[Federal Register Volume 71, Number 153 (Wednesday, August 9, 2006)]
[Proposed Rules]
[Pages 45457-45467]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E6-12945]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2004-19961; Directorate Identifier 2004-CE-48-AD]
RIN 2120-AA64


Airworthiness Directives; Air Tractor, Inc. Models AT-501, AT-
502, AT-502A, AT-502B, and AT-503A Airplanes

AGENCY: Federal Aviation Administration (FAA), Department of 
Transportation (DOT).

ACTION: Supplemental notice of proposed rulemaking (NPRM); reopening of 
the comment period.

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SUMMARY: The FAA proposes to revise an earlier proposed airworthiness 
directive (AD) that applies to certain Air Tractor, Inc. (Air Tractor) 
Models AT-502, AT-502A, AT-502B, and AT-503A airplanes, which proposes 
to supersede AD 2002-26-05. AD 2002-26-05 lowers the safe life for the 
wing lower spar caps for Models AT-502, AT-502A, AT-502B, and AT-503A 
airplanes and those that incorporate or have incorporated Marburger 
Enterprises, Inc. (Marburger) winglets. AD 2002-26-05 also requires you 
to eddy-current inspect the wing lower spar caps immediately before 
modifying to correct any crack in a bolt hole before it extends to the 
modified center section of the wing and report the results of the 
inspection to the FAA if cracks are found. AD 2002-11-05 R1 currently 
requires similar action on Model AT-501 airplanes. Since issuing the 
earlier NPRM, we determined that Model AT-501 airplanes should be added 
to the Applicability section of this proposed AD and that this proposed 
AD should also supersede AD 2002-11-05 R1. We have revised the 
alternative method of compliance (AMOC) to include inspection 
procedures for airplanes that have or have had Marburger winglets 
installed. We have also updated the safe life of the replacement and 
new production spar cap based on additional data we have received from 
the manufacturer. Since these actions impose an additional burden over 
that proposed in the earlier NPRM, we are reopening the comment period 
to allow the public the chance to comment on these additional actions.

DATES: We must receive any comments on this proposed AD by October 10, 
2006.

ADDRESSES: Use one of the following addresses to comments on this 
proposed AD:
     DOT Docket Web site: Go to http://dms.dot.gov and follow 
the instructions for sending your comments electronically.
     Government-wide rulemaking Web site: Go to http://www.regulations.gov and follow the instructions for sending your 
comments electronically.
     Mail: Docket Management Facility, U.S. Department of 
Transportation, 400 Seventh Street, SW., Nassif Building, Room PL-401, 
Washington, DC 20590-0001.
     Fax: (202) 493-2251.
     Hand Delivery: Room PL-401 on the plaza level of the 
Nassif Building, 400 Seventh Street, SW., Washington, DC, between 9 
a.m. and 5 p.m., Monday through Friday, except Federal holidays.
    For service information identified in this proposed AD, contact Air 
Tractor, Incorporated, P.O. Box 485, Olney, Texas 76374; or Marburger 
Enterprises, Inc., 1227 Hillcourt, Williston, North Dakota 58801; 
telephone: (800) 893-1420 or (701) 774-0230; facsimile: (701) 572-2602.

FOR FURTHER INFORMATION CONTACT: Direct all questions to:
     For the airplanes that do not incorporate and never have 
incorporated Marburger Enterprises, Inc. winglets: Rob Romero, 
Aerospace Engineer, FAA, Fort Worth Airplane Certification Office, 2601 
Meacham Boulevard, Fort Worth, Texas 76193-0150; telephone: (817) 222-
5102; facsimile: (817) 222-5960; e-mail: [email protected]; and
     For airplanes that incorporate or have incorporated 
Marburger Enterprises, Inc. winglets: John Cecil, Aerospace Engineer, 
Los Angeles Aircraft Certification Office, FAA, 3960 Paramount 
Boulevard, Lakewood, California 90712; telephone: (562) 627-5228; 
facsimile: (562) 627-5210.

SUPPLEMENTARY INFORMATION:

Comments Invited

    We invite you to send any written relevant data, views, or 
arguments regarding this proposed AD. Send your comments to an address 
listed under the ADDRESSES section. Include the docket number, ``FAA-
2004-19961; Directorate Identifier 2004-CE-48-AD'' at the beginning of 
your comments. We specifically invite comments on the overall 
regulatory, economic, environmental, and energy aspects of this 
proposed AD. We will consider all comments received by the closing date 
and may amend this proposed AD in light of those comments.
    We will post all comments we receive, without change, to http://dms.dot.gov, including any personal information you provide. We will 
also post a report summarizing each substantive verbal contact we 
receive concerning this proposed AD.

Discussion

    Prior to issuing this supplemental notice of proposed rulemaking 
(NPRM), 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 Air Tractor Models AT-502, AT-502A, AT-502B, and AT-503A 
airplanes. That proposal was published in the Federal Register as an 
NPRM on February 9, 2005 (70 FR 6786). The NPRM proposed to supersede 
AD 2002-26-05 with a new AD that would retain the actions required in 
AD 2002-26-05, add additional airplanes to the applicability, and 
incorporate an AMOC to the actions retained from AD 2002-26-05.
    AD 2002-26-05, Amendment 39-12991 (68 FR 18, January 2, 2003), 
currently applies to certain Air Tractor Models AT-502, AT-502A, AT-
502B, and AT-503A airplanes. AD 2002-26-05 supersedes AD 2002-11-03 and 
requires the following:
     Maintaining the original requirements from AD 2002-11-03 
for a lowered safe life, inspection, replacement/modification, and if 
cracks are found, reporting the results to the FAA;
     Further lowering the safe life for the wing lower spar cap 
established in AD 2002-11-03 for Models AT-502, AT-502B, and AT-503A 
airplanes; and
     Expanding the applicability of Models AT-502A and AT-502B 
airplanes to account for future manufactured airplanes.
    With this supplemental NPRM we are also proposing to supersede AD 
2002-11-05 R1, Amendment 39-14564 (71 FR 19629, April 17, 2006), which 
currently applies to certain Air Tractor Model AT-501 airplanes. We 
issued AD 2002-11-05 R1 to revise AD 2002-11-05 to remove AT-400 series 
and Models AT-802 and AT-802A airplanes from the applicability because 
separate AD actions were issued for those airplanes.

[[Page 45458]]

AD 2002-11-05 R1 retains the actions required in AD 2002-11-05 for 
Model AT-501 airplanes.
    The following is a list of ADs that have been issued to date that 
are related to the wing spar inspection and safe life on Air Tractor 
airplanes:

----------------------------------------------------------------------------------------------------------------
                                     Affected air tractor model
             AD No.                          airplanes                                 Status
----------------------------------------------------------------------------------------------------------------
2000-14-51.....................  AT-501, AT-502, and AT-502A......  Superseded by AD 2001-10-04.
2001-10-04.....................  AT-400, AT-500, and AT-800 Series  Revised by AD 2001-10-04 R1.
2001-10-04 R1..................  AT-400, AT-500, and AT-800 Series  Superseded by AD 2002-11-05.
2002-11-05.....................  AT-400, AT-401, AT-401B, AT-402,   Revised by AD 2002-11-05 R1.
                                  AT-402A, AT-402B, AT-501, AT-
                                  802, and AT-802A.
2002-13-02.....................  AT-300, AT-301, AT-302, AT-400,    Superseded by AD 2003-06-01.
                                  and AT-400A Airplanes.
2002-11-03.....................  AT-502, AT-502A, AT-502B, and AT-  Superseded by AD 2002-26-05.
                                  503A.
2002-26-05.....................  AT-502, AT-502A, AT-502B, and AT-  Current.
                                  503A.
2003-06-01.....................  AT-300, AT-301, AT-302, AT-400,    Current.
                                  and AT-400A.
2002-11-05 R1..................  AT-501...........................  Current.
2006-08-08.....................  AT-400, AT-401, AT-401B, AT-402,   Current.
                                  AT-402A, and AT-402B.
2006-08-09.....................  AT-802 and AT-802A...............  Current.
----------------------------------------------------------------------------------------------------------------

    You may view these ADs at the following Internet Web site 
addresses: http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAD.nsf/MainFrame?OpenFrameSet or http://www.gpoaccess.gov/fr/index.html.

Comments

    We provided the public the opportunity to participate in developing 
the proposed AD on Air Tractor Models AT-502, AT-502A, AT-502B, and AT-
503A airplanes. The following presents the comments received on this 
earlier proposed AD and FAA's response to each comment:

Comment Issue No. 1: Allow Repetitive Inspection and an Upper Life 
Limit on the New Cap

    Lewis Air Service states there is a need to incorporate an 
alternative solution that includes repetitive inspections and an upper 
life limit on the new cap. Based on the way the NPRM is currently 
written, the commenter believes the low cap replacement time is too 
burdensome and not cost effective.
    Although we agree that repetitive inspections may reduce the 
economic impact and minimize the risk of reduced agricultural 
production, this will not meet the safety intent of this proposed AD. 
We determined that reliance on critical repetitive inspections carries 
an unnecessary safety risk when parts replacement or modifications 
exist. In determining what inspections are critical, the FAA considers 
(1) the safety consequences of the airplane if the known problem is not 
detected by the inspection; (2) the reliability of the inspection, such 
as the probability of not detecting the known problem; (3) whether the 
inspection area is difficult to access; and (4) the possibility of 
damage to an adjacent structure as a result of the problem.
    Since the initial publication of the earlier proposed AD, Air 
Tractor has completed fatigue testing on the replacement spar cap. The 
life of the cap has been updated in this proposed AD to reflect the 
results of this testing and subsequent analysis.
    We are not changing this proposed AD based on this comment but are 
changing it based on new data from the manufacturer.

Comment Issue No. 2: Proposed AD Is Not Necessary

    M&M Air Service states that they operate eight different Air 
Tractor airplanes and to date have not found any cracks. The commenter 
indicates that the proposed rulemaking is confusing, not cost 
beneficial, and excessive.
    Based on these comments, we infer that the commenter wants the NPRM 
withdrawn.
    We do not agree with the commenter. Fatigue analysis/testing/fleet 
history shows that the wing spar will crack and fail over time. The 
commenter's airplanes not cracking to date does not prevent the unsafe 
condition from developing on the commenter's airplanes or other 
airplanes of the same type design in the future.
    To date, we have received over 50 reports of cracked spar caps on 
AT-502 series airplanes and one report of complete wing separation. We 
realize that there are many different wing configurations in-service on 
these airplanes and each has different requirements. However, analysis 
shows that the airplane could fail in the affected area based on the 
design and normal utilization of the type design airplanes.
    We are not changing this proposed AD based on this comment.

Comment Issue No. 3: Compliance Time To Accommodate Flying Schedules

    The National Agricultural Aviation Association requests the FAA 
consider the flying schedules of the airplanes and accommodate a 
program that can be done during the off-season. The commenter suggests 
the FAA allow repetitive inspections until an ultimate solution is 
reached, assuming no cracks are found.
    We have considered the importance of the financial and operational 
impact this proposed rulemaking may have on owners and operators and, 
in this specific case, aerial application businesses. This proposed AD 
uses inspections to manage the safety of the wing centerline joint 
instead of reducing the compliance times for replacing parts. However, 
this approach cannot be used indefinitely. Extending the service life 
of fatigue-critical, primary structure areas requires not only ensuring 
the safety of the area being inspected or modified, but also ensuring 
the safety of the complete structure when extending the service life.
    Fatigue analysis shows that the safe life is the solution to the 
unsafe condition, not repetitive inspections over the life of the 
airplane. For eligible airplanes, we are providing an AMOC that 
provides an aggressive repetitive inspection program until 8,000 hours 
time-in-service (TIS), provided no cracks are found.
    The FAA has shown a history of accommodating flying schedules 
through AMOCs on previous ADs for this subject. We will continue to 
consider AMOCs provided they maintain a level of safety acceptable to 
the FAA.
    For the replacement spar cap, we have received new data that 
justifies a much higher safe life than was previously published in the 
NPRM.

[[Page 45459]]

    We are not changing this proposed AD based on this comment.

Comment Issue No. 4: Lack of Wing Life-Limit Information

    Julie Broussard of Lewis Flying and Maintenance Service, Inc., 
states that she was never informed in writing of a 1,600 hour safe life 
or replacement life of 8,000 hours TIS for the AT-502 wing. The 
commenter also urges the FAA to make the manufacturer ``fix the wing.''
    We issued AD 2002-26-05, Amendment 39-12991 (68 FR 18, January 2, 
2003), which applies to Air Tractor Models AT-502, AT-502A, AT-502B, 
and AT-503A airplanes. That AD lowers the safe life for the wing lower 
spar caps to 1,650 hours TIS. AD 2002-26-05 supersedes AD 2002-11-03, 
Amendment 39-12764 (67 FR 38371, June 4, 2002). We also issued Special 
Airworthiness Information Bulletin (SAIB) CE-05-28, dated January 21, 
2005, announcing an AMOC to AD 2002-26-05. The AMOC allows an 
inspection program instead of the safe life replacement program 
required by AD 2002-26-05, which allows operation of a modified wing up 
to 8,000 hours TIS, provided no cracks are found during required 
inspections.
    We are legally bound to notify the public of an AD through 
publication in the Federal Register. AD 2002-26-05 was published in the 
Federal Register on January 2, 2003. In the past, we have sent copies 
of ADs and SAIBs to registered owners of the affected airplanes, which 
could be a bank or holding company. This may be the reason the 
commenter did not receive notification of the change in the safe life 
limit and replacement schedule.
    This supplemental NPRM is still only a proposal at this time. The 
previous NPRM on this subject was published in the Federal Register on 
February 9, 2005 (70 FR 6786).
    We will always encourage modifications that incorporate design 
changes that make critical parts stronger and safer. However, our 
responsibility is to address the continued operational safety of the 
airplane fleet, ensure that current design regulations are met, and 
correct any unsafe conditions.
    Establishing a safe life and an option of an aggressive repetitive 
inspection schedule until 8,000 hours TIS (provided no cracks are 
found) meets the FAA's responsibility. Further, the replacement spar 
cap has been substantiated to a much higher safe life than previously 
published.
    We are not changing this proposed AD based on this comment.

Comment Issue No. 5: New Production Airplanes Have a 27 Percent 
Increase in Safe Life

    The National Transportation Safety Board (NTSB) questions the 
rationale for new production AT-502B airplanes having a 27 percent 
increase in the safe life limit on the wing from 1,650 hours TIS to 
2,100 hours TIS. The commenter also states a concern for the 
conservatism in the initial and repetitive inspection program.
    Other items of concern to the commenter are:
     The wording proposed in section (e)(2) of the earlier 
proposed AD may allow for inspections to continue indefinitely. The 
commenter states that airplanes using the AMOC who find cracks should 
report them to the FAA.
     Airplanes that have been modified with a replacement cap 
should follow the inspection program for later serial number airplanes.
     There has been nothing done to address the use of winglets 
as it applies to inspection intervals.
    The safe life for new production AT-502B airplanes was determined 
as a result of fatigue testing performed by the manufacturer. The 
initial and repetitive inspection program was based on a thorough 
damage tolerance analysis using a validated load spectrum and coupon 
testing.
    It should be noted that since publication of the earlier NPRM, the 
manufacturer has completed more extensive testing, and we are now 
proposing a safe life for new production AT-502B airplanes that 
represents much more than the 27 percent increase the commenter states.
    We do not agree that paragraph (e)(2) of the previously proposed AD 
allowed for indefinite inspections. Paragraph (e)(2) of the proposed AD 
refers to Appendix 2, which has clearly defined upper limits on 
inspection times (8,000 hours TIS for eligible airplanes).
    We agree that any cracks detected should be reported to the FAA. We 
are retaining the reporting requirement from the earlier NPRM in this 
proposed AD.
    Airplanes with replacement spar caps, as well as new production 
airplanes, are no longer required to follow an inspection program.
    We agree that we did not address an inspection program for 
airplanes with winglets installed. We are revising this proposed AD to 
include an AMOC inspection program for airplanes that have or have had 
winglets installed. Further, this proposed AD states that airplanes 
with the new or replacement spar caps are not eligible to have the 
winglet STC installed without proper fatigue substantiation.

Comment Issue No. 6: Include Model AT-501 Airplanes in the 
Applicability

    Leland Snow, President of Air Tractor, Inc., states that Model AT-
501 airplanes should be included in the Applicability section and that 
new airplanes should not have a safe life limit of 3,100 hours TIS.
    The commenter states the costs for doing the inspection is too low. 
The inspection typically costs from $450 to $550. Parts cost for the 
replacement spar cap is approximately $16,500 plus approximately 
$16,500 for labor (a total of $33,000).
    The commenter also states that winglets should be removed before 
allowing the AMOC.
    We agree with the commenter that Model AT-501 airplanes should be 
included in the Applicability section. We also agree to update the Cost 
Impact section. We are revising this proposed AD to include those 
changes.
    We do not agree that airplanes with winglets installed should be 
excluded from the AMOC. We are adding an AMOC inspection program in 
this proposed AD to cover airplanes that have winglets installed 
following Supplemental Type Certificate (STC) SA00490LA.

Comment Issue No. 7: Torsion Loads

    John R. Janssen states that torsion loads need to be accounted for 
to properly address the wing safe life limit for the affected 
airplanes.
    We agree with the commenter that the torsion load is a contributing 
factor to the fatigue life of the wings, as are all the other loads 
(ground, gust, maneuver, etc.). These loads have been accounted for in 
the load spectrum that was used in developing the inspection program 
and the life of the new/replacement spar cap.
    We are not changing this proposed AD based on this comment.

Comment Issue No. 8: Marburger Winglets

    Lewis Broussard, Owner, Lewis Flying and Maintenance Service, Inc., 
states that installing Marburger Enterprise, Inc. winglets increases 
the safe life of the wing.
    We do not agree with the commenter. We have data that shows adding 
winglets increases the operating stresses at the wing root and 
consequently leads to a reduced safe life.
    We are not changing this proposed AD based on this comment.

Comment Issue No. 9: AMOC Should Apply to Airplanes With Winglets

    Rick Marburger of Marburger Enterprises, Inc., states that 
airplanes

[[Page 45460]]

with winglets installed should be included in the AMOC repetitive 
inspection program.
    We agree with the commenter. We included procedures in the AMOC 
repetitive inspection program to address airplanes that have or have 
had winglets installed.
    We are revising this proposed AD to incorporate this change.

Comment Issue No. 10: Unfair Safe Life Limit for the New Spar Cap

    Tom Miller of Ingalls Aerial Sprayers, Inc., states the safe life 
limit of 3,100 hours TIS for the new/replacement spar cap is unfair. 
Numerous other commenters have similar concerns. The commenters state 
the new design should be given a safe life limit that is equivalent to 
the old design, which is 8,000 hours TIS.
    We agree with the commenters. The 3,100-hour TIS safe life limit 
was based on data submitted by Air Tractor and approved by the FAA. 
However, since the earlier proposed AD was published, Air Tractor began 
a new test program using a recently validated load spectrum to 
determine a new safe life for this design configuration. That testing 
has been completed and the new safe life limit is being published in 
this proposed AD.
    We are revising this proposed AD to incorporate this change.

Relevant Service Information

    The following service information from AD 2002-11-05 R1 and the 
previous NPRM are still valid for this supplemental NPRM:
     Snow Engineering Drawing Number 21050;
     Snow Engineering Service Letters 197 or 
205, both revised March 26, 2001; and
     Snow Engineering Service Letter 244, dated April 
25, 2005.
    Snow Engineering Co. has a licensing agreement with Air Tractor 
that allows them to produce technical data for use on Air Tractor 
products.

FAA's Determination and Requirements of This Proposed AD

    Since issuing the earlier NPRM, we determined that Model AT-501 
airplanes should be added to the Applicability section. We also 
developed an AMOC to the requirements of AD 2002-26-05 for airplanes 
that have or have had winglets installed. We are extending the safe 
life for new production airplanes and replacement spar caps.
    After examining the circumstances and reviewing all available 
information related to the incidents described above, we have 
determined that:
     The unsafe condition referenced in this document exists or 
could develop on other Air Tractor Models AT-501, AT-502, AT-502A, AT-
502B, and AT-503A airplanes of the same type design that are on the 
U.S. registry;
     We should change this proposed AD to include Model AT-501 
airplanes in the Applicability section and revise the AMOC.
     We should take AD action to correct this unsafe condition.

The Supplemental NPRM

    Adding additional models to the Applicability section goes beyond 
the scope of what was originally proposed in the earlier NPRM. 
Therefore, we are reopening the comment period and allowing the public 
the chance to comment.
    This proposed AD would supersede AD 2002-26-05 and AD 2002-11-05 R1 
with a new AD that would:
     Retain the actions required in AD 2002-26-05 and AD 2002-
11-05 R1;
     Add additional airplanes to the Applicability section;
     Incorporate a revised AMOC to include inspection 
procedures for airplanes that have or have had winglets installed 
following STC SA00490LA; and
     Extend the safe life for new production airplanes and 
replacement spar caps.
    The following table summarizes the effects this proposed AD would 
have on the airplane models affected by this proposed AD:

----------------------------------------------------------------------------------------------------------------
                                                                                                          Proposed
                                                                         Model                             action
-------------------------------------------------------------------------------------------------------- ----------
AT-501.......................................   Supersede AD 2002-11-05 R1.
                                                Retain the safe lives from AD 2002-11-05 R1.
                                                Provide an AMOC that allows extension of the
                                                safe life through an inspection and modification
                                                program.
AT-502.......................................   Supersede AD 2002-26-05.
                                                Retain the safe lives from AD 2002-26-05 and add
                                                S/Ns to applicability. AD 2002-26-05 provided safe lives
                                                for S/Ns 0003 through 0236. Proposed action applies the
                                                same safe life to all S/Ns beginning with 0003.
                                                Provide an AMOC that allows extension of the
                                                safe life through an inspection and modification
                                                program.
AT-502A......................................   Supersede AD 2002-26-05.
                                                Retain the safe lives from AD 2002-26-05.
                                                Provide an AMOC that allows extension of the
                                                safe life through an inspection and modification
                                                program.
AT-502B......................................   Supersede AD 2002-26-05.
                                                Retain the safe lives from AD 2002-26-05 for S/
                                                Ns 0187 through 0654, except 0643.
                                                Increase the safe lives beyond those listed in
                                                AD 2002-26-05 for S/Ns 0655 and greater, as well as S/N
                                                0643.
                                                Add requirement to cold work outboard wing
                                                center splice block bolt holes in the lower spar cap on
                                                S/Ns 0643 and 0655 through 0692.
                                                Provide an AMOC that allows extension of the
                                                safe life through an inspection and modification program
                                                for S/Ns 187 through 654, except 643.
AT-503A......................................   Supersede AD 2002-26-05.
                                                Retain the safe lives from AD 2002-26-05.
                                                Provide an AMOC that allows extension of the
                                                safe life through an inspection and modification
                                                program.
----------------------------------------------------------------------------------------------------------------

Costs of Compliance

    We estimate that this proposed AD affects approximately 500 
airplanes in the U.S. registry.
    We estimate the following costs to do each proposed inspection:

[[Page 45461]]



----------------------------------------------------------------------------------------------------------------
                                                            Total cost per
           Labor cost                    Parts cost            airplane         Total cost on U.S.  operators
----------------------------------------------------------------------------------------------------------------
8 work-hours x $80 per hour =     No parts required for               $640  $640 x 500 = $320,000.
 $640.                             inspection.
----------------------------------------------------------------------------------------------------------------

    We estimate the following costs to do the proposed modification:

--------------------------------------------------------------------------------------------------------------------------------------------------------
            Labor cost                  Parts cost                  Total cost per airplane                       Total cost on U.S. operators
--------------------------------------------------------------------------------------------------------------------------------------------------------
120 work-hours x $80 per hour =    Approximately $3,700  $9,600 + $3,700 = $13,300                     $13,300 x 500 = $6,650,000.00.
 $9,600.
--------------------------------------------------------------------------------------------------------------------------------------------------------

    We estimate the following costs to do the proposed replacement:

--------------------------------------------------------------------------------------------------------------------------------------------------------
             Labor cost                      Parts cost                   Total cost per airplane                    Total cost on U.S. operators
--------------------------------------------------------------------------------------------------------------------------------------------------------
254 work-hours x $80 per hour =       Approximately $16,500..  $20,320 + $16,500 = $36,820                   $36,820 x 500 = $18,410,000.00.
 $20,320.
--------------------------------------------------------------------------------------------------------------------------------------------------------

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 
rulemaking action.

Regulatory Findings

    We have determined that this proposed AD would not have federalism 
implications under Executive Order 13132. This proposed AD would not 
have a substantial direct effect on the States, on the relationship 
between the national Government and the States, or on the distribution 
of power and responsibilities among the various levels of government.
    For the reasons discussed above, I certify that the proposed 
regulation:
    1. Is not a ``significant regulatory action'' under Executive Order 
12866;
    2. Is not a ``significant rule'' under the DOT Regulatory Policies 
and Procedures (44 FR 11034, February 26, 1979); and
    3. Will not 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 regulatory evaluation of the estimated costs to 
comply with this proposed AD and placed it in the AD docket.

Examining This Proposed AD Docket

    You may examine the AD docket that contains the proposed AD, the 
regulatory evaluation, any comments received, and other information on 
the Internet at http://dms.dot.gov; or in person at the Docket 
Management Facility between 9 a.m. and 5 p.m., Monday through Friday, 
except Federal holidays. The Docket Office (telephone (800) 647-5227) 
is located at the street address stated in the ADDRESSES section. 
Comments will be available in the AD docket shortly after receipt.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, under the authority delegated to me by the 
Administrator, the Federal Aviation Administration proposes to amend 14 
CFR part 39 as follows:

PART 39--AIRWORTHINESS DIRECTIVES

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

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


Sec.  39.13  [Amended]

    2. FAA amends Sec.  39.13 by removing Airworthiness Directive (AD) 
2002-26-05, Amendment 39-12991 (68 FR 18, January 2, 2003) and AD 2002-
11-05 R1, Amendment 39-14564 (71 FR 19628, April 17, 2006), and by 
adding a new AD to read as follows:

Air Tractor, Inc.: Docket No. FAA-2004-19961; Directorate Identifier 
2004-CE-48-AD.

Comment Due Date

    (a) We must receive comments on this proposed airworthiness 
directive (AD) by October 10, 2006.

Affected AD

    (b) This AD supersedes AD 2002-26-05, Amendment 39-12991, and AD 
2002-11-05 R1, Amendment 39-14564.

Applicability

    (c) This AD applies to certain Models AT-501, AT-502, AT-502A, 
AT-502B, and AT-503A airplanes. Use Table 1 in paragraph (c)(1) of 
this AD for airplanes that do not incorporate and never have 
incorporated Marburger Enterprises, Inc. (Marburger) winglets. Use 
Table 2 in paragraph (c)(4) of this AD for certain AT-500 series 
airplanes that incorporate or have incorporated Marburger winglets.
    (1) The following table applies to airplanes (certificated in 
any category) that do not incorporate and never have incorporated 
Marburger winglets along with the safe life (presented in hours 
time-in-service (TIS)) of the wing lower spar cap for all affected 
airplane models and serial numbers:

[[Page 45462]]



    Table 1.--Safe Life for Airplanes That Do Not Incorporate and Never Have Incorporated Marburger Winglets
----------------------------------------------------------------------------------------------------------------
                Model                                Serial Nos.                  Wing lower spar cap safe life
----------------------------------------------------------------------------------------------------------------
AT-501...............................  0002 through 0061......................  4,531 hours TIS.
AT-501...............................  All serial numbers beginning with 0062.  7,693 hours TIS.
AT-502...............................  All serial numbers beginning with 0003.  1,650 hours TIS.
AT-502A..............................  All serial numbers beginning with 0158.  1,650 hours TIS.
AT-502B..............................  0187 through 0654, except 0643.........  1,650 hours TIS.
AT-502B..............................  0643, and 0655 through 0692............  9,000 hours TIS.
AT-502B..............................  0693 through 0701......................  9,500 hours TIS.
AT-502B..............................  All serial numbers beginning with 0702.  9,800 hours TIS.
AT-503A..............................  All serial numbers beginning with 0067.  1,650 hours TIS.
----------------------------------------------------------------------------------------------------------------

