Rule2026-05264
Special Conditions: Textron Aviation Inc. (Textron) Model MU-300-10, 400, 400A Airplanes; Rechargeable Lithium Batteries and Battery System Installations
Primary source
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Published
March 18, 2026
Effective
March 18, 2026
Issuing agencies
Transportation DepartmentFederal Aviation Administration
Abstract
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.
Full Text
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<title>Federal Register, Volume 91 Issue 52 (Wednesday, March 18, 2026)</title>
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[Federal Register Volume 91, Number 52 (Wednesday, March 18, 2026)]
[Rules and Regulations]
[Pages 12915-12917]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2026-05264]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. FAA-2026-1132; Special Conditions No. 25-887-SC]
Special Conditions: Textron Aviation Inc. (Textron) Model MU-300-
10, 400, 400A Airplanes; Rechargeable Lithium Batteries and Battery
System Installations
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final special conditions; request for comments.
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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:
<bullet> Federal eRegulations Portal: Go to <a href="http://www.regulations.gov">www.regulations.gov</a> and
follow the online instructions for sending your comments
electronically.
<bullet> 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.
<bullet> 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.
<bullet> Fax: Fax comments to Docket Operations at 202-493-2251.
[[Page 12916]]
Docket: Background documents or comments received may be read at
<a href="http://www.regulations.gov">www.regulations.gov</a> 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
<a href="/cdn-cgi/l/email-protection#93fdf2e9fafbbdf8fbf2fce6ffead3f5f2f2bdf4fce5"><span class="__cf_email__" data-cfemail="1f717e6576773174777e706a73665f797e7e31787069">[email protected]</span></a>.
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 <a href="http://www.regulations.gov">www.regulations.gov</a>, 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 Sec. 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 Sec. 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 Sec. 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 Sec. 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.
[[Page 12917]]
Special Conditions 3, 7, and 8 are self-explanatory.
Special Condition 4 clarifies that the flammable-fluid fire-
protection requirements of Sec. 25.863 apply to rechargeable lithium
battery installations. Sec. 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 Sec.
25.1353(b)(1) through (4) at amendment 25-123, or Sec. 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 Sec. 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 Sec. 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
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</html>Indexed from Federal Register on March 18, 2026.
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