R.W. Martin, Inc. has issued Service Bulletin No. 00160/2, Revision A, dated November 15, 2007.

The actions described in this service information are intended to correct the unsafe condition identified in the MCAI.

FAA's Determination and Requirements of the Proposed AD

This product has been approved by the aviation authority of another country, and is approved for operation in the United States. Pursuant to our bilateral agreement with this State of Design Authority, they have notified us of the unsafe condition described in the MCAI and service information referenced above. We are proposing this AD because we evaluated all information and determined the unsafe condition exists and is likely to exist or develop on other products of the same type design.
Differences Between This Proposed AD and the MCAI or Service Information

We have reviewed the MCAI and related service information and, in general, agree with their substance. But we might have found it necessary to use different words from those in the MCAI to ensure the AD is clear for U.S. operators and is enforceable. In making these changes, we do not intend to differ substantively from the information provided in the MCAI and related service information.

We might also have proposed different actions in this AD from those in the MCAI in order to follow FAA policies. Any such differences are highlighted in a NOTE within the proposed AD.

Costs of Compliance

Based on the service information, we estimate that this proposed AD would affect about 157 products of U.S. registry. We also estimate that it would take about 18 workhours per product to comply with the basic requirements of this proposed AD. The average labor rate is $80 per workhour.

Based on these figures, we estimate the cost of the proposed AD on U.S. operators to be $226,080 or $1,440 per product.

In addition, we estimate that any necessary followon actions would take about 200 workhours and require parts costing $3,696 for a cost of $19,696 per product. We have no way of determining the number of products that may need these actions.

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 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 this 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
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this proposed AD and placed it in the AD docket.

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 adding the following new AD: Viking Air Limited: Docket No. FAA20080368; Directorate Identifier 2008CE007AD.
Comments Due Date
(a) We must receive comments by April 30, 2008.
Affected ADs
(b) None.
Applicability
(c) This AD applies to Models DHC61, DHC6100, DHC6200, and DHC6300 airplanes, all serial numbers, that are:
(1) Equipped with wing boxes, part numbers (P/Ns) C6W10021, C6W10023, WR6100259, or WR6100261, that incorporate a P/N
C6WM10271 front spar adapter assembly with 10 or more years of service; and
(2) Certificated in any category.
Subject
(d) Air Transport Association of America (ATA) Code 57: Wings. Reason
(e) The mandatory continuing airworthiness information (MCAI) states:

There have been reports of interrivet cracking on several wing front spar adapter assemblies (P/N C6WM10271) on the horizontal and vertical flanges. It was determined that the cracking was caused by stress corrosion in the short transverse grain initiated by local riveting induced stresses. This directive mandates modification and inspection of the wing front spar adapter fitting and replacement of cracked fittings.
Actions and Compliance
(f) Unless already done, do the following actions:
(1) Within the next 180 days after the effective date of this AD, install inspection holes in the lefthand (LH) and righthand (RH) lower wing skins following Viking DHC6 Twin Otter Service Bulletin Number V6/541, dated October 1, 2007.
(2) Before further flight after installing the inspection holes required in paragraph (f)(1) of this AD, inspect the LH and RH front spar adapter assemblies for cracks. For wing box P/Ns C6W10021 and C6W10023, inspect following Viking DHC6 Twin Otter Service
Bulletin Number V6/540, dated October 1, 2007. For wing box P/Ns WR6100259 and WR6100261, inspect following R.W. Martin, Inc. Service Bulletin No. 00160/2, Revision A, dated November 15, 2007. Repetitively inspect all affected wing box P/Ns thereafter at intervals not to exceed 1,200 hours timeinservice or 12 months, whichever occurs first, until the replacement required in paragraph (f)(3) of this AD is done.
(3) Before further flight after doing any inspection required in paragraph (f)(2) of this AD where cracks are found, replace the cracked front spar adapter assembly with a front spar adapter assembly, P/N C6WM10273. Do the replacement following Viking DHC6 Twin Otter Service Bulletin Number V6/542, dated October 1, 2007. This replacement terminates the repetitive inspections required in paragraph (f)(2) of this AD for the replaced front spar adapter assembly.
(4) As a terminating action for the repetitive inspections required in paragraph (f)(2) of this AD, at any time after the initial inspection required in paragraph (f)(2) of this AD, you may replace P/N C6WM10271 with P/N C6WM10273.

FAA AD Differences

Note: This AD differs from the MCAI and/or service information as follows: (1) MCAI Transport Canada AD No. CF200731, dated December 17, 2007, requires incorporating task C571018 of the DHC 6 Corrosion Prevention and Control Manual (CPCM), PSM 165, within 90 days after the effective date of this AD.
(2) We are not incorporating task C571018 of the DHC6 CPCM, PSM 165, into this AD because we are currently examining Transport Canada AD No. CF9412R1, dated April 13, 1999; and AD No. CF9911, dated May 28, 1999. Transport Canada issued these ADs to incorporate a Corrosion Prevention and Control Program that identifies specific areas that must be inspected to ensure the structural integrity of the DHC6 fleet.
Other FAA AD Provisions
(g) The following provisions also apply to this AD:
(1) Alternative Methods of Compliance (AMOCs): The Manager, New York 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: Pong Lee, Aerospace Engineer, FAA, New York Aircraft Certification Office,1600 Stewart Avenue, Suite 410, Westbury, New York 11590; telephone: (516) 228 7324; fax: (516) 7945531. 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.
(2) Airworthy Product: For any requirement in this AD to obtain corrective actions from a manufacturer or other source, use these actions if they are FAAapproved. Corrective actions are considered FAAapproved if they are approved by the State of Design Authority (or their delegated agent). You are required to assure the product is airworthy before it is returned to service.
(3) Reporting Requirements: For any reporting requirement in this AD, under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.), the Office of Management and Budget (OMB) has approved the information collection requirements and has assigned OMB Control Number 21200056.
Related Information
(h) Refer to MCAI Transport Canada AD No. CF200731, dated December 17, 2007; Viking DHC6 Twin Otter Service Bulletins No. V6/ 540, dated October 1, 2007; No. V6/541, dated October 1, 2007; and No. V6/542, dated October 1, 2007; and R.W. Martin, Inc. Service Bulletin No. 00160/2, Revision A, dated November 15, 2007, for related information.

Issued in Kansas City, Missouri, on March 8, 2008. David R. Showers,
Acting Manager, Small Airplane Directorate, Aircraft Certification Service.
[FR Doc. E86469 Filed 32808; 8:45 am]
BILLING CODE 491013P

FOR FURTHER INFORMATION CONTACT Pong Lee, Aerospace Engineer, FAA, New York Aircraft Certification Office, 1600 Stewart Avenue, Suite 410, Westbury, New York 11590; telephone: (516) 2287324; fax: (516) 794 5531.