DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2024-2013; Project Identifier AD-2024-00363-A;
Amendment 39-22812; AD 2024-16-06]
RIN 2120-AA64

Airworthiness Directives; Air Tractor, Inc. Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule; request for comments.

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SUMMARY: The FAA is superseding Airworthiness Directive (AD) 2023-15-
07, which applied to all Air Tractor, Inc. (Air Tractor) Model AT-802
and AT-802A airplanes with Wipaire, Inc. Supplemental Type Certificate
(STC) No. SA01795CH installed. AD 2023-15-07 required repetitively
inspecting the left and right forward horizontal stabilizer spars for
cracks, replacing any forward horizontal stabilizer spar found cracked,
and reporting inspection results to the FAA. This AD requires
repetitively inspecting the left and right, forward and rear,
horizontal stabilizer spars for cracks at shorter intervals than those
required by AD 2023-15-07, replacing any horizontal stabilizer spar
found cracked or damaged, installing bathtub fittings, and reporting
inspection results to the FAA. This AD was prompted by additional
reports of cracks in the horizontal stabilizer spars and the need to
incorporate a new finlet attach design on the horizontal stabilizer
spars to reduce the cracking. The FAA is issuing this AD to address the
unsafe condition on these products.

DATES: This AD is effective September 4, 2024.
The Director of the Federal Register approved the incorporation by
reference of a certain publication listed in this AD as of September 4,
2024.
The FAA must receive comments on this AD by October 4, 2024.

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 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.
AD Docket: You may examine the AD docket at regulations.gov under
Docket No. FAA-2024-2013; 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 street address for Docket Operations is listed above.
Material Incorporated by Reference:
For Wipaire, Inc. material identified in this AD, contact
Wipaire, Inc., 1700 Henry Avenue, Fleming Field (KSGS), South St. Paul,
MN 55075; phone: (651) 451-1205; email: customerservice@wipaire.com;
website: wipaire.com.
You may view this material 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 (817) 222-5110. It is also available at regulations.gov under
Docket No. FAA-2024-2013.

FOR FURTHER INFORMATION CONTACT: Tim Eichor, Aviation Safety Engineer,
Central Certification Branch, FAA, 1801 S. Airport Road, Wichita, KS
67209; phone: (847) 294-7141; email: tim.d.eichor@faa.gov.

SUPPLEMENTARY INFORMATION:

Comments Invited

The FAA invites you to send any written data, views, or arguments
about this final rule. Send your comments to an address listed under
the ADDRESSES section. Include ``Docket No. FAA-2024-2013; Project
Identifier AD-2024-00363-A'' at the beginning of your comments. The
most helpful comments reference a specific portion of the final rule,
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 this final rule 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
regulations.gov, including any personal information you provide. The
agency will also post a report summarizing each substantive verbal
contact received about this final rule.

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 AD 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 AD, 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 AD. Submissions containing CBI should be sent to Tim
Eichor, Aviation Safety Engineer, Central Certification Branch, FAA,
1801 S. Airport Road, Wichita, KS 67209. 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 2023-15-07, Amendment 39-22519 (88 FR 53761,
August 9, 2023) (AD 2023-15-07), for all Air Tractor Model AT-802 and
AT-802A airplanes with Wipaire, Inc. STC No. SA01795CH installed. AD
2023-15-07 required repetitively inspecting the left and right forward
horizontal stabilizer spars for cracks, replacing any forward
horizontal stabilizer spar found cracked, and reporting inspection
results to the FAA. For certain airplanes, AD 2023-15-07 required the
inspection before the airplane accumulated 200 hours time-in-service
(TIS) after installation of STC No. SA01795CH. AD 2023-15-07 resulted
from cracks found in the forward horizontal stabilizer spar bend radius
located at the STC finlet mounting locations. The FAA issued AD 2023-
15-07 to detect and correct cracks in the forward horizontal stabilizer
spar, which could result in structural failure of the horizontal tail
with consequent loss of control of the airplane.

Actions Since AD 2023-15-07 Was Issued

As a result of the reports of the inspections required by AD 2023-
15-07, additional cracks have been found in the forward horizontal
stabilizer spar, including cracks found before the airplane accumulated
200 hours TIS after installation of the STC.

Accordingly, the FAA determined that reducing the inspection interval
is necessary. In addition, based on a new fatigue analysis, the FAA
determined that there is the potential for cracks in the rear
horizontal stabilizer spar. Wipaire, Inc. has developed a change to STC
No. SA01795CH, which incorporates an improved design that includes
modification kits to install bathtub fittings on the horizontal
stabilizer spars to mitigate this condition by improving the structural
load path. This includes more accessible repetitive inspection
intervals of 110 hours TIS. The FAA is issuing this AD to address the
unsafe condition on these products.

FAA's Determination

The FAA is issuing this AD because the agency determined the unsafe
condition described previously is likely to exist or develop in other
products of the same type design.

Material Incorporated by Reference Under 1 CFR Part 51

The FAA reviewed Wipaire, Inc. Service Letter 253, Revision D,
dated July 3, 2024 (Wipaire SL 253D), which specifies procedures for
repetitively inspecting the left and right, forward and rear,
horizontal stabilizer spars for cracks and installing bathtub fittings
using Service Kit 1012347-01 or 1012347-02. This material also
specifies procedures for repetitively inspecting the left and right,
forward and rear, horizontal stabilizer spars for cracks, elongated
holes, and corrosion after installation of the bathtub fittings. 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 the ADDRESSES section.

