DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2020-0710; Project Identifier 2019-CE-037-AD; Amendment
39-21457; AD 2021-05-14]
RIN 2120-AA64

Airworthiness Directives; Air Tractor, 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 all
Air Tractor, Inc., (Air Tractor) Models AT-250, AT-300, AT-301, AT-302,
AT-400, AT-400A, AT-401, AT-401A, AT-401B, AT-402, AT-402A, AT-402B,
AT-501, AT-502, AT-502A, AT-502B, AT-503, AT-503A, AT-504, AT-602, AT-
802, and AT-802A airplanes. This AD was prompted by reports of cracks
in the flap torque tube actuator attachment brackets that may cause the
flap actuator to detach from the flap torque tube. This AD requires
repetitive visual and dye penetrant inspections of the flap actuator
attachment bracket welds for cracks and replacement if cracks are
identified. The FAA is issuing this AD to address the unsafe condition
on these products.

DATES: This AD is effective April 29, 2021.
The Director of the Federal Register approved the incorporation by
reference of a certain publication listed in this AD as of April 29,
2021.

ADDRESSES: For service information identified in this final rule,
contact Air Tractor, P.O. Box 485, Olney, TX 76374: phone: (940) 564-
5616: email: info@airtractor.com: website: https://airtractor.com/. You
may view this service information at the FAA, Airworthiness Products
Section, Operational Safety Branch, 901 Locust, Kansas City, MO 64106.
For information on the availability of this material at the FAA, call
816-329-4148. It is also available at https://www.regulations.gov by
searching for and locating Docket No. FAA-2020-0710.

Examining the AD Docket

You may examine the AD docket at https://www.regulations.gov by
searching for and locating Docket No. FAA-2020-0710; 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: Kenneth A. Cook, Aviation Safety
Engineer, Fort Worth ACO Branch, AIR-7F0, FAA, 10101 Hillwood Pkwy.,
Fort Worth, TX 76177; phone: (817) 222-5475; email:
kenneth.a.cook@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 all Air Tractor Models
AT-250, AT-300, AT-301, AT-302, AT-400, AT-400A, AT-401, AT-401A, AT-
401B, AT-402, AT-402A, AT-402B, AT-501, AT-502, AT-502A, AT-502B, AT-
503, AT-503A, AT-504, AT-602, AT-802, and AT-802A airplanes. The NPRM
published in the Federal Register on July 28, 2020 (85 FR 45347). The
NPRM was prompted by multiple reports of cracks in the brackets
attaching the flap actuator motor to the flap torque tube on several
models of Air Tractor airplanes.
One of the reports was on a Model AT-802A airplane where the
brackets separated from the torque tube at the welds. The flaps
suddenly retracted while maneuvering, and the pilot temporarily lost
control of the airplane. The pilot was able to regain control of the
airplane before it impacted the ground. Since then, there have been 13
reported airplanes with cracks in the flap torque tube attachment
brackets.
The design of the flap actuator motor brackets on the Model AT-802A
airplane is the same as on Models AT-250, AT-300, AT-301, AT-302, AT-
400, AT-400A, AT-401, AT-401A, AT-401B, AT-402, AT-402A, AT-402B, AT-
501, AT-502, AT-502A, AT-503, AT-503A, AT-504, AT-602, and AT-802
airplanes.
In the NPRM, the FAA proposed to require repetitive dye penetrant
and visual inspections with replacement of the flap torque tube if
cracks are found. The FAA is issuing this AD to address the unsafe
condition on these products.

Discussion of Final Airworthiness Directive Comments

The FAA received comments from two commenters. The commenters were
Air Tractor and Field Air Sales and Maintenance Pty Ltd (Field Air).
The following presents the comments received on the NPRM and the FAA's
response to each comment.

Requests Regarding the Compliance Times

Air Tractor requested the FAA clarify whether the hours time-in-
service (TIS) compliance times are based on aircraft time or flap
torque tube component time. The commenter requested that the AD require
compliance based on the hours TIS of the flap torque tube component to
account for new torque tubes installed on an existing aircraft.
The FAA disagrees with this comment. The hours TIS compliance
required by this AD refers to the hours TIS the airplane operates after
the effective date of the AD and after each inspection. Air Tractor has
not provided data analysis to identify the root cause of the failures
of the torque tubes or to indicate whether the failures are related to
the hours TIS of the torque tubes.
Air Tractor and Field Air requested the FAA remove the proposed
requirement to perform a dye penetrant inspection within 300 hours TIS
after the effective date of the AD. Air Tractor said the proposed
requirement does not provide consideration for flap torque tubes that
have accumulated less than 900 hours and requested the FAA instead
require visual inspections every 300 hours until the flap torque tube
accumulates 900 hours TIS. Field Air requested the FAA provide its
justification for requiring a dye penetrant inspection within 300 hours
TIS.
The FAA disagrees with this comment. The FAA has received no data
to indicate that torque tubes with less than 900 hours TIS are
unaffected by the unsafe condition. The initial dye penetrant
inspection should reveal cracking that might be present on affected
airplanes and ensure those cracks are addressed before the repetitive
visual and dye penetrant inspections start.
Field Air requested the FAA explain why the proposed AD does not
allow the +/- 15 percent tolerance for the visual inspections as
specified in Air Tractor Service Letter #347, Revision A, dated
December 9, 2019 (SL #347A).
The FAA acknowledges this comment and has changed the compliance
time for the visual inspections from 300 hours TIS to 345 hours TIS.

