ASTM F3338-21

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: F3338 −21
Standard Specification for
Design of Electric Engines for General Aviation Aircraft
This standard is issued under the fixed designation F3338; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Rules”), refer to ASTM Committee F39 webpage
(www.ASTM.org/COMITTEE/F39.htm), which includes CAA
1.1 This specification covers minimum requirements for the
website links.
design of electric engines.
1.6 When applicable, this specification may be used for
1.2 Distributed propulsion is not excluded; however, addi-
electric engines with a fixed-pitch propeller or fan. These
tional requirements will be needed to address the additional
configurations may be type-certificated as an electric engine
issues that distributed propulsion can create. Some of those
including a thruster. There may be additional requirements not
issuesmayinclude:useofacommonmotorcontroller/inverter,
currently included in this specification for this type configura-
segregated electric harnesses, cooling systems, electric power
tion. In addition, 5.25 is included as a test requirement for the
supplies, and others.
electric engine. That section recognizes that when the electric
1.3 This specification does not address all of the require-
engine does not have an integral thruster it will need to be
ments that may be necessary for possible hybrid configurations
testedwitharepresentativeloadonthedriveshafttoensurethe
where an electric engine and a combustion engine drive a
engine’s ability to operate properly with static and dynamic
common thruster. This specification may be used for the
loads.
electric engine aspects with supplemental requirements for the
1.7 The values stated in inch-pound units are to be regarded
thruster and the combustion engine.
as standard. The values given in parentheses are mathematical
1.4 Although this specification does not include specific
conversions to SI units that are provided for information only
requirements for electric engines that include gearboxes,
and are not considered standard.
thrusters, or any energy storage systems, it also does not
1.8 This standard does not purport to address all of the
preclude such capabilities. This specification may be used for
safety concerns, if any, associated with its use. It is the
the base electric engine aspects of the design, with supplemen-
responsibility of the user of this standard to establish appro-
tal requirements for any additional features prepared by the
priate safety, health, and environmental practices and deter-
manufacturer and submitted to the CivilAirworthinessAuthor-
mine the applicability of regulatory limitations prior to use.
ity for acceptance. This version of this ASTM specification
1.9 This international standard was developed in accor-
also does not address all of the requirements necessary for
dance with internationally recognized principles on standard-
configurations of motor driven ducted-fans. It is anticipated
ization established in the Decision on Principles for the
that the fan would be subject to parts of 14 CFR 33 or CS-E
Development of International Standards, Guides and Recom-
and/or 14 CFR 35 or CS-P, or equivalent, in particular
mendations issued by the World Trade Organization Technical
blade-off and bird strike. These would be conducted on the fan
Barriers to Trade (TBT) Committee.
as a unit (including motor) rather than on motor or fan alone.
2. Referenced Documents
1.5 The applicant for a design approval should seek the
individual guidance of their respective civil aviation authority
2.1 ASTM Standard:
(CAA) body concerning the use of this specification as part of
F3060 Terminology for Aircraft
a certification plan. For information on which CAAregulatory
2.2 Code of Federal Regulations:
bodies have accepted this specification (in whole or in part) as
14 CFR 33 Airworthiness Standards: Aircraft Engines
a means of compliance to their general aviation aircraft
14 CFR 35 Airworthiness Standards: Propellers
airworthiness regulations (hereinafter referred to as “the
2.3 EASA Standards:
CS-E Engines
CS-P Propellers
ThisspecificationisunderthejurisdictionofASTMCommitteeF39onAircraft
Systems and is the direct responsibility of Subcommittee F39.05 on Design,
Alteration, and Certification of Electric Propulsion Systems. Available from U.S. Government Publishing Office (GPO), 732 N. Capitol St.,
Current edition approved Aug. 1, 2021. Published August 2021. Originally NW, Washington, DC 20401, http://www.gpo.gov.
approved in 2018. Last previous edition approved in 2020 as F3338–20. DOI: Available from European Aviation Safety Agency (EASA), Postfach 10 12 53,
10.1520/F3338-21. D-50452 Cologne, Germany, http://www.easa.europa.eu.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F3338 − 21
2.4 IEC Standards: 3.2.6 motor, n—a machine that converts electrical power
IEC 60034-1 Rotating electrical machines – Part 1 Rating into rotational mechanical power.
and performance
3.2.7 motor controller, n—a device or devices that serves to
IEC 60349-4 Electric traction – Rotating electric machines
manage the operation of an electric motor.
for rail and road vehicles – Part 4: Permanent magnet
3.2.7.1 Discussion—It could include a manual or automatic
synchronous electrical machines connected to an elec-
means for energizing, starting or stopping the motor, selecting
tronic converter
direction of rotation, selecting and regulating motor speeds,
2.5 SAE Standard:
regulating or limiting the torque, and protecting against over-
SAE J245 Engine-Rating Code~Spark Ignition
loads and faults.The inverter is often integrated with the motor
controller.
3. Terminology
3.2.8 rated maximum continuous power, n—with respect to
3.1 Terminology specific to this specification is provided
an electric engine, the approved brake power that is developed
below. For general terminology, refer to ASTM F3060, Stan-
statically or in flight, in standard atmosphere at a specified
dard Terminology for Aircraft.
altitude, within the engine operating limitations established
3.2 Definitions:
under CAA requirements, and approved for unrestricted peri-
3.2.1 duty types, n—
ods of use.
3.2.1.1 non-periodic duty, n—in which generally load and
3.2.8.1 Discussion—Brake power is defined in SAE J245 as
speed vary within the permissible operating range.
the power available at the flywheel or other output member(s)
3.2.1.2 periodic duty, n—comprising one or more loads for doing useful work.
remaining constant for the duration specified.
3.2.9 rated takeoff power, n—with respect to electric engine
3.2.2 electric engine, n—A type of aircraft engine that type certification, the approved brake horsepower that is
developedstaticallyunderstandardsealevelconditions,within
converts electric power into mechanical power or thrust used
for propulsion, including those components necessary for the engine operating limitations established under CAA
requirements, and limited in use to periods of not over 5 min
proper control and functioning.
3.2.2.1 Discussion—In the context of this specification, the for takeoff operation.
minimum essential components of an electric engine are an
3.2.10 shaft power, n—the brake power delivered at an
electric motor and its associated motor controller(s),
engine’s drive shaft.
disconnect(s), wiring, and sensor(s). Other components and
3.2.10.1 Discussion—References to electrical power are
accessories necessary for proper control and function are
called out as such.
typically considered part of the engine; for example: inverters,
3.2.11 thrust, n—The propulsive force generated by the
liquid cooling components, liquid lubrication components,
aircraft engine that is used to move an aircraft through the air.
thrusters, etc.
3.2.11.1 Discussion—As used in this specification, applies
3.2.3 energize, v—the act of connecting the electric engine
to endurance, durability, and systems tests.
to the electrical power source such that the engine enters a
3.2.12 thruster, n—as used in this specification, a device
ready state where throttle input results in shaft rotation.
such as propeller, rotor, or fan for translating mechanical/
De-energize is the opposite of energize.
rotational energy to thrust.
3.2.4 hazardous electric engine effects, n—the following
3.3 Abbreviations:
effects are regarded as hazardous electric engine effects:
3.3.1 EMI—electromagnetic interference
(1) Non-containment of high-energy debris;
3.3.2 HIRF—high-intensity radiated field
(2) Significant brake power in the opposite direction to that
commanded by the pilot;
4. Significance and Use
(3) Uncontrolled fire;
(4) Failure of the engine mount system leading to inadver- 4.1 This specification provides designers and manufacturers
tent engine separation; of electric propulsion for General Aviation aircraft references
(5) Release of the propeller or fan or any major portion of and criteria to use in designing and developing electric engines
the propeller or fan by the engine, if applicable; with the intent of gaining approval from a civil aviation
(6) Complete inability to shut the engine down; and authority.
(7) The serious or fatal injury to flight crew, passengers, or
4.2 Appendix X1 provides additional (but not necessarily
ground-handling personnel arising from electric shock.
all) information and guidance to meet certification or airwor-
3.2.5 inverter, n—a power electronic device or circuitry that
thiness requirements, or both, for a particular country or area
changes direct current (DC) to alternating current (AC). The
under the jurisdiction of a civil aviation authority.
motor controller is often integrated with the inverter.
5. Requirements in Support of Certification or Approval
Available from International Electrotechnical Commission (IEC), 3, rue de
5.1 Instructions for Continued Airworthiness:
Varembé, 1st Floor, P.O. Box 131, CH-1211, Geneva 20, Switzerland, http://
5.1.1 Instructions for the continued airworthiness of the
www.iec.ch.
electric engine must be prepared. The instructions may be
Available from SAE International (SAE), 400 Commonwealth Dr.,Warrendale,
PA 15096, http://www.sae.org. incomplete at the time of certification or approval:
F3338 − 21
5.1.1.1 If a program exists to ensure their completion prior (4) A list of the instruments necessary for the control and
to delivery of the first aircraft with the engine installed, or operation of the electric engine, including the overall limits of
accuracyandtransientresponserequirements,mustbestatedin
5.1.1.2 Upon CAAapproval for the aircraft with the engine
a manner that allows the satisfactory nature of instruments as
installed, whichever occurs later.
installed to be determined.
5.1.2 A maintenance manual shall be provided that defines
maintenance requirements for the continued airworthiness of
NOTE 1—“Instrument” is used to refer to any device necessary to
the engine, such as periodic installed maintenance, major
measure engine parameters and convey them to the appropriate decision-
making center, be that a pilot or software-based control.
inspections, repairs, replacement or overhaul intervals, and any
(5) Thelimitsonenvironmentalconditions,includingEMI,
other maintenance limitations including limited life compo-
HIRF, and lightning for which the engine was designed and
nents requiring replacement between overhaul intervals. Main-
qualified.
tenance requirements for the continued airworthiness of the
engine also includes special equipment or testing required to
5.2.1.2 Operating Instructions:
ensure the electrical propulsion system is safe to continued
(1) The operating limitations established within the show-
operation.
ing of compliance.
5.1.3 If applicable, an overhaul manual that provides in-
(2) The power ratings and procedures for correcting for
structions for disassembling, replacing, or overhauling compo-
nonstandard atmosphere.
nents identified in the manual for such, in order to return the
(3) The recommended procedures, under normal and criti-
enginetoairworthyconditionthatissafeforoperationuntilthe
cal ambient conditions for:
next major overhaul.
(a) Powering on;
5.1.4 Updates to the Instructions for Continued Airworthi- (b) Operating on the ground;
ness must be made available by the engine manufacturer or (c) Operating during flight.
other responsible party such that those instructions remain (4) A description of the primary and all alternate modes,
current. and any back-up system, together with any associated
limitations, of the engine control system and its interface with
5.2 Instruction Manual for Installing and Operating the
the aircraft systems, including the propeller or fan if these are
Electric Engine:
integral with the engine.
5.2.1 Instructions for installing and operating the engine
5.3 Electric Engine Operating Limitations and Ratings:
must be made available to the CAA as part of the certification
5.3.1 Ratings and operating limitations are established by
process and to the customer at the time of delivery. The
the administrator and included in the product certificate data
instructions must include directly, or by reference to appropri-
sheet, including ratings and limitations based on the operating
ate documentation, at least the following:
conditions and information specified in this section, as
5.2.1.1 Installation Instructions—Coordination is recom-
applicable, and any other information found necessary for safe
mended between the engine manufacturer and the installer.
operation of the engine.
