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[Federal Register: January 20, 2010 (Volume 75, Number 12)]
[Rules and Regulations]               
[Page 3127-3141]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr20ja10-2]                         

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2007-27862; Directorate Identifier 2007-CE-036-AD; 
Amendment 39-16150; AD 2009-26-11]
RIN 2120-AA64

 
Airworthiness Directives; Thrush Aircraft, Inc. Model 600 S2D and 
S2R Series Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: We are adopting a new airworthiness directive (AD) to 
supersede AD (AD) 2006-07-15, which applies to Thrush Aircraft, Inc. 
Model 600 S2D and S2R (S-2R) series airplanes (type certificate 
previously held by Quality Aerospace, Inc. and Ayres Corporation). AD 
2006-07-15 currently requires repetitive inspections of the 1/4-inch 
and 5/16-inch bolt hole areas on the wing front lower spar caps for 
fatigue cracking; replacement or repair of any wing front lower spar 
cap where fatigue cracks are found; and reporting of any fatigue cracks 
found to the FAA. AD 2006-07-15 also puts the affected airplanes into 
groups for compliance time and applicability purposes. Since we issued 
AD 2006-07-15, FAA analysis reveals that inspections are not detecting 
all existing cracks and shows the incidences of undetected cracks will 
increase as the airplanes age. Consequently, this AD retains the 
actions of AD 2006-07-15 and imposes a life limit on the wing front 
lower spar caps that requires replacement of the wing front lower spar 
caps when the life limit is reached. This AD also changes the 
requirements and applicability of the groups discussed above and 
removes the ultrasonic inspection method. We are issuing this AD to 
prevent wing front lower spar cap failure caused by undetected fatigue 
cracks. Such failure could result in loss of a wing in flight.

DATES: This AD becomes effective on February 24, 2010.
    On February 24, 2010, the Director of the Federal Register approved 
the incorporation by reference of Thrush Aircraft, Inc. Custom Kit No. 
CK-AG-41, Revision A, dated March 8, 2007, listed in this AD.
    As of May 20, 2003 (68 FR 15653), the Director of the Federal 
Register approved the incorporation by reference of Quality Aerospace, 
Inc. Custom Kit No. CK-AG-30, dated December 6, 2001, listed in this 
AD.
    As of July 25, 2000 (65 FR 36055), the Director of the Federal 
Register approved the incorporation by reference of Ayres Corporation 
Service Bulletin No. SB-AG-39, dated September 17, 1996; and Ayres 
Corporation Custom Kit No. CK-AG-29, dated December 23, 1997, listed in 
this AD.

ADDRESSES: To get the service information identified in this AD, 
contact Thrush Aircraft, Inc., 300 Old Pretoria Road, P.O. Box 3149, 
Albany, Georgia 31706-3149. The service

[[Page 3128]]

information is also available on the Internet at http://www.thrushaircraft.com.
    To view the AD docket, go to U.S. Department of Transportation, 
Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 
New Jersey Avenue, SE., Washington, DC 20590, or on the Internet at 
http://www.regulations.gov. The docket number is FAA-2007-27862; 
Directorate Identifier 2007-CE-036-AD.

FOR FURTHER INFORMATION CONTACT:
--Cindy Lorenzen, Aerospace Engineer, ACE-115A, Atlanta Aircraft 
Certification Office, 1701 Columbia Avenue, College Park, Georgia 
30337; telephone: (404) 474-5524; facsimile: (404) 474-5606; e-mail: 
cindy.lorenzen@faa.gov; or
--William O. Herderich, Aerospace Engineer, ACE-117A, Atlanta Aircraft 
Certification Office, 1701 Columbia Avenue, College Park, Georgia 
30337; telephone: (404) 474-5547; facsimile: (404) 474-5606; e-mail: 
william.o.herderich@faa.gov.

SUPPLEMENTARY INFORMATION: 

Discussion

    On April 27, 2009, we issued a proposal to amend part 39 of the 
Federal Aviation Regulations (14 CFR part 39) to include an AD that 
would apply to certain Thrush Aircraft, Inc. Model 600 S2D and S2R (S-
2R) series airplanes (type certificate previously held by Quality 
Aerospace, Inc. and Ayres Corporation). This proposal was published in 
the Federal Register as a notice of proposed rulemaking (NPRM) on May 
4, 2009 (74 FR 20431). The NPRM proposed to supersede AD 2006-07-15, 
Amendment 39-14542 (71 FR 19788, April 17, 2006) with a new AD that 
would:
     Retain the actions of AD 2006-07-15;
     Add life limits for the wing front lower spar caps;
     Lower the initial and repetitive inspection times for 
Group 5 airplanes;
     Correct some airplane Group classifications;
     Add an airplane to the Applicability section; and
     Remove the use of ultrasonic inspection methods.
    For replacement of the wing front lower spar caps, the initial 
compliance time for all airplanes will be at least an additional 500 
hours time-in-service (TIS) after the effective date of this AD. 
Calculated from actual flight hour data from 285 S2R series airplanes, 
500 hours TIS equates to the average yearly operational time. The 
compliance schedules should give owner/operators enough time to 
schedule the replacement of the wing front lower spar caps.
    Although not required in this AD, we recommend installing ``big 
butterfly'' and lower splice plates, P/N 20211-09 and P/N 20211-11, or 
Thrush Aircraft, Inc. Custom Kit No. CK-AG-41, Revision A, since they 
increase the strength of the wing beyond the minimum safety standards.

Comments

    We provided the public the opportunity to participate in developing 
this AD. The following presents the comments received on the proposal 
and FAA's response to each comment:

Comment Issue No. 1: Extend Compliance Time To Replace the Spar Caps

    Marc Fries states that a large portion of the affected airplanes 
will need to address a spar replacement within a very short period of 
time, overwhelming a limited number of repair facilities. Mr. Fries 
also states that most operators have a short ``down time'' during their 
season in which to do this type of repair, and many operators will run 
out of flying hours before a repair facility can do the work or even 
get the kits from the factory.
    Mr. Fries requests an extension of the compliance time because 
there are a limited number of repair facilities, and the replacement 
parts may not be available immediately. Mr. Fries also requests to 
insert into the AD an allowance for an extension of the compliance time 
while continuing the spar cap inspections.
    We do not agree with the commenter. As stated in the NPRM, 
allowance for the compliance time based on the limited number of repair 
facilities and the limited availability of replacement parts has 
already been made. For airplanes that have already exceeded the life 
limit replacement time for the wing front lower spar caps, the minimum 
compliance time for those with the highest hours TIS, which are the 
airplanes with the highest risk of spar cap failure, is 500 hours TIS. 
Five hundred hours TIS equates to an average year of operation for 
these airplanes. Airplanes that have exceeded the life limit 
replacement time, but are not at the highest level of risk, will be 
allowed an even longer compliance time of 1,000 hours TIS, 1,500 hours 
TIS, or 2,000 hours TIS based on the current number of hours TIS on the 
wing front lower spar caps. Airplanes that have not yet reached the 
life limit replacement time are allowed a minimum of 2,000 hours TIS to 
comply with the AD. These compliance times result in an average 
operator having at least one year to comply with the AD; however, most 
operators will have much longer than one year to replace the wing front 
lower spar caps. These graduated compliance times should allow enough 
time for adequate supply of parts and repair facility availability.
    We are not changing the final rule AD action based on this comment.

Comment Issue No. 2: Withdraw the AD

    Charles Brumley states that the pilot should be allowed to make his 
own decision whether a new spar cap is needed and requests an 
alternative to this AD.
    Mr. Brumley further states that he believes the AD is unnecessary 
for the following reasons:
     If the pilot is involved in the maintenance of the 
airplane, then the pilot can make an informed decision about whether or 
not to install a new spar cap and whether or not the aircraft is in a 
condition for safe operation;
     The AD will cause undue economic hardship on the airplane 
operators and the farms that use aerial application services;
     There have only been a few cracks found, i.e., that there 
is not enough service history to support issuance of an AD; and
     The large butterfly plates are adequate to ensure safety 
of the pilot until a spar cap crack is found.
    We infer this as a request for the FAA to withdraw the AD.
    We do not agree with the commenter. While the commenter may have 
maintained his airplane adequately, the formation of fatigue cracks 
mainly relates to the airplane's design and operation. Replacement of 
the wing front lower spar caps when they have reached their life limits 
is currently the only means known to the FAA to address the unsafe 
condition.
    We have extensive crack data that currently shows 176 wings on 123 
airplanes had cracks in the wing front lower spar caps. As the 
incidences of cracking increase, which has occurred in the Thrush 
airplanes, the chance of an existing crack not being detected during an 
inspection increases. Airplanes with cracks in the wing front lower 
spar caps are unable to meet ultimate strength requirements, which 
could lead to a wing failure. The only known way of mitigating this 
risk is to replace the wing front lower spar caps.
    There are already procedures in place for owner/operators to 
request an alternative to any AD. Use the alternative method of 
compliance (AMOC) procedures provided in this AD

[[Page 3129]]

to request an AMOC. The request for an AMOC must include any 
substantiating information, such as stress and fatigue data. The AMOC 
will be approved if we find it provides an acceptable level of safety.
    We are not changing the final rule AD action based on this comment.

Comment Issue No. 3: Adjusted Life Limits Based on Environmental 
Conditions

    Avenger Aircraft and Services (Avenger) states the life limits for 
the wing front lower spar caps should be adjusted if environmental 
conditions were not taken into account when determining the life 
limits. The commenter states that metal fatigue is influenced by 
environmental conditions.
    We do not agree with the commenter's request to adjust the life 
limits. We did take environmental conditions into consideration during 
our analysis for determining the life limits. The risk-based analysis 
used by the FAA used actual reported crack data from in-service 
airplanes. These in-service data came from airplanes operated in a 
variety of environments; therefore, the raw data used in the FAA's 
analysis include the effects caused by environmental conditions.
    We are not changing the final rule AD action based on this comment.

Comment Issue No. 4: Adjust Life Limits Based on Crack Sizes

    Avenger states that the life limit of the wing front lower spar cap 
could be much shorter if crack sizes are taken into account during the 
risk assessment. Avenger also states that this can be particularly 
significant when some fleet crack sizes may have exceeded the critical 
size without failing due to the airplane not exceeding limit load at 
that particular time.
    We do not agree with the commenter's request. Although we did not 
include the crack size in our analysis, we did use a statistical 
approach and took into account the TIS on the wing front lower spar cap 
when the crack was found and reported to the FAA. There are other 
factors in place in the AD to mitigate the risk associated with not 
using crack size to determine the life limit of the wing front lower 
spar caps. We determined a life limit for continued operational safety 
of the S2R fleet and did not propose a life limit as defined in FAA 
guidance for type certification of newly certificated airplanes. Our 
analysis of the crack data, which includes allowances for both the 
statistically significant amount of crack data on the Thrush fleet and 
the existence of an inspection program for the wing front lower spar 
caps, yielded the life limits times for the wing front lower spar caps 
shown in the NPRM.
    We are not changing the final rule AD action based on this comment.

Comment Issue No. 5: Remove Magnetic Particle Inspection Method

    Avenger states that the flaw size that can be detected by the 
magnetic particle inspection method is 0.69 inches, which is in excess 
of the flaw size that would allow the wing front lower spar cap to 
continue to carry limit load.
    Avenger states, therefore, magnetic particle inspections should not 
be utilized as a valid inspection method and should be removed from the 
AD.
    We do not agree with the commenter. The magnetic particle 
inspection interval was originally set at 500 hours TIS by AD 2000-11-
16 and was based on crack growth analysis provided by Ayres Corporation 
(Ayres). We accepted Ayres' proposed usage of U.S. Air Force data from 
Report AFWAL 3-5-852, which showed a reliably detectable crack size (90 
percent probability/95 percent confidence) of 0.12 inch when using 
magnetic particle inspection methods. Using this detectable crack size 
with a repetitive inspection of 500 hours TIS allowed for at least two 
inspections to occur after crack initiation and prior to a crack 
reaching its critical size. As the fleet aged and as more cracks 
occurred in-service, the risk to the fleet increased. To help mitigate 
this risk, we doubled the frequency of the inspections required in AD 
2006-07-15. In this AD we are requiring inspections every 250 hours 
TIS, which allows for four chances of detecting a crack based on the 
data originally used by Ayres. This same 250-hour TIS inspection 
interval, along with imposing a wing front lower spar cap life limit to 
further mitigate risk, was included in the proposed AD. The detectable 
crack size of 0.12 inch used by Ayres is very near the values of 
detectable size currently suggested for use by the FAA (Ref. Website 
sponsored by the FAA in conjunction with Iowa State University http://www.cnde.iastate.edu/faa-casr/engineers/index.html) of 0.13 to 0.15 
inch. With the added conservatism of four inspections to detect cracks 
before reaching a critical crack size, when two inspections are what is 
normally required in a more ideal environment, the inspection interval 
in this AD is well within the current guidelines.
    We are not changing the final rule AD action based on this comment.

Comment Issue No. 6: Require Calibration Standards and Level 2 NDT 
Personnel To Perform Eddy Current Inspections

    Avenger states that calibration standards and Level 2 Non-
destructive Testing (NDT) personnel are necessary to achieve 
reliability and repeatability in the inspections. These calibration 
standards are designed to replicate the structure being inspected with 
simulated flaws and are used every time as a setup tool by the 
inspector prior to conducting the on-aircraft inspection. Utilization 
of these standards is the current practice by all major aircraft 
manufacturers and should be required for the Thrush inspections in 
order to ensure a 90 percent probability of detection. In addition, the 
inspectors should be fully certified Level 2 NDT personnel with bolt 
hole eddy current qualifications.
    We do not agree with the commenter's request that a change is 
needed to the AD. This AD and the ADs that this AD supersedes allow for 
eddy current inspection procedures to be approved only through the 
FAA's Aircraft Certification Office (ACO). The FAA ACO already requires 
each procedure to have the correct type of calibration standard as this 
is a basic requirement for ensuring a good inspection. The FAA ACO has 
not and will not approve an eddy current inspection procedure that does 
not include a requirement to use only Level 2, or even more qualified 
Level 3, certified NDT inspectors for these eddy current inspections.
    We are not changing the final rule AD action based on this comment.

Comment Issue No. 7: Allow Installing Supplemental Type Certificate 
(STC) SA03654AT as a Terminating Action in This AD

    Avenger states that a solution that was not available at the time 
the proposed AD was written is now currently on the market. Avenger 
requests that the following information be included in the AD. This 
solution is the Avenger STC SA03654AT Avenger Extended Performance 
Front Spar Enhancement Kit.
    STC SA03654AT installs FAA-approved replacement wing front lower 
spar caps for all airplanes that are the subject of this AD, except for 
Model S2D airplanes. The replacement spars have a life limit of 40,000 
hours TIS with a parts cost of $40,000 and an installation cost of 
$25,500.
    Avenger's FAA STC replacement kit includes the following:
     2 lower wing front lower spar caps (made from stainless 
steel, not 4000 series steel);

[[Page 3130]]

     2 front spar web doublers;
     1 large butterfly plate (redesigned);
     2 larger splice blocks (redesigned); and
     All associated hardware for installation.
    Avenger requests that the AD be amended to include the installation 
of the Avenger Extended Performance (AXP) kit as a terminating action 
to this AD.
    We agree with the commenter. The replacement wing front lower spar 
caps and other modification parts that are approved by STC SA03654AT, 
Installation of Avenger Extended Performance Front Spar Enhancement Kit 
(new wing front spar lower caps, center splice and doublers), in 
accordance with Part II of Avenger Master Data List AAS-MDL-08-001, 
Revision B, dated November 26, 2008, or later FAA-approved revision, 
are a viable terminating action to this AD. The installation of STC 
SA03654AT is an alternative to replacing the wing front lower spar caps 
with Ayres/Thrush wing front lower spar caps.
    We will change the final rule AD action to allow installing STC 
SA03654AT as a terminating action for this AD.

Comment Issue No. 8: Require Reaming Bolt Hole Before Cold Working

    Avenger states it is their opinion that the cold working process 
accomplished as part of the Ayres Corporation Service Bulletin No. SB-
AG-39, dated September 17, 1996, is not being conducted correctly, and 
fatigue damage is being introduced and made more critical than if cold 
working was not accomplished at all. In order to utilize mandrel 
expansion in a safe manner, the hole in question must first be reamed 
to remove any corrosion or existing cracks that are too small to be 
detected. This ``insurance cut'' is required to remove any anomaly in 
the hole that may cause an issue during the cold working process.
    Avenger requests the AD be amended to explicitly state that prior 
to mandrel expansion, an insurance ream, capable of cleaning up a .03 
inch undetected crack followed by a bolt hole eddy current inspection 
using a calibration standard, be accomplished prior to the mandrel 
expansion process.
    We do not agree with the commenter. The AD already requires using 
the cold working procedure found in Ayres Service Bulletin SB-AG-39, 
dated September 17, 1996. Steps 7 and 8 in the Rework section of this 
service bulletin require the bolt holes to be reamed before cold 
working of the holes. These procedures must be accomplished in order to 
be in compliance with this AD.
    We are not changing the final rule AD based on this comment.

Comment Issue No. 9: Require Installing Big Butterfly Plates

    Michael Morris and Mr. Brumley state that instead of mandating the 
replacement of the wing lower spar caps, they would like the FAA to 
require installing big butterfly plates. In addition to installing the 
big butterfly plates, Mr. Morris also requests to keep the current 
inspection intervals for magnetic particle and eddy current 
inspections, and add a visual inspection every 100 hours TIS.
    Mr. Morris states that he believes replacing the spar cap is 
unnecessary for the following reasons:
     The inspection program will continue to work;
     The economic impact is too great; and
     Some operators do not fly as aggressively as others and 
should not be penalized for the actions of the other pilots.
    We do not agree with the commenters. The ``big butterfly'' plate 
does not have enough strength to carry all of the possible flight loads 
in the event the wing spar cap is severed. This plate cannot be solely 
relied upon to ensure the safety of the airplane.
    Even if the spar cap is not completely severed but has a crack that 
is large enough to see when performing the commenter's proposed 100-
hour TIS visual inspection, the remaining strength in the wing spar 
joint is not enough to carry all of the possible flight loads. As 
explained in the proposed AD, inspection reliability for any type of 
inspection method is not 100 percent; therefore, over time the 
probability of an inspection failing to detect a crack increases and 
something more needs to be done to ensure the safety of the airplanes.
    As shown in the Initial Regulatory Flexibility Analysis section of 
the proposed AD, the economic impact was extensively studied. While we 
agree the AD will have a significant economic impact on small 
businesses, the only known way to ensure the safety of the airplane is 
to replace the wing front lower spar caps.
    We also agree that there are many variables affecting the life 
limit of the wing front lower spar caps, including the operating 
weights and operating G loads. Higher weights and higher G loads reduce 
the life limit of the wing front lower spar caps. The only way to 
consider giving credit to those who operate at lower weights and lower 
G loads would be if each individual airplane had recorded data for 
every flight since the wings were installed showing the weights and G 
loads. Each individual airplane owner would then need to have fatigue 
analysis and tests done by a qualified engineer to determine the life 
limit for that particular set of wings based on that recorded data. The 
expense of conducting this type of study for each airplane may be 
higher than the cost of replacement wing front lower spar caps; 
therefore, it may not be an economically viable alternative.
    We are not changing the final rule AD action based on this comment.

Conclusion

    We have carefully reviewed the available data and determined that 
air safety and the public interest require adopting the AD as proposed 
except for the changes previously discussed and minor editorial 
corrections. We have determined that these minor corrections:
     Are consistent with the intent that was proposed in the 
NPRM for correcting the unsafe condition; and
     Do not add any additional burden upon the public than was 
already proposed in the NPRM.

Costs of Compliance

    We estimate that this AD will affect 808 airplanes in the U.S. 
registry, including those airplanes affected by AD 2006-07-15.
    We estimate the following costs to do each inspection:

----------------------------------------------------------------------------------------------------------------
                                                                                 Total cost per   Total cost on
                          Labor cost                              Parts cost        airplane      U.S. operators
----------------------------------------------------------------------------------------------------------------
3 work-hours x $80 = $240....................................            $525             $765         $618,120
----------------------------------------------------------------------------------------------------------------


[[Page 3131]]

    We estimate the following costs to do cold work of bolt holes for 
the repair that may be required based on the results of the inspection. 
We have no way of determining the number of airplanes that may need 
such repair:

------------------------------------------------------------------------
                                                         Total cost per
            Labor cost                  Parts cost          airplane
------------------------------------------------------------------------
1 work-hour x $80 = $80...........              $100               $180
------------------------------------------------------------------------

    We estimate the following costs to do any reaming of outer holes to 
5/16-inch diameter for the repair that may be required based on the 
results of the inspection. We have no way of determining the number of 
airplanes that may need such repair:

------------------------------------------------------------------------
                                                         Total cost per
           Labor cost                 Parts cost            airplane
------------------------------------------------------------------------
1 work-hour x $80 = $80........  None................               $80
------------------------------------------------------------------------

     We estimate the following costs to do any drilling and reaming of 
outer holes and adding three holes to install a Kaplan splice block for 
the repair that may be required based on the results of the inspection. 
We have no way of determining the number of airplanes that may need 
such modification:

------------------------------------------------------------------------
                                                          Total cost per
           Labor cost                  Parts cost            airplane
------------------------------------------------------------------------
65 work-hours x $80 = $5,200...  $4,400 for splice              $10,200
                                  block and $600 for
                                  hardware.
------------------------------------------------------------------------

    We estimate the following costs to do any necessary wing front 
lower spar cap replacement with the optional Ayres or Thrush part 
numbers (P/Ns) 20207-1, 20207-2, 20207-11, 20207-12, 20207-13, 20207-
14, 20207-15, or 20207-16 that will be required based on the results of 
the inspection or by the wing front lower spar cap reaching the life 
limit:

------------------------------------------------------------------------
                                  Parts cost per
Labor cost per wing front lower     wing front        Total cost per
            spar cap              lower spar cap         airplane
------------------------------------------------------------------------
200 work-hours x $80 = $16,000.          $8,000   Each spar cap
                                                   replacement = $24,000
                                                  Two wing front lower
                                                   spar caps per
                                                   airplane = $48,000.
------------------------------------------------------------------------

     However, the supply of individual wing front lower spar caps (new 
or used) is very limited.
    We estimate the following costs to do the optional installation of 
Thrush Aircraft, Inc. Custom Kit No. CK-AG-41, Revision A, dated March 
8, 2007. This kit may be used to do any necessary wing front lower spar 
cap replacements that will be required based on the results of the 
inspection or that will be required based on reaching the life limit:

------------------------------------------------------------------------
                                                         Total cost per
            Labor cost                  Parts cost          airplane
------------------------------------------------------------------------
300 work-hours x $80 = $24,000....           $40,000            $64,000
------------------------------------------------------------------------

     We estimate the following costs to do the optional installation of 
Avenger Aircraft and Services STC SA03654AT for Avenger Extended 
Performance Front Spar Enhancement Kit. This kit may be used to do any 
necessary wing front lower spar cap replacements that will be required 
based on the results of the inspection or that will be required based 
on reaching the life limit:

------------------------------------------------------------------------
                                                         Total cost per
            Labor cost                  Parts cost          airplane
------------------------------------------------------------------------
319 work-hours x $80 = $25,520....           $40,000            $65,500
------------------------------------------------------------------------

     The FAA estimates that 501 airplanes affected by this AD will 
retire before their wing front lower spar cap life limits are reached.

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.

[[Page 3132]]

    We are 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 AD.

Final Regulatory Flexibility Analysis

Introduction and Purpose of This Analysis

    The Regulatory Flexibility Act of 1980 (Pub. L. 96-354) (RFA) 
establishes ``as a principle of regulatory issuance that agencies shall 
endeavor, consistent with the objectives of the rule and of applicable 
statutes, to fit regulatory and informational requirements to the scale 
of the businesses, organizations, and governmental jurisdictions 
subject to regulation.'' To achieve this principle, the RFA requires 
agencies to solicit and consider flexible regulatory proposals and to 
explain the rationale for their actions to assure that such proposals 
are seriously considered. The RFA covers a wide-range of small 
entities, including small businesses, not-for-profit organizations, and 
small governmental jurisdictions.
    Agencies must perform a review to determine whether a rule will 
have significant economic impact on a substantial number of small 
entities. If the agency determines that it will, the agency must 
prepare a regulatory flexibility analysis as described in the RFA.
    We determined that this final rule will have a significant economic 
impact on a substantial number of small entities and, accordingly, as 
required by section 603(a) of the RFA, we prepared and published an 
initial regulatory flexibility analysis (IRFA) as part of the NPRM for 
this final rule (74 FR 20431, May 4, 2009). Section 604 of the RFA also 
requires an agency to publish a final regulatory flexibility analysis 
(FRFA) in the Federal Register when issuing a final rule. Section 
604(a) requires that each FRFA contain:
     A succinct statement of the need for, and objectives of, 
the final rule;
     A summary of the significant issues raised by the public 
comments in response to the IRFA, a summary of agency's assessment of 
such issues, and a statement of any changes made to the proposed final 
rule resulting from such comments;
     A description of the steps the agency has taken to 
minimize the significant economic impact on small entities consistent 
with the stated objectives of applicable statues, including a statement 
of the factual, policy, and legal reasons for selecting the alternative 
adopted in the final rule and why each one of the other significant 
alternatives to the final rule considered by the agency that affect the 
impact on small entities was rejected.
     A description of and an estimate of the number of small 
entities for which the final rule will apply; and
     A description of the projected reporting, recordkeeping, 
and other compliance requirements of the final rule, including an 
estimate of the classes of small entities that will be subject to the 
requirement and the type of professional skills necessary for 
preparation of the report or record.

Need for, and Objectives of Final Rule

    A series of ADs, beginning in 1997 and culminating in AD 2006-07-15 
in 2006, addressed the issue of fatigue cracking of the wing front 
lower spar caps in Thrush Aircraft, Inc. Model 600 S2D and S2R (S-2R) 
series airplanes (type certificate previously held by Quality 
Aerospace, Inc. and Ayres Corporation). This type of fatigue cracking, 
if not addressed, could result in catastrophic wing failure. The 
original 1997 AD was issued after an accident on an S2R series airplane 
in which the wing separated from the airplane in flight. Requirements 
of inspection and possible replacement were changed in 2000 to 
repetitive inspections and possible replacement. In 2006, the 
inspection rate was doubled after a completely severed wing front lower 
spar cap was found on one of the affected airplanes and the FAA noted 
that it was working with Thrush Aircraft, Inc. to develop a future 
terminating action. Analysis indicated that an undetected crack had 
existed during the previous two repetitive inspections of that wing 
front lower spar cap.
    Subsequent FAA analysis has shown that wing front lower spar cap 
fatigue cracking has increased as the fleet has aged and will continue 
to increase. Consequently, the incidences of undetected cracks will 
increase, increasing the probability of catastrophic wing failure. The 
FAA has concluded that repetitive inspections, as required since the 
2000 AD, are insufficient by themselves to ensure the safety of these 
airplanes and, accordingly, in this final rule the FAA is requiring 
wing front lower spar cap life limits to address this safety issue.

Summary of Significant Issues Raised by the Public in Response to the 
IRFA, Summary of FAA's Assessment of Such Issues, Statement of Changes 
Made to the Final Rule as a Result of Such Issues, Description of the 
Steps the Agency Has Taken To Minimize a Significant Economic Impact on 
Small Entities, and Why Other Significant Alternatives to the Final 
Rule That Affect Small Entities Were Rejected

    There were no public comments to the IRFA, but there were public 
comments to the proposed rule, which have relevance for small and large 
entities alike.
    As noted in the preamble to the final rule, Avenger commented that 
it has developed a wing front lower spar replacement kit, which was not 
available when the proposed rule was issued. The FAA has approved their 
kit for a 40,000-hour TIS life limit. Avenger requested that the FAA 
approve the installation of its kit as a terminating action to the AD. 
As noted in the preamble, the FAA agrees with Avenger that installation 
of its kit is a viable terminating action to this AD. Accordingly, it 
is an alternative to replacing the wing front lower spar caps with 
Ayres/Thrush spar caps; and the FAA has incorporated this change in the 
final rule. This is a significant issue because the Ayres/Thrush kit, 
although priced slightly lower than the Avenger kit, has a lower life 
limit (ranging from 5,400 to 28,800 hours TIS.) Many of the affected 
airplanes with the Ayres/Thrush kit installed will require multiple 
replacements over their lifetimes and installation of the Ayres/Thrush 
kit does not eliminate the requirement of repetitive inspections and 
reporting requirements. Consequently, the estimated cost of the final 
rule is lower given the availability of the Avenger kit as a 
terminating action. In the cost analysis for the proposed rule, we 
estimated the total cost to be $37.1 million. In the final rule, we 
estimate total cost to be $20.1 million.\1\
---------------------------------------------------------------------------

    \1\ Individual replacement of the two original equipment spars 
is cheaper (for one installation) than installing the Ayres/Thrush 
kit or the Avenger kit, but as noted in the ``Cost of Compliance'' 
section, the supply of these spar caps is very limited. Accordingly, 
total cost is overestimated, but only slightly, by our assumption 
that all operators would comply by installing a kit (NPRM: Ayres/
Thrush kit, final rule: Avenger kit).
---------------------------------------------------------------------------

    As an alternative to replacing the wing front lower spar caps, two 
commenters suggested that the FAA require installation of ``big 
butterfly'' plates. But, as the FAA noted in the preamble, the ``big 
butterfly plate'' does not have enough strength to carry all the

[[Page 3133]]

possible flight loads if the wing front lower spar caps were severed. 
Accordingly, this plate cannot be solely relied upon to ensure the 
safety of the airplane and is not an acceptable alternative method of 
compliance to replacing the wing front lower spar caps.
    Additionally, one commenter suggested 100-hour TIS visual 
inspections. As discussed in the preamble, even if the wing front lower 
spar cap is not completely severed, but has a crack that is large 
enough to see when performing the 100-hour TIS visual inspection, the 
remaining strength in the wing spar joint is not enough to carry all 
possible flight loads. Therefore, the 100-hour TIS visual inspection 
alone is not a sufficient alternative method of compliance.
    The FAA believes there are currently no other available alternative 
methods of compliance to the final rule that will allow the safety 
objectives of the final rule to be achieved. The FAA, however, has 
allowed a generous compliance period that will significantly reduce the 
economic impact on small and large entities alike. As already noted in 
the preamble, airplanes that have already exceeded the life limit on 
their wing front lower spar caps are allowed 500, 1,000, 1,500, or 
2,000 hours TIS to comply with the final rule, depending on the current 
number of accumulated hours TIS. Since the average usage rate for the 
affected airplanes is about 500 hours TIS per year, these allowances 
are equivalent, on average, to 1, 2, 3, and 4 years to comply with the 
final rule. Airplanes that have not yet reached their wing front lower 
spar cap life limit are allowed a minimum of 2,000 hours TIS or, on 
average, 4 years to comply with the final rule.
    For a complete summary of public comments and the FAA's responses, 
please see the Comments section in the preamble above.

A Description of and an Estimate of the Number of Small Entities for 
Which the Final Rule Will Apply

    This final rule will affect 808 U.S.-registered and -operated 
Thrush Aircraft, Inc. Model 600S2D and S2R (S-2R) series airplanes. \2\ 
In conducting this analysis, the FAA reviewed data from the FAA 
Registry to ascertain how many Thrush Aircraft, Inc. were registered 
and operated by small entities. The FAA Registry indicates that these 
808 airplanes are owned by 546 separate entities in agricultural 
aviation. All but one of these entities are small entities as defined 
by the Small Business Administration (SBA). Although the FAA Registry 
does not record financial or business data about the registered owners 
of aircraft, and such data for these entities are not readily available 
elsewhere, it appears that most, if not all, of the 546 entities are 
engaged in crop dusting, spraying, and seeding operations. These 
activities are classified in North American Industry Classification 
System (NAICS) industry, NAICS 115112--Soil Preparation, Planting, and 
Cultivating (including Crop Dusting, Crop Spraying). The concentration 
of these entities in a single NAICS industry reflects the specialized 
nature of agricultural airplanes with restricted airworthiness 
certificates. Furthermore, several of these entities were classified in 
the Standard Industrial Classification (SIC) equivalent of NAICS 115112 
by http://www.manta.com. Although a few of these entities may also be 
engaged in firefighting, which is classified in NAICS 115310--Support 
Activities for Forestry (including Forest Fire Suppression), the FAA is 
unable to identify any of these entities as being principally engaged 
in firefighting. The SBA small business classification for NAICS 115112 
is a maximum of $6.5 million in business receipts, and for NAICS 115310 
it is a maximum of $16.5 million in business receipts. Only one entity 
in this sample appears to have business receipts over $6.5 million, and 
no entity has business receipts in excess of $16.5 million. Using the 
total number of airplanes owned as a size criterion, the FAA selected a 
sample of 41 of the largest affected entities and found median sales 
shown by http://www.manta.com to be just $250,000 annually. Firms in 
agricultural aviation appear to be inherently of small size. 
Accordingly, the FAA estimates that 545 small entities will be affected 
by this final rule.
---------------------------------------------------------------------------

    \2\ FAA Registry, http://www.faa.gov/licenses_certificates/aircraft_certification/aircraft_registry/releasable_aircraft_download/. Data downloaded on 4/14/08.
---------------------------------------------------------------------------

Reporting, Record Keeping, and Other Compliance Requirements

    Small entities will incur no new reporting and record-keeping 
requirements as a result of this final rule. In fact, such 
requirements, for small and large firms alike, will be greatly reduced 
since installation of the Avenger kit has been incorporated as an 
alternative terminating action to this final rule.
    This final rule will affect U.S. operators of Thrush Aircraft, Inc. 
Model 600S2D and S2R (S-2R) series agricultural airplanes airplanes. 
The affected airplanes were produced by Thrush Aircraft, Inc. 
predecessor firms over the period 1965-2000. This final rule largely 
retains the requirements of superseded AD 2006-07-15 to inspect/repair/
replace the currently installed Ayres/Thrush wing front lower spar 
caps. The new requirements set life limits on the Ayres/Thrush wing 
front lower spar caps and requires replacing of these wing front lower 
spar caps when the life limits are reached.

Economic Impact on Small Entities

    Replacing the wing front lower spar caps is expensive and, 
consequently, as we show below, the final rule will have a significant 
economic impact on the substantial number of small firms we identified 
above.
    The total compliance cost (undiscounted) is $65,520 for an affected 
airplane for which the wing front lower spar caps are replaced before 
retirement, or zero for an affected airplane that will retire before 
its compliance date. Individual airplane compliance costs will result 
in costs to the small entities that own these airplanes and will vary 
depending on the number of affected airplanes owned by the entity. The 
ownership table below shows the variation in the number of owners with 
particular numbers of airplanes. The table shows that almost 75 percent 
of the 546 individual owners have only one affected airplane, and more 
than 90 percent of owners have no more than two affected airplanes. The 
average (mean) number of affected airplanes held is 1.48, while the 
median number held is just 1.00, so the median airplane cost is 
equivalent to the median owner cost.

[[Page 3134]]



             Number of Thrush Aircraft, Inc. Owners Having Particular Numbers of Affected Airplanes
----------------------------------------------------------------------------------------------------------------
                                                                     Number of
                                                                     affected
                                                                  airplanes held     Number of     Cumulative %
                                                                     by single        owners
                                                                       owner
----------------------------------------------------------------------------------------------------------------
                                                                               1             406            74.4
                                                                               2              86            90.1
                                                                               3              26            94.9
                                                                               4              13            97.3
                                                                               5               7            98.5
                                                                               6               2            98.9
                                                                               7               2            99.3
                                                                               8               1            99.5
                                                                               9               2            99.8
                                                                              13               1           100.0
Total...........................................................  ..............             546  ..............
Mean............................................................            1.48  ..............  ..............
Median..........................................................            1.00  ..............  ..............
----------------------------------------------------------------------------------------------------------------
Source: FAA Registry. Data downloaded on 4/18/08.

    In the ``Cost of Compliance'' section of this final rule, we 
estimate total cost (undiscounted) to be $20.1 million and the present 
value cost to be $18.2 million. As noted above, the FAA estimates that 
545 of the 546 affected by this final rule are small firms, and, in 
fact, 99.7 percent of the final rule's estimated cost is attributed to 
small entities. The following document analyzes the impact of this cost 
on the substantial number of small firms identified above.
    Because the FAA Registry does not collect financial or business 
data on these entities, and such data are not readily available 
elsewhere, the FAA also used Census Bureau size distribution data to 
assess the economic impact on small firms. The FAA used data from the 
2002 Census since this is the latest census for which size distribution 
by business receipts is readily available. These data are available in 
a special census compilation for the SBA.\3\ The FAA used the data for 
NAICS 115112--Soil Preparation, Planting, and Cultivating (including 
Crop Dusting, Crop Spraying), but did not use the data for NAICS 
115310--Support Activities for Forestry (including Forest Fire 
Suppression) since, as noted above, a very high percentage of the 
affected small firms, if not all, meet the classification standard of 
NAICS 115112. Moreover, the size distribution of NAICS 115310 appears 
to be similar to that of NAICS 115112. The concentration of the 
affected airplanes in one NAICS industry, noted above, makes the use of 
census data feasible and appropriate.
---------------------------------------------------------------------------

    \3\ Small Business Administration, Office of Advocacy. http://www.sba.gov/advo/research/us_rec02.txt.
---------------------------------------------------------------------------

    The relevant census data are provided in the table below:

         2002 Census Data for NAICS 115112--Soil Preparation, Planting, and Cultivating (Incl. Crop Dusting, Crop Spraying)--Small Size Classes
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                              $0-100         $100-500     $500 thousand-
                         Measure                               Total         thousand        thousand        1 million     $1-5 million    $5-10 million
--------------------------------------------------------------------------------------------------------------------------------------------------------
Firms...................................................            2336             509             992             412             394              29
Percentage of firms.....................................  ..............           21.8%           42.5%           17.6%           16.9%            1.2%
Upper bound percentile..................................  ..............           21.8%           64.3%           81.9%           98.8%          100.0%
Est. Receipts ($000)....................................      $1,531,004         $25,681        $257,447        $286,462        $772,401        $189,013
Receipts/Firm ($).......................................        $655,396         $50,454        $259,523        $695,296      $1,960,409      $6,517,690
--------------------------------------------------------------------------------------------------------------------------------------------------------
Source: ``Firms'' and ``Est. Receipts'' from Small Business Administration, Office of Advocacy. http://www.sba.gov/advo/research/us_rec02.txt.

    The table above shows the number of firms and business receipt data 
for the five smallest size classes of NAICS 115112 that encompass the 
size range of the firms affected by this final rule. In the 
``Percentage of firms'' row, for each size class, the FAA calculates 
that class's number of firms as a percentage of the total number of 
firms in the five size classes. Cumulating this percentage from the 
smallest to largest size class establishes the ``Upper bound 
percentile''--the cumulated percentage of firms of business receipt 
size ranging up to the upper bound of the size class. The final rule's 
cost for the firms at the upper bound percentiles is then estimated as 
the corresponding percentiles in the estimated firm-level compliance 
cost data. In order to assess the economic impact of the final rule, 
these costs are calculated as a percentage of the census data upper 
bounds.
    For example, the upper bound percentile for the $100-500 thousand 
size class is 64.3 percent, so we estimate the NAICS 115112 firms at 
that percentile to have business receipts of $500,000. As shown in the 
table below, the FAA then determined the estimated compliance cost of 
firms at the same percentile in the compliance cost data to be $57,584. 
The FAA assumes these firms are the same, so the percentage cost impact 
(AD Cost/Firm Size) is 11.5 percent. This procedure assumes the size 
distribution of the 808 firms affected by the final rule has a

[[Page 3135]]

distribution similar to the overall distribution of the small firms in 
NAICS 115112. It also assumes there is a perfect rank correlation 
between the size of the affected firms and the firms' present value 
compliance cost. While the latter assumption is certainly not the case, 
any deviation from such perfect correlation can only increase the 
impact of the final rule because smaller firms will have larger costs. 
Accordingly, the FAA's determination that the final rule will have a 
significant impact on a substantial number of small entities is 
unaffected.

                                      Economic Impact of AD on Small Firms
----------------------------------------------------------------------------------------------------------------
                                                                        Estimated firm
                                                                         size (Census                 Cumulative
             AD cost to firm                     Firm percentile           Bureau's       AD cost/    number of
                                                                        receipts upper   firm size      firms
                                                                            bound)
----------------------------------------------------------------------------------------------------------------
$0.......................................  21.8 percentile............        $100,000         0.0%        119.2
$57,584..................................  64.3 percentile............        $500,000        11.5%        351.5
$63,220..................................  81.9 percentile............      $1,000,000         6.3%        447.9
$203,502.................................  98.8 percentile............      $5,000,000         4.1%        540.2
----------------------------------------------------------------------------------------------------------------

    The table above shows a zero-cost impact on a firm at the 21.8 
percentile. This result reflects the estimate in the FRFA cost analysis 
(see docket) that more than 500 older airplanes will retire before 
their wing front lower spar cap life limits are reached. As already 
mentioned, the AD cost for a firm at the 64.3 percentile is $61,754, 
which as a percentage of estimated firm size (size class upper bound) 
is 11.5 percent of annual business receipts. This impact declines to 
6.3 percent for a firm at the 81.9 percentile and to 4.1 percent for a 
firm at the 98.8 percentile. The overall pattern is zero impact for the 
smallest of the small firms owners of the oldest airplanes, but a 
highly positive impact for the medium-sized small firms. In percentage 
terms, this impact falls for the largest small firms, but remains at a 
substantial level. While the FAA can make no definitive inference on 
the impact of the final rule on firms between the 21.8 and 64.3 
percentiles, the FAA notes the cost varies from 6.3 percent up to 11.5 
percent of annual business receipts for 96 firms between the 81.9 and 
64.3 percentiles and from 4.1 percent to 6.3 percent of annual business 
receipts for 92 firms between the 98.8 and 81.9 percentiles. These 
estimated percentage impacts are substantial. Therefore, the FAA 
concludes that this final rule will have a significant impact on a 
substantial number of small entities.

International Trade Impact Analysis

    The Trade Agreement Act of 1979 prohibits Federal agencies from 
establishing any standards or engaging in related activities that 
create unnecessary obstacles to the foreign commerce of the United 
States. The statute does not consider legitimate domestic objectives, 
such as safety, as unnecessary. The statute also requires consideration 
of international standards and, where appropriate, that they be the 
basis for U.S. standards. The FAA is issuing this final rule because of 
a known safety problem. Therefore, this final rule AD action applies 
only to U.S. registered airplanes and is not considered an unnecessary 
obstacle to international trade.

Unfunded Mandates Reform Act Assessment

    Title II of the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-
4) requires each Federal agency to prepare a written statement 
assessing the effects of any Federal mandate in a proposed or final 
agency rule that may result in an expenditure of $100 million or more 
(adjusted annually for inflation with the base year 1995) in any one 
year by State, local, and Tribal governments in the aggregate, or by 
the private sector. The Act deems such a mandate to be a ``significant 
regulatory action.'' The FAA currently uses an inflation-adjusted value 
of $136.1 million. This rule does not contain such a mandate.

Regulatory Findings

    We have determined that 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. Is not a ``significant rule'' under the DOT Regulatory Policies 
and Procedures (44 FR 11034, February 26, 1979); and
    3. Will have a significant economic impact, positive or negative, 
on a substantial number of small entities under the criteria of the 
Regulatory Flexibility Act.
    We prepared a summary of the costs to comply with this AD (and 
other information as included in the Regulatory Evaluation) and placed 
it in the AD Docket. You may get a copy of this summary by sending a 
request to us at the address listed under ADDRESSES. Include ``Docket 
No. FAA-2007-27862; Directorate Identifier 2007-CE-036-AD'' in your 
request.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Incorporation by 
reference, Safety.

Adoption of the Amendment

0
Accordingly, under the authority delegated to me by the Administrator, 
the Federal Aviation Administration amends part 39 of the Federal 
Aviation Regulations (14 CFR part 39) as follows:

PART 39--AIRWORTHINESS DIRECTIVES

0
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]

0
2. The FAA amends Sec.  39.13 by removing Airworthiness Directive (AD) 
2006-07-15, Amendment 39-14542 (71 FR 16691, April 4, 2006), and adding 
the following new AD:

2009-26-11 Thrush Aircraft, Inc. (Type Certificate Previously Held 
by Quality Aerospace, Inc. and Ayres Corporation): Amendment 39-
16150; Docket No. FAA-2007-27862; Directorate Identifier 2007-CE-
036-AD.

Effective Date

    (a) This AD becomes effective on February 24, 2010.

Affected ADs

    (b) The following lists a history of the ADs affected by this AD 
action:
    (1) This AD supersedes AD 2006-07-15, Amendment 39-14542;

[[Page 3136]]

    (2) AD 2006-07-15 superseded AD 2003-07-01, Amendment 39-13097;
    (3) AD 2003-07-01 superseded AD 2000-11-16, Amendment 39-11764;
    (4) AD 2000-11-16 superseded AD 97-17-03, Amendment 39-10195; 
and
    (5) AD 97-17-03 superseded AD 97-13-11, Amendment 39-10071.

Applicability

    (c) This AD affects the following airplane models and serial 
numbers (S/Ns) in Table 1 that are certificated in any category when 
wing front lower spar cap part numbers (P/Ns) 20207-1, 20207-2, 
20207-11, 20207-12, 20207-13, 20207-14, 20207-15, or 20207-16 are 
installed. This AD applies to the S/Ns in Table 1 with or without a 
``DC'' suffix. This AD does not affect airplanes with any other wing 
front lower spar cap part number, e.g. Thrush P/N 22507 (any dash 
number) or Supplemental Type Certificate (STC) SA03654AT parts. The 
table also identifies the group that each airplane belongs in when 
determining inspection compliance times and life limit times for the 
parts:

               Table 1--Applicability and Airplane Groups
------------------------------------------------------------------------
               Model                           S/Ns               Group
------------------------------------------------------------------------
(1) S-2R..........................  5000R through 5100R,               1
                                     except 5010R, 5031R,
                                     5038R, 5047R, and 5085R.
(2) S2R-G1........................  G1-101 through G1-106.....         1
(3) S2R-R1820.....................  R1820-001 through R1820-           1
                                     035.
(4) S2R-T15.......................  T15-001 through T15-033            1
                                     (also see paragraph (d)
                                     of this AD).
(5) S2R-T34.......................  6000R through 6049R, T34-          1
                                     001 through.
                                    T34-143, T34-145, T34-171,
                                     T34[dash]180, and.
                                    T34-181 (also see
                                     paragraph (e) of this AD).
(6) S2R-G10.......................  G10-101 through G10-138,           2
                                     G10-140, and.
                                    G10-141...................
(7) S2R-G5........................  G5-101 through G5-105.....         2
(8) S2R-G6........................  G6-101 through G6-147.....         2
(9) S2RHG-T65.....................  T65-002 through T65-018...         2
(10) S2R-R1820....................  R1820-036.................         2
(11) S2R-T34......................  T34-144, T34-146 through           2
                                     T34-170, T34-172 through
                                     T34-179, and T34-189
                                     through T34-234 (also see
                                     paragraph (e) of this AD).
(12) S2R-T45......................  T45-001 through T45-014...         2
(13) S2R-T65......................  T65-001 through T65-018...         2
(14) 600 S2D......................  All serial numbers                 3
                                     beginning with 600-1311D.
(15) S-2R.........................  1380R, 1416R through               3
                                     2592R, 3000R, and 3002R.
(16) S2R-R1340....................  R1340-001 through R1340-           3
                                     035.
(17) S2R-R3S......................  R3S-001 through R3S-011...         3
(18) S2R-T11......................  T11-001 through T11-005...         3
(19) S2R-G1.......................  G1-107 through G1-115.....         5
(20) S2R-G10......................  G10-139, G10-142 through           5
                                     G10-165.
(21) S2R-G6.......................  G6-148 through G6-155.....         5
(22) S2RHG-T34....................  T34HG-102.................         5
(23) S2R-T15......................  T15-034 through T15-040            5
                                     (also see paragraph (d)
                                     of this AD).
(24) S2R-T34......................  T34-236 through T34-270            5
                                     (also see paragraph (e)
                                     of this AD).
(25) S2R-T45......................  T45-015...................         5
(26) S-2R.........................  5010R, 5031R, 5038R,               6
                                     5047R, and 5085R.
------------------------------------------------------------------------

    (d) The S/Ns of Model S2R-T15 airplanes could incorporate T15-
xxx and T27-xxx (xxx is the variable for any of the S/Ns beginning 
with T15- and T27-). This AD applies to both of these S/N 
designations as they are both Model S2R-T15 airplanes.
    (e) The S/Ns of Model S2R-T34 airplanes could incorporate T34-
xxx, T36-xxx, T41-xxx, or T42-xxx (xxx is the variable for any of 
the S/Ns beginning with T34-, T36-, T41-, and T42-). This AD applies 
to all of these S/N designations as they are all Model S2R-T34 
airplanes.
    (f) Any Group 3 airplane that has been modified with a hopper of 
a capacity more than 410 gallons, a piston engine greater than 600 
horsepower, or a gas turbine engine greater than 600 horsepower, is 
a Group 1 airplane for the purposes of this AD. Inspect the airplane 
at the Group 1 compliance time specified in this AD. Replace the 
wing front lower spar caps in accordance with the formulas given in 
paragraph (k) of this AD.
    (g) Group 6 airplanes were originally manufactured with higher 
horsepower radial engines, but were converted to lower horsepower 
radial engines. They are now configured identically to Group 3 
airplanes.

Unsafe Condition

    (h) This AD is the result of the analysis of data from 117 wing 
front lower spar cap fatigue cracks found on similar design Model 
600 S2D and S2R (S-2R) series airplanes and the FAA's determination 
that the replacement of high time wing front lower spar caps is 
necessary to address the unsafe condition for certain airplanes. 
Since we issued AD 2006-07-15, analysis reveals that inspections are 
not detecting all existing cracks, and incidences of undetected 
cracks are increasing. This AD retains the actions of AD 2006-07-15 
and imposes a life limit on the wing front lower spar caps that 
requires you to replace the wing front lower spar caps when the life 
limit is reached. This AD also changes the requirements and 
applicability of the groups discussed above and removes the 
ultrasonic inspection method. We are issuing this AD to prevent wing 
front lower spar cap failure caused by undetected fatigue cracks. 
Such failure could result in loss of a wing.

Compliance

    (i) To address the problem, do the following, unless already 
done:
    (1) If you have already done an inspection required by AD 2006-
07-15, within the next 30 days after February 24, 2010 (the 
effective date of this AD), identify the number of hours time-in-
service (TIS) since your last inspection required by AD 2006-07-15. 
You will need this to establish the inspection interval for the next 
inspection required by this AD.
    (2) Inspect the two outboard bolt hole areas (whether \1/4\-inch 
and \5/16\-inch diameter bolt holes or both \5/16\-inch diameter 
bolt holes) on each wing front lower spar cap for fatigue cracking 
using magnetic particle or eddy current procedures. If Kaplan splice 
blocks, P/N 22515-1/-3 or P/N 88-251, are installed following 
Quality Aerospace, Inc. Custom Kit No. CK-AG-30, dated December 6, 
2001, inspect the three outboard bolt hole areas on each wing front 
lower spar cap for fatigue cracking using magnetic particle or eddy 
current procedures. Use the compliance times listed in paragraph 
(i)(3) of this AD for the initial inspection and the compliance time 
listed in paragraphs (i)(5), (i)(6), or (i)(7) of this AD for the 
repetitive inspections. The cracks may emanate from the bolt hole on 
the face of the wing front lower spar cap or they may occur in the 
shaft of the hole. Inspect both of those areas.

[[Page 3137]]

    (i) If using the magnetic particle method, inspect using the 
``Inspection'' portion of the ``Accomplishment Instructions'' and 
``Lower Splice Fitting Removal and Installation Instructions'' in 
Ayres Corporation Service Bulletin No. SB-AG-39, dated September 17, 
1996. Do the inspection following FAA Advisory Circular (AC) 43.13-
1B, Chapter 5, Section 4, Magnetic Particle Inspection, using the 
wet particle method. You may obtain a copy of AC 43.13-1B at http://www.faa.gov/regulations_policies/. Caution: Firmly support the 
wings during the inspection to prevent movement of the wing front 
lower spar caps when the splice blocks are removed. This will allow 
easier realignment of the splice block holes and the holes in the 
wing front lower spar cap for bolt insertion and prevent damage to 
the bolt hole. Damage to the bolt hole inner surface or edge of the 
bolt hole can cause cracks to begin prematurely.
    (ii) The inspection must be done by or supervised by a Level 2 
or Level 3 inspector certified following the guidelines in FAA AC 
65-31A. You may obtain a copy of AC 65-31A at http://www.faa.gov/regulations_policies/.
    (iii) If using eddy current methods, a procedure must be sent to 
the FAA, Atlanta Aircraft Certification Office (ACO), for approval 
before doing the inspection. Send your proposed procedure to the 
FAA, Atlanta ACO, Attn: Cindy Lorenzen, 1701 Columbia Avenue, 
College Park, Georgia 30337. You are not required to remove the 
splice block for the eddy current inspections, unless corrosion is 
visible. Eddy current inspection procedures previously approved 
under AD 2006-07-15, AD 2003-07-01, AD 2000-11-16, AD 97-13-11, and/
or AD 97-17-03 remain valid for this AD.
    (iv) If you change the inspection method used (magnetic particle 
or eddy current), the TIS intervals for repetitive inspections are 
based on the method used for the last inspection.
    (3) If airplanes have not yet reached the threshold for the 
initial inspection required in AD 2006-07-15, initially inspect 
following the wing front lower spar cap hours total TIS schedule 
below or within the next 50 hours TIS after February 24, 2010 (the 
effective date of this AD), whichever occurs later:

                    Table 2--Initial Inspection Times
------------------------------------------------------------------------
                                Initially inspect upon accumulating the
        Airplane group           following hours total TIS on the wing
                                          front lower spar cap
------------------------------------------------------------------------
(i) Group 1..................  2,000 hours TIS.
(ii) Group 2.................  1,400 hours TIS.
(iii) Group 3................  6,400 hours TIS.
(iv) Group 5.................  1,000 hours TIS.
(v) Group 6..................  (A) S/N 5010R: 5,530 hours TIS.
                               (B) S/N 5038R: 5,900 hours TIS.
                               (C) S/N 5031R: 6,400 hours TIS.
                               (D) S/N 5047R: 6,400 hours TIS.
                               (E) S/N 5085R: 6,290 hours TIS.
(vi) Any airplane with the     2,000 hours TIS.
 entire Custom Kit CK-AG-41
 installed.
------------------------------------------------------------------------

    (4) Airplanes in all groups must meet the following conditions 
before doing the repetitive inspections required in paragraphs 
(i)(5), (i)(6), or (i)(7) of this AD:
    (i) No cracks have been found previously on wing front lower 
spar cap; or
    (ii) Small cracks have been repaired through cold work (or done 
as an option if never cracked) following Ayres Corporation Service 
Bulletin No. SB-AG-39, dated September 17, 1996; or
    (iii) Small cracks have been repaired by reaming the \1/4\-inch 
bolt hole to \5/16\ inches diameter (or done as an option if never 
cracked) following Ayres Corporation Custom Kit No. CK-AG-29, Part 
I, dated December 23, 1997; or
    (iv) Small cracks have been repaired through previous 
alternative methods of compliance (AMOC); or
    (v) Small cracks have been repaired by installing Kaplan splice 
blocks, P/N 22515-1/-3 or P/N 88-251 (or done as an option if never 
cracked) following Quality Aerospace, Inc. Custom Kit No. CK-AG-30, 
dated December 6, 2001.
    (5) Repetitively inspect Groups 1, 2, 3, and 6 airplanes that do 
not have ``big butterfly'' plates and lower splice plates, P/Ns 
20211-09 and 20211-11, installed following Ayres Corporation Custom 
Kit No. CK-AG-29, Part II, dated December 23, 1997; or that do not 
have ``big butterfly'' plates and lower splice plates, P/Ns 94418-5 
and 94418-7 or P/Ns 94418-13 and 94418-15, installed following 
Thrush Aircraft, Inc. Custom Kit No. CK-AG-41, Revision A, dated 
March 8, 2007; and meet the conditions in paragraph (i)(4) of this 
AD. Follow the wing front lower spar cap hours TIS compliance 
schedule below:

  Table 3--Repetitive Inspection Times for Airplane Groups 1, 2, 3, and 6 Without ``Big Butterfly'' Plates and
                                               Lower Splice Plates
----------------------------------------------------------------------------------------------------------------
 When airplanes accumulate the following   Inspect within the following
  hours TIS on the wing front lower spar        hours TIS after the       Inspect thereafter at intervals not to
cap since the last inspection required in   effective date of this AD,                 exceed . . .
         AD 2006[dash]07[dash]15,
----------------------------------------------------------------------------------------------------------------
(i) Magnetic Particle inspection:........  ............................  250 hours TIS.
    (A) 350 or more hours TIS............  (A) 50 hours TIS............
    (B) 175 through 349 hours TIS........  (B) 75 hours TIS............
    (C) Less than 175 hours TIS..........  (C) upon accumulating 250
                                            hours TIS.
(ii) Eddy Current inspection:............  ............................  350 hours TIS.
    (A) 500 or more hours TIS............  (A) 50 hours TIS............
    (B) 275 through 499 hours TIS........  (B) 75 hours TIS............
    (C) Less than 275 hours TIS..........  (C) upon accumulating 350
                                            hours TIS.
----------------------------------------------------------------------------------------------------------------

    (6) Repetitively inspect Groups 1, 2, 3, 5, and 6 airplanes that 
have ``big butterfly'' plates and lower splice plates, P/Ns 20211-09 
and 20211-11, installed following Ayres Corporation Custom Kit No. 
CK-AG-29, Part II, dated December 23, 1997; or that have ``big 
butterfly'' plates and lower splice plates, P/Ns 94418-5 and 94418-
7, or P/Ns 94418-13 and 94418-15, installed following Thrush 
Aircraft, Inc. Custom Kit No. CK-AG-41, Revision A, dated March 8, 
2007; and meet the conditions in paragraph (i)(4) of this AD. Follow 
the wing front lower spar cap hours TIS compliance schedule below:

[[Page 3138]]



  Table 4--Repetitive Inspections Times for Airplane Groups 1, 2, 3, 5, and 6 With ``Big Butterfly'' Plates and
                                               Lower Splice Plates
----------------------------------------------------------------------------------------------------------------
 When airplanes accumulate the following   Inspect within the following
  hours TIS on the wing front lower spar        hours TIS after the       Inspect thereafter at intervals not to
cap since the last inspection required in   effective date of this AD,                 exceed . . .
         AD 2006[dash]07[dash]15,
----------------------------------------------------------------------------------------------------------------
(i) Magnetic particle inspection:........  ............................  450 hours TIS.
    (A) 650 or more hours TIS............  (A) 50 hours TIS............
    (B) 375 through 649 hours TIS........  (B) 75 hours TIS............
    (C) Less than 375 hours TIS..........  (C) upon accumulating 450
                                            hours TIS.
(ii) Eddy Current inspection:............  ............................  625 hours TIS.
    (A) 900 or more hours TIS............  (A) 50 hours TIS............
    (B) 550 through 899 hours TIS........  (B) 75 hours TIS............
    (C) Less than 550 hours TIS..........  (C) upon accumulating 625
                                            hours TIS.
----------------------------------------------------------------------------------------------------------------


    Note 1: Group 5 airplanes had P/Ns 20211-09 and 20211-11 
installed at the factory.

    (7) Repetitively inspect airplanes that incorporate Thrush 
Aircraft, Inc. Custom Kit No. CK-AG-41, Revision A, dated March 8, 
2007, in its entirety that meet the conditions in paragraph (i)(4) 
of this AD. Follow the wing front lower spar cap hours TIS 
compliance schedule below:

Table 5--Repetitive Inspection Times for Airplanes With Thrush Aircraft,
 Inc. Custom Kit No. CK-AG-41, Revision A, Incorporated in Its Entirety
------------------------------------------------------------------------
   When using the following     Repetitively inspect at intervals not to
     inspection methods,                      exceed . . .
------------------------------------------------------------------------
(i) Magnetic particle          900 hours TIS.
 inspection.
(ii) Eddy current inspection.  1,250 hours TIS.
------------------------------------------------------------------------

     (j) Initially replace the wing front lower spar caps, P/Ns 
20207-1, 20207-2, 20207-11, 20207-12, 20207-13, 20207-14, 20207-15, 
or 20207-16, at the times specified in Table 6 of this AD. 
Repetitively replace thereafter at the life limit times specified in 
Table 7 of this AD. Do the replacements as specified in paragraph 
(l)(4) of this AD.

     Table 6--Initial Compliance Time for Wing Front Lower Spar Cap
                               Replacement
------------------------------------------------------------------------
                                 Replace the wing front lower spar cap
 Total hours TIS on the wing   upon accumulating the following hours TIS
     front lower spar cap       on the spar cap after the effective date
                                               of this AD
------------------------------------------------------------------------
(i) Group 1 with a radial      500 hours.
 engine and more than 15,000
 hours TIS.
(ii) Group 1 with a radial     1,000 hours.
 engine and 12,000 to 15,000
 hours TIS.
(iii) Group 1 with a radial    1,500 hours.
 engine and 9,000 to 11,999
 hours TIS.
(iv) Group 1 with a radial     2,000 hours.
 engine and 7,400 to 8,999
 hours TIS.
(v) Group 1 with a radial      Use Table 7(xxii).
 engine and less than 7,400
 hours TIS.
(vi) Group 1 with a turbine    500 hours.
 engine and more than 14,000
 hours TIS.
(vii) Group 1 with a turbine   1,000 hours.
 engine and 11,000 to 14,000
 hours TIS.
(viii) Group 1 with a turbine  1,500 hours.
 engine and 8,000 to 10,999
 hours TIS.
(ix) Group 1 with a turbine    2,000 hours.
 engine and 4,200 to 7,999
 hours TIS.
(x) Group 1 with a turbine     Use Table 7(xxiii).
 engine and less than 4,200
 hours TIS.
(xi) Group 2 with more than    500 hours.
 9,000 hours TIS.
(xii) Group 2 with 6,000 to    1,000 hours.
 9,000 hours TIS.
(xiii) Group 2 with 3,900      1,500 hours.
 hours to 5,999 hours TIS.
(xiv) Group 2 with less than   Use Table 7(xxiv).
 3,900 hours TIS.
(xv) Group 3 and 6 with more   500 hours.
 than 28,800 hours TIS.
(xvi) Group 3 and 6 with       1,000 hours.
 27,800 to 28,799 hours TIS.
(xvii) Group 3 and 6 with      Use Table 7(xxv).
 less than 27,800 hours TIS.
(xviii) Group 5 with more      500 hours.
 than 8,000 hours TIS.
(xix) Group 5 with 5,000 to    1,000 hours.
 7,999 hours TIS.
(xx) Group 5 with 2,400 to     1,500 hours.
 4,999 hours TIS.
(xxi) Group 5 with less than   Use Table 7(xxvi).
 2,400 hours TIS.
------------------------------------------------------------------------


             Table 7--Wing Front Lower Spar Cap Life Limits
------------------------------------------------------------------------
                                 Replace wing front lower spar cap upon
        Airplane group          the accumulation of the following hours
                                          TIS on the spar cap:
------------------------------------------------------------------------
(xxii) Group 1 with a radial   9,400 hours TIS.
 engine.

[[Page 3139]]


(xxiii) Group 1 with a         6,200 hours TIS.
 turbine engine.
(xxiv) Group 2...............  5,400 hours TIS.
(xxv) Groups 3 and 6.........  28,800 hours TIS.
(xxvi) Group 5...............  3,900 hours TIS with original wing front
                                lower spar cap P/N 20207-11 or P/N 20207-
                                12.
                               5,400 hours TIS after original wing front
                                lower spar cap has been replaced with
                                any P/N 20207-xx wing front lower spar
                                cap.
------------------------------------------------------------------------


    Note 2: There is evidence of sharp, uneven edges on the spar cap 
bolt holes that resulted from the manufacturing process in Group 5 
airplanes. Once the original wing front lower spar caps are 
replaced, the life limit increases.

    (k) As previously stated in paragraph (f) of this AD, any Group 
3 airplane that has been modified with a hopper of a capacity more 
than 410 gallons, a piston engine greater than 600 horsepower, or a 
gas turbine engine greater than 600 horsepower, is a Group 1 
airplane for the purposes of this AD. Replace the wing front lower 
spar caps using the following formulas.
    (1) For airplanes that were originally Group 3 airplanes and 
later modified by installing a piston engine of greater than 600 
horsepower and/or a hopper capacity of greater than 410 gallons, 
calculate the equivalent Group 1 hours TIS on each spar cap as 
follows:
[GRAPHIC] [TIFF OMITTED] TR20JA10.000

    (ii) Equivalent Group 1 hours TIS = 9,400 x Usage Factor
    (2) For airplanes that were originally Group 3 airplanes and 
later modified by installing a turbine engine of greater than 600 
horsepower, with or without installing a hopper with greater than 
410 gallon capacity, calculate the equivalent Group 1 hours TIS on 
each spar cap as follows:
[GRAPHIC] [TIFF OMITTED] TR20JA10.001

    (ii) Equivalent Group 1 hours TIS = 6,200 x Usage Factor
    (3) When the equivalent Group 1 hours TIS on the wing front 
lower spar cap equals the life limit of 9,400 hours TIS if a radial 
piston engine is installed or reaches 6,200 hours TIS if a turbine 
engine is installed, the wing front lower spar cap must be replaced. 
Use Table 6 if over the life limit.
    (4) See the appendix to this AD for examples of how to calculate 
the applicable life limit.
    (l) If any cracks are found during any inspection required by 
this AD, you must repair the cracks or replace the wing front lower 
spar cap before further flight.
    (1) Use the cold work process to ream out small cracks as 
defined in Ayres Corporation Service Bulletin No. SB-AG-39, dated 
September 17, 1996, and deburr the bolt hole edges with the splice 
blocks removed after cold work is performed; or
    (2) If the crack is found in a \1/4\-inch bolt hole, ream the 
\1/4\-inch bolt hole to \5/16\ inches diameter as defined in Part I 
of Ayres Corporation Custom Kit No. CK-AG-29, dated December 23, 
1997; or
    (3) Install Kaplan splice blocks, P/N 22515-1/3 or P/N 88-251, 
following Quality Aerospace, Inc. Custom Kit No. CK-AG-30, dated 
December 6, 2001; or
    (4) Replace the affected wing front lower spar cap following an 
FAA-approved procedure. Contact the FAA at the address in paragraph 
(t) of this AD to obtain an FAA-approved replacement procedure 
unless previously provided by the manufacturer at delivery of the 
airplanes. An alternative to replacing just the affected wing front 
lower spar cap is to replace both wing front lower spar caps and the 
surrounding structure following Thrush Aircraft, Inc. Custom Kit No. 
CK-AG-41, Revision A, dated March 8, 2007. Another alternative to 
replacing just the affected wing front lower spar cap is to replace 
both wing front lower spar caps and the surrounding structure 
following Avenger Aircraft and Services FAA STC SA03654AT for 
Avenger Extended Performance Front Spar Enhancement Kit. You may 
obtain a copy of FAA STC SA03654AT at http://www.faa.gov/aircraft/air_cert/design_approvals/stc/. If you chose to install Thrush 
Custom Kit No. CK-AG-41, the FAA recommends installing Custom Kit 
No. CK-AG-41, Revision A, in its entirety although this is not 
mandatory. The additional structure provided in Thrush Aircraft, 
Inc. Custom Kit No. CK-AG-41, Revision A, dated March 8, 2007, will 
provide a greater level of safety than the minimum acceptable level 
of safety provided by replacing just the wing front lower spar cap. 
If choosing to install the Avenger FAA STC kit, it is mandatory to 
install the entire FAA STC kit.
    (m) If a crack is found, the reaming associated with the cold 
work process may remove a crack if it is small enough. Some aircraft 
owners/operators were issued AMOCs with AD 97-17-03 to ream the \1/
4\-inch bolt hole to \5/16\ inches diameter to remove small cracks. 
Ayres Corporation Custom Kit No. CK-AG-29, Part I, dated December 
23, 1997, also provides procedures to ream the \1/4\-inch bolt hole 
to \5/16\ inches diameter, which may remove a small crack. Resizing 
the holes to the required size to install a Kaplan splice block may 
also remove small cracks. If you use any of these methods to remove 
cracks and the airplane is re-inspected before further flight and no 
cracks are found, you may continue to follow the repetitive 
inspection intervals for your airplane listed in paragraphs (i)(5), 
(i)(6), or (i)(7) of this AD.
    (n) For all inspection methods (magnetic particle or eddy 
current), hours TIS for initial and repetitive inspection intervals 
and wing front lower spar cap life limit start over when

