SUPPLEMENTARY INFORMATION:

Comments Invited

The FAA invites you to send any written relevant data, views, or arguments about this proposal. Send your comments using a method listed under the ADDRESSES section. Include “Docket No. FAA-2025-3438; Project Identifier AD-2025-01163-A” at the beginning of your comments. The most helpful comments reference a specific portion of the proposal, explain the reason for any recommended change, and include supporting data. The FAA ( printed page 51614) will consider all comments received by the closing date and may revise this proposal because of those comments.

Except for Confidential Business Information (CBI) as described in the following paragraph, and other information as described in 14 CFR 11.35, the FAA will post all comments received, without change, to regulations.gov, including any personal information you provide. The agency will also post a report summarizing each substantive verbal contact received about this NPRM.

Confidential Business Information

CBI is commercial or financial information that is both customarily and actually treated as private by its owner. Under the Freedom of Information Act (FOIA) (5 U.S.C. 552), CBI is exempt from public disclosure. If your comments responsive to this NPRM contain commercial or financial information that is customarily treated as private, that you actually treat as private, and that is relevant or responsive to this NPRM, it is important that you clearly designate the submitted comments as CBI. Please mark each page of your submission containing CBI as “PROPIN.” The FAA will treat such marked submissions as confidential under the FOIA, and they will not be placed in the public docket of this NPRM. Submissions containing CBI should be sent to Lekebis Russell, Aviation Safety Engineer, FAA, 1701 Columbia Avenue, College Park, GA 30337. Any commentary that the FAA receives which is not specifically designated as CBI will be placed in the public docket for this rulemaking.

Background

The FAA received reports of fatigue cracking throughout the fuselage and vertical stabilizer's structural components on Twin Commander Model 685, 690, 690A, 690B, 690C, 690D, 695, and 695A airplanes. The fatigue cracking was found in areas with insufficient access for inspections, which led to undetected crack development. Specifically, cracking was observed at FS 409, the vertical stabilizer's aft spar, the horizontal stabilizer's forward spar, and the vertical stabilizer skin.

AD 95-13-02, Amendment 39-9283 (60 FR 32583, June 23, 1995) (AD 95-13-02) was issued to address cracking in the vertical stabilizer. This AD requires initially inspecting the vertical stabilizer for cracks, modifying any cracked vertical stabilizer, and, if not cracked, either repetitively inspecting or modifying the vertical stabilizer, and allowed for terminating action through modification or repair. Since the issuance of AD 95-13-02, continued cracking has been observed at FS 409. These findings show that previously implemented modifications in AD 95-13-02 did not provide an effective terminating action, along with the detection of additional cracking at FS 386 and FS 429 during later inspections. FS 386 and FS 429, where cracks were recently found, were not part of the inspections required by AD 95-13-02. Therefore, this proposed AD, while not superseding AD 95-13-02, addresses continued cracking in FS 409, including areas adjacent to prior repairs, by requiring inspections around repaired members, thereby complementing the ongoing requirements of AD 95-13-02.

The FAA is proposing this AD to prevent the failure of the aft fuselage or empennage structural members. The unsafe conditions, if not addressed, could result in structural failure of the empennage, which could lead to loss of control of the airplane.

FAA's Determination

The FAA is issuing this NPRM after determining that the unsafe condition described previously is likely to exist or develop on other products of the same type design.

Proposed AD Requirements in This NPRM

This proposed AD would require inspecting certain structural components within the fuselage and vertical stabilizer for any evidence of cracks, corrosion, or loose hardware, and inspecting the working fasteners at the diagonal braces of FS 386 for cracks, elongation, or deformation; and depending on the results of the inspections, replacing with new parts or used parts or repairing, as applicable. This proposed AD would also require reporting the inspection results to the FAA.

Interim Action

The FAA considers that this proposed AD would be an interim action. An investigation is ongoing, and the final corrective action has not yet been determined. Once corrective action has been determined, the FAA may consider additional rulemaking action.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would affect 589 airplanes of U.S. registry.

The FAA estimates the following costs to comply with this proposed AD:

The extent of the fatigue cracking within the fuselage or empennage structural components may vary significantly from airplane to airplane. The FAA has no way to determine how much damage may be found on each airplane, the extent of the damage, the cost to repair the damaged areas (or replace the part, if needed), or the number of airplanes that might require repair or replacement.

Paperwork Reduction Act

A federal agency may not conduct or sponsor, and a person is not required to respond to, nor shall a person be subject to a penalty for failure to comply with a collection of information subject to the requirements of the Paperwork Reduction Act unless that collection of information displays a currently valid OMB Control Number. The OMB Control Number for this information collection is 2120-0056. Public reporting for this collection of information is estimated to be approximately 1 hour per response, including the time for reviewing instructions, searching existing data ( printed page 51615) sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. All responses to this collection of information are mandatory. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to: Information Collection Clearance Officer, Federal Aviation Administration, 10101 Hillwood Parkway, Fort Worth, TX 76177-1524.

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.

The FAA is 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 FAA 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) Would not affect intrastate aviation in Alaska, and

(3) Would not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act.

The Proposed Amendment

Accordingly, under the authority delegated to me by the Administrator, the FAA proposes to amend 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:

Twin Commander Aircraft LLC: Docket No. FAA-2025-3438; Project Identifier AD-2025-01163-A.

(a) Comments Due Date

The FAA must receive comments on this airworthiness directive (AD) by January 2, 2026.

(b) Affected ADs

None.

(c) Applicability

This AD applies to Twin Commander Aircraft LLC Model 685, 690, 690A, 690B, 690C, 690D, 695, and 695A airplanes, all serial numbers, certificated in any category.

(d) Subject

Joint Aircraft System Component (JASC) Code 5500, Empennage Structure.

(e) Unsafe Condition

This AD was prompted by reports of fatigue cracking affecting structural components within the fuselage and empennage structure. The FAA is issuing this AD to prevent the failure of the aft fuselage or empennage structural members. The unsafe condition, if not addressed, could result in structural failure of the empennage, which could lead to loss of control of the airplane.

(f) Compliance

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

(g) Required Actions

(1) Within 50 hours time-in-service (TIS) after the effective date of this AD, thoroughly clean the empennage interior structure and perform the inspections in paragraphs (g)(1)(i), (ii), and (iii) of this AD.

(i) A detailed visual inspection for cracks, corrosion, or loose hardware, using at least 10x magnification, and the figures provided in appendix 1 of this AD, at the locations identified in paragraphs (g)(1)(i)(A) through (P).

(A) Fuselage Station (FS) 386: Frame Web at each corner radius

(B) FS 386: Horizontal Brace Joggles

(C) FS 386: Frame Upper Cable Cutouts

(D) FS 386: Diagonal Braces

(E) FS 409: Horizontal Stabilizer Front Spar

(F) FS 409: Vertical Stabilizer Spar Web

(G) FS 409: Frame Web at each corner fillet radius

(H) FS 409: Frame Web below horizontal stabilizer spar

(I) FS 409: Frame Tangs attaching fuselage skin

(J) FS 409: Exterior Fuselage Skin at cutouts corners

(K) FS 409: Exterior Fuselage Skin at frame tang attachment

(L) FS 409: Vertical Stabilizer Spar Web Forward and Aft Clips

(M) FS 429: Aft Frame Channel and Web

(N) FS 429: Forward Channel attached to frame

(O) Vertical Stabilizer Skin: Repair Skin Doubler

(P) Vertical Stabilizer: Mid Spar Flange

(ii) A detailed visual inspection for cracks, elongation, or deformation of the working fasteners at location (D) FS 386 diagonal braces, using at least 10x magnification.

(iii) A general visual inspection of areas adjacent to the structures in paragraphs (g)(1)(i)(A) through (P) of this AD within the empennage structure for any evidence of cracks, corrosion, or loose hardware. Additional access or teardown is not required for this inspection.

(iv) For inspections required by paragraph (g)(1)(i), (ii), and (iii) of this AD, it is satisfactory to inspect the immediate area adjacent to previously installed repairs for any cracking, or corrosion, or loose hardware. Repairs or modifications previously installed will not be required to be removed from the airplane unless damage is found.

Note 1 to paragraph (g)(1): Paragraph 5-18, Visual Inspection Procedures, of Chapter 5, Nondestructive Inspection (NDI), Section 2, Visual Inspection, of FAA Advisory Circular 43.13-1B, “Acceptable Methods, Techniques, and Practices—Aircraft Inspection and Repair,” Change 1, dated September 8, 1998; with Editorial Update dated September 27, 2001, provides guidance on performing visual inspections.

(2) If, during the inspections required by paragraph (g)(1)(i), (ii), or (iii)of this AD, any evidence of cracks, corrosion, or loose hardware is found at FS 386, or FS 409, or FS 429 or the vertical stabilizer or cracks, elongation, or deformation are found to the holes of the working fasteners at the diagonal braces of FS 386, before further flight, replace with new parts with zero hours TIS or used parts that have been inspected per paragraphs (g)(1)(i), (ii), and (iii) of this AD and found to be free of cracks corrosion, or loose hardware, or repair using a method approved by the Manager, East Certification Branch, FAA. For a repair method to be approved by the Manager, East Certification Branch, FAA as required by this paragraph, the Manager's approval letter must specifically refer to this AD.

Note 2 to paragraph (g)(2): If a repair in FS 409 is necessary, then an alternative method of compliance would also be necessary in this area for those doing repetitive inspections in accordance with AD 95-13-02; Amendment 39-9283; (87 FR 32583; June 23, 1995) per 14 CFR 39.17. This would include if a repair was necessary that was different than that required by AD 95-13-02. ( printed page 51616)

(h) Reporting Requirement

Within 30 days after performing the inspections required by paragraphs (g)(1)(i), (ii), and (iii) of this AD or within 30 days after the effective date of this AD, whichever occurs later, report the results of the inspections, including no findings, to the FAA at ecb-cos@faa.gov. The report must include the following:

(1) The name and address of owner;

(2) The date of the inspection;

(3) The name, address, telephone number, and email address of person submitting the report;

(4) The airplane serial number, registration number, total flight hours, flight hours during the last 12 months, airplane usage ( e.g., 14 CFR part 91/135—general, forest service, fire attack roles, low aerial survey, etc.);

(5) The flight hours of any usage under forest service, fire attack roles, or aerial survey (nonstandard usage).

(6) A description of cracks, corrosion, or loose hardware of the fuselage structure or vertical stabilizer or cracks, elongation, or deformation of the working fasteners at the diagonal braces of FS 386. Include affected structure, dimensions, including length and location.

(i) Alternative Methods of Compliance (AMOCs)

(1) The Manager, East Certification Branch, 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 East Certification Branch, send it to the attention of the person identified in paragraph (j)(1) of this AD and email to: AMOC@faa.gov.

(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.

(j) Additional Information

(1) For more information about this AD, contact Lekebis Russell, Aviation Safety Engineer, FAA, 1701 Columbia Avenue, College Park, GA 30337; phone: (404) 474-5510; email: ecb-cos@faa.gov.

(2) FAA Advisory Circular 43.13-1B, “Acceptable Methods, Techniques, and Practices—Aircraft Inspection and Repair,” Change 1, dated September 8, 1998; with Editorial Update dated September 27, 2001, may be found at drs.faa.gov.

(k) Material Incorporated by Reference

None.

( printed page 51617)

Appendix 1 to Docket FAA-2025-3438

Figure 1 to Appendix 1 ( printed page 51618)

Appendix 1 to Docket FAA-2025-3438

Figure 2 to Appendix 1 ( printed page 51619)

Appendix 1 to Docket FAA-2025-3438

Figure 3 to Appendix 1 ( printed page 51620)

Appendix 1 to Docket FAA-2025-3438

Figure 4 to Appendix 1