AD Requirements

This AD retains none of the requirements of AD 2023-15-07. This AD
requires repetitively inspecting both the left and right, forward and
rear, horizontal stabilizer spars for cracks, replacing any horizontal
stabilizer spar found cracked or damaged, installing bathtub fittings
(Service Kit 1012347-01 or 1012347-02), and reporting inspection
results to the FAA. The inspection intervals in this AD are shorter
than the intervals required by AD 2023-15-07.

Differences Between This AD and the Referenced Material

As part of the instructions for installing the bathtub fittings,
Wipaire SL 253D specifies that to be eligible for reinstallation,
finlet mount weldments must include a certain welded gusset, but that
constraint is not required by this AD.
Wipaire SL 253D includes an inspection of the finlets and forward
bathtub fittings at intervals of 1,500 hours TIS and establishes a life
limit of 7,800 hours TIS on the forward spar and forward bathtub
fittings. This AD does not include those requirements because the
compliance times would allow sufficient time to provide notice and
opportunity for public comment. The FAA is evaluating these actions and
may consider future rulemaking.
This AD requires an initial compliance time of within 7 days or
before the airplane accumulates 110 hours TIS since installation of STC
No. SA01795CH, whichever occurs later, while Wipaire SL 253D specifies
different compliance times for different configurations of STC No.
SA01795CH.
Wipaire SL 253D specifies repeating the inspections at intervals of
200 hours TIS, but this AD requires the repetitive inspections at
intervals not to exceed 110 hours TIS.

Interim Action

The FAA considers this AD to be an interim action. The FAA is
evaluating the need to establish a life limit (potentially as low as
2,000 hours TIS) on the horizontal stabilizer spars to further mitigate
the unsafe condition long term. The FAA may consider future rulemaking
on this subject.

Justification for Immediate Adoption and Determination of the Effective
Date

Section 553(b) of the Administrative Procedure Act (APA) (5 U.S.C.
551 et seq.) authorizes agencies to dispense with notice and comment
procedures for rules when the agency, for ``good cause,'' finds that
those procedures are ``impracticable, unnecessary, or contrary to the
public interest.'' Under this section, an agency, upon finding good
cause, may issue a final rule without providing notice and seeking
comment prior to issuance. Further, section 553(d) of the APA
authorizes agencies to make rules effective in less than thirty days,
upon a finding of good cause.
An unsafe condition exists that requires the immediate adoption of
this AD without providing an opportunity for public comments prior to
adoption. The FAA has found that the risk to the flying public
justifies forgoing notice and comment prior to adoption of this rule
because cracks in the horizontal stabilizer spars could lead to
structural failure of the horizontal tail with consequent loss of
control of the airplane. Airplanes with the affected STC installed are
used in fire-fighting missions and put frequent high repetitive fatigue
loads in this area at a high utilization rate (about 100 hours TIS
monthly). Based on the number of cracks found to date, a significant
number of airplanes need to be inspected within 7 days after the
effective date of this AD and modified with bathtub fittings within 300
hours TIS (about 3 months for the high utilization airplanes). These
compliance times are shorter than the time necessary for the public to
comment and for publication of the final rule. Accordingly, notice and
opportunity for prior public comment are impracticable and contrary to
the public interest pursuant to 5 U.S.C. 553(b).
In addition, the FAA finds that good cause exists pursuant to 5
U.S.C. 553(d) for making this amendment effective in less than 30 days,
for the same reasons the FAA found good cause to forgo notice and
comment.

Regulatory Flexibility Act

The requirements of the Regulatory Flexibility Act (RFA) do not
apply when an agency finds good cause pursuant to 5 U.S.C. 553 to adopt
a rule without prior notice and comment. Because FAA has determined
that it has good cause to adopt this rule without prior notice and
comment, RFA analysis is not required.

Costs of Compliance

The FAA estimates that this AD affects 30 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 would be required based on the results of the
inspection. The agency has no way of determining the number of
airplanes that might need this replacement:

On-Condition Costs

The FAA has included all known costs in its cost estimate.
According to the manufacturer, however, some of the costs of this AD
may be covered under warranty, thereby reducing the cost impact on
affected operators.

Paperwork Reduction Act

A federal agency may not conduct or sponsor, and a person is not
required to respond to, nor shall a person be subject to a penalty for
failure to comply with a collection of information subject to the
requirements of the Paperwork Reduction Act unless that collection of
information displays a currently valid OMB Control Number. The OMB
Control Number for this information collection is 2120-0056. Public
reporting for this collection of information is estimated to be
approximately 1 hour per response, including the time for reviewing
instructions, searching existing data sources, gathering and
maintaining the data needed, and completing and reviewing the
collection of information. All responses to this collection of
information are mandatory. Send comments regarding this burden estimate
or any other aspect of this collection of information, including
suggestions for reducing this burden to: Information Collection
Clearance Officer, Federal Aviation Administration, 10101 Hillwood
Parkway, Fort Worth, TX 76177-1524.

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, and
(2) Will not affect intrastate aviation in Alaska.

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:

a. Removing Airworthiness Directive 2023-15-07, Amendment 39-22519 (88
FR 53761, August 9, 2023); and

b. Adding the following new airworthiness directive: