AD 2000-11-05

This amendment adopts a new airworthiness directive (AD) that applies to certain Air Tractor Incorporated (Air Tractor) Models AT-301, AT-401, and AT-501 airplanes that are equipped with a 3/16-inch thick aluminum fin front spar fitting and an all metal rudder. This AD requires that you repetitively inspect the vertical fin front spar attachment fittings for fatigue cracks, and rework the vertical fin if any cracks are found. This AD is the result of reports of a vertical fin front spar fitting failure on a Model AT-401 airplane. The actions specified by this AD are intended to detect and correct cracks in the vertical fin front spar attachment fittings, which could result in failure of the vertical fin. This condition could lead to loss of directional control and eventual loss of airplane control.

Final rule; request for comments

2000-11-05 AIR TRACTOR INCORPORATED: Amendment 39-11753; Docket No. 2000-CE-21-AD.

(a) What airplanes are affected by this AD? The following airplane models and serial numbers that are:
(1) certificated in any category; and
(2) equipped with a 3/16-inch fin front spar fitting and an all metal rudder.

Models
Serial Numbers
AT-301
301-0100 through 301-0736
AT-401
401-0662 through 401-0736
AT-501
501-0002 through 501-0030

Note: This AD does not affect the requirements of AD 97-14-05, Amendment 39-10063 (62 FR 38445, July 18, 1997). AD 97-14-05 requires similar actions to this AD on Models AT-302, AT-400, AT-400A airplanes, and certain Models AT301, AT-401, and AT-501 airplanes that are not affected by this AD.

(b) Who must comply with this AD? Anyone who wishes to operate any of the above airplanes on the U.S. Register.

(c) What problem does this AD address? The actions required by this AD are intended to detect and correct cracks in the spar plates, which could result in failure of the vertical fin. This condition could lead to loss of directional control and eventual loss of control of the airplane.

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

Action
Compliance Time
Procedures
(1) Initial inspection of the fin front spar attachment fittings for fatigue cracks.
At whichever of the following that occurs later:

(i) Upon accumulating 4,000 hours time-in-service (TIS); or

(ii) Within the next 25 hours TIS after the June 23, 2000 (the effective date of this AD).
Accomplish in accordance with the Inspection Requirements section of Snow Engineering Company Service Letter #138, Issued July 29, 1995;
Revised August 7, 1996.
(2) Repetitive inspections of the fin front spar attachment fittings.

Repetitive inspection requirement only applies if no cracks are found and you choose not to rework the fin front spar attachment.
Within 100 hours TIS after the initial inspection and thereafter at intervals not to exceed 100 hours TIS if you have no cracks and choose not to rework the fin front spar attachment.
Accomplish in accordance with the Inspection Requirements section of Snow Engineering Company Service Letter #138, Issued July 29, 1995;
Revised August 7, 1996.
(3) Rework the fin front spar attachment fittings.
(i) Prior to further flight after any inspection where a crack is found in the front or rear spar area.

(ii) This eliminates the repetitive inspection requirement of this AD.
Accomplish in accordance with the Vertical Fin Rework Instructions section of Snow Engineering Company Service Letter #196, Issued February 9, 2000; Revised March 7, 2000.
(4) Optional rework of the fin front spar attachment fittings.
Any time to eliminate the repetitive inspection requirement of this AD.
Accomplish in accordance with the Vertical Fin Rework Instructions section of Snow Engineering Company Service Letter#196, Issued February 9, 2000; Revised March 7, 2000.

Note: The applicability of Snow Engineering Company Service Letter #138 refers to different airplanes than are referenced in this document. AD 97-14-05, Amendment 39-10063 (62 FR 38445, July 18, 1997), covers the airplanes referenced in Snow Engineering Company Service Letter #138. The inspection procedures also apply for the airplanes referenced in this AD. Therefore, Snow Engineering Company Service Letter #138 also applies to this AD, as well as AD 97-14-05. This service letter also specifies repetitive inspection intervals of 25 hours TIS. Paragraph (d)(2) of this AD requires the repetitive inspections at 100 hours TIS.

(e) Can I comply with this AD in any other way? You may use an alternative method of compliance or adjust the compliance time if:

(1) Your alternative method of compliance provides an equivalent level of safety; and

(2) The Manager, Fort Worth Airplane Certification Office (ACO), approvesyour alternative. Submit your request through an FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Fort Worth ACO.

Note: This AD applies to each airplane identified in paragraph (a) 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) Where can I get information about any already-approved alternative methods of compliance? Contact Rob Romero, Aerospace Engineer, FAA,Fort Worth ACO, 2601 Meacham Boulevard, Fort Worth, Texas 76193-0150; telephone: (817) 222-5102; facsimile: (817) 222-5960.

(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.

(h) Are any service bulletins incorporated into this AD by reference? You must accomplish the actions required by this AD in accordance with Snow Engineering Company Service Letter #138, Revised August 7, 1996, and Snow Engineering Company Service Letter #196, Revised March 7, 2000.

(1) The Director of the Federal Register previously approved the incorporation by reference of Snow Engineering Company Service Letter #138, Revised August 7, 1996, as of August 25, 1997.

(2) The Director of the Federal Register approved the incorporation by reference of Snow Engineering Company Service Letter #196, Revised March 7, 2000 under 5 U.S.C. 552(a) and 1 CFR part 51.

(3) You may get copies from Air Tractor Incorporated, P.O. Box 485, Olney, Texas 76374. You may look at copies at 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) When does this amendment become effective? This amendment becomes effective on June 23, 2000.

Discussion
What events have caused this AD? The FAA has received a report of an incident involving an Air Tractor Model AT-401 airplane. The following describe this incident:

1. The vertical fin front spar plate cracked and caused failure of the vertical fin front spar fitting;

2. The rear spar consequently failed and the fin contacted the elevator, which caused difficulty in controlling the airplane; and

3. The front spar failure occurred in the 3/16-inch thick aluminum fin front spar fitting across one of the bolt holes where the fitting attaches to the fuselage frame.

What are the consequences if the condition is not corrected? Fatigue cracking of the vertical fin front spar attachment fittings, if not detected and corrected, could result in structural failure of the front spar and consequently the rear spar. This could result in loss of directional control and loss of control of the airplane.

Is there service information that applies to this subject? Snow Engineering Company has issued the following service information that relates to this subject:

Service Letter #
Issue/Revision Dates
Procedures For
Service Letter 196
Issued February 9, 2000; Revised March 7, 2000.
Reworking the vertical fin.
Service Letter 138
Issued July 29, 1995;
Revised August 7, 1996.
Repetitively inspecting the vertical fin front spar attachment fittings for fatigue cracks.

The FAA's Determination and an Explanation of the Provisions of the AD
What has FAA decided? After examining the circumstances and reviewing all available information related to the incidents described above, including the relevant service information, we determined that:

- an unsafe condition exists or could develop on certain Air Tractor Models AT-301, AT-401, and AT-501 airplanes of the same type design to the incident airplane that are equipped with a 3/16-inch thick aluminum fin front spar fitting and an all metal rudder; and- AD action should be taken in order to detect and correct cracks in the vertical fin front spar attachment fittings, which could result in failure of the vertical fin. This condition could lead to loss of directional control and eventual loss of airplane control.

What does this AD require? This AD requires you to:
1. repetitively inspect vertical fin front spar attachment fittings for fatigue cracks; and
2. rework the vertical fin if any cracks are found.

Once you rework the vertical fin, you may discontinue the repetitive inspections.

The applicability of Snow Engineering Company Service Letter #138 refers to different airplanes than are referenced in this AD action. AD 97-14-05, Amendment 39-10063 (62 FR 38445, July 18, 1997), covers the airplanes referenced in Service Letter #138. The inspection procedures also apply for the airplanes referenced in this AD action. Therefore, Snow Engineering Company Service Letter #138 also applies to this AD, as well as AD 97-14-05. This service letter also specifies repetitive inspection intervals of 25 hours time-in-service (TIS). Paragraph (d)(2) of this AD requires the repetitive inspections at 100 hours TIS.

Will I have the opportunity to comment prior to the issuance of the rule? Because the unsafe condition described in this document could result in loss of directional control and eventual loss of airplane control, FAA finds that notice and opportunity for public prior comment are impracticable. Therefore, good cause exists for making this amendment effective in less than 30 days.

Comments Invited
Although this action is in the form of a final rule and was not preceded by notice and opportunity for public comment, FAA invites comments on this rule. You may submit whatever written data, views, or arguments you choose. You need to include the rule's docket number and submit your comments in triplicate to the address specified under the caption "ADDRESSES." The FAA will consider all comments received on or before the closing date. We may amend this rule in light of comments received. Factual information that supports your ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether we need to take additional rulemaking action.

The FAA is re-examining the writing style we currently use in regulatory documents, in response to the Presidential memorandum of June 1, 1998. That memorandum requires federal agencies to communicate more clearly with the public. We are interested in your comments on whether the style of this document is clearer, and any other suggestions you might have to improve the clarity of FAA communications that affect you. You can get more information about the Presidential memorandum and the plain language initiative at http://www.plainlanguage.gov.

The FAA specifically invites comments on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the rule. You may examine all comments we receive before and after the closing date of the rule in the Rules Docket. We will file a report in the Rules Docket that summarizes each FAA contact with the public that concerns the substantive parts of this AD.

If you want us to acknowledge the receipt of your comments, you must include a self-addressed, stamped postcard. On the postcard, write "Comments to Docket No. 2000-CE-21-AD." We will date stamp and mail the postcard back to you.

Regulatory Impact
These regulations 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, FAA has determined that this final rule does not have federalism implications under Executive Order 13132.

The FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and is not a significant regulatory action under Executive Order 12866. We have determined that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If FAA determines that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, we will prepare a final regulatory evaluation. You may obtain a copy of the evaluation (if required) from the Rules Docket.

List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.

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.

39.13 [Amended]
2. FAA amends Section 39.13 by adding a new airworthiness directive (AD) to read as follows: