DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2024-2143; Project Identifier AD-2024-00008-A]
RIN 2120-AA64

Airworthiness Directives; Piper Aircraft, Inc. Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: The FAA proposes to adopt a new airworthiness directive (AD)
for certain Piper Aircraft, Inc. (Piper) Model PA-28-140, PA-28-150,
PA-28-160, PA-28-180, PA-28S-160, PA-28S-180, PA-28-236, PA-28-201T,
PA-32-300, PA-32R-300, PA-32RT-300, PA-32RT-300T, PA-32-301FT, PA-32-
301XTC, PA-32R-301 (HP), PA-32R-301 (SP), PA-32R-301T, PA-32-301, and
PA-32-301T airplanes. This proposed AD was prompted by a report of a
wing separation caused by fatigue cracking in a visually inaccessible
area of the lower main wing spar cap and additional reports of fatigue
cracking in the wing spars of airplanes that share common type design
features. This proposed AD would require reviewing airplane maintenance
records to determine if an eddy current inspection of the lower main
wing spar bolt holes was done and, depending on the result, doing a
one-time eddy current inspection of the lower wing spar bolt holes for
crack(s), and replacing any cracked main wing spar. 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 November 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-2024-2143; 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, any comments received, and other information. The
street address for Docket Operations is listed above.

Material Incorporated by Reference:

For Piper material identified in this proposed AD, contact
Piper Aircraft, Inc., 2926 Piper Drive, Vero Beach, Florida 32960;
phone: (772) 567-4361; email: piper.com">customerservice@piper.com; website:
piper.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.

FOR FURTHER INFORMATION CONTACT: Fred Caplan, Aviation Safety Engineer,
FAA, 1701 Columbia Avenue, College Park, GA 30337; phone: (404) 474-
5507; email: 9-ASO-ATLACO-ADS@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-2024-2143;
Project Identifier AD-2024-00008-A" 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 revise this 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
regulations.gov, including any personal information you provide. The
agency will also post a report summarizing each substantive verbal
contact received about this NPRM.

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 Fred
Caplan, Aviation Safety Engineer, FAA, 1701 Columbia Avenue, College
Park, GA 30337. 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 2020-26-16, Amendment 39-21371 (86 FR 3769,
January 15, 2021) (AD 2020-26-16), for certain Piper Model PA-28-151,
PA-28-161, PA-28-181, PA-28-235, PA-28R-180, PA-28R-200, PA-28R-201,
PA-28R-201T, PA-28RT-201, PA-28RT-201T, PA-32-260, PA-32-300, PA-32R-
300, PA-32RT-300, and PA-32RT-300T airplanes. AD 2020-26-16 was
prompted by an accident involving wing separation on a Piper Model PA-
28R-201 airplane. An investigation by the National Transportation
Safety Board (NTSB) revealed a fatigue crack in a visually inaccessible
area of the lower main wing spar cap. The applicability of the NPRM for
AD 2020-26-16 included additional Piper model airplanes with similar
main wing spar structures as the Model PA-28R-201. Based on airplane
usage history, the FAA determined that only those airplanes with a
higher risk for fatigue cracks (airplanes with a significant history of
operation in flight training or other high-load environments) should be
subject to the inspection requirements proposed in that NPRM.

AD 2020-26-16 requires calculating the factored service hours for
each main wing spar to determine when an inspection is required,
inspecting the lower main wing spar bolt holes for cracks, and
replacing any cracked main wing spar. The agency issued AD 2020-26-16
to detect and correct fatigue cracks in the lower main wing spar cap
bolt holes.

Actions Since AD 2020-26-16 Was Issued

The preamble to AD 2020-26-16 explains that the FAA considers the
requirements "interim action" and was considering further rulemaking.
The FAA has now determined that further rulemaking is necessary, and
this proposed AD and a separate proposed rulemaking action (Docket No.
FAA-2024-2142) that would supersede AD 2020-26-16 follows from that
determination. Similar to AD 2020-26-16, this proposed AD is also
considered to be an interim action that would determine the need for
additional actions in the fleet addressed currently. The FAA evaluated
the inspection reports submitted by operators as required by AD 2020-
26-16 and determined that wing spars from additional Piper airplane
models should be inspected.

Since the FAA issued AD 2020-26-16, the FAA has analyzed the
accident history of the airplanes affected by AD 2020-26-16 and other
Piper airplanes operated in a similar fashion. The following paragraphs
communicate the FAA's findings on this subject.

Accident History

Fatigue cracking was present in the main wing spars of Piper Model
PA-28-181, Model PA-28R-201, and Model PA-28-161 airplanes involved in
the following accidents. The following NTSB reports are related to this
issue and can be found on ntsb.gov.

NTSB Accident Number FTW87FA088: March 30, 1987--Marlin,
TX--Piper Model PA-28-181--7,490 hours time-in-service (TIS). This
accident was determined to have been caused by fatigue cracking in the
outboard bolt holes of the main wing spar. This airplane's primary
usage was a "Pipeline Patrol" mission.

NTSB Accident Number NYC93FA140: August 2, 1993--
Provincetown, MA--Piper Model PA-28-181--11,683 hours TIS. This
accident was determined to have been caused by structural overloading
related to weather, but fatigue cracks were present near the outboard
bolt holes. This airplane's usage history included personal use, flight
instruction, and charter flights.

NTSB Accident Number ERA18FA120: April 4, 2018--Daytona
Beach, FL--Piper Model PA-28R-201--7,691 hours TIS. This accident was
determined to have been caused by fatigue cracking in the outboard bolt
holes of the main wing spar. This airplane's primary usage was flight
instruction.

Bolt Hole Cracks and Other Findings

Following the release of AD 2020-26-16, the FAA and Piper received
over 2,800 bolt-hole eddy current inspection reports. The inspections
performed in the field revealed a mix of observations that warrant
further discussion. Of the total inspections, over 100 reported a
positive eddy current indication, with several including pictures of
the bolt hole showing the source of the indication.

Piper later conducted more detailed inspections in a study of 24
main wing spars with 20 having positive eddy current indications. Out
of the 20 positive indications, 3 were identified as fatigue cracks,
where 1 was confirmed by Piper, and 2 were confirmed by the NTSB. The
remaining were determined to be features not consistent with a crack,
and 1 overstress crack as confirmed by the NTSB.

Though not all are confirmed, many of the indications are likely
not fatigue cracks but are a variety of anomalies in the hole. These
can include corrosion pitting, scratches, gouges, and threading marks
possibly caused by forceful insertion and removal of the close-fit
bolts without proper unloading of the wing or other reasons. While
these may not present as fatigue cracks at the time of inspection,
anomalies in the hole create a stress concentration where cracks can
begin to grow. Therefore, it is still crucial to inspect the critical
bolt holes for these issues and take corrective action to prevent the
formation of fatigue cracks. Piper Service Bulletin No. 1345, Revision
A, dated September 17, 2021 (Piper SB No. 1345, Revision A); and Piper
Service Bulletin No. 1412, dated May 7, 2024 (Piper SB No. 1412),
include procedures for distinguishing between indications caused by
hole damage or other anomalies from those caused by cracks.

In addition to the various forms of non-crack hole damage, the
inspections revealed several cracks in and around the bolt holes. As
part of the AD 2020-26-16 inspection reports, 6 cracks were found,
including 2 later verified by NTSB lab examination and 1 verified by
Piper (from the Piper study referenced above), and 3 visible cracks in
photos. Other known cracks include those found in an airplane in the
same fleet as the 2018 accident airplane, a separately submitted crack
finding confirmed with dye penetrant, and a crack located on the lower
spar cap surface running alongside the inspection bolt holes. Given
these findings, additional cracks may be present among the other
unconfirmed reported indications.

Other cracks have been discovered that may be caused by overload
rather than by fatigue. While use of the airplane within its limits
should not cause an overload crack, some crack findings have revealed
that airplanes have been operated outside their limits. Though cracks
due to overload are not the primary source of this corrective action,
this emphasizes the need for and importance of inspecting the spar bolt
holes for evidence of any cracking.

Long-Term Continued Operational Safety

The AD 2020-26-16 inspection report results indicated that
additional inspections are needed to manage the safety of the fleet.
Data indicates that more airplanes will need to be inspected, including
the need to expand inspections to Piper airplane models that share a
similar structural design of the main wing spar beyond the models
addressed in AD 2020-26-16.

Crack development is a function of many factors, including the
design of the structure, how severely the aircraft is flown, and
manufacturing processes. Small imperfections may exist in any aircraft
structure from an early age; however, through operation, these
imperfections may slowly grow into fatigue cracks. Fatigue cracks have
the effect of weakening the structure and its ability to support the
stresses the airplane was originally designed to handle.

The 2018 accident, along with other accidents in this fleet
attributed to fatigue cracking, and the AD 2020-26-16 inspection
reports, indicate an aging fleet that requires intervention to ensure
any fatigue cracking does not reach a critical state prior to being
detected.

Ensuring further damage is not caused by an inspection itself is
important; however, inspecting for fatigue cracks as well as other hole
anomalies is critical and outweighs the risk associated with doing the
inspections. Piper has developed service actions, most recently in
Piper SB No. 1345, Revision A; and Piper SB No. 1412, that mitigate
inspection-induced damage by emphasizing proper unloading of the wing
for both bolt and wing removal and replacement, if necessary, along
with other instructions for ensuring care of the bolt holes.

Corrective Action Development

Each requirement outlined in this proposed AD has been developed to
both address the unsafe condition and limit the number of required
inspections, reducing the burden on operators where possible. A brief
discussion of each aspect of the requirements continues below.

Airplane Model Grouping

The inspection data received via the reporting requirement in AD
2020-26-16, along with testing of the baseline spar common to all Piper
Model PA-28 and PA-32 airplanes, has shown that inspections should be
extended to include Piper airplane models that share similar structural
design but were not included in the applicability of AD 2020-26-16. It
is likely that a significant contributing factor in the formation of
cracks found in the main wing spar bolt attachment area is the cold
bending of the spar to achieve the wing's dihedral. This method of
forming the spar dihedral combined with the proximity to the wing
attachment bolt holes leads to high residual stress in that area. The
potential for fatigue cracking in and around the bolt holes, as well as
higher variability in crack location and severity, is higher under this
constant additional stress.

In an attempt to support less onerous inspections and to understand
the causal factors, Piper investigated the residual stresses in the
critical bolt-hole area. That investigation showed that the residual
stress due to the spar cold bending process is a significant
contributing factor in reducing the fatigue life of the spar bolt
holes. An additional outcome of this investigation is a change to all
new manufactured spars having machined dihedral bends to eliminate the
residual stresses in the critical area.

Though there are differences between all Model PA-28 and PA-32
airplanes, such as additional reinforcing structure and lower
operational loads, all airplane models share this same baseline spar
with the cold bent dihedral. Differing characteristics allow for a
grouping and tailoring of the requirements for each airplane model, but
all airplane models need to be inspected. The airplane models in the
applicability of this proposed AD are not the same airplane models that
are included in the applicability of the proposed rulemaking action
(Docket No. FAA-2024-2142) that would supersede AD 2020-26-16, and the
proposed required actions are different between these two proposed
rulemaking actions.

The remaining Piper Model PA-28 and PA-32 airplanes that would not
be included in the applicability of this proposed AD either experience
higher operational loads or have less structure. Both of these
conditions increase the stress experienced in the subject bolt holes of
the baseline spar and thus are subject to the proposed rulemaking
action (Docket No. FAA-2024-2142) to supersede AD 2020-26-16.

Determination of Inspection Compliance Time

The proposed compliance time for the eddy-current inspection
specified in this proposed AD was based on an inspection report
received in response to AD 2020-26-16 that showed a crack indication in
a Model PA-32-300 wing
spar, later verified by Piper as a crack. Some airplanes in the
proposed applicability of this AD may have been inspected as part of
the requirements of AD 2020-26-16; however, if cracks in the wing spar
are not expected as early due to the structural differences discussed
above, these inspections may not yield the intended insight into the
state of the wing spars. Therefore, the current proposed compliance
time was set near and prior to the time-in-service of this confirmed
crack finding in a wing spar of the same population as those in the
airplanes in the applicability of this proposed AD.

Wing spars on the affected Piper airplanes could develop cracks
that, if not addressed, would result in a wing separating from the
fuselage in flight.

FAA's Determination

The FAA is issuing this NPRM after determining that the unsafe
condition described previously is likely to exist or develop on other
products of the same type design.

Material Incorporated by Reference Under 1 CFR Part 51

The FAA reviewed Piper Service Bulletin 1412, dated May 7, 2024.
This material specifies procedures for doing a one-time eddy current
inspection of the lower wing spar bolt holes for crack(s) and replacing
any cracked main wing spar. This material also includes instructions to
report the results of the inspection to Piper. 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.

Proposed AD Requirements in This NPRM

This proposed AD would require reviewing airplane maintenance
records to determine if an eddy current inspection of the lower main
wing spar bolt holes was done and depending on the result, doing an
eddy current inspection of the lower wing spar for crack(s) if not
previously done or if done prior to 12,000 hours TIS, and replacing any
cracked main wing spar. This proposed AD would also require sending all
inspection results to Piper and the FAA.

Differences Between This Proposed AD and the Referenced Material

Piper SB 1412 specifies to contact Piper for disposition if any
non-crack damage is found in the main wing spar bolt holes or any
crack(s) or non-crack damage is found in the spar box bolt holes but
this proposed AD would require contacting either the Manager, East
Certification Branch, FAA, or the Piper Organization Designation
Authorization (ODA) for instructions and doing those actions. To be
approved, the repair method, modification deviation, or alteration
deviation must meet the certification basis of the airplane, and the
approval must specifically refer to the proposed AD.

Piper SB 1412 specifies using its feedback form to report the
inspection results but this proposed AD would require using the form
included as Appendix 1 to this proposed AD.

Interim Action

The FAA considers that this proposed AD would be an interim action.
The proposed inspection reports would provide the FAA with additional
data for determining the number of cracks present in the fleet. After
analyzing the data, the FAA may take further rulemaking action.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would
affect 10,927 airplanes of U.S. registry.

The FAA estimates the following costs to comply with this proposed AD:

Estimated Costs

The FAA estimates the following costs to do any necessary actions
that would be required based on the results of the proposed airplane
maintenance records review. The agency has no way of determining the
number of airplanes that might need these actions:

On-Condition Costs

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

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 adding the following new airworthiness
directive: