E8-29165. Airworthiness Directives; Air Tractor, Inc., Models AT-400, AT-401, AT-401B, AT-402, AT-402A, and AT-402B Airplanes

AGENCY:

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

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

We propose to revise Airworthiness Directive (AD) 2006-08-08, which applies to certain Air Tractor, Inc. (Air Tractor), Models AT-400, AT-401, AT-401B, AT-402, AT-402A, and AT-402B airplanes. AD 2006-08-08 currently requires you to repetitively eddy current inspect the wing lower spar cap in order to reach the safe life and, for certain Models AT-402A and AT-402B airplanes and those that incorporate or have incorporated Marburger Enterprises, Inc. (Marburger), winglets, lowers the safe life for the wing lower spar cap. Since we issued AD 2006-08-08, we have received information to update inspection intervals for the Models AT-401B, AT-402A, and AT-402B airplanes based on a revised damage tolerance analysis. Consequently, this proposed AD would not only retain the actions of AD 2006-08-08, but would reduce the number of repetitive inspections for all affected Model AT-401B airplanes and certain Models AT-402A and AT-402B airplanes. We are proposing this AD to prevent fatigue cracks from occurring in the wing lower spar cap before the originally established safe life is reached. Fatigue cracks in the wing lower spar cap, if not detected and corrected, could result in wing separation and loss of control of the airplane.

DATES:

We must receive comments on this proposed AD by February 9, 2009.

ADDRESSES:

Use one of the following addresses to comment on this proposed AD:

• Federal eRulemaking Portal: Go to http://www.regulations.gov. Follow the instructions for submitting comments.
• Fax: [phone].
• Mail: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue, SE., Washington, DC 20590.
• Hand Delivery: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue, SE., Washington, DC 20590, 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, Inc., P.O. Box 485, Olney, Texas 76374; telephone: [phone]; facsimile: [phone]; Internet: http://www.airtractor.com;​; or Marburger Enterprises, Inc., 1227 Hillcourt, Williston, North Dakota 58801; telephone: [phone] or [phone]; facsimile: [phone].

FOR FURTHER INFORMATION CONTACT:

Direct all questions to:

—For airplanes that do not incorporate and never have incorporated Marburger winglets: Rob Romero, Aerospace Engineer, FAA, Fort Worth Airplane Certification Office, 2601 Meacham Boulevard, Fort Worth, Texas 76193-0150; telephone: [phone]; facsimile: [phone]; 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: [phone]; facsimile: [phone].

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-2006-23646; Directorate Identifier 2006-CE-005-AD” at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of the proposed AD. We will consider all comments received by the closing date and may amend the proposed AD in light of those comments.

We will post all comments we receive, without change, to http://www.regulations.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

An Air Tractor Model AT-502A experienced an in-flight wing separation. As a result, the FAA issued AD 2000-14-51 as an emergency AD. That AD required the 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. Since the release of that AD, the manufacturer has evaluated the AT-400, AT-500, AT-600, and AT-800 series lower spar cap fatigue life.

AD 2006-08-08 currently requires you to repetitively eddy current inspect the wing lower spar cap for fatigue cracks in order to reach the safe life and, for certain Models AT-402A and AT-402B airplanes and those that incorporate or have incorporated Marburger winglets, lowers the safe life for the wing lower spar cap.

Since we issued AD 2006-08-08, we have received updated inspection intervals for fatigue cracks for the Models AT-401B, AT-402A, and AT-402B airplanes based on a revised damage tolerance analysis. Any occurrence of fatigue cracks in the wing lower spar cap, if not detected and corrected, could result in wing separation and loss of control of the airplane.

The following table contains AD actions that address the wing spar safe life of the Air Tractor airplane fleet:

Related AD Actions

AD No.	Affected Air Tractor Airplane Model	Issue date
2003-07-04	AT-300, AT-400, AT-400A, AT-401, AT-401B, AT-402, AT-402A, AT-402B, AT-501, AT-502, and AT-502B	March 25, 2003.
2006-08-08	AT-400, AT-401, AT-401B, AT-402, AT-402A, and AT-402B	April 10, 2006.
2006-08-09	AT-802 and AT-802A	April 10, 2006.
2006-23-09	AT-602	October 26, 2006.
2006-24-10	AT-501, AT-502, AT-502A, AT-502B, and AT-503A	November 22, 2006.
2008-09-10	AT-300, AT-301, AT-302, AT-400, and AT-400A	April 18, 2008.