    (2) If piston-powered airplanes have been converted to turbine 
power, you must use the limits for the corresponding serial number 
(S/N) turbine-powered airplanes.
    (3) Airplanes that have been modified to install lower spar 
caps, part numbers (P/N) 21058-1 and 21058-2, should use a safe life 
of 9,800 hours TIS.
    (4) The following table applies to airplanes (certificated in 
any category) that incorporate or have incorporated Marburger 
winglets. These winglets are installed following Supplemental Type 
Certificate (STC) SA00490LA. Use the winglet usage factor in Table 2 
of this paragraph, the safe life specified in Table 1 in paragraph 
(c)(1) of this AD, and the instructions included in Appendix 1 to 
this AD to determine the new safe life of airplanes that incorporate 
or have incorporated Marburger winglets:

  Table 2.--Winglet Usage Factor To Determine the Safe Life for Airplanes That Incorporate or Have Incorporated
                              Marburger Winglets Installed Following STC SA00490LA
----------------------------------------------------------------------------------------------------------------
                                                                                                   Winglet usage
                     Model                                         Serial Nos.                        factor
----------------------------------------------------------------------------------------------------------------
AT-501........................................  0002 through 0061...............................             1.6
AT-501........................................  All serial numbers beginning with 0062..........             1.6
AT-502........................................  0003 through 0236...............................             1.6
AT-502A.......................................  0158 through 0238...............................             1.6
AT-502A.......................................  All serial numbers beginning with 0239..........             1.2
AT-502B.......................................  All serial numbers beginning with 0187..........             1.2
----------------------------------------------------------------------------------------------------------------

    (5) Model AT-502B airplanes, S/N 0643, all S/Ns beginning with 
0655, and all other airplanes that have been modified with 
replacement spar caps, P/N 21058-1 and P/N 21058-2, are not eligible 
to have STC SA00490LA installed without additional fatigue data 
being provided to the FAA at the address in paragraph (f) of this 
AD.

Unsafe Condition

    (d) This AD is the result of service reports and analysis done 
on wing lower spar caps of Air Tractor, Inc. airplanes. The actions 
specified by this AD are intended to prevent fatigue cracks from 
occurring in the wing lower spar cap before the established safe 
life is reached. Fatigue cracks in the wing lower spar cap, if not 
detected and corrected, could result in failure of the spar cap and 
lead to wing separation and loss of control of the airplane.

Compliance

    (e) To address this problem, you must do the following:

------------------------------------------------------------------------
           Actions                 Compliance            Procedures
------------------------------------------------------------------------
(1) For all affected          For airplanes         Airplane Records
 airplanes: Modify the         previously affected   Modification: The
 applicable airplane records   by AD 2002-26-05:     owner/operator
 (logbook) as follows to       Do the logbook        holding at least a
 show the reduced safe life    entry within the      private pilot
 for the wing lower spar cap   next 10 hours TIS     certificate as
 (use the information from     after January 15,     authorized by
 Table 1 in paragraph          2003 (the effective   section 43.7 of the
 (c)(1), Table 2 in            date of AD 2002-26-   Federal Aviation
 paragraph (c)(4), and         05). For airplanes    Regulations (14 CFR
 Appendix 1 of this AD, as     not previously        43.7) may modify
 applicable):                  affected by AD 2002-  the airplane
 (i) Incorporate the           26-05: Do the         records as
 following into the airplane   logbook entry         specified in
 logbook ``In accordance       within the next 10    paragraph (e)(1) of
 with AD **-**-** (AD 2002-    hours TIS after the   this AD. Make an
 26-05 or AD 2002-11-05, as    effective date of     entry into the
 applicable) the wing lower    this AD, unless       airplane records
 spar cap is life limited to   already done. The     showing compliance
 ----.'' Insert the            logbook language      with this portion
 applicable safe life number   for AT-501            of the AD in
 from the applicable tables    airplanes is          accordance with
 in paragraphs (c)(1) and      referenced as AD      section 43.9 of the
 (c)(4) of this AD and         2002-11-05 instead    Federal Aviation
 Appendix 1 of this AD.        of AD 2002-11-05 R1   Regulations (14 CFR
 (ii) If, as of the time of    to maintain           43.9). Spar Cap
 the logbook entry             continuity and        Replacement: Do the
 requirement of paragraph      assures no further    replacement when
 (e)(1)(i) of this AD, your    action is necessary.  the safe life is
 airplane is over or within                          reached following
 50 hours of the safe life,                          Snow Engineering
 an additional 50 hours TIS                          Drawing Number
 after the effective date of                         21050, Snow
 this AD is allowed to do                            Engineering Service
 the replacement.                                    Letters 197 or 205, both revised
                                                     March 26, 2001, as
                                                     applicable. The
                                                     owner/operator may
                                                     not do the spar cap
                                                     modification/
                                                     replacement, unless
                                                     he/she holds the
                                                     proper mechanic
                                                     authorization.

[[Page 45463]]

 
(2) For all affected          Inspection schedule   Procedures included
 airplanes: To extend the      included as part of   as part of the AMOC
 safe life of the wing lower   the alternative       in Appendix 2 to
 spar cap, you may eddy-       method of             this AD.
 current inspect and modify    compliance (AMOC)
 the wing lower spar cap.      in Appendix 2 to
 The inspection schedule and   this AD.
 modification procedures are
 included in Appendix 2 to
 this AD.
(3) For all affected          Only if cracks are    Send the form
 airplanes: Report to the      found, send the       (Figure 1 of this
 FAA any cracks detected as    report within 10      AD) to FAA, Fort
 the result of each            days after the        Worth Airplane
 inspection required by        inspection required   Certification
 paragraph (e)(2) of this AD   in paragraph (e)(2)   Office, Attn: Rob
 on the form in Figure 1 of    of this AD.           Romero, 2601
 this AD. The Office of                              Meacham Boulevard,
 Management and Budget (OMB)                         Fort Worth, Texas
 approved the information                            76193-0150;
 collection requirements                             telephone: (817)
 contained in this                                   222-5102;
 regulation under the                                facsimile: (817)
 provisions of the Paperwork                         222-5960.
 Reduction Act and assigned
 OMB Control Number 2120-
 0056.
(4) For Model AT-502B         Before accumulating   Following Snow
 airplanes, S/Ns 502B-0643,    2,000 hours TIS or    Engineering Service
 and 502B-0655 through 502B-   within the next 100   Letter 244, dated April
 hand and right-hand two       effective date of     25, 2005.
 outboard wing center splice   this AD, whichever
 block bolt holes (4 total)    occurs later.
 in the lower spar cap.
(5) For all affected          Not applicable......  Not applicable.
 airplanes: Airplanes that
 have the two-part
 modification done following
 the applicable service
 bulletins (Snow Engineering
 Service Letters 197 or 205, both
 revised March 26, 2001; or
 Snow Engineering Service
 Letter 244, dated
 April 25, 2005), but have
 over-sized outboard bolt
 holes at the splice block,
 must obtain an AMOC from
 FAA as specified in
 paragraph (f) of this AD to
 determine applicable
 inspection intervals.
------------------------------------------------------------------------

