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Proposed Rule

Airworthiness Directives; Air Tractor, Inc. Model AT-602 Airplanes

Document Details

Information about this document as published in the Federal Register.

Published Document

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Start Preamble

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

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

SUMMARY:

The FAA proposes to revise an earlier proposed airworthiness directive (AD) that applies to all Air Tractor, Inc. (Air Tractor) Model AT-602 airplanes. The earlier NPRM would have required you to repetitively inspect (using the eddy current method) the wing center splice joint two outboard fastener holes on both of the wing main spar lower caps for fatigue cracking; repair or replace any wing main spar lower cap where fatigue cracking is found; and report any fatigue cracking found. The NPRM resulted from fatigue cracking at the wing center splice joint outboard fastener hole in one of the wing main spar lower caps. Since issuing the NPRM, the FAA has received and evaluated new information that decreases the compliance time to initially inspect certain serial numbers. This proposed AD includes the new compliance times in the table located in paragraph (e)(2) of this AD. Since these actions impose an additional burden over that proposed in the earlier NPRM, we are reopening the comment period to allow the public the chance to comment on these additional actions.

DATES:

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

ADDRESSES:

Use one of the following to submit comments on this proposed AD:

  • DOT Docket Web site: Go to http://dms.dot.gov and follow the instructions for sending your comments electronically.
  • Government-wide rulemaking Web site: Go to http://www.regulations.gov and follow the instructions for sending your comments electronically.
  • Mail: Docket Management Facility; U.S. Department of Transportation, 400 Seventh Street, SW., Nassif Building, Room PL-401, Washington, DC 20590-0001.
  • Fax: 1-202-493-2251.
  • Hand Delivery: Room PL-401 on the plaza level of the Nassif Building, 400 Seventh Street, SW., Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

To get service information identified in this AD, contact Air Tractor, Inc. at P.O. Box 485, Olney, Texas 76374; telephone: (940) 564-5616; or facsimile: (940) 564-5612.

You may examine the comments on this proposed AD in the AD docket on the Internet at http://dms.dot.gov.

Start Further Info

FOR FURTHER INFORMATION CONTACT:

Andrew McAnaul, Aerospace Engineer, ASW-150 (c/o MIDO-43), 10100 Reunion Place, Suite 650, San Antonio, Texas 78216; telephone: (210) 308-3365; facsimile: (210) 308-3370.

End Further Info End Preamble Start Supplemental Information

SUPPLEMENTARY INFORMATION:

Comments Invited

We invite you to send any written relevant data, views, or arguments regarding this proposal. Send your comments to an address listed under ADDRESSES. Include the docket number, “FAA-2004-20007; Directorate Identifier 2004-CE-50-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://dms.dot.gov, including any personal information you provide. We will also post a report summarizing each substantive verbal contact with FAA personnel concerning this proposed rulemaking.

Discussion

The FAA received a report of fatigue cracking of the wing main spar lower cap at the wing center splice joint outboard fastener hole on one Air Tractor Model AT-602 airplane. The airplane had 2,895 hours time-in-service (TIS) at the time the cracking was discovered. The fatigue cracking is similar to that found on other Air Tractor airplane model wings.

Cracks in the wing main spar lower cap could result in failure of the spar cap and lead to 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 model airplanesStatus
2000-14-51AT-501, AT-502, and AT-502ASuperseded by AD 2001-10-04.
2001-10-04AT-400, AT-500, and AT-800 SeriesRevised by AD 2001-10-04 R1.
Start Printed Page 45468
2001-10-04 R1AT-400, AT-500, and AT-800 SeriesSuperseded by AD 2002-11-05.
2002-11-05AT-400, AT-401, AT-401B, AT-402, AT-402A, AT-402B, AT-501, AT-802, and AT-802ARevised by AD 2002-11-05 R1.
2002-13-02AT-300, AT-301, AT-302, AT-400, and AT-400A AirplanesSuperseded by AD 2003-06-01.
2002-11-03AT-502, AT-502A, AT-502B, and AT-503ASuperseded by AD 2002-26-05.
2002-26-05AT-502, AT-502A, AT-502B, and AT-503ACurrent.
2003-06-01AT-300, AT-301, AT-302, AT-400, and AT-400ACurrent.
2002-11-05 R1AT-501Current.
2006-08-08AT-400, AT-401, AT-401B, AT-402, AT-402A, and AT-402BCurrent.
2006-08-09AT-802 and AT-802ACurrent.

