[Federal Register Volume 89, Number 184 (Monday, September 23, 2024)]
[Proposed Rules]
[Pages 77457-77467]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-21652]


 ========================================================================
 Proposed Rules
                                                 Federal Register
 ________________________________________________________________________
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 This section of the FEDERAL REGISTER contains notices to the public of 
 the proposed issuance of rules and regulations. The purpose of these 
 notices is to give interested persons an opportunity to participate in 
 the rule making prior to the adoption of the final rules.
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  Federal Register / Vol. 89, No. 184 / Monday, September 23, 2024 / 
Proposed Rules  

[[Page 77457]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2024-2142; Project Identifier AD-2024-00033-A]
RIN 2120-AA64


Airworthiness Directives; Piper Aircraft, Inc. Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

-----------------------------------------------------------------------

SUMMARY: The FAA proposes to supersede Airworthiness Directive (AD) 
2020-26-16, which applies to certain Piper Aircraft, Inc. (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 
requires calculating the factored service hours (FSH) for each main 
wing spar to determine when an inspection is required, inspecting the 
lower main wing spar bolt holes for crack(s), and replacing any cracked 
main wing spar. Since the FAA issued AD 2020-26-16, the FAA evaluated 
the reports required by AD 2020-26-16 and determined that repetitive 
inspections of the lower main wing spar bolt holes for crack(s) and 
non-crack damage (including deep scratches, gouges, and thread marks) 
and replacement or modification of the main wing spar should be 
required, calculated service hours (CSH) should be used instead of FSH 
to determine times for required actions for each main wing spar, and 
that certain airplanes should be removed from the applicability and a 
new airplane model added to the applicability. This proposed AD would 
require calculating the CSH for each main wing spar; repetitively 
inspecting the lower main wing spar bolt holes for crack(s) and non-
crack damage and taking corrective actions as needed; and replacing or 
modifying main wing spars at a specified time. This proposed AD would 
also revise the applicability by removing certain airplanes and adding 
a new airplane model. 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 7, 
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-2024-2142; 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: [email protected].

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 ADDRESSES. Include ``Docket No. FAA-2024-2142; Project Identifier 
AD-2024-00033-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 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 
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-

[[Page 77458]]

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 FSH 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 follows from that determination. The FAA evaluated the 
inspection reports submitted by operators as required by AD 2020-26-16 
and determined that additional action is needed, including requiring 
repetitive inspections of the lower main wing spar bolt holes for 
crack(s) and non-crack damage and replacement or modification of the 
main wing spar, using CSH instead of FSH to determine times for 
required actions, and revising the applicability by removing certain 
serial-numbered Piper Model PA-32-300 airplanes and all Model PA-32R-
300, PA-32RT-300, and PA-32RT-300T airplanes because those airplanes 
would be included in the applicability of a proposed separate 
rulemaking action. The FAA also determined that Piper Model PA-32S-300 
airplanes should be added to the applicability.
    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. 1372, dated April 3, 2024 (Piper SB No. 1372), 
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 of the 
same operator 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. 
While AD 2020-26-16 addressed the immediate safety concern, data 
indicates that more airplanes will need to be inspected and, due to 
aging, the airplanes already inspected will need additional 
inspections. This includes the need to expand inspections to include 
Piper Model PA-32S-300 airplanes in the applicability of this proposed 
AD because these airplanes share a similar structural design of the 
main wing spar

