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[Federal Register Volume 80, Number 213 (Wednesday, November 4, 2015)]
[Proposed Rules]
[Pages 68281-68284]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2015-28125]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 23

[Docket No. FAA-2015-5034; Notice No. 23-15-01-SC]

Special Conditions: Kestrel Aircraft Company, Model K-350 
Turboprop, Lithium Batteries

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed special conditions.

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SUMMARY: This action proposes special conditions for the Kestrel 
Aircraft Company, Model K-350 Turboprop airplane. This airplane will 
have a novel or unusual design feature associated with the installation 
of a rechargeable lithium battery. The applicable airworthiness 
regulations do not contain adequate or appropriate safety standards for 
this design feature. These proposed 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.

DATES: Send your comments on or before December 21, 2015.

ADDRESSES: Send comments identified by docket number FAA-2015-5034 
using any of the following methods:
    [squ] Federal eRegulations Portal: Go to http://www.regulations.gov 
and follow the online instructions for sending your comments 
electronically.
    [squ] 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.
    [squ] 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.
    [squ] Fax: Fax comments to Docket Operations at 202-493-2251.
    Privacy: The FAA will post all comments it receives, without 
change, to http://regulations.gov, including any personal information 
the commenter provides. Using the search function of the docket Web 
site, anyone can find and read the electronic form of all comments 
received into any FAA docket, including the name of the individual 
sending the comment (or signing the comment for an association, 
business, labor union, etc.). DOT's complete Privacy Act Statement can 
be found in the Federal Register published on April 11, 2000 (65 FR 
19477-19478), as well as at http://DocketsInfo.dot.gov.
    Docket: Background documents or comments received may be read at 
http://www.regulations.gov at any time. Follow the online instructions 
for accessing the docket or go to the 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: Ruth Hirt, Federal Aviation 
Administration, Small Airplane Directorate, Aircraft Certification 
Service, 901 Locust; Kansas City, Missouri 64106; telephone (816) 329-
4108; facsimile (816) 329-4090.

SUPPLEMENTARY INFORMATION: 

Comments Invited

    We invite 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. We ask 
that you send us two copies of written comments.
    We will consider all comments we receive on or before the closing 
date for comments. We will consider comments filed late if it is 
possible to do so without incurring expense or delay. We may change 
these special conditions based on the comments we receive.

[[Page 68282]]

Background

    On November 22, 2011, Kestrel Aircraft Company applied for a type 
certificate for their new Model K-350. The Kestrel Aircraft Company 
Model K-350 is a single-engine turboprop airplane with the primary 
structure constructed largely of carbon and epoxy composite material. 
The turboprop engine will be a Honeywell Model TPE331-14GR-801KT that 
is integrated with a Hartzell 4 bladed, 110-inch carbon composite 
propeller. The standard seating configuration offers a one plus five 
cabin (one pilot and five passengers). Alternate interior 
configurations will be available from two seats (cargo configuration) 
up to eight seats total. The K-350 will incorporate an integrated 
avionics system, retractable landing gear, and a conventional tail 
configuration.
    Specifications expected for the K-350 include the following:

 Maximum altitude: 31,000 Feet
 Maximum cruise speed: 320 Knots True Air Speed
 Maximum takeoff weight: 8,900 Pounds
 Maximum economy cruise: 1,200 Nautical Miles

    The K-350 will be certified for single-pilot operations under part 
91 and part 135 operating rules. The following operating conditions 
will be included:

 Day and Night Visual Flight Rules
 Instrument Flight Rules
 Flight Into Known Icing (Phase B certification)

    Kestrel Aircraft Company proposes to utilize a rechargeable lithium 
Main Battery on their new Model K-350 turboprop airplane. The current 
regulatory requirements for part 23 airplanes do not contain adequate 
requirements for the application of rechargeable lithium batteries in 
airborne applications. This type of battery possesses certain failure 
and operational characteristics with maintenance requirements that 
differ significantly from that of the nickel cadmium and lead acid 
rechargeable batteries currently approved in other normal, utility, 
acrobatic, and commuter category airplanes. Therefore, the FAA is 
proposing this special condition to require that (1) all 
characteristics of the rechargeable lithium batteries and their 
installation that could affect safe operation of the K-350 are 
addressed, and (2) appropriate Instructions for Continued Airworthiness 
that include maintenance requirements are established to ensure the 
availability of electrical power from the batteries when needed.

Type Certification Basis

    Under the provisions of 14 CFR 21.17, Kestrel Aircraft Company must 
show that the K-350 meets the applicable provisions of part 23, as 
amended by amendments 23-1 through 23-62 thereto.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., 14 CFR part 23) do not contain adequate or 
appropriate safety standards for the K-350 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 or similar 
novel or unusual design feature, the special conditions would also 
apply to the other model under Sec.  21.101.
    In addition to the applicable airworthiness regulations and special 
conditions, the K-350 must comply with the fuel vent and exhaust 
emission requirements of 14 CFR part 34 and the noise certification 
requirements of 14 CFR part 36, and the FAA must issue a finding of 
regulatory adequacy under Sec.  611 of Public Law 92-574, the Noise 
Control Act of 1972.
    The FAA issues special conditions, as defined in 14 CFR 11.19, in 
accordance with Sec.  11.38, and they become part of the type-
certification basis under Sec.  21.17(a)(2).

Novel or Unusual Design Features

    The K-350 will incorporate the following novel or unusual design 
feature: Installation of a rechargeable lithium battery as the Main or 
Engine Start aircraft battery.

Discussion

    The current regulatory requirements for part 23 airplanes do not 
contain adequate requirements for the application of rechargeable 
lithium batteries in electrical system design. This type of battery 
possesses certain failures with operational characteristics and 
maintenance requirements that differ significantly from that of the 
nickel cadmium and lead acid rechargeable batteries currently approved 
in other normal, utility, acrobatic, and commuter category airplanes. 
Therefore, the FAA is proposing this special condition to require that 
(1) all characteristics of the rechargeable lithium batteries and their 
installation that could affect safe operation of the K-350 are 
addressed, and (2) appropriate Instructions for Continuous 
Airworthiness which include maintenance requirements are established to 
ensure the availability of electrical power from the batteries when 
needed.
    As previously mentioned, Kestrel Aircraft Company proposes to 
utilize a rechargeable lithium Main Battery on their new Model K-350 
turboprop airplane. At the Kestrel Preliminary Type Certification Board 
Meeting it was brought to the attention of the FAA that the Lithium 
battery used in the K-350 will be qualified to RTCA standards DO-311, 
titled Minimum Operational Performance Standards for Rechargeable 
Lithium Battery Systems. Additionally, on July 18, 2013, Kestrel 
advised the Civil Aviation Contingency Operations (CACO) that the 
battery will have Technical Standard Order Authorization for TSO C-
179a, titled Permanently Installed Rechargeable Lithium Cells, 
Batteries and Battery Systems. Finally, Kestrel plans to use the same 
manufacturer for both the lithium battery and the battery controller.
    Presently, there is limited experience with use of rechargeable 
lithium batteries in applications involving commercial aviation. 
However, other users of this technology, ranging from wireless 
telephone manufacturers to the electric vehicle industry, have noted 
safety problems with lithium batteries. These problems include 
overcharging, over-discharging, and flammability of cell components, 
described in the following:
    1. Overcharging: In general, lithium batteries are significantly 
more susceptible to internal failures that can result in self-
sustaining increases in temperature and pressure (i.e., thermal 
runaway) than the nickel-cadmium or lead-acid counterparts. This is 
especially true for overcharging which causes heating and 
destabilization of the components of the cell, leading to the formation 
(by plating) of highly unstable metallic lithium. The metallic lithium 
may ignite, resulting in a fire or explosion. Finally, the severity of 
thermal runaway due to overcharging increases with increasing battery 
capacity and physical size.
    2. Over-discharging: Discharge of some types of lithium battery 
cells beyond a certain voltage (typically 2.4 volts) can cause 
corrosion of the electrodes of the cell, resulting in loss of battery 
capacity that cannot be reversed by recharging. This loss of capacity 
may not be detected by the simple voltage measurements commonly 
available to flight crews as a means of checking battery status, which 
is a problem shared with nickel-cadmium batteries.

[[Page 68283]]

    3. Flammability of Cell Components: Unlike nickel-cadmium and lead-
acid batteries, some types of lithium batteries use liquid electrolytes 
that are flammable. The electrolyte may serve as a source of fuel for 
an external fire, if there is a breach of the battery container.
    These problems experienced by users of lithium batteries raise 
concern about the use of these batteries in commercial aviation. The 
intent of the proposed special condition is to establish appropriate 
airworthiness standards for lithium battery installations in the K-350 
and to ensure, as required by Sec. Sec.  23.1309 and 23.601, that these 
battery installations are not hazardous or unreliable.

Applicability

    As previously discussed, these special conditions are applicable to 
the K-350. Should Kestrel Aircraft Company apply at a later date for a 
change to the type certificate to include another model incorporating 
the same novel or unusual design feature, the special conditions would 
apply to that model as well.

Conclusion

    This action affects only certain novel or unusual design features 
on one model of airplane. It is not a rule of general applicability.

List of Subjects in 14 CFR Part 23

    Aircraft, Aviation safety, Signs and symbols.

0
The authority citation for these special conditions is as follows:

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

The Proposed Special Conditions

0
Accordingly, the Federal Aviation Administration (FAA) proposes the 
following special conditions as part of the type certification basis 
for Kestrel Aircraft Company, Model K-350 Turboprop airplanes.
    1. Kestrel Aircraft Company, Model K-350 Turboprop, Lithium 
Batteries.
    The FAA proposes special conditions that adopt the following 
requirements:
    (a) The flammable fluid fire protection requirement is Sec.  
23.863. In the past, this rule was not applied to batteries of normal, 
utility, acrobatic, and commuter category airplanes since the 
electrolytes utilized in lead-acid batteries and nickel-cadmium 
batteries are not flammable.
    (b) New Instructions for Continuous Airworthiness that include 
maintenance requirements to ensure that batteries used as spares have 
been maintained in an appropriate state of charge and installed lithium 
batteries have been sufficiently charged at appropriate intervals. 
These instructions must also describe proper repairs, if allowed, and 
battery part number configuration control.
    (c) The applicant must conduct a system safety assessment for the 
failure condition classification of a failure of the battery charging 
and monitoring functionality (per Advisory Circular 23.1309-1E), and 
develop mitigation to preclude any adverse safety effects. Mitigation 
may include software, Airborne Electronic Hardware (AEH) or a 
combination of software and hardware, which should be developed to the 
appropriate Design Assurance Level(s) (DALs), respectively (per 
Advisory Circular 20-115C and Advisory Circular 20-152).
    (d) New requirements, listed in paragraph (e), address the hazards 
of overcharging and over-discharging that are unique to lithium 
batteries, which should be applied to all rechargeable lithium battery 
and battery installations on the Model K-350 airplane in lieu of the 
requirements of Sec.  23.1353(a)(b)(c)(d)(e), amendment 23-62.
    Note 1: These special conditions are not intended to replace Sec.  
23.1353(a)(b)(c)(d)(e) at amendment 23-62 in the certification basis of 
airplane K-350 series airplanes. These special conditions apply only to 
rechargeable lithium batteries and lithium battery systems and their 
installations. The requirements of Sec.  25.1353 at amendment 23-62 
remains in effect for batteries and battery installations on K-350 
series that do not use newly technologically developed batteries.
    (e) Rechargeable lithium batteries and battery installations on the 
Model K-350 airplane must be designed and installed as follows:
    (1) Safe cell temperatures and pressures must be maintained 
during--
    i. Normal operations;
    ii. Any probable failure conditions of charging or discharging or 
battery monitoring system;
    iii. Any failure of the charging or battery monitoring system not 
shown to be extremely remote.
    (2) The rechargeable lithium battery installation must be designed 
to preclude explosion or fire in the event of (e)(1)(ii) and 
(e)(1)(iii) failures.
    (3) Design of the rechargeable lithium batteries must preclude the 
occurrence of self-sustaining, uncontrolled increases in temperature or 
pressure.
    (4) No explosive or toxic gasses emitted by any rechargeable 
lithium battery in normal operation or as the result of any failure of 
the battery charging system, monitoring system, or battery installation 
which is not shown to be extremely remote, may accumulate in hazardous 
quantities within the airplane.
    (5) Installations of rechargeable lithium batteries must meet the 
requirements of Sec.  23.863(a) through (d) at amendment 23-34.
    (6) No corrosive fluids or gases that may escape from any 
rechargeable lithium battery may damage surrounding structure or any 
adjacent systems, equipment, electrical wiring, or the airplane in such 
a way as to cause a major or more severe failure condition, in 
accordance with Sec.  23.1309(c) at amendment 23-62 and applicable 
regulatory guidance.
    (7) Each rechargeable lithium battery installation must have 
provisions to prevent any hazardous effect on structure or essential 
systems that may be caused by the maximum amount of heat the battery 
can generate during a short circuit of the battery or of its individual 
cells.
    (8) Rechargeable lithium battery installations must have--
    i. A system to automatically control the charging rate of the 
battery to prevent battery overheating and overcharging, or;
    ii. A battery temperature sensing and over-temperature warning 
system with a means for automatically disconnecting the battery from 
its charging source in the event of an over-temperature condition, or;
    iii. A battery failure sensing and warning system with a means for 
automatically disconnecting the battery from its charging source in the 
event of battery failure.
    (9) Any rechargeable lithium battery installation functionally 
required for safe operation of the airplane must incorporate a 
monitoring and warning feature that will provide an indication to the 
appropriate flight crewmembers whenever the State of Charge (SOC) of 
the batteries has fallen below levels considered acceptable for 
dispatch of the airplane.
    (10) The Instructions for Continued Airworthiness required by Sec.  
23.1529 at amendment 23-26 must contain maintenance requirements to 
assure that the battery has been sufficiently charged at appropriate 
intervals specified by the battery manufacturer and the equipment 
manufacturer that contain the rechargeable lithium battery or 
rechargeable lithium battery system. This is required to ensure that 
lithium rechargeable batteries and lithium rechargeable battery systems 
will not degrade below specified ampere-hour

[[Page 68284]]

levels sufficient to power the aircraft system. The Instructions for 
Continued Airworthiness must also contain procedures for the 
maintenance of replacement batteries in spares storage to prevent the 
installation of batteries that have degraded charge retention ability 
or other damage due to prolonged storage at a low state of charge. 
Replacement batteries must be of the same manufacturer and part number 
as approved by the FAA.
    Note 2: The term ``sufficiently charged'' means that the battery 
will retain enough of a charge, expressed in ampere-hours, to ensure 
that the battery cells will not be damaged. A battery cell may be 
damaged by lowering the charge below a point where there is a reduction 
in the ability to charge and retain a full charge. This reduction would 
be greater than the reduction that may result from normal operational 
degradation.
    (11) In showing compliance with the proposed special conditions 
herein, paragraphs (e)(1) through (e)(8), and the RTCA document, 
Minimum Operational Performance Standards for Rechargeable Lithium 
Battery Systems, DO-311, may be used. The list of planned DO-311 tests 
should be documented in the certification or compliance plan and agreed 
to by the CACO. Alternate methods of compliance other than DO-311 tests 
must be coordinated with the directorate and CACO.

    Issued in Kansas City, Missouri, on October 28, 2015.
Robert Busto,
Acting Manager, Small Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 2015-28125 Filed 11-3-15; 8:45 am]
 BILLING CODE 4910-13-P
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