[Federal Register: January 20, 2010 (Volume 75, Number 12)]
[Rules and Regulations]
[Page 3127-3141]
[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

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:<PHONE_NUMBER>; facsimile:<PHONE_NUMBER>; e-mail:
<EMAIL_ADDRESS>or
--William O. Herderich, Aerospace Engineer, ACE-117A, Atlanta Aircraft
Certification Office, 1701 Columbia Avenue, College Park, Georgia
30337; telephone:<PHONE_NUMBER>; facsimile:<PHONE_NUMBER>; e-mail:
<EMAIL_ADDRESS>
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

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);

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

    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.

    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

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.

             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

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;

    (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.

    (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:

  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.

(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

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:<PHONE_NUMBER>;
facsimile:<PHONE_NUMBER>; e-mail<EMAIL_ADDRESS>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:<PHONE_NUMBER>; e-mail:
<EMAIL_ADDRESS>or William O. Herderich, Aerospace Engineer,
ACE-117A, Atlanta ACO, 1701 Columbia Avenue, College Park, Georgia
30337; telephone:<PHONE_NUMBER>; facsimile:<PHONE_NUMBER>; e-mail:
<EMAIL_ADDRESS>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<PHONE_NUMBER>.
    (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<PHONE_NUMBER>, 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

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