[[Page 3140]]

the wing front lower spar cap is replaced with a new P/N 20207-1, 
20207-2, 20207-11, 20207-12, 20207-13, 20207-14, 20207-15, or 20207-
16. These wing front lower spar caps must be inspected as specified 
in paragraphs (i)(3), (i)(5), (i)(6), and (i)(7) of this AD.
    (1) If the wings or wing front lower spar caps were replaced 
with new or used wings or wing front lower spar caps during the life 
of the airplane and the logbook records positively show the hours 
TIS of the replacement wings or wing front lower spar caps, then 
initially inspect at applicable times specified in paragraph (i)(3) 
of this AD. Repetitively inspect thereafter at intervals specified 
paragraphs (i)(5), (i)(6), or (i)(7) of this AD. Replace the wing 
front lower spar caps upon reaching the life limit specified in 
Table 7 of this AD.
    (2) If the wings or wing front lower spar caps were replaced 
with new or used wings or wing front lower spar caps during the life 
of the airplane and logbook records do not positively show the hours 
TIS of the replacement wings or wing front lower spar caps, then 
inspect within 50 hours TIS after February 24, 2010 (the effective 
date of this AD), unless already done. Repetitively inspect 
thereafter at intervals specified in paragraphs (i)(5), (i)(6), or 
(i)(7) of this AD. Replace the wing front lower spar caps within 500 
hours TIS after February 24, 2010 (the effective date of this AD).
    (3) If both wing front lower spar caps are replaced by 
installing the entire Thrush Aircraft, Inc. Custom Kit No. CK-AG-41, 
Revision A, dated March 8, 2007, then initially inspect at 2,000 
hours TIS as shown in paragraph (i)(3) of this AD. Repetitively 
inspect thereafter at intervals specified in paragraph (i)(7) of 
this AD. Replace the wing front lower spar caps at times specified 
in paragraph (i)(8) of this AD.
    (o) Any wing front lower spar cap that is removed and is at or 
beyond the replacement time specified in this AD must be disposed of 
following the procedures in 14 CFR Part 43.10.
    (p) Replacement times start over when the wing front lower spar 
cap is replaced with a new P/N 20207-1, 20207-2, 20207-11, 20207-12, 
20207-13, 20207-14, 20207-15, or 20207-16. These wing front lower 
spar caps are now life-limited parts and must be replaced upon the 
accumulation of the hours TIS specified in Table 7 of this AD.
    (q) Report any cracks you find within 10 days after the cracks 
are found or within 10 days after February 24, 2010 (the effective 
date of this AD), whichever occurs later. Send your report to Cindy 
Lorenzen, Aerospace Engineer, ACE-115A, Atlanta ACO, 1701 Columbia 
Avenue, College Park, Georgia 30337; telephone: (404) 474-5524; 
facsimile: (404) 474-5606; e-mail: cindy.lorenzen@faa.gov. The 
Office of Management and Budget (OMB) approved the information 
collection requirements contained in this regulation under the 
provisions of the Paperwork Reduction Act and assigned OMB Control 
Number 2120-0056. Include in your report the following information:
    (1) Aircraft model and serial number;
    (2) Engine model;
    (3) Aircraft hours TIS;
    (4) Left and right wing front lower spar cap hours TIS;
    (5) Hours TIS on the spar cap since last inspection;
    (6) Crack location and size;
    (7) Procedure (magnetic particle, ultrasonic, or eddy current) 
used for the last inspection;
    (8) Description of any previous modifications and hours TIS when 
the modification was done, such as engine model change, installation 
of winglets, hopper capacity increase, cold working procedure done 
on bolt holes, installation of butterfly plates, or installation of 
Thrush Aircraft, Inc. Custom Kit No. CK-AG-41.
    (r) Installation of the replacement wing front lower spar caps 
and other modification parts that are approved by FAA STC SA03654AT, 
Installation of Avenger Extended Performance Front Spar Enhancement 
Kit (new wing front spar lower caps, center splice and doublers), in 
accordance with Part II of Avenger Master Data List AAS-MDL-08-001, 
Revision B, dated November 26, 2008, terminates the actions required 
by this AD. The installation of FAA STC SA03654AT is an alternative 
to replacing the wing front lower spar caps with Ayres/Thrush wing 
front lower spar caps.

Special Flight Permits

    (s) Under 14 CFR part 39.23, we are limiting the special flight 
permits for this AD by the following conditions:
    (1) The hopper is empty;
    (2) Vne is reduced to 126 miles per hour (109 knots) indicated 
airspeed (IAS); and
    (3) Flight into known turbulence is prohibited.

Alternative Methods of Compliance (AMOCs)

    (t) The Manager, Atlanta Aircraft Certification Office, (ACO) 
FAA, ATTN: Cindy Lorenzen, Aerospace Engineer, ACE-115A, Atlanta 
ACO, 1701 Columbia Avenue, College Park, Georgia 30337; telephone: 
(404) 474-5524; facsimile: (404) 474-5606; e-mail: 
cindy.lorenzen@faa.gov; or William O. Herderich, Aerospace Engineer, 
ACE-117A, Atlanta ACO, 1701 Columbia Avenue, College Park, Georgia 
30337; telephone: (404) 474-5547; facsimile: (404) 474-5606; e-mail: 
william.o.herderich@faa.gov, has the authority to approve AMOCs for 
this AD, if requested using the procedures found in 14 CFR 39.19. 
Before using any approved AMOC on any airplane to which the AMOC 
applies, notify your appropriate principal inspector (PI) in the FAA 
Flight Standards District Office (FSDO), or lacking a PI, your local 
FSDO.
    (u) AMOCs approved for AD 2006-07-15, AD 2003-07-01, AD 2000-11-
16, AD 97-13-11, and/or AD 97-17-03 are approved as AMOCs for this 
AD except for those pertaining to ultrasonic inspection methods.

Material Incorporated by Reference

    (v) You must use Ayres Corporation Service Bulletin No. SB-AG-
39, dated September 17, 1996; Ayres Corporation Custom Kit No. CK-
AG-29, dated December 23, 1997; Quality Aerospace, Inc. Custom Kit 
No. CK-AG-30, dated December 6, 2001; Thrush Aircraft, Inc. Custom 
Kit No. CK-AG-41, Revision A, dated March 8, 2007; and Part II of 
Avenger Master Data List AAS-MDL-08-001, Revision B, dated November 
26, 2008, to do the actions required by this AD, unless the AD 
specifies otherwise.
    (1) The Director of the Federal Register approved the 
incorporation by reference of Thrush Aircraft, Inc. Custom Kit No. 
CK-AG-41, Revision A, dated March 8, 2007, and Part II of Avenger 
Master Data List AAS-MDL-08-001, Revision B, dated November 26, 
2008, under 5 U.S.C. 552(a) and 1 CFR part 51.
    (2) On May 20, 2003 (68 FR 15653), the Director of the Federal 
Register approved the incorporation by reference of Quality 
Aerospace, Inc. Custom Kit No. CK-AG-30, dated December 6, 2001.
    (3) On July 25, 2000 (65 FR 36055), the Director of the Federal 
Register approved the incorporation by reference of Ayres 
Corporation Service Bulletin No. SB-AG-39, dated September 17, 1996; 
and Ayres Corporation Custom Kit No. CK-AG-29, dated December 23, 
1997.
    (4) For service information identified in this AD, contact 
Thrush Aircraft, Inc., 300 Old Pretoria Road, P.O. Box 3149, Albany, 
Georgia 31706-3149, Internet: http://www.thrushaircraft.com. To 
obtain information about Avenger Master Data List AAS-MDL-08-001 and 
the optional installation of FAA STC SA03654AT, contact Avenger 
Aircraft and Services, 103 N. Main Street, Suite 106, Greenville, 
South Carolina 29601, Internet: http://www.avengeraircraft.com.
    (5) You may review copies of the service information 
incorporated by reference for this AD at the FAA, Central Region, 
Office of the Regional Counsel, 901 Locust, Kansas City, Missouri 
64106. For information on the availability of this material at the 
Central Region, call (816) 329-3768.
    (6) You may also review copies of the service information 
incorporated by reference for this AD at the National Archives and 
Records Administration (NARA). For information on the availability 
of this material at NARA, call (202) 741-6030, or go to: http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html.

Appendix to AD 2009-26-11

    The following are examples of calculating equivalent Group 1 
hours.

    Example 1: S/N xxx was originally a Group 3 airplane; later it 
was modified with a Wright R-1820-71, 1200 horsepower, radial engine 
when the wing front lower spar caps had 15,700 hours TIS on them. 
The wing front lower spar caps have accumulated an additional 8,200 
hours since the engine conversion for a total of 23,900 hours TIS on 
the wing front lower spar caps.

Usage Factor = 15,700 hours/28,800 + 8,200 hours/9,400 = 1.417
Equivalent Group 1 hours = 9,400 x 1.417 = 13,320 hours.

    The wing front lower spar caps will need to be replaced within 
the next 1,000 hours TIS after the effective date of this AD as 
determined by Table 6 for a Group 1 airplane

[[Page 3141]]

with a radial engine with between 12,000 and 15,000 hours TIS.

    Example 2: S/N yyy was originally a Group 3 airplane; later it 
was modified with a PT6A-34, 750 horsepower, turbine engine when the 
wing front lower spar caps had 5,300 hours TIS on them. The wing 
front lower spar caps now have 7,700 hours TIS.

Usage Factor = 5,300 hours/28,800 + (7,700 - 5,300)/6,200 = 0.571
Equivalent Group 1 hours = 6,200 x 0.571 = 3,540 hours.

    The wing front lower spar caps will need to be replaced at 6,200 
equivalent Group 1 total hours TIS, which is within the next 2,660 
hours TIS (6,200 - 3,540 = 2,660).

    Issued in Kansas City, Missouri, on January 8, 2010.
Margaret Kline,
Acting Manager, Small Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 2010-594 Filed 1-19-10; 8:45 am]
BILLING CODE 4910-13-P
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