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[Federal Register Volume 81, Number 128 (Tuesday, July 5, 2016)]
[Rules and Regulations]
[Pages 43469-43471]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2016-15765]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 23

[Docket No. FAA-2015-5034; Special Conditions No. 23-273-SC]

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

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued 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 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: These special conditions are effective July 5, 2016 and are 
applicable on June 23, 2016.

FOR FURTHER INFORMATION CONTACT: Ruth Hirt, Federal Aviation 
Administration, Small Airplane Directorate, Aircraft Certification 
Service, Programs and Procedures Branch, ACE-114, 901 Locust, Room 301, 
Kansas City, MO 64106; telephone (816) 329-4108, facsimile (816) 329-
4090.

SUPPLEMENTARY INFORMATION:

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 plans 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 (Ni-Cd) and lead-
acid rechargeable batteries currently approved in other normal, 
utility, acrobatic, and commuter category airplanes. Therefore, the FAA 
is issuing 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

[[Page 43470]]

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 Ni-Cd and lead-acid rechargeable 
batteries currently approved in other normal, utility, acrobatic, and 
commuter category airplanes. Therefore, the FAA is issuing 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 plans 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-C179a,\1\ 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.
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    \1\ http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgTSO.nsf/0/A3B77A692AE3FF9386257885004B079C?OpenDocument.
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    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 Ni-Cd 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 Ni-Cd batteries.
    3. Flammability of Cell Components: Unlike Ni-Cd 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 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 neither hazardous nor unreliable.
    In showing compliance with the special conditions herein, 
paragraphs (a)(1) through (a)(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.

Discussion of Comments

    Notice of proposed special conditions No. 23-15-01-SC \2\ for the 
Kestrel Aircraft Company Model K-350 Turboprop airplanes was published 
in the Federal Register on November 4, 2015 (80 FR 68281). No comments 
were received, and the special conditions are adopted as proposed.
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    \2\ https://www.regulations.gov/#!documentDetail;D=FAA-2015-
5034-0001.
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Applicability

    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 
Model K-350 airplanes. These special conditions apply only to 
rechargeable lithium batteries and lithium battery systems and their 
installations. The requirements of Sec.  23.1353 at amendment 23-62 
remains in effect for batteries and battery installations on K-350 
series that do not use newly technologically developed batteries.
    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.
    Under standard practice, the effective date of final special 
conditions would be 30 days after the date of publication in the 
Federal Register; however, as the certification date for the Kestrel 
Aircraft Company Model K-350 Turboprop airplane is imminent, the FAA 
finds that good cause exists to make these special conditions effective 
upon issuance.

Conclusion

    This action affects only certain novel or unusual design features 
on one model of airplane. It is not a rule of general applicability and 
it affects only the applicant who applied to the FAA for approval of 
these features on the airplane.

List of Subjects in 14 CFR Part 23

    Aircraft, Aviation safety, Signs and symbols.

Citation

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

    Authority: 49 U.S.C. 106(g), 40113 and 44701; 14 CFR 21.16 and 
21.17; and 14 CFR 11.38 and 11.19.

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 Kestrel Aircraft Company, Model K-350 
Turboprop airplanes.
    1. Kestrel Aircraft Company, Model K-350 Turboprop, Lithium 
Batteries.
    The FAA issues special conditions that adopt the following 
requirements that must be applied to all rechargeable lithium battery 
and lithium battery installations in lieu of the requirements of Sec.  
23.1353(a)(b)(c)(d)(e), amendment 23-62:
    (a) Rechargeable lithium batteries and battery installations must 
be designed and installed as follows:
    (1) Safe cell temperatures and pressures must be maintained 
during--

[[Page 43471]]

    i. normal operations;
    ii. any probable failure conditions of charging or discharging or 
battery monitoring system; or
    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 
that 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;
    ii. a battery temperature sensing and over-temperature warning 
system with a means of automatically disconnecting the battery from its 
charging source in the event of an over-temperature condition; and
    iii. a battery failure sensing and warning system with a means of 
automatically disconnecting the battery from its charging source in the 
event of battery failure.
    (b) 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.
    (c) 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 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.

    Issued in Kansas City, Missouri, on June 23, 2016.
William Schinstock,
Acting Manager, Small Airplane Directorate Aircraft Certification 
Service.
[FR Doc. 2016-15765 Filed 7-1-16; 8:45 am]
BILLING CODE 4910-13-P
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