[[Page 77459]]

with the airplane 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 aircraft 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. This often takes the form of repetitive inspections to be 
able to capture the formation of a detectable crack, requiring repair 
or replacement. The FAA has also determined that inspections alone are 
not sufficient to keep the fleet risk acceptably low long-term. Cracks 
are more likely to develop with aging of the main wing spar, so over 
time it becomes more likely that cracks will exist throughout the fleet 
and could be missed by inspection, due in part to the inherent 
imperfections of the inspection method; therefore, replacement or 
modification of the spars is needed. Both the FAA and Piper attempted 
to determine an inspection program that would manage risk to an 
acceptable level using inspection alone; however, no method could be 
found that did not eventually require spar replacement.
    Ensuring further damage is not caused by the inspection itself is 
important, especially with repetitive inspections; however, inspecting 
for fatigue cracks as well as other hole anomalies is critical and 
outweighs the risk associated with repetitive inspections. 
Additionally, repeated inspections inherently allow for continued 
direct observation of the bolt holes over time and correcting non-crack 
damage if necessary. Piper has developed service actions, most recently 
in Piper SB No. 1345, Revision A, and Piper SB No. 1372, 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 all models that share a similar structural design 
by utilizing the same baseline spar. 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 current proposed 
requirements separate models into two groups, each requiring its own 
actions with a separate action for a third group under a separate 
proposed rulemaking action. The airplane models discussed share similar 
spar structure, while one group experiences higher operational loads 
than the other, due mostly to differences in gross weight and maximum 
airspeed. The remaining Piper Model PA-28 and PA-32 airplanes that 
would not be included in the applicability of this proposed AD either 
experience lower operational loads or have additional structure, both 
effectively lowering the stress experienced in the subject bolt holes 
of the baseline spar.

Hours Calculation

    The potential for fatigue cracking of the main wing spar bolt holes 
is highly influenced by the usage profile of the spar and airplane. For 
airplanes included in the applicability of this proposed AD, the 
primary usage is either flight instruction or personal use. Flight 
instruction consists of more hours spent flying at lower altitudes 
where the airplane is exposed to gusts and more takeoffs and landings 
than is typical for personal usage. These characteristics lead to 
reaching the fatigue life of the spar more quickly than personal usage, 
which generally involves a large time spent in cruise and fewer 
takeoffs and landings. As a result of the usage differences, the same 
TIS for an airplane used in flight instruction is not equivalent to the 
same time for a personal-use airplane.
    An FSH equation was established in AD 2020-26-16 to account for the 
differences in usage and reduce the burden on personal use airplanes. 
This equation is still the best method available to account for 
different usage when determining when inspections should occur. In the 
United States, airplanes used in flight instruction for hire are 
required by FAA regulation to receive 100-hour inspections. Because 
instructional usage is unable to be tracked directly, a count of these 
inspections is used as a method for determining instructional usage to 
differentiate it from personal usage.
    When AD 2020-26-16 was issued, available analysis indicated 
instructional usage was approximately 17 times more severe than 
personal usage, leading to this factor appearing in the FSH equation. 
After AD 2020-26-16 was published, further analysis completed by Piper 
estimated this factor was significantly lower. This has resulted in a 
new equation, now referred to as CSH in Piper SB No. 1372. The CSH 
calculation has the same instructions and intent as the FSH from AD 
2020-26-16, but the value in the equation has been updated based on 
improved analysis and data. For Group 1 airplanes this proposed AD 
would require using a value of 3 instead of the value of 2 that is 
specified in Piper SB No. 1372, and a value of 2 would be used for 
Group 2 airplanes, as specified in Piper SB No. 1372.

Determination of Inspection and Spar Retirement or Modification Timing

    The fleet corrective actions analyzed consist of an initial 
inspection, followed by repetitive inspections until a time is

[[Page 77460]]

