[Federal Register Volume 67, Number 105 (Friday, May 31, 2002)]
[Rules and Regulations]
[Pages 37967-37975]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 02-13609]


=======================================================================
-----------------------------------------------------------------------

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 2001-CE-36-AD; Amendment 39-12766; AD 2002-11-05]
RIN 2120-AA64


Airworthiness Directives; Air Tractor, Inc. Models AT-400, AT-
401, AT-401B, AT-402, AT-402A, AT-402B, AT-501, AT-802, and AT-802A 
Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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

SUMMARY: This amendment supersedes Airworthiness Directive (AD) 2001-
10-04 R1, which lowered the safe life for the wing lower spar cap on 
certain Air Tractor, Inc. (Air Tractor) AT-400, AT-500, and AT-800 
series airplanes. AD 2001-10-04 R1 resulted from numerous reports of 
cracks in the \3/8\-inch bolthole of the wing lower spar cap on the 
affected airplanes. This AD retains the safe life for the wing lower 
spar cap and requires you to eddy-current inspect the wing lower spar 
cap immediately prior to the replacement/modification in order to 
detect and correct any crack in a bolthole before it extends to the 
modified center section of the wing. This AD further reduces the safe 
life for certain Models AT-401, AT-401B, AT-402, AT-402A, AT-402B, and 
AT-501 airplanes that incorporate or have incorporated Marburger 
Enterprises, Inc. winglets and removes the Models AT-502, AT-502A, AT-
502B, and AT-503A airplanes from the applicability. We are issuing 
another AD action to cover these 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 the wing separating from the airplane during 
flight.

DATES: This AD becomes effective on July 12, 2002.
    The Director of the Federal Register previously approved the 
incorporation by reference of certain publications listed in the 
regulation as of June 8, 2001 (66 FR 27014, May 16, 2001).

ADDRESSES: You may get the service information referenced in this AD 
from 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. You may view this information at the Federal Aviation 
Administration (FAA), Central Region, Office of the Regional Counsel, 
Attention: Rules Docket No. 2001-CE-36-AD, 901 Locust, Room 506, Kansas 
City, Missouri 64106; or at the Office of the Federal Register, 800 
North Capitol Street, NW., suite 700, Washington, DC.

FOR FURTHER INFORMATION CONTACT: Direct all questions to:
    --For 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; and
    --For certain Models AT-402, AT-402A, AT-402B, and AT-501 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:

Discussion

Has FAA Taken Any Action to This Point?

    Several reports of cracked wing lower spar caps on Air Tractor AT-
500 series airplanes caused the manufacturer (Air Tractor) to 
recalculate the fatigue life of the wing lower spar cap on Air Tractor 
AT-400, AT-500, and AT-800 series airplanes. One report was of an 
accident where the wing separated from the

[[Page 37968]]

airplane during flight. The cracks are originating in the outboard \3/
8\-inch bolthole of the wing lower spar cap. To address this condition, 
FAA issued AD 2001-10-04, Amendment 39-12230 (66 FR 27014, May 16, 
2001), to lower the safe life for the wing lower spar cap on Air 
Tractor AT-400, AT-500, and AT-800 series airplanes.
    AD 2001-10-04 also allowed for inspection, using eddy current 
methods, of the wing lower spar cap for airplanes that are at or over 
the lower safe life and parts are not available. Operation of the 
airplane was not allowed if cracks were found and inspections had to be 
terminated when parts become available or after three repetitive 
inspections were done.
    AD 2001-10-04 superseded AD 2000-14-51, Amendment 39-11837 (65 FR 
46567, July 31, 2000). AD 2000-14-51 required inspection of the wing 
lower spar cap for cracks on Air Tractor Models AT-501, AT-502, and AT-
502A airplanes, and modification or replacement of any cracked wing 
lower spar cap.
    We inadvertently included certain AT-800 series airplanes in the 
Applicability of AD 2001-10-04. The AD should not have affected the AT-
800 series airplanes equipped with the factory-supplied part number 
80540 computerized fire gate. Therefore, we revised AD 2001-10-04 to 
incorporate this change. AD 2001-10-04 R1, Amendment 39-12247, was 
published in the Federal Register on June 4, 2001 (66 FR 29900).

What Has Happened Since AD 2001-10-04 R1 To Initiate This Action?

    In response to AD 2001-10-04 R1, FAA received a comment from the 
National Transportation Safety Board that recommended an eddy-current 
inspection requirement immediately prior to the accomplishment of the 
two-part modification described in Snow Engineering Service Letters 
#202 or #203, both Revised March 26, 2001, as applicable. This is to 
eliminate the possibility that a crack existing in a bolt hole prior to 
the modification is still present after accomplishing the modification. 
Prior to the modification, any crack present will be larger than it 
would appear after the outermost bolt holes are enlarged. This makes 
the crack easier to detect and gives the mechanic an area to 
concentrate on any post-modification inspections.
    Additional analysis also indicates a higher wing root bending 
moment, which reveals the need to further reduce the safe life for 
certain AT-400 and AT-500 series airplanes with a certain 
configuration. Airplanes with this configuration either incorporate or 
have incorporated Marburger Enterprises, Inc. winglets on the wing 
lower spar cap. These winglets are installed in accordance with 
Supplemental Type Certificate (STC) SA00490LA. We have developed 
criteria for determining what the new safe life will be for airplanes 
that either incorporate or have incorporated these winglets.

What Is The Potential Impact if FAA Took No Action?

    This condition could result in fatigue cracks 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 
the wing separating from the airplane during flight.

Has FAA Taken Any Action to This Point?

    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, Inc. (Air Tractor) AT-400, AT-500, and AT-800 
series airplanes. This proposal was published in the Federal Register 
as a notice of proposed rulemaking (NPRM) on December 27, 2001 (66 FR 
66823). The NPRM proposed to supersede AD 2001-10-04 R1 with a new AD 
that would retain the safe life and would require you to eddy-current 
inspect the wing lower spar cap immediately prior to the replacement/
modification in order to detect and correct any crack in a bolthole 
before it extends to the modified center section of the wing. The NPRM 
also proposed to further reduce the safe life for AT-400 and AT-500 
series airplanes that incorporate or have incorporated Marburger 
Enterprises, Inc. winglets.

Was the Public Invited To Comment on the NPRM?

    The FAA encouraged interested persons to participate in the making 
of this amendment. In addition to the comments, we received reports of 
several cracks originating in the outboard \3/8\-inch hole of the main 
spar lower cap on Air Tractor Models AT-502, AT-502A, AT-502B, and AT-
503A airplanes at hours time-in-service (TIS) lower than the 
established safe life.
    Based on this information, we have determined that:
    --The safe life on Models AT-502, AT-502A, AT-502B, and AT-503A 
airplanes should be further reduced;
    --These airplanes should be removed from the NPRM; and
    --Final rule; request for comments (immediately adopted rule) AD 
action should be taken to address this condition.
    We received one comment in favor of the NPRM as written. The 
following presents other comments received on the proposal and FAA's 
response to each comment:

Comment Issue No. 1: Change Step 8 of the Winglet Calculation

What Is the Commenter's Concern?

    Several commenters state that Step 8 of the Appendix to the 
proposed AD gives an overly conservative safe life for airplanes with 
the Marburger winglets installed when compared to that recommended by 
Air Tractor. The commenters recommend that FAA revise this calculation 
to be more in line with Air Tractor's recommendation.

What Is FAA's Response to the Concern?

    After further evaluating this step in the calculation, we concur 
that Step 8 results in a more conservative safe life than we intended. 
We have modified these instructions for computing the safe life of the 
airplanes with the winglets installed. These modified instructions are 
included in the Appendix to this AD.
    The accomplishment of these instructions will provide an increase 
in the safe life of the affected airplanes over that proposed in the 
NPRM. Therefore, the burden upon the public is reduced and there is no 
regulatory requirement for FAA to solicit additional public comments.

Comment Issue No. 2: Allow Repetitive Inspections Instead of 
Mandatory Modification

What Is the Commenter's Concern?

    One commenter recommends repetitive inspections provided no cracks 
are found instead of mandatory modification as proposed in the NPRM and 
required by AD 2001-10-04 R1. The commenter states that this would 
reduce the economic impact on operators and minimize the risk of 
reduced agricultural production if the safe life limit is reached 
during the agricultural spraying season.

What Is FAA's Response to the Concern?

    Although we concur that repetitive inspections may reduce the 
economic impact and minimize the risk of reduced agricultural 
production, this will not meet the safety intent of the AD. The FAA has 
determined that reliance on critical repetitive inspections carries an 
unnecessary safety risk when parts replacement or modifications exist. 
In determining what inspections are critical, FAA

[[Page 37969]]

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.
    We have included a provision for an alternative method of 
compliance that allows for repetitive 400-hour time-in-service (TIS) 
inspections up to 1,200 hours TIS after the safe life limit is reached. 
However, the replacement/modification must be scheduled. This will 
allow operators to continue operating during the agricultural spraying 
season.
    We have not changed the final rule AD based on this comment.

Comment Issue No. 3: Incorporate One or More Proposed Options 
Instead of the Required Life Limits for Airplanes with Winglets

What Is the Commenter's Concern?