BILLING CODE 4910-13-P

[[Page 45464]]

[GRAPHIC] [TIFF OMITTED] TP09AU06.007

BILLING CODE 4910-13-C

Alternative Methods of Compliance (AMOC)

    (f) The Manager, Fort Worth or Los Angeles Airplane 
Certification Office (ACO), as applicable (see paragraphs (f)(1)(i) 
and (f)(2)(ii) of this AD below for specific contacts), has the 
authority to approve AMOCs for this AD, if requested using the 
procedures found in 14 CFR 39.19.
    (1) For information on any already approved AMOCs, contact:
    (i) For the airplanes that do not incorporate and never have 
incorporated Marburger Enterprises, Inc. winglets: Rob Romero, 
Aerospace Engineer, FAA, Fort Worth Airplane Certification Office, 
2601 Meacham Boulevard, Fort Worth, Texas 76193-0150; telephone: 
(817) 222-5102; facsimile: (817) 222-5960; e-mail: 
[email protected].
    (ii) For airplanes that incorporate or have incorporated 
Marburger Enterprises, Inc. winglets: John Cecil, Aerospace 
Engineer, Los Angeles Aircraft Certification Office, FAA,

[[Page 45465]]

3960 Paramount Boulevard, Lakewood, California 90712; telephone: 
(562) 627-5228; facsimile: (562) 627-5210.
    (2) AMOCs approved for AD 2001-10-04 and/or AD 2000-14-51 are 
not considered approved for this AD.
    (3) AMOCs approved for AD 2001-10-04 R1, AD 2002-11-03, AD 2002-
11-05, AD 2002-11-05 R1, or AD 2002-26-05 are considered approved 
for this AD.

Special Flight Permit

    (g) Under 14 CFR part 39.23, we are limiting the special flight 
permits for this AD by the following conditions:
    (1) Operate only in day visual flight rules (VFR).
    (2) Ensure that the hopper is empty.
    (3) Limit airspeed to 135 miles per hour (mph) indicated 
airspeed (IAS).
    (4) Avoid any unnecessary g-forces.
    (5) Avoid areas of turbulence.
    (6) Plan the flight to follow the most direct route.

Related Information

    (h) To get copies of the documents referenced in this AD, 
contact Air Tractor, Incorporated, P.O. Box 485, Olney, Texas 76374; 
or Marburger Enterprises, Inc., 1227 Hillcourt, Williston, North 
Dakota 58801. To view the AD docket, go to the Docket Management 
Facility, U.S. Department of Transportation, 400 Seventh Street, 
SW., Nassif Building, Room PL-401, Washington, DC, or on the 
Internet at http://dms.dot.gov. The docket number is FAA-2004-19961.

Appendix 1 to Docket No. FAA-2004-19961

    The following provides procedures for determining the safe life 
for those Models AT-501, AT-502, AT-502A, and AT-502B airplanes that 
incorporate or have incorporated Marburger Enterprises, Inc. 
(Marburger) winglets. These winglets are installed in accordance 
with Supplemental Type Certificate (STC) No. SA00490LA.
    If you have removed the Marburger winglets before further flight 
after the effective date of this AD or before the effective date of 
this AD, do the following:
    1. Review your airplane's logbook to determine your airplane's 
time-in-service (TIS) with winglets installed per Marburger STC No. 
SA00490LA. This includes all time spent with the winglets currently 
installed and any previous installations where the winglet was 
installed and later removed.

Example: A review of your airplane's logbook shows that you have 
accumulated 350 hours TIS since incorporating the Marburger STC. 
Further review of the airplane's logbook shows that a previous owner 
had installed the STC and later removed the winglets after 
accumulating 150 hours TIS. Therefore, your airplane's TIS with the 
winglets installed is 500 hours.

    If you determine that the winglet STC has never been 
incorporated on your airplane, then your safe life is presented in 
Table 1 in paragraph (c)(1) of this AD. Any future winglet 
installation will be subject to a reduced safe life per these 
instructions.
    2. Determine your airplane's unmodified safe life from Table 1 
in paragraph (c)(1) of this AD.

Example: Your airplane is a Model AT-502B, serial number (S/N) 0292. 
From Table 1 in paragraph (c)(1) of this AD, the unmodified safe-
life of your airplane is 1,650 hours TIS.

    All examples from hereon will be based on the Model AT-502B, S/N 
0292 airplane.
    3. Determine the winglet usage factor from Table 2 in paragraph 
(c)(4) of this AD.

Example: Again, your airplane is a Model AT-502B, S/N 0292. From 
Table 2 in paragraph (c)(4) of this AD, your winglet usage factor is 
1.2.

    4. Adjust the winglet TIS to account for the winglet usage 
factor. Multiply the winglet TIS (result of Step 1 above) by the 
winglet usage factor (result of Step 3 above).

Example: Winglet TIS is 500 hours x a winglet usage factor of 1.2. 
The adjusted winglet TIS is 600 hours.

    5. Calculate the winglet usage penalty. Subtract the winglet TIS 
(result of Step 1 above) from the adjusted winglet TIS (result of 
Step 4 above).

Example:
    Adjusted winglet TIS - the winglet TIS = Winglet usage penalty.
    (600 hours TIS) - (500 hours TIS) = (100 hours TIS).

    6. Adjust the safe life of your airplane to account for winglet 
usage. Subtract the winglet usage penalty (result of Step 5 above) 
result from the unmodified safe life from Table 1 in paragraph 
(c)(1) of this AD (the result of Step 2 above).

Example:
    Unmodified safe life - winglet usage penalty = Adjusted safe 
life.
    (1,650 hours TIS) - (100 hours TIS) = (1,550 hours TIS).

    7. If you remove the winglets from your airplane before further 
flight or no longer have the winglets installed on your airplane, 
the safe life of your airplane is the adjusted safe life (result of 
Step 6 above). Enter this number in paragraph (e)(1)(i) of this AD 
and the airplane logbook.
    If you have the Marburger winglets installed as of the effective 
date of this AD and plan to operate your airplane without removing 
the winglets, do the following:
    1. Review your airplane's logbook to determine your airplane's 
TIS without the winglets installed.

Example: A review of your airplane's logbook shows that you have 
accumulated 1,500 hours TIS, including 500 hours with the Marburger 
winglets installed. Therefore, your airplane's TIS without the 
winglets installed is 1,000 hours.

    2. Determine your airplane's unmodified safe life from Table 1 
in paragraph (c)(1) of this AD.

Example: Your airplane is a Model AT-502B, S/N 0292. From Table 1 in 
paragraph (c)(1) of this AD, the unmodified safe life of your 
airplane is 1,650 hours TIS.

    All examples from hereon will be based on the Model AT-502B, S/N 
0292 airplane.
    3. Determine the winglet usage factor from Table 2 in paragraph 
(c)(4) of this AD.

Example: Again, your airplane is a Model AT-502B, S/N 0292. From 
Table 2 in paragraph (c)(4) of this AD, your winglet usage factor is 
1.2.

    4. Determine the potential winglet TIS. Subtract the TIS without 
the winglets installed (result of Step 1 above) from the unmodified 
safe life (result of Step 2 above).

Example:
    Unmodified safe life - TIS without winglets = Potential winglet 
TIS.
    (1,650 hours TIS) - (1,000 hours TIS) = (650 hours TIS).

    5. Adjust the potential winglet TIS to account for the winglet 
usage factor. Divide the potential winglet TIS (result of Step 4 
above) by the winglet usage factor (result of Step 3 above).

Example:
    Potential winglet TIS / winglet usage factor = Adjusted 
potential winglet TIS.
    (650 hours TIS) / (1.2) = (541 hours TIS).

    6. Calculate the winglet usage penalty. Subtract the adjusted 
potential winglet TIS (result of Step 5 above) from the potential 
winglet TIS (result of Step 4 above).

Example:
    Potential winglet TIS - adjusted potential winglet TIS = Winglet 
usage penalty.
    (650 hours TIS) - (541 hours TIS) = (109 hours TIS).

    7. Adjust the safe life of your airplane to account for the 
winglet installation. Subtract the winglet usage penalty (result of 
Step 6 above) from the unmodified safe life from Table 1 in 
paragraph (c)(1) of this AD (the result of Step 2 above).

Example:
    Unmodified safe life - winglet usage penalty = Adjusted safe 
life.
    (1,650 hours TIS) - (109 hours TIS) = (1,541 hours TIS).

    8. Enter the adjusted safe life (result of Step 7 above) in 
paragraph (e)(1)(i) of this AD and the airplane logbook.
    If you install or remove the Marburger winglets from your 
airplane in the future, do the following:
    If, at anytime in the future, you install or remove the 
Marburger winglets STC from your airplane, you must repeat the 
procedures in this Appendix to determine the airplane's safe life.

APPENDIX 2--ALTERNATIVE METHOD OF COMPLIANCE (AMOC) TO DOCKET NO. FAA-
2004-19961

Optional Inspection Program

    For all airplanes listed in this AD; except for Model AT-502B 
airplanes, serial number (S/N) 0643 and all S/Ns beginning with 
0655, and those airplanes that have been modified with the 
replacement spar caps, part number (P/N) 21058-1 and P/N 21058-2; 
you may begin a repetitive inspection interval program as an 
alternative to the safe life requirement of this AD with the 
following provisions:
    For the Model AT-501 airplanes affected by this AD, you may 
elect to follow this AMOC program and continue to operate your 
airplane up to 8,000 hours TIS, provided you comply with this AMOC 
in its entirety. If at the time of the effective date of this AD, 
you are over 1,600 hours TIS (the time required for the first 
inspection), you must inspect within 50 hours TIS. If at the time of 
the

[[Page 45466]]

effective date of this AD, you are over 4,000 hours TIS (the time 
required for 2-part modification), you must have the modification 
done within 50 hours TIS. If you choose not to follow this 
inspection program, then you must replace your lower spar caps and 
associated hardware at the applicable safe life listed in this AD 
following the procedures in paragraph (e).
    For airplanes that do not and never have had Marburger 
Enterprise, Inc. winglets installed following Supplemental Type 
Certificate (STC) SA00490LA:
    1. Upon accumulating 1,600 hours time-in-service (TIS) or within 
the next 50 hours TIS after [effective date] (the effective date of 
AD **-**-**), whichever occurs later, eddy-current inspect the 
outboard two lower spar cap bolt holes following Snow Engineering 
Process Specification 197, page 1, revised June 4, 2002; 
pages 2 through 5, revised May 3, 2002. The inspection must be done 
by one of the following:
    a. A Level 2 or Level 3 inspector that is certified for eddy-
current inspection using the guidelines established by the American 
Society for Nondestructive Testing or MIL-STD-410; or
    b. A person authorized to do AD work and has completed and 
passed the Air Tractor, Inc. training course on Eddy Current 
Inspection on wing lower spar caps.
    2. Repeat these inspections at intervals of (as applicable):
    a. 800 hours TIS (all S/Ns except as noted in b); or
    b. 600 hours TIS (S/Ns 502B-0187 through 502B-0618 that do not 
have P/N 20998-1/2 web plate installed).
    c. If the outboard two lower spar cap bolt holes have been cold 
worked following Snow Engineering Service Letter 233, dated 
May 18, 2004, then you may double (1,600 hours TIS or 1,200 hours 
TIS, as applicable) the inspection interval (See Step 8--re: mid 
cycle cold work).
    d. Your logbook entry must include the work done and the 
inspection intervals that are upcoming, as follows:
    Following AD **-**-**, at XXXX {insert hours TIS of the initial 
pre-modification inspection{time}  hours TIS an eddy-current 
inspection has been performed. As of now, the safe life listed in 
the AD no longer applies to this airplane. This airplane must be 
eddy-current inspected at intervals not to exceed {800/600/1,600/
1,200, as applicable{time}  hours TIS. The first of these 
inspections is due at {insert the total number of hours TIS the 
first of these inspections is due{time}  hours TIS.''
    3. If at any time a crack is found, and:
    a. The crack indication goes away by doing the modification 
following the applicable sheet of Snow Engineering Modification--
Wing Centersplice--502, Drawing Number 20989, then you may modify 
your center splice following Snow Engineering Drawing 20989. After 
modification, proceed to Step 5.
    b. The crack indication does not go away by doing the 
modification following the applicable sheet of Snow Engineering 
Modification--Wing Centersplice--502, Drawing Number 20989, you must 
replace all parts and hardware listed in Step 7.
    c. Report to the FAA any cracks found using the form in Figure 1 
of this AD.
    4. For all S/Ns, upon accumulating 4,000 hours TIS, you must:
    a. Modify your center splice connection following the applicable 
sheet of Snow Engineering Modification--Wing Centersplice--502, 
Drawing Number 20989, unless already done following Snow Engineering 
Service Letter 197 or 205, both revised March 26, 
2001, as applicable. The owners/operator may not do the spar cap 
modification unless that person holds the proper mechanic 
authorization. If, as of [effective date] (the effective date of AD 
**-**-**), your airplane is over or within 50 hours of reaching the 
4,000 hour TIS modification requirement, do the modification within 
the next 50 hours TIS.
     b. Before doing the modification, do an eddy-current inspection 
following Snow Engineering Process Specification 197, page 
1, revised June 4, 2002; pages 2 through 5, revised May 3, 2002, 
unless already done following the applicable Snow Engineering 
Service Letter 197 or 205, both revised March 26, 
2001.
    c. Your logbook entry must include the work done and the 
inspection intervals that are upcoming, as follows:
    ``Following AD **-**-**, at XXXX {insert hours TIS of the 
modification{time}  hours TIS an eddy-current inspection has been 
done. As of now, the safe life listed in the AD no longer applies to 
this airplane. This airplane must be eddy-current inspected at 
{insert the number of hours TIS at modification plus 1,600 hours 
TIS{time}  hours TIS.
    5. For all S/Ns, upon accumulating 1,600 hours TIS after 
modification, inspect the left-hand and right-hand outboard two 
lower spar cap bolt holes following Snow Engineering Process 
Specification 197, page 1, revised June 4, 2002; pages 2 
through 5, revised May 3, 2002.
    6. Repeat the inspection at intervals of:
    a. 800 hours TIS; or
    b. 1,600 hours TIS if the outboard two lower spar cap bolt holes 
have been cold worked following Snow Engineering Service Letter 
234, dated May 18, 2004 (See Step 8).
    c. Your logbook entry must include the work done and the post-
modification inspection intervals that are upcoming, as follows:
    ``This airplane must be eddy-current inspected at intervals not 
to exceed {800/1,600, as applicable{time}  hours TIS. The first of 
these inspections is due at {insert the total number of hours TIS 
the first of these inspections is due{time}  hours TIS.''
    d. If a crack is found at any time, before further flight you 
must replace the lower spar caps, splice blocks, and wing attach 
angles and hardware. You must also notify the FAA using the form in 
Figure 1 of this AD.
    7. Upon accumulating 8,000 hours TIS, before further flight you 
must replace the lower spar caps, splice blocks, and wing attach 
angles (P/N 20693-1), and associated hardware. No additional time 
will be authorized for airplanes that are at or over 8,000 hours TIS 
(see Step 9).
    8. (OPTIONAL): If you decide to cold work your bolt holes 
following Snow Engineering Service Letter 233 or 
234, both dated May 18, 2002, at a TIS that does not 
coincide with a scheduled inspection following this AD, then eddy-
current inspect at the time of cold working and then begin the 
1,600/1,200 hour TIS inspection intervals (2 times the intervals 
listed in Steps 2.a., 2.b., and 6.a. listed above).
    9. (OPTIONAL): If you have modified your airplane in accordance 
with Step 4 above before accumulating 4,000 hours TIS, then you may 
continue to fly your airplane past (modification + 4,000 hours TIS) 
provided you cut your inspection intervals in half. Make a logbook 
entry following Step 6.c. above to reflect these reduced inspection 
intervals. Upon accumulating 8,000 hours TIS, you must comply with 
Step 7 above.
    EXAMPLE: An AT-502B airplane had the two-part modification 
installed at 3,000 hours TIS and the bolt holes have not been cold 
worked.
    The first inspection would occur at 4,600 hours TIS. From Step 
5, this is modification plus 1,600 hours TIS.
    Inspections would follow at 5,400 hours TIS, 6,200 hours TIS, 
and 7,000 hours TIS. From Step 6.a. above, this is 800-hour TIS 
inspection intervals.
    Regarding the inspection at 7,000 hours TIS (modification plus 
4,000 hours TIS), this relates to the 8,000-hour TIS inspection from 
Step 7 above, which is modification plus 4,000 hours TIS, except in 
this example the modification took place at 3,000 hours TIS instead 
of 4,000 hours TIS as specified in Step 4 above.
    This airplane may continue to fly if inspected again at 7,400 
hours TIS and 7,800 hours TIS, which is 400-hour TIS inspection 
intervals. This 400-hour TIS inspection interval corresponds to Step 
9 where you cut your inspection interval from Step 6.a. in half.
    Upon accumulating 8,000 hours TIS (this is the same as Step 7 
above), you must replace the parts listed in Step 7.
    For airplanes that have or have had Marburger Enterprise, Inc. 
winglets installed following Supplemental Type Certificate (STC) 
SA00490LA:
    If you have removed the winglets, calculate new, reduced hours 
for Steps 1, 4, 5, and 7, as applicable, based on the winglet usage 
factor listed in Table 2 of paragraph (c)(4) and Appendix 2 of this 
AD.
    You may repetitively inspect at the same intervals listed in 
Step 2 above provided that you do not re-install the winglets.
    EXAMPLE: An AT-502 airplane, S/N 502-0200, had winglets 
installed at 200 hours TIS and removed at 800 hours TIS.

The winglet usage factor is: 1.6
Calculate equivalent hours: 600 hours TIS with winglets X 1.6 = 960 
hours TIS
Winglet usage penalty = 960 - 600 = 360
New Step 1 Pre-Modification Initial Inspection Time = 1,600 - 360 = 
1,240 hours TIS
Retained Step 2 Pre-Modification Inspection Interval: Since the 
winglets are removed, the Pre-Modification Inspection Interval 
remains 800 hours TIS.
New Step 4 Modification time = 4,000 - 360 = 3,640 hours TIS
New Step 5 Post-Modification Initial Inspection time = 3,640 + 1,600 
= 5,240 hours TIS.
Retained Step 6 Post-Modification Inspection interval: Since the 
winglets are removed

[[Page 45467]]

the Post-Modification Inspection interval remains at 800/1,600 hours 
TIS.
New Step 7 replacement time = 8,000 - 360= 7,640 hours TIS

    Use the Retained Step 2 interval, the New Step 5 time, and the 
Retained Step 6 interval to make appropriate logbook entries for the 
pre- and post-modification intervals, using the format presented in 
Steps 2.d., 4.c., and 6.c.
    If you have not removed the winglets, then calculate new, 
reduced hours for Step 1, 2, 4, 5, 6, and 7 above, as applicable, 
based on the winglet usage factor listed in Table 2 of paragraph 
(c)(4) of this AD and Appendix 2 of this AD.
    Repetitively inspect at the appropriate interval listed in the 
step above divided by the winglet usage factor.
    EXAMPLE: An AT-502B, S/N 502B-0550, that has not had P/N 20998-
1/-2 web plate installed and has had winglets on since new.

The winglet usage factor is: 1.2
New Step 1 Pre-modification initial inspection time: 1,600 / ( 1.2 = 
1,333 hours TIS.
New Step 2 Pre-modification inspection interval: 600 / ( 1.2 = 500 
hours TIS.
New Step 4 Modification time: 4,000 / ( 1.2 = 3,333 hours TIS.
New Step 5 Post-modification initial inspection time: 3,333 + 1,333 
(1,600 / (1.2) = 4,666 hours TIS.
New Step 6 Post-modification inspection interval: 800 / (1.2 = 667 
hours TIS.
New Step 7 Replacement time: 8,000 / ( 1.2 = 6,667 hours TIS

    Use the reduced hours you calculate in New Step 2, New Step 5, 
and New Step 6 to make appropriate logbook entries for the pre- and 
post-modification inspection intervals, using the format presented 
in Steps 2.d., 4.c., and 6.c above.

    Issued in Kansas City, Missouri, on August 3, 2006.
John R. Colomy,
Acting Manager, Small Airplane Directorate, Aircraft Certification 
Service.
 [FR Doc. E6-12945 Filed 8-8-06; 8:45 am]
BILLING CODE 4910-13-P