reached when the spar should be modified or replaced. The FAA has 
worked with Piper to develop the specific timing for these actions 
using actual service data to determine current and future risk of 
fatigue cracks developing, and analysis using the physical properties 
of the structure to estimate formation and growth of cracks in the 
critical area of the spar. These efforts have resulted in inspection 
timing estimates that provide opportunities to locate cracks before 
reaching a critical size.
    The proposed initial inspection time requirements for Group 1 and 
Group 2 airplanes have been determined using data from AD 2020-26-16 
inspection reports and prior inspections consisting of known crack 
findings and known inspections that did not find an anomaly that 
exceeds the eddy current size threshold, to estimate times when a crack 
will exist in each group's fleet. An initial inspection time is then 
set just prior to when cracks would be expected in the fleet. This 
proposed initial inspection serves as a baseline inspection and will be 
followed by repetitive inspections to ensure a crack is not missed.
    The proposed repetitive inspection programs have been set 
differently for each airplane group. For Group 1 airplanes, a tiered 
approach of inspecting more often with increasing age has been proposed 
as a method of reducing the burden on lower TIS airplanes. It is 
possible to inspect less used airplanes less often because these carry 
the least risk of developing a fatigue crack within the population. As 
age increases, and therefore risk increases, the proposed inspections 
are set to be more frequent. A similar approach would be possible for 
Group 2 airplanes, but the inspection intervals are estimated to be 
much shorter based on inspection data, structural design, and airplane 
performance, so stepping down with age would not be practical.
    As an airplane ages, the likelihood or risk of a crack developing 
increases. A potential solution to this would be to continue to 
increase the frequency of inspections to ensure a crack is found before 
reaching a critical length; however, frequent and increased inspections 
are not a practical or safe approach due to the inherent risk in 
repeated bolt removal and reinsertion. At the fleet level, an ever-
increasing age of the fleet means a higher risk that cracks are present 
in the fleet and may be missed, even with frequent inspections. This 
leaves a solution of removing or modifying the highest age spars to 
reduce and maintain the fleet risk, therefore spar retirement or 
modification where possible is proposed.
    These proposed fleet inspection requirements must be adjusted as 
needed to ensure cracks are found before they reach a critical size. A 
recent inspection of a Model PA-28-181 airplane main wing spar was 
performed at a time earlier than required by AD 2020-26-16 and revealed 
cracks at a TIS earlier than anticipated. A section of the main wing 
spar was sent to an independent materials lab, and under high 
magnification normally spaced fatigue striations were found, confirming 
this crack was caused by fatigue. This new finding required the FAA to 
adjust the Group 1 inspection schedules to earlier times to ensure a 
similar crack would be found in time.
    Although this airplane was used almost exclusively for flight 
instruction, reducing the inspection times resulted in additional 
burden on all airplanes, including those for personal usage. Therefore, 
for this proposed AD, the FAA determined that for Group 1 airplanes a 
value of 3 should be used in the CSH instead of the value of 2 that is 
specified in Piper SB No. 1372. An increase in this value from 2 to 3 
serves to mitigate the increased burden on Group 1 airplanes resulting 
from the reduced inspection times and provides relief for operators of 
personal-use airplanes.

Spar Modification and Replacement Options

    Piper has developed a reinforcement kit as an option and 
alternative to retirement of the main wing spar, applicable to certain 
Group 1 airplanes. There is currently no spar modification developed 
for Piper Model PA-28R-180 and PA-28R-200 airplanes that are included 
in Group 1 or any airplanes designated as Group 2 airplanes, as 
specified in Piper SB No. 1372. The proposed inspection times after 
installing a reinforcement kit would provide an extended life of the 
main wing spar and longer intervals between the proposed repetitive 
inspections. The reinforcement kit provides additional structure that 
lowers and distributes the stress in the critical areas, allowing for 
slower crack growth. Piper used damage tolerance analysis when 
developing the inspection times after a reinforcement kit is installed.
    Finally, new wing spars are available from Piper that have machined 
the spar dihedral bend instead of the cold bending process, eliminating 
the residual stress factor in these spars. These new wing spars have a 
different life limit and will not require any inspections.
    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 SB No. 1372. This material specifies 
procedures for reviewing airplane maintenance records to determine the 
number of 100-hour inspections completed on the airplane since new and 
any record of main wing spar replacement; calculating the service 
hours; doing eddy current inspections of the main wing spar bolt holes 
for crack(s) and non-crack damage; repairing bolt holes with non-
cracking damage; for certain airplanes installing a main wing spar 
reinforcement kit; and replacing a main wing spar.
    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.