Request To Allow Replacement Parts With More Than Zero Hours TIS

Air Tractor and Field Air disagreed with the proposal to replace a
cracked torque tube with a new (zero hours time-in-service) torque
tube. Field Air requested the FAA explain its justification for this
proposal. Air Tractor stated there is no safety reason to require
replacement with a zero-time flap torque tube instead of a flap torque
tube that has passed the inspection. Air Tractor noted that allowing
replacement with an airworthy flap torque tube would minimize aircraft
down time.
The FAA agrees with this comment and has changed the AD to allow
the replacement with a used (more than zero hours TIS) torque tube
provided the dye penetrant inspection was completed and the part passed
the inspection.

Request Regarding Reporting Requirement

Air Tractor requested the FAA add a statement to the AD that the
agency recommends that cracks be reported to the FAA or to Air Tractor
for tracking. Air Tractor stated the language used in the proposed AD
suggests that reporting is no longer recommended. Field Air requested
the FAA explain its justification for not having a requirement in the
AD to report to Air Tractor any cracked welds identified during the
inspections.
The FAA acknowledges this comment. This AD is not an interim
action. Mandating a report of the results of the inspection is not
necessary to correct the unsafe condition. However, the FAA agrees that
voluntarily reporting to Air Tractor when cracks are found could aid
safety analysis of the fleet.

Request To Expand Service Letter References

Air Tractor requested that the requirement in the AD to perform a
dye penetrant inspection include step 4B(1) from SL #347A, which
specifies gaining access to the flap actuator area by removing skin
panels and conducting a visual inspection of the flap control system.
The FAA disagrees with adding step 4B(1) since this step is not
required to address the unsafe condition.
Air Tractor also requested the AD require step 4B(11) from SL
#347A, which specifies recording in the aircraft records the results of
the dye penetrant inspection and what type of dye penetrant was used.
Air Tractor referenced the recommendations in FAA Special Airworthiness
Bulletin CE-18-26, Liquid Penetrant Inspection: Using Visible Dye
Penetrant, dated September 4, 2018, and noted that the type of dye
penetrant is important information for future inspections.
The FAA disagrees that a change to the AD is necessary. Persons
performing maintenance are required by 14 CFR part 43 to make an entry
in the airplane maintenance records describing the
work performed. That description should identify the same information
specified in step 4B(11).
The FAA did not change this AD based on this comment.

Conclusion

The FAA reviewed the relevant data, considered any 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 these products. 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 Air Tractor, Inc. Service Letter #347, Revision A,
dated December 9, 2019. The service letter specifies procedures for
repetitive visual inspections and dye penetrant inspections of the flap
torque tube brackets for cracks and instructs operators to replace the
torque tube as necessary. 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
ADDRESSES.

Differences Between the AD and the Service Information

Air Tractor SL #347, Rev A specifies performing the dye penetrant
inspection within 900 hours TIS, and this AD requires the initial dye
penetrant inspection within 300 hours TIS. Air Tractor SL #347, Rev A
specifies replacing a cracked torque tube, while this AD requires
replacing a cracked torque tube with a torque tube that has zero hours
TIS. Air Tractor SL #347, Rev A specifies reporting any cracked welds
identified during the inspections.

Costs of Compliance

The FAA estimates that this AD affects 1,662 airplanes of U.S. registry.
The FAA estimates the following costs to comply with this AD:

Estimated Costs

The FAA estimates the following costs to do any necessary
replacements that will be required based on the results of the
inspection. The FAA has no way of determining the number of airplanes
that might need this replacement.

On-Condition Costs for Model AT-802 and AT-802A
[Potential 485 Airplanes]

On-Condition Costs for Model AT-602
[Potential 236 Airplanes]

On-Condition Costs for Models AT-501, AT-502, AT-502A, AT-502B,
AT-503, AT-503A, and AT-504
[Potential 512 Airplanes]

On-Condition Costs for Models AT-250, AT-300, AT-301, AT-302, AT-400,
AT-400A, AT-401, AT-401A, AT-401B, AT-402, AT-402A, and AT-402B
[Potential 429 Airplanes]

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: