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Rule

Special Conditions: Textron Aviation Inc. (Textron) Model MU-300-10, 400, 400A Airplanes; Rechargeable Lithium Batteries and Battery System Installations

A Rule by the Federal Aviation Administration on 03/18/2026

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3. Document Details Published Content - Document Details Agencies Department of Transportation Federal Aviation Administration Agency/Docket Numbers Docket No. FAA-2026-1132 Special Conditions No. 25-887-SC CFR 14 CFR 25 Document Citation 91 FR 12915 Document Number 2026-05264 Document Type Rule Pages 12915-12917 (3 pages) Publication Date 03/18/2026 Published Content - Document Details

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• Document Details Published Content - Document Details Agencies Department of Transportation Federal Aviation Administration Agency/Docket Numbers Docket No. FAA-2026-1132 Special Conditions No. 25-887-SC CFR 14 CFR 25 Document Citation 91 FR 12915 Document Number 2026-05264 Document Type Rule Pages 12915-12917 (3 pages) Publication Date 03/18/2026 Published Content - Document Details
• Document Dates Published Content - Document Dates Comments Close 05/04/2026 Effective Date 2026-03-18 Dates Text This action is effective on Textron on March 18, 2026. Send comments on or before May 4, 2026. Published Content - Document Dates

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  • AGENCY:
  • ACTION:
  • SUMMARY:
  • DATES:
  • ADDRESSES:
  • FOR FURTHER INFORMATION CONTACT:
  • SUPPLEMENTARY INFORMATION:
  • Privacy
  • Confidential Business Information
  • Comments Invited
  • Background
  • Type Certification Basis
  • Novel or Unusual Design Features
  • Discussion
  • Applicability
  • Conclusion
  • List of Subjects in 14 CFR Part 25
  • Authority Citation
  • The Special Conditions Enhanced Content - Table of Contents

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Department of Transportation

Federal Aviation Administration

1. 14 CFR Part 25
2. [Docket No. FAA-2026-1132; Special Conditions No. 25-887-SC]

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Final special conditions; request for comments.

SUMMARY:

These special conditions are issued for the Textron Model MU-300-10, 400, and 400A airplanes. These airplanes will have a novel or unusual design feature when compared to the state of technology envisioned in the airworthiness standards for transport-category airplanes. This design feature is an emergency lighting power supply containing rechargeable lithium batteries. The applicable airworthiness regulations do not contain adequate or appropriate safety standards for this design feature. These special conditions contain the additional safety standards that the Administrator considers necessary to establish a level of safety equivalent to those established by the existing airworthiness standards.

DATES:

This action is effective on Textron on March 18, 2026. Send comments on or before May 4, 2026.

ADDRESSES:

Send comments identified by Docket No. FAA-2026-1132 using any of the following methods:

• Federal eRegulations Portal: Go to www.regulations.gov and follow the online instructions for sending your comments electronically.
• Mail: Send comments to Docket Operations, M-30, U.S. Department of Transportation (DOT), 1200 New Jersey Avenue SE, Room W12-140, West Building Ground Floor, Washington, DC 20590-0001.
• Hand Delivery or Courier: Take comments to Docket Operations in Room W12-140 of the West Building Ground Floor at 1200 New Jersey Avenue SE, Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.
• Fax: Fax comments to Docket Operations at 202-493-2251. ( printed page 12916) Docket: Background documents or comments received may be read at www.regulations.gov at any time. Follow the online instructions for accessing the docket or go to Docket Operations in Room W12-140 of the West Building Ground Floor at 1200 New Jersey Avenue SE, Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

FOR FURTHER INFORMATION CONTACT:

Nazih Khaouly, Electrical Systems Unit, AIR-626A, Technical Policy Branch, Policy and Standards Division, Aircraft Certification Service, Federal Aviation Administration, 2200 S 216th Street, Des Moines, WA 98198-6547; telephone 206-231-3160; email nazih.khaouly@faa.gov.

SUPPLEMENTARY INFORMATION:

The substance of these special conditions has been published in the Federal Register for public comment in several prior instances with no substantive comments received. Therefore, the FAA finds, pursuant to 14 CFR 11.38(b), that new comments are unlikely, and notice and comment prior to this publication are unnecessary.