You may view these Airworthiness Directives at the following Internet Web site addresses: http://rgl.faa.gov or http://www.gpoaccess.gov/​fr/​index.html.

Relevant Service Information

We have reviewed this Snow Engineering Co. service information:

• Process Specification #197, page 1, revised June 4, 2002, pages 2 through 4, dated February 23, 2001, and page 5, dated May 3, 2002;
• Drawing Number 21088, dated November 3, 2004; and
• Service Letter #202, page 3, dated October 16, 2000.

Snow Engineering Co. has a licensing agreement with Air Tractor that allows them to produce technical data to use for Air Tractor products.

The process specification and drawing include procedures for doing the eddy-current inspection and replacing the spar caps and associated hardware. The service letter provides information for installing access panels, if not already installed.

FAA's Determination and Requirements of the Proposed AD

We are proposing this AD because we evaluated all information and determined the unsafe condition described previously is likely to exist or develop on other products of the same type design. This proposed AD would revise AD 2006-08-08 with a new AD that would not only retain the actions AD 2006-08-8, but would reduce the number of repetitive inspections for:

• All affected Model AT-401B airplanes;
• Model AT-402A airplanes, all serial numbers beginning with 0952; and
• Model AT-402B airplanes, all serial numbers beginning with 0966.

This proposed AD would require you to use the service information described previously to perform these actions.

Costs of Compliance

We estimate that this AD affects 343 airplanes in the U.S. registry.

We estimate the following costs to do the inspection. We have no way of determining the number of airplanes that may need repair or modification as a result of any inspection:

Labor cost	Parts cost	Total cost per airplane	Total cost on U.S. operators
* $500 to $800	Not Applicable	$500 to $800	$171,500 to $274,400.
* Eddy-current inspections are an estimated flat cost that includes labor and use of equipment.

We estimate the following costs to do the modification. We have no way of determining the number of airplanes that may need this modification:

Labor cost	Parts cost	Total cost per airplane
120 work-hours × $80 = $9,600	$11,500	$21,100

We estimate the following costs to do the replacement. We have no way of determining the number of airplanes that may need this replacement:

Labor cost	Parts cost	Total cost per airplane
$16,500	$16,500	$33,000
* The labor costs of the replacement are an estimated flat cost that includes labor and use of equipment.

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 the 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://www.regulations.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 [phone]) 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
• Incorporation by reference
• Safety

The Proposed Amendment

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

PART 39—AIRWORTHINESS DIRECTIVES

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

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

§ 39.13

[Amended]

2. The FAA amends § 39.13 by removing Airworthiness Directive (AD) 2006-08-08, Amendment 39-14563 (71 FR 19986, April 19, 2006), and adding the following new AD:

Air Tractor, Inc.: Docket No. FAA-2006-23646; Directorate Identifier 2006-CE-005-AD.

Comments Due Date

(a) We must receive comments on this AD action by February 9, 2009.

Affected ADs

(b) This AD revises AD 2006-08-08, Amendment 39-14563.

Applicability

(c) This AD applies to certain Models AT-400, AT-401, AT-401B, AT-402, AT-402A, and AT-402B airplanes that are certificated in any category. Use paragraph (c)(1) of this AD for affected airplanes that do not incorporate and never have incorporated Marburger winglets. Use paragraph (c)(3) of this AD for airplanes that have been modified to install lower spar caps, part number (P/N) 21058-1 and P/N 21058-2. Use paragraph (c)(4) of this AD for certain Models AT-401, AT-401B, AT-402, AT-402A, and AT-402B airplanes that incorporate or have incorporated Marburger winglets.

(1) The following table applies to airplanes 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:

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 (hours TIS)
AT-400	All beginning with 0416	13,300
AT-401	0662 through 0951	10,757
AT-401B	0952 through 1020, except 1015	6,948
AT-401B	1015 and all beginning with 1021	7,777
AT-402	0694 through 0951	7,440
AT-402A	0738 through 0951	7,440
AT-402A	0952 through 1020	2,000
AT-402A	All beginning with 1021	2,300
AT-402B	0966 through 1020, except 1015	2,000
AT-402B	1015 and all beginning with 1021	2,300

(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) If you have an aircraft that has been modified by installing lower spar caps, P/N 21058-1 and P/N 21058-2, you must use a wing lower spar cap safe life of 9,800 hours TIS. No inspections are required to reach this life.

