Therefore, we are incorporating the service letter revision into the proposed AD, and we are issuing a supplemental NPRM and extending the comment period to allow the public additional time to comment. Costs of Compliance

We estimate that this proposed AD would affect 1,264 airplanes in the U.S. registry, including those airplanes affected by AD 20071317.

We estimate the following costs to do the proposed inspection: Total cost per Total cost on Labor cost Parts cost airplane U.S. operators 1.5 workhours x $80 per hour = $120......................... $0 $120 $151,680

We estimate the following costs to do the repair/modification: Total cost per Total cost on Labor cost Parts cost airplane U.S. operators 24 workhours x $80 per hour = $1,920........................ $80 $2,000 $2,528,000

The estimated total cost on U.S. operators includes the cumulative costs associated with AD 20071317 and those airplanes and actions being added in this proposed AD.

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. [[Page 71088]]

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://dms.dot.gov; or in person at the Docket Management Facility between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Office (telephone (800) 6475227) is located at the street address stated in the ADDRESSES section. Comments will be available in the AD docket shortly after receipt. List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Safety. The Proposed Amendment

Accordingly, under the authority delegated to me by the Administrator, the FAA proposes to amend 14 CFR part 39 as follows: PART 39AIRWORTHINESS 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. The FAA amends Sec. 39.13 by removing Airworthiness Directive (AD) 20071317, Amendment 3915121 (72 FR 36863, July 6, 2007), and adding the following new AD:
Air Tractor, Inc.: Docket No. FAA20070258; Directorate Identifier 2007CE090AD.
Comments Due Date
(a) We must receive comments on this airworthiness directive (AD) action by February 29, 2008 (an additional 30 days after the comment close date for the NPRM of January 30, 2008).
Affected ADs
(b) This AD supersedes AD 20071317, Amendment 3915121.
Applicability
(c) This AD applies to the following airplane models and serial numbers that are certificated in any category:
Model Serial Nos. AT400, AT400A, AT402, AT402A, 0001 through 1175.
and AT402B.
AT502, AT502A, AT502B, and AT 0001 through 2597.
503A.
AT602........................... 0001 through 1141.
AT802 and AT802A............... 0001 through 0227.
Unsafe Condition
(d) This AD results from a report of a Model AT502B airplane with a crack located where the lower engine mount tube is welded to the engine mount ring. The airplane had 8,436 total hours timein service (TIS). We are issuing this AD to detect and correct cracks in the engine mount, which could result in failure of the engine mount. Such failure could lead to separation of the engine from the airplane.
Compliance
(e) To address this problem, you must do the following, unless already done:
(1) For all airplanes with less than 5,000 hours total TIS that do not have gussets installed on the engine mount in accordance with Snow Engineering Co. Service Letter #253 Rev. A, dated October 16, 2007: Visually inspect the engine mount as follows:
Affected airplanes Compliance Procedures (i) For all Models AT602, Initially before the Follow one of the AT802, and AT802A airplane reaches a following: airplanes. total of 1,300 (A) Snow Engineering hours TIS or within Co. Service Letter the next 100 hours 253, Rev. TIS after August B, dated November 10, 2007 (the 30, 2007; effective date of (B) Snow Engineering AD 20071317), Co. Service Letter whichever occurs 253, Rev. later. Repetitively A, dated October thereafter at 16, 2007; or intervals not to (C) Snow Engineering exceed 300 hours Co. Service Letter TIS. 253, revised January 22, 2007.
(ii) For all Model AT502A Initially before the Follow Snow airplanes. airplane reaches a Engineering Co. total of 1,300 Service Letter hours TIS or within 253 Rev. the next 100 hours B, dated November TIS after the 30, 2007. effective date of
this AD, whichever
occurs later.
Repetitively
thereafter at
intervals not to
exceed 300 hours
TIS.
[[Page 71089]]
(iii) For all Models AT400, Initially within the Follow Snow AT400A, AT402, AT402A, next 12 months Engineering Co. AT402B, AT502, AT502B, after the effective Service Letter and AT503A airplanes. date of this AD. 253 Rev. Repetitively B, dated November thereafter at 30, 2007. intervals not to
exceed 12 months.
(2) For all airplanes: Before further flight after any inspection required by paragraph (e)(1) of this AD where crack damage is found, repair and modify the engine mount by installing gussets following Snow Engineering Co. Service Letter 253 Rev. B, dated November 30, 2007. This modification terminates the repetitive inspections required in paragraphs (e)(1)(i), (e)(1)(ii), and (e)(1)(iii) of this AD.
(3) For all airplanes: Before the airplane reaches 5,000 hours total TIS after the effective date of this AD or within the next 100 hours TIS after the effective date of this AD, whichever occurs later; inspect, repair if cracked, and modify the engine mount by installing gussets following Snow Engineering Co. Service Letter 253 Rev. B, dated November 30, 2007. This modification terminates the repetitive inspections required in paragraphs (e)(1)(i), (e)(1)(ii), and (e)(1)(iii) of this AD.

Note: As a terminating action to the repetitive inspections required in paragraphs (e)(1)(i), (e)(1)(ii), and (e)(1)(iii) of this AD, you may install the gussets before finding cracks or reaching 5,000 hours total TIS.
Alternative Methods of Compliance (AMOCs)
(f) The Manager, Forth Worth Aircraft Certification Office, FAA, has the authority to approve AMOCs for this AD, if requested using the procedures found in 14 CFR 39.19. Send information to ATTN: Andy McAnaul, Aerospace Engineer, ASW150, FAA San Antonio MIDO43, 10100 Reunion Place, San Antonio, Texas 78216; phone: (210) 3083365; fax: (210) 3083370. 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.
Related Information
(g) To get copies of the service information referenced in this AD, contact Air Tractor Inc., P.O. Box 485, Olney, Texas 76374; telephone: (940) 5645616; fax: (940) 5645612. To view the AD docket, go to U.S. Department of Transportation, Docket Operations, M30, West Building Ground Floor, Room W12140, 1200 New Jersey Avenue, SE., Washington, DC 20590, or on the Internet at http://www.regulations.gov .

Issued in Kansas City, Missouri, on December 10, 2007. John R. Colomy,
Acting Manager, Small Airplane Directorate, Aircraft Certification Service.
[FR Doc. E724215 Filed 121307; 8:45 am]
BILLING CODE 491013P

FOR FURTHER INFORMATION CONTACT Andy McAnaul, Aerospace Engineer, 10100 Reunion Pl., San Antonio, Texas 78216; telephone: (210) 3083365; fax: (210) 3083370.