Privacy

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

Confidential Business Information

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 these special conditions contain commercial or financial information that is customarily treated as private, that you actually treat as private, and that is relevant or responsive to these special conditions, 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 the indicated comments will not be placed in the public docket of these special conditions. Send submissions containing CBI to the individual listed in the For Further Information Contact section above. Comments the FAA receives, which are not specifically designated as CBI, will be placed in the public docket for these proposed special conditions.

Comments Invited

The FAA invites interested people to take part in this rulemaking by sending written comments, data, or views. The most helpful comments reference a specific portion of the special conditions, explain the reason for any recommended change, and include supporting data.

The FAA will consider all comments received by the closing date for comments. The FAA may change these special conditions based on the comments received.

Background

On September 5, 2024, Textron applied for a change to Type Certificate No. A16SW for Textron MU-300-10, 400, and 400A airplanes. These airplanes, currently approved under Type Certificate No. A16SW, are twin-engine, transport-category business jets, with a maximum seating capacity for 9 passengers, and a maximum takeoff weight between 15,780 and 16,300 pounds, depending on model.

Type Certification Basis

Under the provisions of 14 CFR 21.101, Textron must show that changes to the Textron MU-300-10, 400, and 400A airplanes, continue to meet the applicable provisions of the regulations listed in Type Certificate No. A16SW or the applicable regulations in effect on the date of application for the change, except for earlier amendments as agreed upon by the FAA.

If the Administrator finds that the applicable airworthiness regulations (e.g., 14 CFR part 25) do not contain adequate or appropriate safety standards for the Textron Model MU-300-10, 400, and 400A airplanes because of a novel or unusual design feature, special conditions are prescribed under the provisions of § 21.16.

Special conditions are initially applicable to the model for which they are issued. Should the type certificate for that model be amended later to include any other model that incorporates the same novel or unusual design feature, or should any other model already included on the same type certificate be modified to incorporate the same novel or unusual design feature, these special conditions would also apply to the other model under § 21.101.

In addition to the applicable airworthiness regulations and special conditions, the Textron Model MU-300-10, 400, and 400A airplanes must comply with the exhaust-emission requirements of 14 CFR part 34, and the noise-certification requirements of 14 CFR part 36.

The FAA issues special conditions, as defined in 14 CFR 11.19, in accordance with 14 CFR 11.38, and they become part of the type certification basis under § 21.101.

Novel or Unusual Design Features

The Textron Model MU-300-10, 400, and 400A airplanes will incorporate the following novel or unusual design feature:

An emergency lighting power supply containing rechargeable lithium batteries.

Discussion

Rechargeable lithium batteries and battery systems are considered to be a novel or unusual design feature in transport-category airplanes, with respect to the requirements in § 25.1353. This type of battery has certain failure, operational, and maintenance characteristics that differ significantly from those of the nickel-cadmium and lead-acid rechargeable batteries currently approved for installation on transport-category airplanes. These batteries and battery systems introduce higher energy levels into airplane systems through new chemical compositions in various battery-cell sizes and construction. Interconnection of these cells in battery packs introduces failure modes that require unique design considerations, such as provisions for thermal management.

Special Condition 1 requires that each individual cell within a battery and battery system be designed to maintain safe temperatures and pressures. Special Condition 2 addresses these same issues but for the entire battery system.

Special Condition 2 requires that the batteries and battery system be designed to prevent propagation of a thermal event, such as self-sustained, uncontrolled increases in temperature or pressure from one cell to adjacent cells.

Special Conditions 1 and 2 are intended to ensure that the cells and battery system are designed to eliminate the potential for uncontrollable failures. However, a certain number of failures will occur due to various factors beyond the control of the designer. Therefore, other special conditions are intended to protect the airplane and its occupants if failure occurs. ( printed page 12917)

Special Conditions 3, 7, and 8 are self-explanatory.

Special Condition 4 clarifies that the flammable-fluid fire-protection requirements of § 25.863 apply to rechargeable lithium battery installations. § 25.863 is applicable to areas of the airplane that could be exposed to flammable fluid leakage from airplane systems. Rechargeable lithium batteries contain electrolyte that is a flammable fluid.

Special Condition 5 requires each rechargeable lithium battery and battery system installation to not damage surrounding structure or adjacent systems, equipment, or electrical wiring from corrosive fluids or gases that may escape in such a way as to cause a major or more severe failure condition.

Special Condition 6 requires each rechargeable lithium battery and battery system installation to have provisions to prevent any hazardous effect on airplane structure or systems caused by the maximum amount of heat it can generate due to any failure of it or its individual cells. The means of meeting special conditions 5 and 6 may be the same, but they are independent requirements addressing different hazards. Special Condition 5 addresses corrosive fluids and gases, whereas special condition 6 addresses heat.

Special Condition 9 requires rechargeable lithium batteries and battery systems to have “automatic” means, for charge rate and disconnect, due to the fast-acting nature of lithium battery chemical reactions. Manual intervention would not be timely or effective in mitigating the hazards associated with these batteries.

These special conditions apply to all rechargeable lithium batteries and battery system installations in lieu of § 25.1353(b)(1) through (4) at amendment 25-123, or § 25.1353(c)(1) through (4) at earlier amendments. Those regulations will remain in effect for other battery installations on these airplanes.

The special conditions contain the additional safety standards that the Administrator considers necessary to establish a level of safety equivalent to that established by the existing airworthiness standards.

Applicability

As discussed above, these proposed special conditions are applicable to Textron Model MU-300-10, 400, and 400A airplanes. Should Textron apply at a later date for a change to the type certificate to include another model incorporating the same novel or unusual design feature, these special conditions would apply to that model as well.

Conclusion

This action affects only a certain novel or unusual design feature on Textron Model MU-300-10, 400, and 400A airplanes. It is not a rule of general applicability.

List of Subjects in 14 CFR Part 25

• Aircraft
• Aviation safety
• Reporting and recordkeeping requirements

Authority Citation

The authority citation for these special conditions is as follows:

Authority: 49 U.S.C. 106(f), 40113, 44701, 44702, and 44704.

The Special Conditions

Accordingly, pursuant to the authority delegated to me by the Administrator, the following special conditions are issued as part of the type certification basis for Textron Model MU-300-10, 400, and 400A airplanes.

In lieu of Title 14, Code of Federal Regulations (14 CFR) 25.1353(b)(1) through (4) at amendment 25-123 or § 25.1353(c)(1) through (4) at earlier amendments, each rechargeable lithium battery installation must:

1. Be designed to maintain safe cell temperatures and pressures under all foreseeable operating conditions to prevent fire and explosion.

2. Be designed to prevent the occurrence of self-sustaining, uncontrollable increases in temperature or pressure, and automatically control the charge rate of each cell to protect against adverse operating conditions, such as cell imbalance, back charging, overcharging, and overheating.

3. Not emit explosive or toxic gases, either in normal operation or as a result of its failure, that may accumulate in hazardous quantities within the airplane.

4. Meet the requirements of § 25.863.

5. Not damage surrounding structure or adjacent systems, equipment, or electrical wiring from corrosive fluids or gases that may escape in such a way as to cause a major or more severe failure condition.

6. Have provisions to prevent any hazardous effect on airplane structure or systems caused by the maximum amount of heat it can generate due to any failure of it or its individual cells.

7. Have a failure sensing and warning system to alert the flightcrew if its failure affects safe operation of the airplane.

8. Have a monitoring and warning feature that alerts the flightcrew when its charge state falls below acceptable levels if its function is required for safe operation of the airplane.

9. Have a means to automatically disconnect from its charging source in the event of an over-temperature condition, cell failure or battery failure.

Note:

A battery system consists of the battery, battery charger and any protective, monitoring and alerting circuitry or hardware inside or outside of the battery. It also includes vents (where necessary) and packaging. For the purpose of this special condition, a battery and the battery system is referred to as a battery.

Issued in Forth Worth, Texas, on March 12, 2026.

Jorge R. Castillo,

Manager, Technical Policy Branch, AIR-620, Policy and Standards Division, Aircraft Certification Service.

[FR Doc. 2026-05264 Filed 3-17-26; 8:45 am]

BILLING CODE 4910-13-P

Published Document: 2026-05264 (91 FR 12915)