Proposed AD Requirements in This NPRM

    This proposed AD would retain none of the requirements of AD 2020-
26-16. This proposed AD would revise the applicability by removing 
certain serial-numbered Model PA-32-300 airplanes and all Piper Model 
PA-32R-300, PA-32RT-300, and PA-32RT-300T airplanes because those 
airplanes will be included in a separate proposed rulemaking action. 
This proposed AD would add serial-numbered Model PA-28R-200 and PA-28R-
201 airplanes to the applicability to include all serial numbers and 
would also add Piper Model PA-32S-300 airplanes to the applicability. 
This proposed AD would require accomplishing the actions specified in 
the material already described, except as discussed under ``Differences 
Between this AD and the Referenced Material.'' This proposed AD would 
also require reporting inspection results to Piper and the FAA if any 
cracks are found during any inspection.

Differences Between This Proposed AD and the Referenced Material

    For Group 1 airplanes, to determine the CSH, instead of using the 
value of 2 provided in the simplified formula in Part 1, paragraph 2.b 
of the Instructions

[[Page 77461]]

in Piper SB No. 1372, this proposed AD would require using a value of 
3.
    In addition, for Group 1 airplanes, the compliance times for the 
initial and repetitive inspections and the replacement or modification 
of the main wing spars specified in paragraphs (i) and (j) of this 
proposed AD are different from what is in Table 1 of Piper SB No. 1372.

Costs of Compliance

    The FAA estimates that this AD, if adopted as proposed, would 
affect 10,665 airplanes of U.S. registry.
    The FAA estimates the following costs to comply with this proposed 
AD:

                                                 Estimated Costs
----------------------------------------------------------------------------------------------------------------
                                                                                                 Cost on U.S.
              Action                    Labor cost        Parts cost      Cost per product        operators
----------------------------------------------------------------------------------------------------------------
Review airplane maintenance        3 work-hours x $85               $0  $255, per records    $2,719,575, per
 records and determine CSH for      per hour = $255,                     review.              records review.
 each main wing spar.               per records review.
----------------------------------------------------------------------------------------------------------------

    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 and CSH calculation. The agency has no way 
of determining the number of airplanes that might need these actions:

                                               On-Condition Costs
----------------------------------------------------------------------------------------------------------------
                 Action                           Labor cost            Parts cost         Cost per product
----------------------------------------------------------------------------------------------------------------
Eddy current inspections of the left-     1 work-hour contracted                 $20  $960 per inspection.
 hand (LH) and right-hand (RH)             service x $600 per hour =
 inspection areas LH and RH lower main     $600 for the eddy current
 wing spar (including access and           inspection.
 restoring the airplane).                 4 work-hours x $85 per
                                           hour for access and
                                           restoring = $340.
Report inspection results to the FAA and  1 work-hour x $85 per hour               0  85 per report.
 Piper Aircraft, Inc.                      = $85 per report.
Repair holes with non-crack damage......  2 work-hours x $85 per                  20  190.
                                           hour = $170.
Replace main wing spar..................  40 work-hours x $85 per             10,983  14,383 per main wing spar.
                                           hour = $3,400 per main
                                           wing spar.
Install modification (reinforcement) kit  190 work-hours x $85 per             4,000  20,150 per wing spar.
                                           hour = $16,150 per main
                                           wing spar.
----------------------------------------------------------------------------------------------------------------

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 that the 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

0
1. The authority citation for part 39 continues to read as follows:


[[Page 77462]]


    Authority:  49 U.S.C. 106(g), 40113, 44701.


Sec.  39.13   [Amended]

0
2. The FAA amends Sec.  39.13 by:
0
a. Removing Airworthiness Directive 2020-26-16, Amendment 39-21371 (86 
FR 3769, January 15, 2021); and
0
b. Adding the following new airworthiness directive:

Piper Aircraft, Inc.: Docket No. FAA-2024-2142; Project Identifier 
AD-2024-00033-A.