However, if the installer is not identified at the time of the
5.3.2 Electric engine operating limitations are established as
engine design, the following aspects still need definition in the
applicable, including:
installation instructions.
5.3.2.1 Maximum transient overspeed and time;
(1) An outline drawing of the engine including overall
5.3.2.2 Maximum transient overtorque and time, and num-
dimensions.
ber of overtorque occurrences;
(2) Adefinition of the physical and functional interfaces of
5.3.2.3 Maximum overtorque and time;
all elements of the engine, with the aircraft and aircraft
5.3.2.4 Electrical power, voltage, current, frequency, and
equipment, including the propeller or fan, when applicable.
electrical power quality limits;
Including the location and description of the engine connec-
5.3.2.5 Maximum rated temperature(s);
tions for attachment of accessories, wires, cables, cooling
5.3.2.6 Maximum and minimum continuous temperature,
ducts, cowling, and any other equipment attached to the
current, voltage;
engine.
5.3.2.7 Vibration limits; and
(3) Where an electric engine relies on components that are
not part of the engine type design, the interface conditions and 5.3.2.8 Any other information necessary for safe operation
of the engine.
reliability requirements for those components, as used in the
safety analysis, must be specified in the engine installation 5.3.3 Electric engine ratings are established, as applicable,
and are based on the intended duty cycle and the assignment of
instructions. If reliability values used in the safety analysis are
based on assumptions, these assumed values must be specified ratings as defined below, including:
in the engine installation instructions. Requirements for miti- 5.3.3.1 Power, torque, speed, and time for:
gation means, that are not part of the engine, must be specified (1) Rated maximum continuous power, and
in the engine installation instructions and the engine operating (2) Rated maximum temporary power and associated time
instructions. limit.
F3338 − 21
5.3.4 Duty Cycle: 5.5.1 The design and construction of the engine and the
materials used must minimize the probability of the occurrence
5.3.4.1 Declaration of Duty—Theintendeddutycycleofthe
and spread of fire during normal operation and engine failure
motor of the electric engine sets the framework for establish-
conditions and must minimize the effect of such a fire. The
ment of the ratings. There are a number of typical duty cycles
engine high voltage electrical wiring interconnect systems
used for electric motors. (See IEC 60034-1.)As the duty cycle
should be protected against arc-faults. Any nonprotected elec-
combined with the rating at that duty cycle establishes the
trical wiring interconnects should be analyzed to show that arc
capability and the limits for the engine’s use, the manufacturer
faults do not cause a hazardous condition. If flammable fluids
declares the duty cycle or cycles. These can be based on the
are used, then this must be stated in any required installation
manufacturer’s intended use for the engine or may be based on
instructions so that consideration may be given (at the aircraft
the required duty cycle of the installer. As detailed in IEC
level) to determining if a fire zone must be established under
60034-1, multiple duties and their associated ratings may be
the associated aircraft certification rules.
established to address various operational conditions. The duty
may be described by one of the following:
5.6 Durability:
(1) Numerically, where the load does not vary or where it
5.6.1 Electric engine design and construction must mini-
varies in a known manner; or
mize the development of an unsafe condition of the engine
(2) As a time sequence graph of the variable quantities; or
between maintenance intervals, removal from service or over-
(3) By selecting one of the typical duty types in accordance
haul periods or mandated life defined in the Instructions for
with IEC 60034-1, Paragraph 4 Duty, that is no less onerous
Continued Airworthiness, as applicable.
than the expected duty.
5.7 Electric Engine Cooling:
5.3.5 Assignment of Rating—The rating, as defined by “set
of rated values and operating conditions,” shall be assigned by 5.7.1 Engine cooling shall be sufficient under all conditions
the manufacturer. In assigning the rating, the manufacturer
within the declared operational limitations to prevent compo-
shall select one of the classes of rating as defined in the IEC nent temperatures exceeding applicable limits.
60034-1 Paragraph 5 Ratings.
5.7.2 If aspects of the cooling require the installer to ensure
5.3.6 Motor Rate Output—The rated output is the mechani-
that the temperature limits are met, those limits shall be
cal power available at the shaft and shall be expressed in watts
specified in the installation manual.
(W).
5.7.3 Instrumentation or sensors shall be provided to enable
the flight crew or the automatic control system to monitor the
NOTE 2—It is the practice in some countries for the mechanical power
functioning of the engine cooling system unless appropriate
available at the shafts of motors to be expressed in horsepower (1 hp is
equivalent to 745,7W; 1 ch (cheval or metric horsepower) is equivalent to
inspections are published in the relevant manuals and evidence
736 W).
shows that:
5.7.3.1 Failure of the cooling system would not lead to
5.3.7 Machines with More Than One Rating—For machines
with more than one rating, the machine shall comply with this hazardous electric engine effects defined in 3.2.4 before detec-
specification in all respects at each rating. For multi-speed tion; or
machines, a rating shall be assigned for each speed. When a
5.7.3.2 Other existing instrumentation or sensors provides
ratedquantity(output,voltage,speed,etc.)mayassumeseveral
adequate warning of failure or impending failure; or
values or vary continuously within two limits, the rating shall
5.7.3.3 The probability of failure of the cooling system is
be stated at these values or limits.
extremely remote.
5.3.8 Each selected rating must be for the lowest power that
5.7.4 An electric engine with a liquid cooling system shall
all electric engines of the same type may be expected to
also meet the applicable requirements of 5.18.
produce under the conditions used to determine that rating at
5.8 Electric Engine Mounting Attachments and Structure:
all times between overhaul periods or other maintenance.
5.8.1 The maximum allowable limit and ultimate load for
5.4 Materials:
the integral engine mounting attachment points and related
5.4.1 Thematerialsandcomponentsusedintheenginemust
engine structure must be specified.
be established on the basis of industry or military specifica-
5.8.2 The engine mounting attachments and related engine
tion(s) for the intended design conditions of the system. The
structure must be able to withstand:
assumed design values of properties of materials must be
5.8.2.1 The specified limit loads without permanent defor-
suitably related to the minimum properties stated in the
mation; and
material specification. Otherwise, proof of suitability and
5.8.2.2 The specified ultimate loads without failure but
durability acceptable to the CAA must be established on the
allowing for permanent deformation.
basis of tests or other means that ensure their having the
strength and other properties assumed in the design data. 5.8.3 If flammable fluids are used within the electric engine,
the mounts and the mounting features must be demonstrated to
5.4.2 Manufacturingmethodsandprocessesmustbesuchas
be fireproof.
to produce sound structure and mechanisms, and electrical
systems that retain the design properties under reasonable
5.9 Electric Engine Rotor Overspeed:
service conditions. This includes the effects of corrosion.
5.9.1 The rotors must, including any integral fan rotors used
5.5 Fire Protection: for cooling:
F3338 − 21
5.9.1.1 Possess sufficient strength with a margin to burst 5.9.4.2 Failures external to the e-motor, and
above certified operating conditions and above failure condi- 5.9.4.3 Combinations of failures unless those combinations
tions leading to rotor overspeed, and
can be shown to be extremely remote.
5.9.5 Growth—In addition, each engine rotor must comply
5.9.1.2 Do not exhibit a level of growth or damage that
could lead to a hazardous electric engine effect. with 5.9.5.1 and 5.9.5.2 of this section for the maximum
overspeed achieved when subjected to the conditions specified
5.9.2 Burst—For each rotor of the electric engine, it must be
in 5.9.3 of this section. It must be established using the
established by test, analysis, or a combination of both, that
approach in 5.9.2 of this section that specifies the required test
eachrotorwillnotburstwhensubjectedtotheanalysisandtest
conditions.
conditions in accordance with IEC 60349, Part 4, or an
5.9.5.1 Rotor growth must not cause the motor operation to
equivalent standard.
lead to a hazardous electric engine effect.
5.9.2.1 Unless otherwise specified in IEC 60349, Part 4, test
5.9.5.2 Following an overspeed event and after continued
rotors used to demonstrate compliance with this section that do
operation, the rotor may not exhibit conditions such as crack-
not have the most adverse combination of material properties
ing or distortion, which preclude continued safe operation.
and dimensional tolerances must be tested at conditions which
5.9.6 Controls—The design and functioning of engine con-
have been adjusted to ensure the minimum specification rotor
trolsystems,instruments,andothermethodsnotcoveredunder
possesses the required overspeed capability. This can be
5.10 must ensure that the engine operating limitations that
accomplished by increasing test speed, temperature, or loads,
or combinations thereof. affect rotor structural integrity will not be exceeded in service.
5.9.7 Shaft Failure—Failure of a shaft section may be
5.9.2.2 When an electric engine test is being used to
excluded from consideration in determining the highest over-
demonstratecompliancewiththeoverspeedconditionslistedin
speed that would result from a complete loss of load on a rotor
5.9.3 of this section and the failure of a component or system
if it can be shown that:
is sudden and transient, it may not be possible to operate the
5.9.7.1 The shaft is identified as an engine life-limited-part
electric engine for 5 min after the failure. Under these
and complies with 5.15.
circumstances, the actual overspeed duration is acceptable if
5.9.7.2 Theengineusesmaterialanddesignfeaturesthatare
the required maximum overspeed is achieved as required by
IEC 60349-4. well understood and that can be analyzed by well-established
and validated stress analysis techniques.
5.9.3 Max Overspeed—When determining the maximum
5.9.7.3 It has been determined, based on an assessment of
overspeedconditionapplicabletoeachrotorinordertocomply
the environment surrounding the shaft section, that environ-
with 5.9.2 of this section, the evaluation must include the test
mental influences are unlikely to cause a shaft failure. This
conditions as specified in IEC 60034-1 and the following:
assessment must include complexity of design, corrosion,
5.9.3.1 One hundred twenty percent of the maximum per-
wear, vibration, fire, contact with adjacent components or
missible rotor speed associated with any continuous, periodic,
structure, overheating, and secondary effects from other fail-
or non-periodic duty rating, including ratings for short time
ures or combination of failures.
duty.
5.9.7.4 It has been identified and declared, in accordance
5.9.3.2 One hundred fifteen percent of the maximum no-
with 5.2, any assumptions regarding the engine installation in
load speed associated with any continuous, periodic, or non-
making the assessment described above in 5.9.7.3 of this
periodic duty rating, including ratings for short time duty.
section.
5.9.3.3 One hundred five percent of the highest rotor speed
5.9.7.5 It has been assessed, and considered as appropriate,
that would result from either:
experience with shaft sections of similar design.
(1) The failure of the component or system which, in a
5.9.7.6 The entire shaft has not been excluded.
representative installation of the engine, is the most critical
5.9.7.7 Rationale is provided that the e-motor electrody-
with respect to overspeed when operating at any continuous,
namic principle yields intrinsic safety against uncontrollable
periodic, or non-periodic duty rating, including ratings for
overspeed in case of rotor shaft failure.
short time duty.
5.9.8 Use of Analysis—If analysis is used to meet the
(2) The failure of any component or system in a represen-
overspeed requirements, then the analytical tool must be
tative installation of the engine, in combination with any other
validated to prior overspeed test results of a similar rotor. The
failure of a component or system that would not normally be
tool must be validated for each material. The rotor being
detected during a routine pre-flight check or during normal
certified must not exceed the boundaries of the rotors being
flight operation, that is the most critical with respect to
used to validate the analytical tool in terms of geometric shape,
overspeed, except as provided by 5.9.4 of this section, when
operating stress, and temperature. Validation includes the
operating at any continuous, periodic, or non-periodic duty
ability to accurately predict rotor dimensional growth and the
rating, including ratings for short time duty.
burst speed. The predictions must also show that the rotor
5.9.4 Loss of Load—Thehighestoverspeedthatresultsfrom
being certified does not have lower burst and growth margins
a complete loss of load on an engine rotor, must be determined
than rotors used to validate the tool.
and included in the overspeed conditions considered by 5.9.3
of this section. The complete loss of load must also consider:
5.10 Electric Engine Controls:
5.9.4.1 Demagnetization in combination with excessive ex- 5.10.1 The software and complex electronic hardware, in-
ternal torque imposed (propeller induced no-load overspeed), cluding programmable logic devices, shall be designed and
F3338 − 21
developed using a structured and methodical approach that 5.10.4.3 Thereisameanstosignaltheaircrafttotakeaction
provides a level of assurance for the logic, that is commensu- or monitor the control transition.The means to alert the aircraft
rate with the hazard associated with the failure or malfunction mustbedescribedintheinstallationinstructions,andtheaction
of the systems in which the devices are located, and is or monitoring required must be described in the engine
substantiated by a verification methodology acceptable to the operating instructions.
CAA. 5.10.4.4 The magnitude of any change in power and the
associated transition time must be identified and described in
5.10.2 Applicability—These requirements are applicable to
the engine installation instructions and the engine operating
any system or device that controls, limits, monitors, or protects
instructions.
the engine operation, and is necessary for the continued
airworthiness of the engine. If items that influence the engine 5.10.5 Electric Engine Control System Failures—The en-
system are outside of the engine manufacturer’s control, the gine control system must:
assumptions with respect to the reliability and functionality of
5.10.5.1 Have a maximum rate of Loss of Power Control
these parts must be clearly stated in the safety analysis (see
(LOPC) events that is consistent with the intended application;
5.19).
5.10.5.2 Be, in the full-up configuration (that is, with no
5.10.3 Validation: currently active faults), essentially single fault tolerant, as
determined by the CAA, for electrical, electrically detectable,
5.10.3.1 Functional Aspects—It must be substantiated by
and electronic failures with respect to LOPC events;
tests,analysis,oracombinationthereof,thattheenginecontrol
5.10.5.3 Not have single failures that result in hazardous
system performs the intended functions in a manner which:
electric engine effect(s); and
(1) Enables selected values of relevant control parameters
to be maintained and the engine kept within the approved 5.10.5.4 Nothavelikelyfailuresormalfunctionsthatleadto
operating limits over changing atmospheric conditions in the local events in the intended aircraft installation, such as arcing,
declared flight envelope; fire, overheat, or other failures that result in a hazardous
(2) Complies with the operability requirements of opera- electric engine effect due to an engine control system’s failure
tion and power response tests, as appropriate, under all likely or malfunction.
system inputs and allowable engine power demands, unless it
5.10.6 System Safety Assessment—This assessment must
can be demonstrated that failure of the control function results
identify faults or failures that affect normal operation together
in a nondispatchable condition in the intended application;
with the predicted frequency of occurrence of these faults or
(3) Allows modulation of the engine output power with
failures.
adequate sensitivity over the declared range of engine operat-
5.10.7 Protection Systems:
ing conditions; and
5.10.7.1 The design and functioning of the engine control
(4) Does not create unacceptable power oscillations.
devices and systems, together with the engine instruments and
5.10.3.2 Environmental Limits—Environmental limits that operating and maintenance instructions, must provide reason-
cannot be adequately substantiated in accordance with endur-
able assurance that those engine operating limitations that
ance testing must be demonstrated, by means of electric engine affect the structural integrity of the rotating parts, or the
systemandcomponenttests(see5.13).Thesetestsdemonstrate
electrical integrity of the engine electrical system will not be
that the engine control system functionality will not be exceeded in service.
