements, allows operators to record AD compliance once after
updating the maintenance records, rather than recording compliance
after every inspection and part replacement.

Differences Between This Proposed AD and the MCAI

The MCAI applies to Viking Air Limited Model DHC-6 series 110, DHC-
6 series 210, DHC-6 series 310, and DHC-6 series 320, and this proposed
AD would not because these models do not have an FAA type certificate.
Transport Canada Models DHC-6 series 1, DHC-6 series 100, DHC-6 series
200, DHC-6 series 300, and DHC-6 series 400 airplanes correspond to FAA
Model DHC-6-1, DHC-6-100, DHC-6-200, DHC-6-300, and DHC-6-400
airplanes, respectively.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would
affect 33 airplanes of U.S. registry.
The FAA also estimates that it would take about 1 work-hour per
airplane to incorporate life limits, modification limits, and
inspection or overhaul intervals, into maintenance records. The average
labor rate is $85 per work-hour.
Based on these figures, the FAA estimates the cost of the proposed
AD on U.S. operators to be $2,805 or $85 per airplane.

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:

a. Removing Airworthiness Directive 80-13-10, Amendment 39-3812 (45 FR
43155, June 26, 1980); Airworthiness Directive 80-13-12 R1, Amendment
39-4135 (46 FR 31251, June 15, 1981); and Airworthiness Directive 2008-
03-01, Amendment 39-15350 (73 FR 5729, January 31, 2008); and

b. Adding the following new airworthiness directive: