Airworthiness Directives; Columbia Helicopters and Restricted Category CH-47D Helicopters

Proposed Rule

Airworthiness Directives; Columbia Helicopters, Inc. and Restricted Category Model CH-47D Helicopters

A Proposed Rule by the Federal Aviation Administration on 04/14/2026

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• Public Inspection Published Document: 2026-07218 (91 FR 19087) Document Headings ###### Department of Transportation

Federal Aviation Administration

1. 14 CFR Part 39
2. [Docket No. FAA-2026-3483; Project Identifier AD-2024-00454-R]
3. RIN 2120-AA64 ( printed page 19087) # AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

The FAA proposes to adopt a new airworthiness directive (AD) for all Columbia Helicopters, Inc. Model 234 helicopters and all Restricted Category Model CH-47D helicopters. This proposed AD was prompted by reports of corrosion detected on certain flight control rigid connecting links (connecting link). This proposed AD would require repetitive borescope inspections of the connecting links for corrosion and, depending on the results of the inspection, repair of the corrosion or replacement of the connecting link with a serviceable part. This proposed AD would also require reporting the results of these inspections and would prohibit installing a certain part-numbered connecting link or a connecting link with an unknown part number on a helicopter unless certain requirements are met. The FAA is proposing this AD to address the unsafe condition on these products.

DATES:

The FAA must receive comments on this proposed AD by May 29, 2026.

ADDRESSES:

You may send comments, using the procedures found in 14 CFR 11.43 and 11.45, by any of the following methods:

• Federal eRulemaking Portal: Go to regulations.gov. Follow the instructions for submitting comments.
• Fax: (202) 493-2251.
• Mail: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue SE, Washington, DC 20590.
• Hand Delivery: Deliver to Mail address above between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. AD Docket: You may examine the AD docket at regulations.gov under Docket No. FAA-2026-3483; or in person at Docket Operations between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The AD docket contains this NPRM, any comments received, and other information. The street address for Docket Operations is listed above.

FOR FURTHER INFORMATION CONTACT:

David Herron, Aviation Safety Engineer, FAA, 3960 Paramount Boulevard, Lakewood, CA 90712; phone: (206) 231-3544; email: david.herron@faa.gov.

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 ADDRESSES. Include “Docket No. FAA-2026-3483; Project Identifier AD-2024-00454-R” 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 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 David Herron, Aviation Safety Engineer, FAA, 3960 Paramount Boulevard, Lakewood, CA 90712. 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 regarding corrosion detected on connecting links with part numbers (P/N) 145C3340-1, -2, -7, -8, -9, -10, -11, and -12 installed on Columbia Helicopters, Inc. Model 234 helicopters and Restricted Category Model CH-47D helicopters. The connecting links are hollow control tubes that have witness holes to facilitate verification of proper rod end thread engagement during installation. When manufactured from non-stainless steel, these links are susceptible to corrosion over time. This corrosion is internal to the connecting link and is attributed to a lack of proper corrosion inhibition methods or damage to corrosion protection during installation or inspection. This condition, if not addressed, could result in connecting link failure within the flight control system that could lead to reduced controllability of the helicopter and reduced ability of the flight crew to maintain the safe flight and landing of the helicopter.

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 repetitive borescope inspections of the connecting links to identify if there is light corrosion (less than 0.001 inches), moderate corrosion (0.001 to 0.005 inches), or severe corrosion (greater than 0.005 inches), as defined in this proposed AD. Depending on the results of these inspections, this proposed AD would require repair of the corrosion or removal of the affected connecting link from service and replacement with a serviceable part. Additionally, this proposed AD would require reporting the results of the borescope inspections to the FAA for four inspection cycles and would prohibit the installation of an affected link on a helicopter unless certain requirements are met.

Costs of Compliance

The FAA estimates that this AD, if adopted as proposed, would affect 36 helicopters of U.S. registry. There are 324 connecting links identified as having this unsafe condition. There are nine connecting links installed per helicopter. The FAA has no way of knowing the number of helicopters of U.S. registry that may have the affected connecting links installed. The estimated cost on U.S. operators reflects ( printed page 19088) the costs based on the number of connecting links that need to be inspected and, if necessary, repaired or replaced.

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

| Action | Labor cost | Parts cost | Cost per
product | Cost on U.S.
operators |
| --- | --- | --- | --- | --- |
| Perform borescope inspection | 1.5 work-hours × $85 per hour = $128 | $0 | $128 | $4,608 |
| Report results | 1 work-hour × $85 per hour = $85 | 0 | 85 | 3,060 |
The FAA estimates the following costs to do any repairs or replacements that would be required based on the results of the proposed borescope inspection. The agency has no way of determining the number of helicopters that might need these repairs or replacements:

| Action | Labor cost | Parts cost | Cost per
product |
| --- | --- | --- | --- |
| Remove corrosion | 2 work-hours × $85 per hour = $170 | $0 | $170 (per link). |
| Replace connecting links | 2 work-hours × $85 per hour = $170 (per link) | Up to $2,535 (per link) | Up to $2,705 (per link). |

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 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.

List of Subjects in 14 CFR Part 39

• Air transportation
• Aircraft
• Aviation safety
• Incorporation by reference
• 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 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. The FAA amends § 39.13 by adding the following new airworthiness directive:

Columbia Helicopters, Inc. and Restricted Category Helicopters: Docket No. FAA-2026-3483; Project Identifier AD-2024-00454-R.

(a) Comments Due Date

The FAA must receive comments on this airworthiness directive (AD) by May 29, 2026.

(b) Affected ADs

None.

(c) Applicability

This AD applies to the helicopters identified in paragraphs (c)(1) and (2) of this AD:

(1) Columbia Helicopters, Inc. Model 234 helicopters, certificated in any category; and

(2) Restricted Category Model CH-47D helicopters; current type certificate holders include, but are not limited to, Billings Flying Service, Inc., Columbia Helicopters, Inc., Tandem Rotor, LLC, and Unical Air Inc.

(d) Subject

Joint Aircraft System Component (JASC) Code 2700, Flight Control System. ( printed page 19089)

(e) Unsafe Condition

This AD was prompted by reports of corrosion detected on certain connecting links. The FAA is issuing this AD to detect and address corrosion on certain connecting links. The unsafe condition, if not addressed, could result in failure of the connecting link within the flight control system that could lead to reduced controllability of the helicopter and reduced ability of the flight crew to maintain the safe flight and landing of the helicopter.

(f) Compliance

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

(g) Required Actions

(1) For helicopters identified in paragraphs (c)(1) and (2) of this AD with a flight control rigid connecting link (connecting link) having part numbers (P/N) 145C3340-1, 145C3340-2, 145C3340-7, 145C3340-8, 145C3340-9, 145C3340-10, 145C3340-11, or 145C3340-12, or a link with an unknownP/N installed, within 30 days after the effective date of this AD, accomplish a borescope inspection to determine the level of corrosion (if any) by accomplishing the actions required by paragraphs (g)(1)(i) and (ii) of this AD:

(i) With connecting links removed from the helicopter, loosen the locknut and unscrew the rod end bearing on non-riveted end.

(ii) Using a borescope, inspect the interior surface of the support rod for corrosion. Complete the following actions depending on the results:

(A) For connecting links properly treated with primer and no corrosion is found, before further flight, using a label or paint pen, if unmarked, mark the tube with the part number, and mark the following, “H-47-24-ASAM-03 Compliant” after each part number, and repeat the borescope inspection at the intervals specified in table 1 to paragraph (g)(1)(ii) of this AD.

Note 1 to paragraph (g)(1)(ii)(A): This note applies to paragraphs (g)(1)(ii)(A) through (C). Aviation Safety Action Message (ASAM) Flight Control Link Corrosion Assessment and Repair, H-47-24-ASAM-03, dated April 26, 2024 (H-47-24-ASAM-03), contains information regarding corrosion and part marking.

(B) If no corrosion is found and the connecting link is not treated with primer, or if any light or moderate corrosion is found on any connecting link during any inspection required by this AD, depending on the condition found, before further flight, repair the primer defects or remove or repair the corrosion by using a method approved by the Manager, West Certification Branch, FAA. For a repair method to be approved by the Manager, West Certification Branch, FAA as required by this paragraph, the Manager's approval letter must specifically refer to this AD. After repair as approved by the FAA, mark the following, “H-47-24-ASAM-03 Compliant” after each part number. Repeat the borescope inspection at the intervals specified in table 1 to paragraph (g)(1)(ii) of this AD.

(C) For connecting links that are determined to have severe corrosion during any inspection required by this AD, before further flight, remove the connecting link from service and replace it with a serviceable part. If the replacement connecting link is not marked “H-47-24-ASAM-03 Compliant”, mark it in accordance with paragraph (g)(1)(ii)(A) of this AD. Repeat the borescope inspection of the replacement connecting link at the intervals specified in table 1 to paragraph (g)(1)(ii) of this AD.

| Type of
corrosion found | Repetitive borescope
inspection intervals |
| --- | --- |
| No Corrosion | At intervals not to exceed 24 months. |
| Light corrosion | At intervals not to exceed 18 months. |
| Moderate corrosion | At intervals not to exceed 12 months. |
| Severe corrosion | No repetitive inspections. |
(2) Within 30 days after each inspection required by paragraph (g)(1) of this AD or within 30 days after the effective date of this AD, whichever occurs later, and for 3 reporting/inspection intervals thereafter, report the results of these inspections to the FAA by either email: 9-AVS-WCB-Correspondence@faa.gov; or mail: Attn: Continued Operational Safety, West Certification Branch (AIR-770), FAA, 3960 Paramount Boulevard, Lakewood, CA 90712-4137.

(h) Parts Installation Limitation

After the effective date of this AD, do not install a connecting link having P/N 145C3340-1, 145C3340-2, 145C3340-7, 145C3340-8, 145C3340-9, 145C3340-10, 145C3340-11, or 145C3340-12 on any helicopter, unless it is a serviceable part as defined in paragraph (i)(1) of this AD.

(i) Definitions

For the purpose of this AD:

(1) A “serviceable” part is a connecting link that has been inspected and repaired if necessary, as required by paragraphs (g)(1)(i) and (ii) of this AD, or a connecting link that is new (zero hours).

(2) Light corrosion involves scaling, blistering, or flaking of the surface and penetrates to a depth less than 0.001 inches.

(3) Moderate corrosion involves scaling, pitting, blistering, or flaking of the surface area and penetrates to a depth between 0.001 inches to 0.005 inches.

(4) Severe corrosion involves scaling, pitting, blistering, or flaking of the surface area and penetrates to a depth greater than 0.005 inches.

(j) Special Flight Permits

Special flight permits, as described in 14 CFR 21.197 and 21.199, are not allowed.

(k) Alternative Methods of Compliance (AMOCs)

(1) The Manager, West 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 West Certification Branch, send it to the attention of the person identified in paragraph (l)(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.

(l) Additional Information

(1) For more information about this AD, contact David Herron, Aviation Safety Engineer, FAA, 3960 Paramount Boulevard, Lakewood, CA 90712; phone: (206) 231-3544; email: david.herron@faa.gov.

(2) For material identified in this AD that is not incorporated by reference, contact U.S. Army Aviation and Missile Command (AMCOM), AMCOM Safety, 5300 Martin Road, Redstone Arsenal, AL 35898-5000; phone: (256) 313-4870.

(m) Material Incorporated by Reference

None.

Issued on April 10, 2026.

Steven W. Thompson,

Acting Deputy Director, Compliance & Airworthiness Division, Aircraft Certification Service.

[FR Doc. 2026-07218 Filed 4-13-26; 8:45 am]

BILLING CODE 4910-13-P

Published Document: 2026-07218 (91 FR 19087)