 (a) Comments Due Date

    The FAA must receive comments on this airworthiness directive 
(AD) by November 7, 2024.

 (b) Affected ADs

    This AD replaces AD 2020-26-16, Amendment 39-21371 (86 FR 3769, 
January 15, 2021) (AD 2020-26-16).

 (c) Applicability

    This AD applies to Piper Aircraft, Inc. (Piper) airplanes, 
certificated in any category, with a model and serial number shown 
in Table 1 to paragraph (c) of this AD.

Table 1 to Paragraph (c)--Applicability and Airplane Group
[GRAPHIC] [TIFF OMITTED] TP23SE24.000

(d) Subject

    Joint Aircraft System Component (JASC) Code 5711, Wing Spar.

(e) Unsafe Condition

    This AD was prompted by a report of a wing separation caused by 
fatigue cracking in a visually inaccessible area of the main wing 
lower spar cap. The FAA is issuing this AD to detect and correct 
fatigue cracks in the lower main wing spar cap bolt holes. The 
unsafe condition, if not addressed, could result in a wing 
separating from the fuselage in flight.

(f) Compliance

    Comply with this AD within the compliance times specified, 
unless already done.

(g) Definitions

    For the purpose of this AD the following definitions apply.
    (1) Group 1 airplanes: Airplanes identified as Group 1 in Piper 
Service Bulletin No. 1372, dated April 3, 2024 (Piper SB No. 1372) 
and Table 1 to paragraph (c) of this AD.
    (2) Group 2 airplanes: Airplanes identified as Group 2 in Piper 
SB No. 1372 and Table 1 to paragraph (c) of this AD.

(h) Review Airplane Maintenance Records and Determine Calculated 
Service Hours for Each Main Wing Spar

    (1) Within 30 days after the effective date of this AD and 
thereafter at intervals not to exceed 100 hours time-in-service 
(TIS) or 12 months, whichever occurs first, review the airplane 
maintenance records and determine the number of 100-hour inspections 
completed on the airplane since new and any record of wing spar 
replacement(s) in accordance with Part I, paragraph 1, of the 
Instructions in Piper SB No. 1372. The owner/operator (pilot) 
holding at least a private pilot certificate may accomplish this and 
must enter compliance with this paragraph of the AD into the 
airplane

[[Page 77463]]

maintenance records in accordance with 14 CFR 43.9(a) and 
91.417(a)(2)(v). The record must be maintained as required by 14 CFR 
91.417, 121.380, or 135.439.
    (2) Before further flight after doing the action required by 
paragraph (h)(1) of this AD, determine the calculated service hours 
(CSH) for each main wing spar using the applicable formula for your 
airplane group specified in Figure 1 or Figure 2 to paragraph (h)(2) 
of this AD and in accordance with Part I, paragraphs 2.a. through 
b., of the Instructions in Piper SB No. 1372. Thereafter, after each 
100-hour or annual inspection, re-calculate the CSH for each main 
wing spar to determine the compliance time for the actions required 
by paragraphs (i) and (j) of this AD. If a factored service hour 
(FSH) inspection required by AD 2020-26-16 was done using Piper 
Service Bulletin No. 1345, dated March 27, 2020; or Piper Service 
Bulletin No. 1345A, dated September 17, 2021, you may use that data, 
including the TIS and number of 100-hour inspections at the time of 
the last inspection, to calculate the CSH for that inspection using 
the requirements of paragraph (h) of this AD and Part I, paragraph 
2.c. of the Instructions in Piper SB No. 1372 to determine the next 
required actions, including if an action is now due according to the 
requirements of paragraphs (i) and (j) of this AD.

Figure 1 to Paragraph (h)(2)--Group 1 Airplanes CSH Calculation
[GRAPHIC] [TIFF OMITTED] TP23SE24.001

    Note 1 to Figure 1 to paragraph (h)(2): This calculation is not 
the same as the simplified calculation specified in Piper SB No. 
1372 because this calculation uses a value of 3, for Group 1 
airplanes only, and Piper SB No. 1372 uses a value of 2.

Figure 2 to paragraph (h)(2)--Group 2 Airplanes CSH Calculation
[GRAPHIC] [TIFF OMITTED] TP23SE24.002

    Note 2 to Figure 2 to paragraph (h)(2): This calculation is the 
same as the simplified calculation specified in Piper SB No. 1372, 
but with a different form, and is for Group 2 airplanes only.

 (i) Bolt Hole Inspections and Corrective Actions

    (1) Do initial and repetitive eddy current inspections of the 
inner surface of each bolt hole in the lower wing spar cap for 
cracks and for non-crack damage (including deep scratches, gouges, 
and thread marks), at the times in Table 2 and Table 3 to paragraph 
(i)(1) of this AD and in accordance with Part II, paragraph 4.a. of 
the Instructions in Piper SB No. 1372. Although Piper SB No. 1372 
specifies NAS 410 Level II or Level III certification to perform 
eddy current and fluorescent penetrant inspections, this AD allows 
Level II or Level III qualification standards for inspection 
personnel using any inspector criteria approved by the FAA.
    Note 3 to paragraph (i)(1): FAA Advisory Circular 65-31B, 
``Training, Qualification, and Certification of Nondestructive 
Inspection Personnel,'' dated February 24, 2014, contains FAA-
approved Level II and Level III qualification standards criteria for 
personnel doing nondestructive test inspections.

Table 2 to Paragraph (i)(1)--Compliance Times for Group 1 Airplane 
Inspections

[[Page 77464]]

[GRAPHIC] [TIFF OMITTED] TP23SE24.003

    Note 4 to Table 2 to Paragraph (i)(1):
    The compliance times are not the same as the times specified in 
Piper SB No. 1372 for Group 1 airplanes.

Table 3 to Paragraph (i)(1)--Compliance Times for Group 2 Airplane 
Inspections
[GRAPHIC] [TIFF OMITTED] TP23SE24.004

    Note 5 to Table 3 to paragraph (i)(1): The compliance times are 
the same as the times specified in Piper SB No. 1372 for Group 2 
airplanes.
    (2) For any Group 1 or Group 2 airplane where the initial CSH 
cannot be calculated due to missing or incomplete airplane 
maintenance records: Do the initial inspection within 100 hours TIS 
or 60 days after the effective date of this AD, whichever occurs 
later.
    (3) If an eddy current inspection does not identify any 
indications, then continue the repetitive eddy current inspections 
required by paragraph (i)(1) of this AD at the applicable times 
specified in Table 2 and Table 3 to paragraph (i)(1) of this AD.
    (4) If any eddy current inspection identifies any indications or 
noisy signal, before further flight, do the applicable actions 
specified in Part II, paragraphs 4.b. through i., and if applicable 
the bolt hole oversize repair specified in Part III, paragraphs 1. 
through 7. and paragraph 9., of the Instructions in Piper SB No. 
1372.
    (5) If any eddy current inspection identifies any crack(s), 
before further flight, do the applicable actions specified in Part 
II, paragraph 4.k., of the Instructions in Piper SB No. 1372, and 
replace the affected main wing spar in accordance with Part IV, 
paragraphs 2.a. through d., of the Instructions in Piper SB No. 
1372.

(j) Replace or Modify Main Wing Spar

    For Group 1 and Group 2 airplanes:
    (1) At the applicable time specified in Table 4 to paragraph (j) 
of this AD replace the affected main wing spars in accordance with 
Part IV, paragraphs 2.a. through d., of the Instructions in Piper SB 
No. 1372 or modify the main wing spars by installing the Piper 
reinforcement kit, in accordance with Part IV, paragraphs 1.a. 
through c., of the Instructions in Piper SB No. 1372.
    (2) As required by paragraph (i)(5) of this AD, replace the 
affected main wing spars in

[[Page 77465]]

accordance with Part IV, paragraphs 2.a. through d., of the 
Instructions in Piper SB No. 1372.

Table 4 to Paragraph (j)--Compliance Times for Main Wing Spar 
Modification or Replacement
[GRAPHIC] [TIFF OMITTED] TP23SE24.005

    If any cracks are found during any inspection required by 
paragraph (i) of this AD: After completing that inspection, using 
Appendix 1, ``Inspection Results Form,'' of this AD, report the 
inspection results to the FAA, East Certification Branch, and to 
Piper Aircraft, Inc. Submit the report at the applicable time 
specified in paragraph (k)(1) or (2) of this AD.
    (1) If the action was done on or after the effective date of 
this AD, submit the report within 30 days after the action was done.
    (2) If the action was done before the effective date of this AD, 
submit the report within 30 days after the effective date of this 
AD.

(l) Special Flight Permit

    A special flight permit may be issued in accordance with 14 CFR 
21.197 and 21.199 to permit a one-time, non-revenue ferry flight to 
a location where the airplane can be inspected. This ferry flight 
must be performed with only essential flight crew. This AD prohibits 
a special flight permit if any inspection reveals a crack in the 
main wing spar.

(m) Alternative Methods of Compliance (AMOCs)

    (1) The Manager, East Certification Branch, FAA, has the 
authority to approve AMOCs for this AD, if requested using the 
procedures found in 14 CFR 39.19. In accordance with 14 CFR 39.19, 
send your request to your principal inspector or local Flight 
Standards District Office, as appropriate. If sending information 
directly to the manager of the East Certification Branch, send it to 
the attention of the person identified in paragraph (n) of this AD 
and email to: [email protected].
    (2) Before using any approved AMOC, notify your appropriate 
principal inspector, or lacking a principal inspector, the manager 
of the local flight standards district office/certificate holding 
district office.
    (3) AMOCs approved for AD 2020-26-16 are not approved as AMOCs 
for the corresponding provisions of this AD.

(n) Additional Information

    (1) For more information about this AD, contact Fred Caplan, 
Aviation Safety Engineer, FAA, East Certification Branch, FAA, 1701 
Columbia Avenue, College Park, GA 30337; phone: (404) 474-5507; 
email: [email protected].
    (2) Piper material identified in this AD that is not 
incorporated by reference is available at the address specified in 
paragraph (o)(3) of this AD.
    (3) FAA Advisory Circular 65-31B, ``Training, Qualification, and 
Certification of Nondestructive Inspection Personnel,'' dated 
February 24, 2014, maybe found at drs.faa.gov.

(o) Material Incorporated by Reference

    (1) The Director of the Federal Register approved the 
incorporation by reference (IBR) of the material listed in this 
paragraph under 5 U.S.C. 552(a) and 1 CFR part 51.
    (2) You must use this material as applicable to do the actions 
required by this AD, unless the AD specifies otherwise.
    (i) Piper Service Bulletin No. 1372, dated April 3, 2024.
    (ii) [Reserved].
    (3) For Piper material identified in this AD, contact Piper 
Aircraft, Inc., 2926 Piper Drive, Vero Beach, FL 32960; phone: (772) 
567-4361; email: piper.com">customerservice@piper.com; website: piper.com.
    (4) 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.
    (5) You may view this material at the National Archives and 
Records Administration (NARA). For information on the availability 
of this material at NARA, visit www.archives.gov/federal-register/cfr/[email protected]">www.archives.gov/federal-register/cfr/[email protected].

Appendix 1 to Docket No. FAA-2024-2142

[[Page 77466]]

[GRAPHIC] [TIFF OMITTED] TP23SE24.006



[[Page 77467]]


    Issued on September 10, 2024.
Victor Wicklund,
Deputy Director, Compliance & Airworthiness Division, Aircraft 
Certification Service.
[FR Doc. 2024-21652 Filed 9-20-24; 8:45 am]
 BILLING CODE 4910-13-P