    One commenter opposes the required life limits for the affected 
airplanes with Marburger winglets installed because the commenter 
believes that there are other alternatives. The commenter believes that 
accomplishing one or more of the following options will meet the safety 
intent of the AD for those affected airplanes with winglets installed:
    --Require a takeoff weight limitation that would include a placard 
and airplane flight manual changes. This weight reduction would offset 
increased wing bending moments due to the winglet installation;
    --Place a maximum maneuver load factor limit (nz) 
limitation to reduce the maximum wing bending moment and alleviate the 
effects of the winglet installation;
    --Incorporate a damage tolerance-based inspection program. This 
program could be based on the initial inspection and subsequent 400-
hour TIS inspections detailed in the alternative method of compliance 
in AD 2001-10-04 R1 and the NPRM and the Snow Engineering service 
letters; and/or
    --Incorporate an inspection program and allow cold-working or 
reaming of the area where small cracks are found. The inspections could 
be based on the initial inspection and subsequent 400-hour TIS 
inspections detailed in the alternative method of compliance in AD 
2001-10-04 R1 and the NPRM and specified in the Snow Engineering 
service letters.

What Is FAA's Response to the Concern?

    We do not concur with incorporating any of these alternatives for 
the following reasons:
    --Takeoff weight limitation: The FAA has determined that a weight 
placard limitation is not a reliable method of reducing wing root 
bending in airplanes utilized in CAM 8 operations. CAM 8 allows for the 
operation of restricted category agricultural airplanes at weights 
higher than that specified in the type certification data sheet (TCDS). 
To effectively alleviate fatigue spectrum loading, any weight 
limitation must reduce the typical or average weight seen in operation. 
We have determined that a maximum weight placard will not reliably 
reduce the fatigue spectrum loading the CAM 8 agricultural operations;
    --Maximum Maneuver Load Factor Limits (nz): These limits 
would have little effect on the fatigue loading spectrum seen in 
operation. Fatigue damage accumulates due to maneuvering, gusts, and 
ground load occurrences. The ground-air-ground cycle also contributes 
to fatigue damage. The aerial application spectrum displayed in DOT/
FAA/CT-91-20 ``General Aviation Aircraft--Normal Acceleration Data 
Analysis and Collection Project'' shows only one occurrence of limit 
load factor in every 16,500 nautical miles flown. It also shows only 
one occurrence of 90 percent of limit load factor in every 3,300 
nautical miles flown. Based on this, we have determined that reducing 
the maximum maneuver limit load factor would affect only a small 
percentage of fatigue damage and would not appreciably affect the 
fatigue safe life;
    --Damage tolerance-based inspection program: Damage tolerance and 
service history-based inspection programs are acceptable methods to 
ensure continuing structural integrity. However, the commenter does not 
provide adequate substantiating data to justify an inspection-based 
system instead of the proposed safe life approach. Such a program 
should include a detailed crack growth analysis with a threshold or 
initial inspection time and repetitive inspection intervals. Such 
intervals would be based on the crack growth analysis. Service history-
based inspection programs should be based on an extensive review and 
statistical analysis of the existing fleet's service experience. The 
commenter provides no substantiating data and refers only to the 
inspections proposed in the NPRM and required by AD 2001-10-04 R1. 
These inspections are limited in duration and used only to provide 
relief in the event that repair or replacement parts are not available; 
and
    --Repair small cracks through cold-working or reaming the affected 
area: This is already allowed in limited capacity. Snow Engineering 
Service Letter #197, which is referenced in the NPRM, specifies 
drilling the bolt hole to the next larger size if a crack is detected 
during the eddy-current inspection. If a crack is still detected after 
the hole is drilled to the next larger size, the service bulletin 
specifies replacing the cracked part. The FAA infers that the commenter 
wants this concept used with an inspection program instead of the 
mandatory safe life modification/replacement program. As previously 
discussed, this would not meet the safety intent of the AD.
    We have not changed the final rule (after NPRM) AD based on this 
comment.

Comment Issue No. 4: Modify the Winglet Usage Factor for Certain 
Model AT-502A Airplanes

What Is the Commenter's Concern?

    One commenter states that certain Model AT-502A airplanes are 
equipped with a modification commonly known as the ``Hoerner Tip.'' The 
commenter suggests that FAA change the winglet usage factor for these 
airplanes.

What Is FAA's Response to the Concern?

    We concur. Later serial numbers of the Model AT-502A airplanes 
should have a lower winglet usage factor. As discussed earlier, we are 
initiating final rule; request for comments (immediately adopted rule) 
AD action to further reduce the safe life of the Models AT-502, AT-
502A, AT-502B, and AT-503A airplanes. We will take the commenter's 
concern into consideration when preparing this AD.
    We have not changed the final rule (after NPRM) AD based on this 
comment.

Comment Issue No. 5: Reduce Winglet Usage Factor for All Airplanes

What Is the Commenter's Concern?

    One commenter recommends that FAA reduce the winglet usage factor 
for all airplanes. This recommendation is based on the weight usage 
penalty used on Dromader M-18 airplanes compared to the winglet usage 
factors on the affected Air Tractor airplanes.

What Is FAA's Response to the Concern?

    We do not concur. We extensively reviewed the safe life limits 
specified in the Snow Engineering service letters along with the 
substantiating

[[Page 37970]]

engineering analysis. We are confident in Air Tractor's relative 
analysis between the baseline airplanes and those modified with the 
Marburger winglet STC.
    Relative fatigue life comparisons between different airplane models 
are difficult when the airplanes operate in different regions of the 
fatigue S-N curve, especially when even later serial numbers of the 
same model may operate at different stress levels. Relative comparisons 
based on ratios (as the commenter performed) assume a linear or ``one-
to-one'' relationship between operating stress and fatigue life. When 
the operating stress of the two airplanes is significantly different, 
this ``one-to-one'' relationship assumption is inaccurate.
    We have not changed the final rule (after NPRM) AD based on this 
comment.

Comment Issue No. 6: Use Configuration Changes To Reduce the 
Aerodynamic Effect of the Winglet Installation

What Is the Commenter's Concern?

    One commenter suggests using airplane configuration changes to 
reduce the aerodynamic effect of the winglet installation and increase 
the inertia relief available from the winglet installation. This 
includes winglet incidence, flap droop, and ballast weight in the 
winglet to offset the increased wing bending moments due to the winglet 
installation.

What Is FAA's Response to the Concern?

    While we acknowledge that configuration changes may successfully 
offset the effect of the winglet installation on the wing bending 
moments, the commenter provides no engineering data to specifically 
show the changes and substantiate reduced aerodynamic effect. The 
commenter may send this information to FAA at any time for 
consideration of an alternative method of compliance to the AD.

FAA's Determination

What Is FAA's Final Determination on This Issue?

    After careful review of all available information related to the 
subject presented above, we have determined that air safety and the 
public interest require the adoption of the rule as proposed except for 
the change in the winglet safe life calculation, the removal of certain 
airplanes from the applicability, and minor editorial corrections. We 
have determined that the change, removal, and minor corrections:
    --Provide 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.

Cost Impact

How Many Airplanes Does This AD Impact?

    We estimate that this AD affects 1,179 airplanes in the U.S. 
registry.

What Is the Cost Impact of This AD on Owners/Operators of the Affected 
Airplanes?

    We estimate the following costs to accomplish the inspection:

 
----------------------------------------------------------------------------------------------------------------
                                                                                  Total cost per   Total cost on
                 Labor cost                               Parts cost                 airplane     U.S. operators
----------------------------------------------------------------------------------------------------------------
2 workhours at $60 per hour = $120.........  No parts required for inspection...            $120        $141,480
----------------------------------------------------------------------------------------------------------------

    We estimate the following costs to accomplish the replacement/
modification:

 
----------------------------------------------------------------------------------------------------------------
                                                                                  Total cost per   Total cost on
                 Labor cost                               Parts cost                 airplane     U.S. operators
----------------------------------------------------------------------------------------------------------------
120 workhours at $60 per hour = $7,200.....  $4,300.............................         $11,500     $13,558,500
----------------------------------------------------------------------------------------------------------------

What Is the Difference Between the Cost Impact of This AD and the Cost 
Impact of AD 2001-10-04 R1?

    AD 2001-10-04 R1 already established the safe life for the lower 
wing spar cap on the affected airplanes. Therefore, the replacement/
modification is already required through that AD. The only difference 
in the cost impact upon the public of this AD and AD 2001-10-04 R1 is 
the cost for the eddy-current inspection upon replacement and the 
further safe life reduction for those AT-400 and AT-500 series 
airplanes that incorporate or have incorporated Marburger Enterprises, 
Inc. winglets.

Regulatory Impact

Does This AD Impact Various Entities?

    The regulations adopted herein 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. Therefore, it 
is determined that this final rule does not have federalism 
implications under Executive Order 13132.

Does This AD Involve a Significant Rule or Regulatory Action?

    For the reasons discussed above, I certify that this action (1) is 
not a ``significant regulatory action'' under Executive Order 12866; 
(2) is not a ``significant rule'' under 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. A copy of the final evaluation prepared for this 
action is contained in the Rules Docket. A copy of it may be obtained 
by contacting the Rules Docket at the location provided under the 
caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Incorporation by 
reference, Safety.

[[Page 37971]]

Adoption of the Amendment

    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

    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) 
2001-10-04 R1, Amendment 39-12247 (66 FR 29900, June 4, 2001), and by 
adding a new AD to read as follows:

2002-11-05  Air Tractor, Inc.: Amendment 39-12766; Docket No. 2001-
CE-36-AD.

    (a) What airplanes are affected by this AD? This AD applies to 
certain Models AT-400, AT-401, AT-401B, AT-402, AT-402A, AT-402B, 
AT-501, AT-802, and AT-802A airplanes. Use paragraph (a)(1) of this 
AD for affected airplanes that do not incorporate and never have 
incorporated winglets. Use paragraph (a)(3) of this AD for certain 
Models AT-401, AT-401B, AT-402, AT-402A, AT-402B, and AT-501 
airplanes that incorporate or have incorporated Marburger 
Enterprises, Inc. winglets.
    (1) The following presents airplanes (certificated in any 
category) that are affected by this AD, along with the new safe life 
(presented in hours time-in-service (TIS)) of the wing lower spar 
cap for all affected airplane models and serial numbers:

------------------------------------------------------------------------
        Model              Serial numbers              Safe life
------------------------------------------------------------------------
AT-400...............  all serial numbers     13,300 hours TIS.
                        beginning with 0416.
------------------------------------------------------------------------
AT-401...............  0662 through 0951....  10,757 hours TIS.
------------------------------------------------------------------------
AT-401B..............  0952 through 1014 and  6,948 hours TIS.
                        1016 though 1020.
------------------------------------------------------------------------
AT-401B..............  1015 and 1021 through  7,777 hours TIS.
                        1124.
------------------------------------------------------------------------
AT-402...............  0694 through 0951....  7,440 hours TIS.
------------------------------------------------------------------------
AT-402A..............  0738 through 0951....  7,440 hours TIS.
------------------------------------------------------------------------
AT-402A..............  0952 through 1020....  4,589 hours TIS.
------------------------------------------------------------------------
AT-402A..............  1021 through 1124....  5,268 hours TIS.
------------------------------------------------------------------------
AT-402B..............  0966 through 1020....  4,589 hours TIS.
------------------------------------------------------------------------
AT-402B..............  1021 through 1124....  5,268 hours TIS.
------------------------------------------------------------------------
AT-501...............  0002 through 0061....  4,531 hours TIS.
------------------------------------------------------------------------
AT-501...............  all serial numbers     7,693 hours TIS.
                        beginning with 0062.
------------------------------------------------------------------------
AT-802...............  0001 through 0059      4,132 hours TIS.
                        except those
                        equipped with the
                        factory-supplied
                        part number 80540
                        computerized fire
                        gate.
------------------------------------------------------------------------
AT-802...............  0060 through 0091      4,188 hours TIS.
                        except those
                        equipped with the
                        factory-supplied
                        part number 80540
                        computerized fire
                        gate.
------------------------------------------------------------------------
AT-802...............  0092 through 0101      8,163 hours TIS.
                        except those
                        equipped with the
                        factory-supplied
                        part number 80540
                        computerized fire
                        gate.
------------------------------------------------------------------------
AT-802A..............  0003 through 0059      4,969 hours TIS.
                        except those
                        equipped with the
                        factory-supplied
                        part number 80540
                        computerized fire
                        gate.
------------------------------------------------------------------------
AT-802A..............  0060 through 0091      4,531 hours TIS.
                        except those
                        equipped with the
                        factory-supplied
                        part number 80540
                        computerized fire
                        gate.
------------------------------------------------------------------------
AT-802A..............  0092 through 0101      8,648 hours TIS.
                        except those
                        equipped with the
                        factory-supplied
                        part number 80540
                        computerized fire
                        gate.
------------------------------------------------------------------------


    Note 1: This AD still applies to those airplanes that have 
converted between fire fighting and agricultural dispersal.

    (2) If piston powered aircraft have been converted to turbine 
power, you must use the limits for the corresponding serial number 
turbine-powered aircraft.
    (3) The following presents airplanes (certificated in any 
category) that could incorporate or could have incorporated 
Marburger Enterprises, Inc. winglets. These winglets are installed 
in accordance with Supplemental Type Certificate (STC) SA00490LA. 
Use the winglet usage factor in the table in this paragraph, the 
safe life specified in paragraph (a)(1) of this AD, and the 
instructions included in the Appendix to this AD to determine the 
new safe life of these airplanes:

------------------------------------------------------------------------
                                                           Winglet usage
           Model                    Serial numbers            factor
------------------------------------------------------------------------
AT-401.....................  0662 through 0951..........  1.6
------------------------------------------------------------------------

[[Page 37972]]

 
AT-401B....................  0952 through 1014 and 1016   1.1
                              though 1020.
------------------------------------------------------------------------
AT-401B....................  1015 and 1021 through 1124.  1.1
------------------------------------------------------------------------
AT-402.....................  0694 through 0951..........  1.6
------------------------------------------------------------------------
AT-402A....................  0738 through 0951..........  1.6
------------------------------------------------------------------------
AT-402A....................  0952 through 1020..........  1.1
------------------------------------------------------------------------
AT-402A....................  1021 through 1124..........  1.1
------------------------------------------------------------------------
AT-402B....................  0966 through 1020..........  1.1
------------------------------------------------------------------------
AT-402B....................  1021 through 1124..........  1.1
------------------------------------------------------------------------
AT-501.....................  0002 through 0061..........  1.6
------------------------------------------------------------------------
AT-501.....................  all serial numbers           1.6
                              beginning with 0062.
------------------------------------------------------------------------

    (b) Who must comply with this AD? Anyone who wishes to operate 
any of the airplanes identified in paragraph (a) of this AD must 
comply with this AD.
    (c) What problem does this AD address? 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 the wing separating from the airplane 
during flight.

    Note 2: The 10-hour TIS compliance time is maintained from AD 
2001-10-04 R1.

    (d) What must I do to address this problem? To address this 
problem, you must accomplish the following actions:

----------------------------------------------------------------------------------------------------------------
               Actions                             Compliance                            Procedures
----------------------------------------------------------------------------------------------------------------
(1) Modify the applicable aircraft    Accomplish the logbook entry within   The owner/operator holding at least
 records (logbook) as follows to       the next 10 hours TIS after July      a private pilot certificate as
 show the reduced safe life for the    12, 2002 (the effective date of       authorized by section 43.7 of the
 wing lower spar cap (use the          this AD).                             Federal Aviation Regulations (14
 information from the table in                                               CFR 43.7) may modify the aircraft
 paragraph (a)(1) of this AD and                                             records as specified in paragraphs
 utilize the information in                                                  (d)(1)(i) and (d)(1)(ii) of this
 paragraph (a)(3) of this AD and the                                         AD. Make an entry into the aircraft
 Appendix to this AD, as applicable.                                         records showing compliance with
(i) For the affected Models AT-802                                           this portion of the AD in
 and AT-802A airplanes: update the                                           accordance with section 43.9 of the
 Owners Manual, Section 6--                                                  Federal Aviation Regulations (14
 Airworthiness Limitations, Life                                             CFR 43.9). Accomplish the actual
 Limited Parts.                                                              replacement/modification when the
(ii) For all affected airplanes                                              safe life is reached in accordance
 other than Models AT-802 and AT-                                            with Snow Engineering Service
 802A airplanes, incorporate the                                             Letter #202 or #203, both Revised
 following into the Aircraft                                                 March 26, 2001, as applicable. The
 Logbook: ``In accordance with this                                          owner/operator may not accomplish
 AD, the wing lower spar cap is life                                         the replacement/modification,
 limited to ______.'' Insert the                                             unless he/she holds the proper
 applicable safe life number from                                            mechanic authorization.
 the applicable tables in paragraphs
 (a)(1) and (a)(3) and the Appendix
 of this AD.
(iii) If, as of the time of the
 logbook entry requirement of
 paragraph (d)(1) of this AD, your
 airplane is over or within 10 hours
 of the safe life, an additional 10
 hours TIS is allowed to accomplish
 the replacement/modification.
----------------------------------------------------------------------------------------------------------------

[[Page 37973]]

 
(2) If you have ordered parts from    Inspect prior to further flight       In accordance with the procedures in
 the factory when it is time to        after ordering the parts and          Snow Engineering Service Letter
 replace the wing lower spar cap (as   thereafter at intervals not to        #202 or #203, both Revised March
 required when you reach the           exceed 400 hours TIS until one of     26, 2001, as applicable.
 established safe life), but the       the criteria in paragraphs
 parts are not available, you may      (d)(2)(i), (d)(2)(ii), and
 eddy-current inspect the wing lower   (d)(2)(iii) of this AD are met.
 spar cap. These inspections are
 allowed until one of the following
 occurs, at which time the
 replacement/modification must be
 accomplished:
(i) Crack(s) is/are found;
(ii) Parts become available from the
 manufacturer; or
(iii) Not more than three
 inspections or 1,200 hours TIS go
 by: the first inspection would have
 to be accomplished upon
 accumulating the safe life; the
 second inspection would have to be
 accomplished within 400 hours TIS
 after accumulating the safe life;
 the third inspection would have to
 be accomplished 400 hours TIS after
 the second inspection; and the
 replacement/modification would have
 to be accomplished within 400 hours
 TIS after the third inspection
 (maximum elapsed time would be
 1,200 hours TIS).
----------------------------------------------------------------------------------------------------------------
(3) Eddy-current inspect the wing     Immediately prior to the replacement/ In accordance with the procedures in
 lower spar cap in order to detect     modification required when you        Snow Engineering Service Letter
 any crack before it extends to the    reach the new safe life. For          #202 or #203, both Revised March
 modified center section of the wing   airplanes that had this replacement/  26, 2001, as applicable.
 and repair that crack or replace      modification accomplished in
 the wing section. This replacement    accordance with either AD 2001-10-
 must be accomplished by a Level 2     04 or AD 2001-10-04 R1, accomplish
 or Level 3 inspector that is          this inspection and any necessary
 certified for eddy-current            corrective action within the next
 inspection using the guidelines       400 hours TIS after July 12, 2002
 established by the American Society   (the effective date of this AD),
 for Nondestructive Testing or MIL-    unless already accomplished (have
 STD-410. The inspection must be       the mechanic who accomplished the
 accomplished by one of the            work mark the logbook accordingly).
 following:
(i) 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
(ii) A person authorized to perform
 AD work who has completed and
 passed the Air Tractor, Inc.
 training course on Eddy Current
 Inspection on wing lower spar caps.
----------------------------------------------------------------------------------------------------------------

    (e) Can I comply with this AD in any other way?
    (1) You may use an alternative method of compliance or adjust 
the compliance time if:
    (i) Your alternative method of compliance provides an equivalent 
level of safety; and
    (ii) The Manager, Fort Worth or Los Angeles Airplane 
Certification Office (ACO), as applicable, approves your 
alternative. Submit your request through an FAA Principal 
Maintenance Inspector. The inspector may add comments before sending 
it to the Manager, Fort Worth or Los Angeles ACO.
    (2) Alternative methods of compliance approved for AD 2001-10-04 
and/or AD 2000-14-51 are not considered approved for this AD.
    (3) Alternative methods of compliance approved for AD 2001-10-04 
R1 are considered approved for this AD.

    Note 3: This AD applies to each airplane identified in 
paragraphs (a)(1) and (a)(3) of this AD, regardless of whether it 
has been modified, altered, or repaired in the area subject to the 
requirements of this AD. For airplanes that have been modified, 
altered, or repaired so that the performance of the requirements of 
this AD is affected, the owner/operator must request approval for an 
alternative method of compliance in accordance with paragraph (e) of 
this AD. The request should include an assessment of the effect of 
the modification, alteration, or repair on the unsafe condition 
addressed by this AD; and, if you have not eliminated the unsafe 
condition, specific actions you propose to address it.

    (f) Are there any alternative methods of compliance already 
approved or being considered for this AD? The FAA may approve, as an 
alternative method of compliance, inspection of the wing lower spar 
cap. You must submit the request in accordance with the procedures 
in paragraph (e) of this AD and adhere to the following:
    (1) If you are over or within 10 hours TIS of the safe life for 
the wing lower spar cap and you have ordered parts and scheduled a 
date for the replacement/modification, but having the replacement/
modification done on this date grounds the airplane, accomplish the 
following:
    (i) Inspect the wing lower spar cap within 10 hours TIS after 
approval of the alternative method of compliance;
    (ii) Reinspect thereafter at intervals not to exceed 400 hours 
TIS until either cracks are found, the date of the scheduled 
replacement/modification occurs, or 1,200 hours TIS after the 
initial inspection are accumulated, whichever occurs first; and
    (iii) Accomplish the inspections in accordance with the 
procedures in Snow Engineering Service Letter #202 or #203, both 
Revised March 26, 2001, as applicable.
    (2) Submit the following to the Fort Worth or Los Angeles ACO, 
as applicable, using the procedures described in paragraph (e) of 
this AD:
    (i) The airplane model serial number designation, and airplane 
registration number (N-number);
    (ii) The number of hours TIS on the airplane;
    (iii) The scheduled date for the replacement/modification; and
    (iv) The name and location of the authorized repair shop.