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

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 all Air Tractor Model AT-602 airplanes. This proposal was published in the Federal Register as a notice of proposed rulemaking (NPRM) on February 22, 2005 (70 FR 8549). The NPRM proposed to require you to repetitively inspect (using the eddy current method) the wing center splice joint two outboard fastener holes on both of the wing main spar lower caps for fatigue cracking; repair or replace any wing main spar lower cap where fatigue cracking is found; and report any fatigue cracking found.

The FAA encouraged interested persons to participate in developing this amendment. The following presents the comments received on the proposal and FAA's response to each comment:

Comment Issue No. 1: Maintenance Required During the Peak Spraying Season

The National Agricultural Aviation Association (NAAA), while recognizing immediate concerns to safety occur, requests the FAA consider the unique operating season of aerial application businesses and attempt to write ADs so compliance can be made during off-season maintenance. Deferring maintenance to the off-season minimizes the financial impact and loss of airplane availability to operators during the peak spraying season. The operators perceive that constant revisions of potential solutions to the wing spar cracking problems prevent them from prorating their potential expenses or planning the timing of required maintenance.

The FAA agrees with the NAAA. We should consider the importance of the financial and operational impact any rulemaking will have on owners and operators and, in this specific case, aerial application businesses. This proposed rule uses inspections to manage the safety of the wing centerline joint instead of reducing the compliance times for replacing parts. However, this approach can not be used indefinitely. Extending the service life of fatigue-critical, primary structure areas requires not only ensuring the safety of the area being inspected or modified, but also ensuring the safety of the complete structure when extending the service life.

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

Comment Issue No. 2: Incorrect Costs of Inspection and Modification

Leland Snow, President of Air Tractor, and Lewis Broussard, owner of Lewis's Flying Service, state that the costs associated with the inspection and modification in the NPRM are not correct.

The FAA partially agrees. We have revised the costs for the inspection and repairs or terminating actions. The proposed rulemaking does not reduce the current safe-life of the lower spar caps. Since the replacement time is not changed from the current safe-life approved at certification, the replacement costs are not applicable to this NPRM.

Comment Issue No. 3: Reference to Aluminum Spar Caps Should be Steel Spar Caps

Leland Snow, President of Air Tractor, states that there are references made to aluminum spar caps, and the Air Tractor Model AT-602 only uses steel spar caps. Also change “lower wing spars caps” to “lower wing spar caps.” The commenter believes this is a typographical error.

The FAA agrees. All references to aluminum spar caps have been removed. The typographical error has also been corrected.

Comment Issue No. 4: Incorrect Telephone Numbers

Leland Snow, President of Air Tractor, requests we change the contact telephone numbers for Air Tractor, Inc. They are incorrect.

The FAA agrees. Contact Air Tractor at telephone number (940) 564-5616 and facsimile number (940) 564-5612. The supplemental NPRM reflects this change.

Comment Issue No. 5: Snow Engineering Co. Process Specification #205

Leland Snow, President of Air Tractor, recommends deleting the reference to Snow Engineering Co. Process Specification #205, dated April 26, 2004, and using serial numbers (S/Ns) 602-0695 and subsequent to identify the factory cold-worked spar caps. Process Specification #205 contains the procedures for cold-working production airplanes and requires a CNC Mill. Airplanes starting with S/N 602-0695 are cold-worked in production using Process Specification #205.

The FAA partially agrees. Snow Engineering Co. Drawing 20776, sheet 2, Revision A, dated August 30, 2004, Note 19 refers to Process Specification #205 to cold work and line-ream the lower spar caps and attach blocks. The drawing applies to S/N 602-0695 and subsequent S/Ns that were cold worked in production, but according to Drawing Note 23, airplanes with S/Ns back to 602-0337 can also be retrofitted with cold worked parts. Therefore, it is possible that an early S/N airplane may Start Printed Page 45469receive replacement spar caps cold-worked and line-reamed by Process Specification #205 according to Drawing 20776. Airplane S/Ns before 602-0695 may also receive cold working by Snow Engineering Co. Service Letter #244, dated April 25, 2005; or by Service Letter #240, dated September 30, 2004, if modified by Snow Engineering Drawing 20998, Revision B, dated September 28, 2004.

To simplify, we will revise the proposed AD as follows: For inspection, we will refer to airplane S/Ns where possible in the AD, refer to the Service Letter #244 for in-service cold working; Drawing Number 20998 and Service Letter #240 as terminating action for inspection and for repair; and Snow Engineering Co. Drawing 20776 for spar cap replacement.

Comment Issue No. 6: Unclear Drill Size and Intent of Repair

For paragraph (f)(1) of the previous proposed AD, Leland Snow, President of Air Tractor, believes the next larger drill size is unclear and the intent of the repair is unclear.

The FAA agrees. We have revised the wording to clarify the intent of the repair of cracks.

Comment Issue No. 7: Dates of Service Information

Leland Snow, President of Air Tractor, wants the AD to call out the date on all drawings and service letters and add the text “or later FAA-approved revision.”

The FAA partially agrees. The AD will include dates with the reference materials. The FAA can not include the text “or later FAA-approved revision” since we can not approve data that does not already exist.

Air Tractor may work with the FAA to include a statement in future revisions that considers that service information as an alternative method of compliance.

Comment Issue No. 8: Modifying the wing versus replacing the lower spar caps

Leland Snow, President of Air Tractor, Inc., asks that we add installation of a steel plate at the wing splice joint, drilling the lower spar caps and installing extended splice blocks, and cold working critical fastener holes in lieu of lower spar cap replacement as a method to extend operating the wing past the current safe-life. The cost of modifying the wing is cheaper than replacing the lower spar caps and associated components and hardware. The manufacturer's resources to supply parts and change spar caps are limited, and the timeliness of spar cap replacement during the spray season when airplanes are operating makes doing this even more difficult.

The FAA disagrees. Extending the safe-life of primary structure requires not only substantiating the safety of the area being inspected or modified, but also ensuring the complete structure remains safe when extending the life. A full-scale fatigue test of the airplane's structure is the preferred method of extending the original safe-life, especially when the original design was substantiated by analysis, as in the case of the Model AT-602 airplane wing.

Based on the data that is currently available, the FAA is unable to extend the safe-life.

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

Comment Issue No. 9: Compliance Times

The National Transportation Safety Board (NTSB) requests we lower the initial inspection time for unmodified wing spars from 2,500 hours TIS to 2,000 hours TIS; and lower the recurring inspection intervals to a time unspecified by the commenter.

The FAA partially agrees. The manufacturer has provided new data since we published the original NPRM that confirms a fatigue life of 2,000 hours TIS for Model AT-602 airplanes, S/N 602-0337 through S/N 602-0584. This fatigue life is based on a recent FAA-approved usage spectrum and applies to airplanes not having a steel spar web plate installed. The same data show all other Model AT-602 airplanes are exempt from inspection. The FAA also did a Weibull analysis for the Model AT-602 fleet based on known service history that supports the 2,000-hour TIS fatigue life. We will establish the initial inspection time at 2,000 hours TIS for airplanes without the steel web plate based on this new information.

The recurring inspection intervals specified in the NPRM are based on FAA-approved damage tolerance testing and analysis. The specified intervals allow for performing at least two inspections before a detectable crack would grow to critical length. For further conservatism, the crack growth testing and analysis and resultant intervals are based on a usage spectrum that the FAA believes represents usage more severe than would be expected in routine service.

Relevant Service Information

We have reviewed the following Snow Engineering Co. service information:

  • Process Specification #197, revised June 4, 2002, Drawing 20776, Sheet 2, Revision A, dated August 30, 2004;
  • Service Letter #204, revised March 26, 2001;
  • Service Letter #240, dated September 30, 2004;
  • Drawing 20998, Revision B, dated September 28, 2004; and
  • Service Letter #244, dated April 25, 2005.

The service information includes procedures for:

  • Preparing the airplane and the eddy current machine for inspection of the lower wing spar caps;
  • Inspecting the lower wing spar caps for cracks;
  • Verifying suspected cracks for steel lower wing spar caps;
  • Repairing the cracks by installing a web plate and 8-bolt splice block; and
  • Replacing the spar caps and associated hardware.

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

FAA's Determination and Requirements of This Proposed AD

Since issuing the earlier NPRM, the FAA has received and evaluated new information that decreases the compliance time to initially inspect on certain S/Ns. This proposed AD includes the new compliance times in the table located in paragraph (e)(2) of this proposed AD.

After examining the circumstances and reviewing all available information related to the incidents described above, we have determined that:

  • The unsafe condition referenced in this document exists or could develop on other Air Tractor Model AT-602 airplanes of the same type design that are on the U.S. registry;
  • We should change the NPRM to eliminate the inspection requirements for all S/Ns beginning with 602-0585, to shorten the compliance times for the initial inspection on S/Ns 602-0337 through S/N 602-0584, and to provide terminating action for repetitive inspections on S/Ns 602-0337 through S/N 602-0584; and
  • We should take AD action to correct this unsafe condition.

The Supplemental NPRM

Proposing a shorter compliance time for the initial inspection for certain airplanes goes beyond the scope of what was originally proposed in the NPRM. Therefore, we are reopening the comment period and allowing the public the chance to comment on these additional actions. Start Printed Page 45470

The proposed AD would require you to repetitively inspect (using the eddy current method) the wing center splice joint two outboard fastener holes in the wing main spar lower caps for cracks and repair or replace any cracked spar cap.

Costs of Compliance

We estimate that this proposed AD affects 107 airplanes in the U.S. registry.

We estimate the following costs to do this proposed inspection:

Labor costParts costEddy current inspectionTotal cost per airplaneTotal cost on U.S. operators
Initial inspection and installation of access panels −24 work-hours × $80 = $1,920$645*$500$3,065$327,955
Repetitive Inspection (each)$60*$800$860$92,020
* Eddy current inspections are an estimated flat cost that includes labor and use of equipment.

We estimate the following costs to do any necessary repairs that would be required based on the results of the proposed inspection. We have no way of determining the number of airplanes that may need this repair:

Labor costParts costTotal cost per airplane
Install web plate, 8-bolt splice blocks, and cold work fastener holes: Air Tractor estimated a labor cost of $12,100. When broken down into work-hours, we estimated 151 work-hours to complete the task. 151 work-hours × $80 = $12,080$6,900$18,980
Cold work fastener holes following Snow Engineering Co. Service Letter #244, dated April 25, 2005: 19 work-hours × $80 = $1,520$1,350$2,870

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 airplanes in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this AD.

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 this proposed AD:

1. Is not a “significant regulatory action” under Executive Order 12866;

2. Is not a “significant rule” under the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and

3. Will 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 summary of the costs to comply with this proposed AD (and other information as included in the Regulatory Evaluation) and placed it in the AD Docket. You may get a copy of this summary by sending a request to us at the address listed under ADDRESSES. Include “AD Docket FAA-2004-20007; Directorate Identifier 2004-CE-50-AD” in your request.

Examining the Dockets

You may examine the docket that contains the proposal, any comments received, and any final disposition on the Internet at http://dms.dot.gov, or in person at the DOT Docket Offices between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Office (telephone 1-800-647-5227) is located on the plaza level of the Department of Transportation NASSIF Building at the street address stated in ADDRESSES. Comments will be available in the AD docket shortly after the Docket Management Facility receives them.

Start List of Subjects

List of Subjects in 14 CFR Part 39

End List of Subjects

The Proposed Amendment

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

Start Part

PART 39—AIRWORTHINESS DIRECTIVES

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

Start Authority

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

End Authority
[Amended]

2. The FAA amends § 39.13 by adding the following new airworthiness directive (AD):

Air Tractor, Inc.: Docket No. FAA-2004-20007; Directorate Identifier 2004-CE-50-AD.

Comments Due Date

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

Affected ADs

(b) None.

Applicability

(c) This AD affects Model AT-602 airplanes, all serial numbers beginning with 602-0337, that are certificated in any category.

Unsafe Condition

(d) This AD is the result of fatigue cracking of the wing main spar lower cap at the centerline 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 Start Printed Page 45471of the spar cap and lead to wing separation and loss of control of the airplane.

Compliance

(e) To address the problem, do the following:

(1) Before doing the initial eddy current inspection required in paragraph (e)(2) of this AD, gain access for the inspection by cutting inspection holes, modifying the vent tube, and installing cover plates; unless already done. Follow Snow Engineering Co. Service Letter #204, dated October 25, 2000, Drawing titled “602 Spar Inspection Holes and Vent Tube Mod.,” dated November 13, 2003.

(2) Eddy current inspect the wing center splice joint outboard two fastener holes in both the right and left wing main spar lower caps for cracks. Follow Snow Engineering Co. Process Specification #197, Revised June 4, 2002. For the following airplanes, use the wing spar lower cap hours time-in-service (TIS) schedule below in Table 1.—Compliance Times for Inspection to do the initial and repetitive inspections:

Table 1.—Compliance Times for Inspection

Serial Nos.ConditionInitially inspectRepetitively inspect thereafter at the following intervals
(i) 602-0337 through 602-0584As manufacturedUpon accumulating 2,000 hours TIS or within 50 hours TIS after the effective date of this AD, whichever occurs later, unless already done1,000 hours TIS.
(ii) 602-0337 through 602-0584Modified with cold-worked fastener holes following Snow Engineering Co. Service Letter #244, dated April 25, 2005If performing the cold-working procedure in Service Letter #244, it includes the eddy current inspection2,000 hours TIS.

(3) Do an eddy current inspection as part of the cold working procedure in Service Letter #244, dated April 25, 2005, even if the wing spar was previously inspected.

(4) One of the following must do the inspection:

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

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

(f) For the airplanes listed in paragraph (e)(2) of this AD, as terminating action for the inspection requirements, you may modify your wing by installing part number (P/N) 20996-2 steel web plate and P/N 20985-1/2 8-bolt splice blocks following Snow Engineering Co. Drawing 20998, Revision B, dated September 28, 2004, and cold work the lower spar cap two outboard fastener holes at the wing center section splice connection following Snow Engineering Co. Service Letter #240, dated September 30, 2004.

(g) For all affected airplanes listed in paragraph (e)(2) of this AD, repair or replace any cracked spar cap before further flight. For repair or replacement, do one of the following:

(1) For cracks that can be removed by performing the terminating action listed in paragraph (f) of this AD above, perform the actions in paragraph (f) of this AD.

(2) For cracks that can not be removed by performing the terminating action in paragraph (f) of this AD, you must replace the lower spar caps and associated parts listed in paragraph (h) of this AD before continued flight.

(h) For all Model AT-602 airplanes, upon accumulating 6,500 hours TIS on the wing spar lower caps or within the next 50 hours TIS after the effective date of this AD, whichever occurs later, replace the wing lower spar caps, splice blocks and hardware, wing attach angles and hardware, and install the steel web plate, P/N 20996-2, if not already installed, following Snow Engineering Co. Drawing 20776, Sheet 2, Revision A, dated August 30, 2004. Compliance with this paragraph terminates the inspection requirements of paragraph (e)(2) of this AD.

(i) Report any cracks you find within 10 days after the cracks are found or within 10 days after the effective date of this AD, whichever occurs later. Include in your report the airplane serial number, airplane TIS, wing spar cap TIS, crack location and size, corrective action taken, and a point of contact name and phone number. Send your report to Andrew McAnaul, Aerospace Engineer, ASW-150 (c/o MIDO-43), 10100 Reunion Place, Suite 650, San Antonio, Texas 78216; telephone: (210) 308-3365; facsimile: (210) 308-3370. The Office of Management and Budget (OMB) approved the information collection requirements contained in this regulation under the provisions of the Paperwork Reduction Act of 1980 (44 U.S.C. 3501 and those following sections) and assigned OMB Control Number 2120-0056.

Alternative Methods of Compliance (AMOCs)

(j) The Manager, Fort Worth Airplane Certification Office, FAA, ATTN: Andrew McAnaul, Aerospace Engineer, ASW-150 (c/o MIDO-43), 10100 Reunion Place, Suite 650, San Antonio, Texas 78216; telephone: (210) 308-3365; facsimile: (210) 308-3370, has the authority to approve AMOCs for this AD, if requested using the procedures found in 14 CFR 39.19.

Related Information

(k) To get copies of the documents referenced in this AD contact Air Tractor, Inc. at address P.O. Box 485, Olney, Texas 76374; telephone: (940) 564-5616; or facsimile: (940) 564-5612. To view the AD docket, go to the Docket Management Facility; U.S. Department of Transportation, 400 Seventh Street, SW., Nassif Building, Room PL-401, Washington, DC, or on the Internet at http://dms.dot.gov. The docket number is FAA-2004-20007.

Start Signature

Issued in Kansas City, Missouri, on August 3, 2006.

John R. Colomy,

Acting Manager, Small Airplane Directorate, Aircraft Certification Service.

End Signature End Part End Supplemental Information

[FR Doc. E6-12949 Filed 8-8-06; 8:45 am]

BILLING CODE 4910-13-P