SUPPLEMENTARY INFORMATION:

Discussion

We were notified of cracks found in the left and right wing main spar frame support channels, the aft pressure bulkhead web, and the left and right picture window upper frame channels of a Twin Commander Aircraft LLC Model 690B airplane. Nineteen airplanes were inspected with one having severe cracking in the left and right wing main spar frame support channels, the aft pressure bulkhead web, and the left and right picture window upper frame channels. Five other of the inspected airplanes had similar but less severe damage. This condition, if not corrected, could result in structural failure of the aircraft.

Relevant Service Information

We reviewed Twin Commander Aircraft LLC Service Bulletin 241, dated September 26, 2012. The service information describes procedures for access, disassembly, and inspecting the outer fuselage attachments, the lower wing main spar, the vertical channels, the upper picture window channels, aft cabin pressure web, external wing to fuselage fillets, and fasteners for cracking. The service information also describes procedures for modifying the structure with reinforced parts and reassembly.

FAA's Determination

We are issuing this AD because we evaluated all the relevant information and determined the unsafe condition described previously is likely to exist or develop in other products of the same type design.

AD Requirements

This AD requires inspection for cracking of the outer fuselage attachments, the lower wing main spar, the vertical channels, the upper picture window channels, aft cabin pressure web, external wing to fuselage fillets, and fasteners; repair or replacement of damaged parts as necessary; and modification of the structure with reinforced parts.

FAA's Justification and Determination of the Effective Date

An unsafe condition exists that requires the immediate adoption of this AD. The FAA has found that the risk to the flying public justifies waiving notice and comment prior to adoption of this rule because cracking in the upper picture window frame channels, left- and right-hand wing main spar frame support channels, and/or aft pressure bulkhead web could result in structural failure of the aircraft. Therefore, we find that notice and opportunity for prior public comment are impracticable and that good cause exists for making this amendment effective in less than 30 days.

Comments Invited

This AD is a final rule that involves requirements affecting flight safety and was not preceded by notice and an opportunity for public comment. However, we invite you to send any written data, views, or arguments about this AD. Send your comments to an address listed under the ADDRESSES section. Include the docket number FAA-2013-0393 and Directorate Identifier 2012-CE-025-AD at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of this AD. We will consider all comments received by the closing date and may amend this AD because 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 about this AD.

Costs of Compliance

We estimate that this AD affects 280 airplanes of U.S. registry.

We estimate the following costs to comply with this AD: ( printed page 28127)

The scope of damage found in the required inspection could vary significantly from airplane to airplane. We have no way of determining how much damage may be found on each airplane or the cost to repair damaged parts on each airplane. The damage could be as minor as replacing rivets or fasteners or as extensive as a major wing/fuselage repair or replacement.

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

The Regulatory Flexibility Act of 1980 (Pub. L. 96-354) (RFA) establishes as a principle of regulatory issuance that agencies shall endeavor, consistent with the objective of the rule and of applicable statutes, to fit regulatory and informational requirements to the scale of the businesses, organizations, and governmental jurisdictions subject to regulation.

To achieve that principle, the RFA requires agencies to solicit and consider flexible regulatory proposals and to explain the rationale for their actions. The RFA covers a wide-range of small entities, including small businesses, not-for-profit organizations, and small governmental jurisdictions.

Agencies must perform a review to determine whether a proposed or final rule will have a significant economic impact on a substantial number of small entities. In accordance with Section 608 of the Regulatory Flexibility Act, an agency head may waive or delay completion of some or all of the requirements of Section 603 by providing a written finding that this final rule is being promulgated in response to an emergency that makes compliance or timely compliance with the provisions of Section 603 impracticable.

We are performing a review to determine whether this final rule AD action will have a significant economic impact on a substantial number of small entities. However, the immediate safety of flight conditions of this AD action make compliance with the provisions of Section 603 impracticable. Our justification for immediate adoption of this rule, and therefore of impracticability, is stated in FAA's Justification and Determination of the Effective Date. After we determine whether this final rule AD action has a significant economic impact on a substantial number of small entities or not, we will publish in the Federal Register our determination and, if required, our final regulatory flexibility analysis.

Adoption of the Amendment

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

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

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

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

2013-09-05 Twin Commander Aircraft LLC: Amendment 39-17446 ; Docket No. FAA-2013-0393; Directorate Identifier 2012-CE-025-AD.

(a) Effective Date

This AD is effective May 29, 2013.

(b) Affected ADs

None.

(c) Applicability

This AD applies to the following Twin Commander Aircraft LLC airplanes, certificated in any category:

(1) Model 690, all serial numbers except 11057;

(2) Model 690A, all serial numbers except 11104, 11106, 11129, 11134, 11146, 11159, 11173, 11192, 11220, 11237, 11252, 11263, 11280, 11287, 11298, 11303, 11317, 11339, and 11341; and

(3) Model 690B, all serial numbers except 11383, 11384, 11401, and 11436.

(4) Aircraft equipped with AVIADESIGN, Inc. STC No. SA5740NM (You may find information on STC No. SA5740NM at Internet: http://rgl.faa.gov/​Regulatory_​and_​Guidance_​Library/​rgstc.nsf/​0/​FEC5B7544E15F14C85256CC200122B19?​OpenDocument&​Highlight=​sa5740nm) are not compatible with the modifications contained in Twin Commander Aircraft LLC Service Bulletin 241, dated September 26, 2012. When an airplane has been modified, altered, or repaired in the area addressed by the AD action, according to 14 CFR part 39.15, the AD action still applies to that airplane. Following 14 CFR 39.19, the owner/operator of that airplane must request approval from the FAA for an alternative method of compliance (AMOC) following the instructions in paragraph (j) of this AD.

(d) Subject

Joint Aircraft System Component (JASC)/Air Transport Association (ATA) of America Code 53; Fuselage.

(e) Unsafe Condition

This AD was prompted by cracks found in the upper picture window frame channels, left- and right-hand wing main spar frame support channels, and aft pressure bulkhead web. This condition, if not corrected, could result in structural failure of the airplane. We are issuing this AD to correct the unsafe condition on these products.

(f) Compliance

Comply with this AD within the compliance times specified, unless already done.

(g) Inspection

(1) Inspect the airplane structural components, at the compliance times specified in paragraphs (g)(1)(i) through (g)(1)(iv) of this AD following Part I of Twin Commander Aircraft LLC Service Bulletin 241, September 26, 2012:

(i) For airplanes with 10,000 or more hours time-in-service (TIS), inspect within the next 30 days after the effective date of this AD. ( printed page 28128)

(ii) For airplanes with 7,500 through 9,999 hours TIS, inspect within the next 60 days after the effective date of this AD.

(iii) For airplanes with 5,000 through 7,499 hours TIS, inspect within the next 6 months after the effective date of this AD.

(iv) For airplanes with less than 5,000 hours TIS, inspect when the airplane accumulates a total of 5,000 hours TIS or within the next 12 months after the effective date of this AD, whichever occurs later.

(h) Repair

If any damage, cracks, and/or cracks that exceed the allowable limits specified in the service bulletin are found during the inspection required in paragraph (g)(1) of this AD, before further flight, repair or replace parts as necessary following Twin Commander Aircraft LLC Service Bulletin 241, dated, September 26, 2012. If Twin Commander Aircraft LLC Service Bulletin 241, dated, September 26, 2012, does not give procedures for repair of the damaged area, before further flight, you must contact Twin Commander Aircraft LLC to obtain repair instructions approved by the Seattle Aircraft Certification Office (ACO) specifically for compliance with this AD and incorporate those instructions. You can find contact information for Twin Commander Aircraft LLC in paragraph (l)(2) of this AD.

(i) Modification and Reassembly

(1) Before further flight after completing the actions in paragraphs (g) and (h) of this AD, modify and reassemble the airplane using the modification and reassembly procedures in Part II of Twin Commander Aircraft LLC Service Bulletin 241, dated, September 26, 2012.

(2) Although Twin Commander Aircraft LLC Service Bulletin 241, dated September 26, 2012, states that at least one person on the modification team must have completed the Twin Commander Aircraft LLC approved training, the FAA does not require that a mechanic complete this specialized training to do the modification work required in this AD. Regulations 14 CFR 65.81(a) and 14 CFR 65.81(b) provide criteria about qualifications of those performing maintenance; in this case, the requirements of this AD.

(j) Alternative Methods of Compliance (AMOCs)

(1) The Manager, Seattle Aircraft Certification Office (ACO), FAA, has the authority to approve AMOCs for this AD, if requested using the procedures found in 14 CFR 39.19. In accordance with 14 CFR 39.19, send your request to your principal inspector or local Flight Standards District Office, as appropriate. If sending information directly to the manager of the ACO, send it to the attention of the person identified in the Related Information section of this AD.

(2) Before using any approved AMOC, notify your appropriate principal inspector, or lacking a principal inspector, the manager of the local flight standards district office/certificate holding district office.

(k) Related Information

For more information about this AD, contact Vince Massey, Aerospace Engineer, FAA, Seattle ACO, 1601 Lind Avenue SW., Renton, WA 98057; telephone: (425) 917-6475; fax: (425) 917-6590; email: vince.massey@faa.gov.

(l) Material Incorporated by Reference

(1) You must use the following service information to do the actions required by this AD, unless the AD specifies otherwise. The Director of the Federal Register approved the incorporation by reference (IBR) under 5 U.S.C. 552(a) and 1 CFR part 51:

(i) Twin Commander Aircraft LLC Service Bulletin 241, dated September 26, 2012.

(ii) Reserved.

(2) For service information identified in this AD, contact Twin Commander Aircraft LLC; 1176 Telecom Drive, Creedmoor, NC 27522; telephone: (360) 403-0258; email: gpence@twincommander.com; Internet: http://www.twincommander.com.

(3) You may review copies of the service information at the FAA, Small Airplane Directorate, 901 Locust, Kansas City, Missouri 64106. For information on the availability of this material at the FAA, call (816) 329-4148.

(4) You may also review copies of the service information that is incorporated by reference at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, call 202-741-6030, or go to: http://www.archives.gov/​federal-register/​cfr/​ibr_​locations.html.