(i) Airplanes that have been modified with replacement spar caps, P/N 21058-1 and P/N 21058-2, are not eligible to have Supplemental Type Certificate (STC) No. SA00490LA, Marburger winglets, installed.

(ii) If your airplane currently has spar caps, P/N 21058-1 and P/N 21058-2, and winglets installed, then you must remove the winglets before further flight and you must contact the FAA at the address in paragraph (m)(1) of this AD for a new safe life.

(iii) Installation of Marburger winglets on airplanes that have been modified with replacement spar caps, P/N 21058-1 and P/N 21058-2, will require additional fatigue data substantiating an appropriate safe-life. If you have replacement spar caps and wish to install winglets, you must contact the FAA at the address in paragraph (m)(2) of this AD for additional information.

(4) The following table applies to airplanes that incorporate or have incorporated Marburger winglets. These winglets are installed following STC No. SA00490LA. Use the winglet usage factor in Table 2 of paragraph (c)(4) of this AD, the wing lower spar cap safe life specified in Table 1 of 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 per STC No. SA00490LA

Model	Serial Nos.	Winglet usage factor
AT-401	0662 through 0951	1.6
AT-401B	0952 through 1020, except 1015	1.1
AT-401B	1015 and all beginning with 1021	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	All beginning with 1021	1.1
AT-402B	0966 through 1020, except 1015	1.1
AT-402B	1015 and all beginning with 1021	1.1

Unsafe Condition

(d) This AD is the result of fatigue cracking of the wing main spar lower cap at the center splice joint outboard fastener hole. The actions specified in this AD are intended to detect and correct cracks in the wing main spar lower cap, which could result in failure of the spar cap and lead to wing separation and loss of control of the airplane.

Compliance

(e) Safe Life Record: For all affected airplanes, modify the applicable aircraft records (logbook) as follows to show the safe life for the wing lower spar cap listed in this AD (use the information from paragraph (c) of this AD and Appendix 1 to this AD, as applicable).

(1) Incorporate the following into the aircraft logbook: “Following this AD, the wing lower spar cap is life limited to __ hours time-in-service (TIS).” Insert the applicable safe life number from the applicable tables in paragraph (c) of this AD and Appendix 1 to this AD.

(i) Do the logbook entry within the next 10 hours TIS after April 21, 2006 (the effective date of AD 2006-08-08).

(ii) A person holding at least a private pilot certificate as authorized by section 43.7 of the Federal Aviation Regulations (14 CFR 43.7) may modify the aircraft records. Make an entry into the aircraft logbook showing compliance with this portion of the AD in accordance with section 43.9 of the Federal Aviation Regulations (14 CFR 43.9)..

(2) Wing Spar Replacement: For all affected airplanes, replace the wing lower spar cap following Snow Engineering Drawing Number 21088, dated November 3, 2004. Replace upon accumulating the safe life used in paragraph (e)(1) of this AD or within the next 50 hours TIS after April 21, 2006 (the effective date of AD 2006-08-08), whichever occurs later. The owner/operator may not do the spar cap replacement, unless he/she is a properly certified mechanic.

(f) Inspection Requirements: For all affected airplanes, except Model AT-402A, all serial numbers beginning with 0952, and Model AT-402B, all serial numbers beginning with 0966, do the initial inspection of the outboard two lower spar cap bolt holes using the wing spar lower cap TIS schedules listed in Table 3. Follow Snow Engineering Co. Process Specification #197, page 1, revised June 4, 2002, pages 2 through 4, dated February 23, 2001, and page 5, dated May 3, 2002. After the initial inspection, perform repetitive inspections at the repetitive inspection intervals listed in Table 3. Use the same procedure for the repetitive inspections as for the initial inspection. If not already done, install access panels at the time of the first inspection following Snow Engineering Service Letter #202, page 3, dated October 16, 2000.

Note:

Hours listed in the table are in hours TIS and the phrase “within the next __ hours” refers to “within the next __ hours after April 21, 2006 (the effective date of AD 2006-08-08).”

Table 3—Inspection Times

Model	Serial Nos.	Current wing spar lower cap TIS hours	Initial inspection	Repetitive inspection interval (hours)
AT-400	All beginning with 0416	Greater than 7,750	Within the next 50 hours TIS or upon the accumulation of 8,000 hours TIS, whichever is later	900
AT-401	0662-0951	Greater than 6,250	Within the next 50 hours TIS or upon the accumulation of 6,500 hours TIS, whichever is later	700
AT-401	0662-0951	Greater than 4,350 but less than or equal to 6,250	Within the next 250 hours TIS or upon the accumulation of 4,850 hours TIS, whichever is later	700
AT-401	0662-0951	Greater than 2,750 but less than or equal to 4,350	Within the next 500 hours TIS	700
AT-401	0662-0951	Less than or equal to 2,750	Upon the accumulation of 3,250 hours TIS	700
AT-401B	0952-1020 except 1015	Greater than 3,950	Within the next 50 hours TIS or upon the accumulation of 4,200 hours TIS, whichever is later	600
AT-401B	0952-1020 except 1015	Greater than 2,650 but less than or equal to 3,950	Within the next 250 hours TIS or upon the accumulation of 3,150 hours TIS, whichever is later	600
AT-401B	0952-1020 except 1015	Greater than 1,600 but less than or equal to 2,650	Within the next 500 hours TIS	600
AT-401B	0952-1020 except 1015	Less than or equal to 1,600	Upon the accumulation of 2,100 hours TIS	600
AT-401B	1015 and 1021-1124	Greater than 4,450	Within the next 50 hours TIS or upon the accumulation of 4,700 hours TIS, whichever is later	600
AT-401B	1015 and 1021-1124	Greater than 3,000 but less than or equal to 4,450	Within the next 250 hours TIS or upon the accumulation of 3,500 hours TIS, whichever is later	600
AT-401B	1015 and 1021-1124	Greater than 1,850 but less than or equal to 3,000	Within the next 500 hours TIS	600
AT-401B	1015 and 1021-1124	Less than or equal to 1,850	Upon the accumulation of 2,350 hours TIS	600
AT-401B	All beginning with 1125	Greater than 4,450	Within the next 50 hours TIS or upon the accumulation of 4,700 hours TIS, whichever is later	1,000
AT-401B	All beginning with 1125	Greater than 3,000 but less than or equal to 4,450	Within the next 250 hours TIS or upon the accumulation of 3,500 hours TIS, whichever is later	1,000
AT-401B	All beginning with 1125	Greater than 1,850 but less than or equal to 3,000	Within the next 500 hours TIS	1,000
AT-401B	All beginning with 1125	Less than or equal to 1,850	Upon the accumulation of 2,350 hours TIS	1,000
AT-402/AT-402A	0694-0951	Greater than 4,250	Within the next 50 hours TIS or upon the accumulation of 4,500, whichever is later	700
AT-402/AT-402A	0694-0951	Greater than 2,850 but less than or equal to 4,250	Within the next 250 hours TIS or upon the accumulation of 3,350 hours TIS, whichever is later	700
AT-402/AT-402A	0694-0951	Greater than 1,750 but less than or equal to 2,850	Within the next 500 hours TIS	700
AT-402/AT-402A	0694-0951	Less than or equal to 1,750	Upon the accumulation of 2,250 hours TIS	700

(g) For all affected airplanes: Before further flight after the inspection in which cracks are found, replace any cracked wing lower spar cap following Snow Engineering Drawing Number 21088, dated November 3, 2004.

(h) For all affected airplanes, except Model AT-402A, all serial numbers beginning with 0952, and except Model AT-402B, all serial numbers beginning with 0966: Report to the FAA any cracks detected as the result of each inspection required by paragraph (f) of this AD on the form in Figure 1 of this AD.

(1) Only if cracks are found, send the report within 10 days after the inspection required in paragraph (f) of this AD.

(2) The Office of Management and Budget (OMB) approved the information collection requirements contained in this regulation under the provisions of the Paperwork Reduction Act and assigned OMB Control Number 2120-0056.

(i) For all affected airplanes: Upon the accumulation of the life used in paragraph (e)(1) of this AD or within the next 50 hours TIS after April 21, 2006 (the effective date of AD 2006-08-08), whichever occurs later, you must replace your wing lower spar cap before further flight following Snow Engineering Drawing Number 21088, dated November 3, 2004.

(j) For Model AT-402A airplanes, all serial numbers beginning with 0952; and Model AT-402B airplanes, all serial numbers beginning with 0966: In lieu of the safe life used in paragraph (e)(1) of this AD, you may eddy-current inspect and modify the wing lower spar cap. The inspection schedule and modification procedures are included in Appendix 2 to this AD.

(k) For all affected airplanes (those complying with the actions in the AD or alternative method of compliance (AMOC)): One of the following must do the inspection:

(1) A level 2 or 3 inspector certified in eddy current inspection using the guidelines established by the American Society for Nondestructive Testing or MIL-STD-410; or

(2) A person authorized to perform AD work and who has completed and passed the Air Tractor, Inc. training course on Eddy Current Inspection on wing lower spar caps.

Mail report to: Manager, Fort Worth ACO, ASW-150, 2601 Meacham Blvd., Fort Worth, TX 76193-0150; or fax to [phone].

Special Flight Permit

(l) Under 14 CFR part 39.23, we are allowing special flight permits for the purpose of compliance with this AD under the following conditions:

(1) Only operate 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.

Alternative Methods of Compliance (AMOCs)

(m) The Manager, Fort Worth or Los Angeles Airplane Certification Office (ACO), FAA, has the authority to approve AMOCs for this AD, if requested using the procedures found in 14 CFR 39.19. Before using any approved AMOC on any airplane to which the AMOC applies, notify your appropriate principal inspector (PI) in the FAA Flight Standards District Office (FSDO), or lacking a PI, your local FSDO. For AMOC approval, send information to ATTN:

(1) For the airplanes that do not incorporate and never have incorporated Marburger winglets: Rob Romero, Aerospace Engineer, FAA, Fort Worth Airplane Certification Office, 2601 Meacham Boulevard, Fort Worth, Texas 76193-0150; telephone: [phone]; facsimile: [phone].

(2) For airplanes that incorporate or have incorporated Marburger winglets: John Cecil, Aerospace Engineer, Los Angeles Aircraft Certification Office, FAA, 3960 Paramount Boulevard, Lakewood, California 90712; telephone: [phone]; facsimile: [phone].

(n) AMOCs approved for AD 2001-10-04, AD 2001-10-04 R1, or AD 2002-11-05 for the AT-400 series airplanes are not considered approved for this AD.

(o) AMOCs approved for the repetitive inspection requirements of AD 2006-08-08 are approved for this AD until the scheduled modification date required by this AD.

Related Information

(p) To get copies of the service information referenced in this AD, contact Air Tractor, Incorporated, P.O. Box 485, Olney, Texas 76374; telephone: [phone]; facsimile: [phone]; Internet: http://www.airtractor.com; or Marburger Enterprises, Inc., 1227 Hillcourt, Williston, North Dakota 58801; telephone: [phone] or [phone]; facsimile: [phone]. To view the AD docket, go to U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue, SE., Washington, DC 20590, or on the Internet at http://www.regulations.gov.

Appendix 1 to Docket No. FAA-2006-23646

The following provides procedures for determining the safe life for those Models AT-401, AT-401B, AT-402, AT-402A, and AT-402B airplanes that incorporate or have incorporated Marburger winglets. These winglets are installed following Supplemental Type Certificate (STC) No. SA00490LA.

What if I removed the Marburger winglets prior to further flight after April 21, 2006 (the effective date of AD 2006-08-08) or prior to April 21, 2006 (the effective date of AD 2006-08-08)?

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 Marburger STC No. SA00490LA. 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 (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 paragraph (c)(1) of this AD.

Example:

Your airplane is a Model AT-401B, serial number 1022. From paragraph (c)(1) of this AD, the unmodified 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 (c)(4) of this AD.

Example:

Again, your airplane is a Model AT-401B, serial number 1022. From paragraph (c)(4) 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 × 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:

Adjusted winglet TIS−the winglet TIS = winglet usage penalty.

(550 hours)−(500 hours TIS) = (50 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 paragraph (c)(1) of this AD (result of Step 2 above.).

Example:

Unmodified safe life−winglet usage penalty = adjusted safe life.

(7,777 hours TIS)−(50 hours TIS) = (7,727 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) of this AD and the airplane logbook.

What if I have the Marburger winglet installed as of April 21, 2006 (the effective date of AD 2006-08-08) 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 (c)(1) of this AD.

Example:

Your airplane is a Model AT-401B, serial number 1022. From paragraph (c)(1) of this AD, the unmodified 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 (c)(4) of this AD.