[[Page 37974]]

    (3) For more information about this issue, 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; and
    (ii) For the airplanes that incorporate or have incorporated 
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.
    (g) What if I need to fly the airplane to another location to 
comply with this AD? The FAA can issue a special flight permit under 
sections 21.197 and 21.199 of the Federal Aviation Regulations (14 
CFR 21.197 and 21.199) to operate your airplane to a location where 
you can accomplish the requirements of this AD provided that the 
following is adhered to:
    (1) Only operate in day visual flight rules (VFR) only.
    (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.
    (h) Are any service bulletins incorporated into this AD by 
reference? Replacement and inspection actions required by this AD 
must be done in accordance with Snow Engineering Service Letter #202 
or 203, both Revised March 26, 2001, as applicable. The Director of 
the Federal Register previously approved this incorporation by 
reference under 5 U.S.C. 552(a) and 1 CFR part 51, as of June 8, 
2001 (66 FR 27014, May 16, 2001). You can get copies from Air 
Tractor, Incorporated, P.O. Box 485, Olney, Texas 76374; or 
Marburger Enterprises, Inc., 1227 Hillcourt, Williston, North Dakota 
58801. You can look at copies at the FAA, Central Region, Office of 
the Regional Counsel, 901 Locust, Room 506, Kansas City, Missouri, 
or at the Office of the Federal Register, 800 North Capitol Street, 
NW., suite 700, Washington, DC.
    (i) Does this AD action affect any existing AD actions? This 
amendment supersedes AD 2001-10-04 R1, Amendment 39-12247.
    (j) When does this amendment become effective? This amendment 
becomes effective on July 12, 2002.

Appendix to AD 2002-11-05

    The following provides procedures for determining the safe life 
for those Models AT-401, AT-401B, AT-402, AT-402A, AT-402B, and AT-
501 airplanes that incorporate or have incorporated Marburger 
Enterprises, Inc. winglets. These winglets are installed in 
accordance with Supplemental Type Certificate (STC) SA00490LA.
    What if I removed the Marburger winglets prior to further flight 
after the effective date of this AD or prior to the effective date 
of this AD:
    1. Review your airplane's logbook to determine your airplane's 
time in service (TIS) with winglets installed per Marburger 
Enterprises STC 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 
paragraph (a)(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 paragraph 
(a)(1) of this AD.
    Example: Your airplane is a Model AT-401B, serial number 1022. 
From paragraph (a)(1) of this AD, the safe life of your airplane is 
7,777 hours TIS.
    All examples from hereon will be based on the Model AT-401B, 
serial number 1022 airplane.
    3. Determine the winglet usage factor from paragraph (a)(3) of 
this AD.
    Example: Again, your airplane is a Model AT-401B, serial number 
1022. From paragraph (a)(3) of this AD, your winglet usage factor is 
1.1.
    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 
1.1. The adjusted winglet TIS is 550 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:
[GRAPHIC] [TIFF OMITTED] TR31MY02.000

    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 paragraph (a)(1) of this 
AD (result of Step 2 above.).

Example:
[GRAPHIC] [TIFF OMITTED] TR31MY02.001

    7. If you remove the winglets from your airplane prior to 
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 (d)(1)(ii) 
of this AD and the airplane logbook.
    What if I have the Marburger winglet installed as of the 
effective date of this AD and plan to operate my airplane without 
removing the winglet?
    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 paragraph 
(a)(1) of this AD.
    Example: Your airplane is a Model AT-401B, serial number 1022. 
From paragraph (a)(1) of this AD, the safe life of your airplane is 
7,777 hours TIS.
    All examples from hereon will be based on the Model AT-401B, 
serial number 1022 airplane.
    3. Determine the winglet usage factor from paragraph (a)(3) of 
this AD.
    Example: Again, your airplane is a Model AT-401B, serial number 
1022. From paragraph (a)(3) of this AD, your winglet usage factor is 
1.1.
    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:

[[Page 37975]]

[GRAPHIC] [TIFF OMITTED] TR31MY02.002

    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:
[GRAPHIC] [TIFF OMITTED] TR31MY02.003

    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:
[GRAPHIC] [TIFF OMITTED] TR31MY02.004

    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 paragraph (a)(1) of 
this AD (the result of Step 2 above).

Example:
[GRAPHIC] [TIFF OMITTED] TR31MY02.005

    8. Enter the adjusted safe life (result of Step 7 above) in 
paragraph (d)(1)(ii) of this AD and the airplane logbook.
    What if I install or remove the Marburger winglet from my 
airplane in the future?
    If, at anytime in the future, you install or remove the 
Marburger winglet STC from your airplane, you must repeat the 
procedures in this Appendix to determine the airplane's safe life.

    Issued in Kansas City, Missouri, on May 23, 2002.
James E. Jackson,
Acting Manager, Small Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 02-13609 Filed 5-30-02; 8:45 am]
BILLING CODE 4910-13-P