Example:

Again, your airplane is a Model AT-401B, serial number 1022. From paragraph (c)(4) 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:

Unmodified safe life−TIS without winglets = Potential winglet TIS.

(7,777 hours TIS)−(1,000 hours TIS) = (6,777 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.

(6,777 hours TIS) ÷ (1.1) = (6,155 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.

(6,777 hours TIS)−(6,155 hours TIS) = (622 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 paragraph (c)(1) of this AD (the result of Step 2 above).

Example:

Unmodified safe life−Winglet usage penalty = Adjusted safe life.

(7,777 hours TIS)−(622 hours TIS) = (7,155 hours TIS).

8. Enter the adjusted safe life (result of Step 7 above) in paragraph (e)(1) of this AD and the airplane logbook.

What if I install or remove the Marburger winglet from my airplane in the future?

If, at any time 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.

Appendix 2

Alternative Method of Compliance (AMOC) to Docket No. FAA-2006-23646

Optional Inspection Program

For Model AT-402A airplanes, all serial numbers (S/Ns) beginning with 0952, and Model AT-402B airplanes, all S/Ns beginning with 0966, that do not incorporate and never have incorporated Marburger winglets installed following STC No. SA00490LA; you may begin a repetitive inspection interval program as an alternative to the safe life requirement of this AD with the following provisions:

1. Upon accumulating 1,600 hours time-in-service (TIS) or within the next 50 hours TIS after April 21, 2006 (the effective date of AD 2006-08-08), 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 4, dated February 23, 2001; and page 5, dated 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 who 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. 600 hours TIS:

i. Model AT-402A, S/Ns 1021 through 1124.

ii. Model AT-402B, S/Ns 1015, and 1021 through 1124.

b. 600 hours TIS:

i. Model AT-402A, S/Ns 0952 through 1020.

ii. Model AT-402B, S/Ns 0966 through 1020, except 1015.

c. 1,000 hours TIS:

i. Model AT-402A, all S/Ns beginning with 1112.

ii. Model AT-402B, all S/Ns beginning with 1125.

d. If the outboard two lower spar cap bolt holes have been cold worked following Snow Engineering Service Letter # 238 or #239, both dated September 30, 2004, then you may double the inspection intervals listed in a., b., and c. above (800 hours TIS, 1,200 hours TIS, or 2,000 hours TIS, as applicable) (See Step 8.—re: mid cycle cold work).

e. Your logbook entry must include the work done and the inspection intervals that are upcoming, as follows:

“Following AD 2006-08-08, at XXXX {insert hours TIS of the initial pre-modification inspection} 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 {400/600/800/1,000/1,200/2,000, as applicable} hours TIS. The first of these inspections is due at {insert the total number of hours TIS the first of these inspections is due} hours TIS.”

3. If at any time a crack is found, and:

a. If the crack indication goes away by doing the initial steps of the modification following the applicable sheet of Snow Engineering Co. Drawing Number 20992, then you may continue to modify your wing. After modification, proceed to Step 5.

b. If the crack indication does not go away by doing the initial steps of the modification following the applicable sheet of Snow Engineering Co. Drawing Number 20992, then 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. Upon accumulating 4,000 hours TIS, you must:

a. Modify your center splice connection following the applicable sheet of Snow Engineering Co. Drawing Number 20992, unless already done. Before doing the modification, do an eddy-current inspection following Snow Engineering Process Specification #197, page 1, revised June 4, 2002; pages 2 through 4, dated February 23, 2001; and page 5, dated May 3, 2002. (See Step 9.). If, as of April 21, 2006 (the effective date of AD 2006-08-08), your airplane is over or within 50 hours of reaching the 4,000-hour TIS modification requirement, then you must perform the modification within 50 hours TIS.

b. Your logbook entry must include the work done and the inspection intervals that are upcoming, as follows:

“Following AD 2006-08-08, at XXXX {insert hours TIS of the modification} 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 {insert the number of hours TIS at modification plus 1,600 hours TIS} hours TIS.

5. 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 4, dated February 23, 2001; and page 5, dated May 3, 2002.

6. Repetitively thereafter inspect at intervals not to exceed:

a. 1,000 hours TIS; or

b. 2,000 hours TIS if the outboard two lower spar cap bolt holes have been cold worked following Snow Engineering Service Letter #239, dated September 30, 2004 (See Step 8.).

c. Your logbook entry must include the work done and the post-modification inspection intervals that are upcoming, as follows:

“Following AD 2006-08-08, at XXXX {insert hours TIS of the initial post-modification inspection} 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 {1,000/2,000, as applicable} hours TIS. The first of these inspections is due at {insert the total number of hours TIS the first of these inspections is due} hours TIS.”

d. If at any time a crack is found, then 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. If you decide to cold work your bolt holes following Snow Engineering Service Letter #238 or #239, both dated September 30, 2004, 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 800/1,200/2000 hour TIS inspection intervals (2 times the intervals listed in Steps 2.a., 2.b., 2.c., and 6.a. listed above).

9. If you have modified your airplane 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. to reflect these reduced inspection intervals. Upon accumulating 8,000 hours TIS, you must comply with Step 7 above. See example:

Example:

An AT-402B 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.

Inspections would follow at 5,600 and 6,600 hours TIS. From Step 6a, this is 1,000-hour TIS inspection intervals.

There is another inspection at 7,000 hours TIS (modification plus 4,000 hours TIS). This relates to the 8,000-hour TIS inspection from Step 7, 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 listed in Step 4.

This airplane may continue to fly if inspected again at 7,500 hours TIS, which is 500 hours TIS. This 500-hour time corresponds to Step 9 where you cut your inspection interval from Step 6a in half.

Upon accumulating 8,000 hours TIS (this is the same as Step 7), you must replace the parts listed in Step 7 above.

For Model AT-402A airplanes, all S/Ns beginning with 0952, and Model AT-402B airplanes, all S/Ns beginning with 0966, that incorporate or have incorporated Marburger winglets installed following STC No. SA00490LA; you may begin a repetitive inspection interval program as an alternative to the safe life requirement of this AD following the steps above with the following provisions:

If you have removed the winglets, then calculate new, reduced hours for Steps 1, 4, 5, and 7 above, as applicable, based on the winglet usage factor listed in 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-402B airplane, S/N 1020, had winglets installed at 200 hours TIS and removed at 800 hours TIS.

The winglet usage factor is: 1.1.

Calculate equivalent hours: 600 hours TIS with winglets × 1.1 = 660 hours TIS.

Winglet usage penalty = 660 − 600 = 60.

New Step 1 Pre-Modification Initial Inspection time = 1,600 − 60 = 1,540 hours TIS.

Retained Step 2 Pre-Modification Inspection interval: Since the winglets are removed, the Pre-Modification Inspection interval remains at 600 hours TIS.

New Step 4 Modification time = 4,000 − 60 = 3,940 hours TIS.

New Step 5 Post-Modification Initial Inspection time = 3,940 + 1,600 = 5,540 hours TIS.

Retained Step 6 Post-Modification Inspection interval: Since the winglets are removed the Post-Modification Inspection interval remains at 1,000/2,000 hours TIS.

New Step 7 Replacement time = 8,000 − 60 = 7,940 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.e., 4.b., and 6.c.

If you have not removed the winglets, then calculate new, reduced hours for Steps 1, 2, 4, 5, 6, and 7 above, as applicable, based on the winglet usage factor listed in paragraph (c)(4) and Appendix 2 of this AD.

Repetitively thereafter inspect at intervals not to exceed the appropriate interval listed in the step above divided by the winglet usage factor.

Example:

An AT-402B, S/N 1,000 has had winglets on since new.

The winglet usage factor is: 1.1.

New Step 1 Pre-Modification Initial Inspection time: 1,600 ÷ 1.1 = 1,455 hours TIS.

New Step 2 Pre-Modification Inspection interval: 600 ÷ 1.1 = 545 hours TIS.

New Step 4 Modification time: 4,000 ÷ 1.1 = 3,636 hours TIS.

New Step 5 Post-Modification Initial Inspection time: 3,636 + (1,600 ÷ 1.1) = 5,090 hours TIS.

New Step 6 Post-Modification Inspection interval: 1,000 ÷ 1.1 = 909 hours TIS.

New Step 7 Replacement time: 8,000 ÷ 1.1 = 7,273 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.e., 4.b., and 6.c.

Issued in Kansas City, Missouri, on December 4, 2008.

Kim Smith,

Manager, Small Airplane Directorate, Aircraft Certification Service.