adversely affected by declared environmental conditions, in-
5.10.7.2 When electronic overspeed protection systems are
cluding electromagnetic interference (EMI), High Intensity
provided, the design must include a means for testing, at least
RadiatedFields(HIRF),andlightning,whenapplicable,forthe
once per engine start/stop cycle, to establish the availability of
intended use.The limits to which the system has been qualified
the protection function. The means must be such that a
must be documented in the engine installation instructions.
complete test of the system can be achieved in the minimum
5.10.4 Control Transitions—It must be demonstrated that number of cycles. If the test is not fully automatic, the
during both normal operation or as a result of fault or failure, requirement for a manual test must be contained in the engine
changes in one control mode to another, from one channel to operating instructions.
another, or from a primary system to a back-up system, the
5.10.7.3 When overspeed protection is provided through
change occurs so that: hydromechanical or mechanical means, it must be demon-
strated by test or other acceptable means that the overspeed
5.10.4.1 The engine does not exceed any of its operating
function remains available between inspection and mainte-
limitations;
nance periods.
5.10.4.2 The engine does not experience any unacceptable
5.10.8 Aircraft-supplied Data—Single failures leading to
operating characteristics or transient exceedances of any limit
loss, interruption or corruption of aircraft-supplied data (other
potentially leading to unsafe operating conditions. Such non-
than power command signals from the aircraft), or data shared
acceptable operating characteristics include but are not limited
between independent electrodynamic systems within a single
to:
engine or fully independent engine systems must:
(1) Field excitation at rotor resonance frequency,
5.10.8.1 Not result in a hazardous electric engine effect for
(2) Electromagnetic lock-up (stall),
any electric engine; and
(3) Unacceptable power changes or oscillations, and
(4) Other unacceptable characteristics, for example, elec- 5.10.8.2 Be detected and accommodated. The accommoda-
trical arcs, overspeed, or overtorque. tion strategy must not result in an unacceptable change in
F3338 − 21
power or an unacceptable change in engine operating charac- 5.13.1 For those systems and components that cannot be
teristics. The effects of these failures on engine power and on adequately substantiated in accordance with endurance testing,
engine operating characteristics throughout the declared oper- additional tests must be conducted to demonstrate that systems
ating envelope and operational environment must be evaluated or components are able to perform the intended functions in all
and documented in the engine installation instructions. declared environmental and operating conditions.
5.10.9 Electric Engine Control System Electrical Power: 5.13.2 Temperature limits must be established for each
component that requires temperature-controlling provisions in
NOTE 3—The historic basis for this section was to address the use of
the aircraft installation to assure satisfactory functioning,
aircraft supplied electrical power to the engine control system in addition
reliability, and durability.
to the use of a dedicated electrical power source, very typically an engine
5.13.3 Voltage and current limits must be established for
driven permanent magnet alternator (PMA). The aircraft supplied electri-
cal power was most often used as a backup to the PMA electrical power.
each component that requires voltage or current controlling
provisions, or both, in the aircraft installation to assure
5.10.9.1 The engine control system must be designed such
satisfactory functioning, reliability, and durability.
that the loss, malfunction, or interruption of the engine control
system electrical power source will not result in any of the
5.14 Stress Analysis:
following:
5.14.1 A mechanical stress analysis, to show complete
(1) A hazardous electric engine effect, or
understanding of the operating conditions that limit the design,
(2) The unacceptable transmission of erroneous data, or
must be performed on each engine showing the design safety
(3) The continued operation, running of the engine in the
margin of each rotor, stator, and housing of the electric engine.
absence of the control function.
5.14.2 An electrical stress analysis must be performed on
5.10.9.2 The primary electrical power source for the engine
each engine showing the electrical design safety margin of
control system must have sufficient capacity to ensure its
each electrical component above 220 VAC or 48 VDC.
operation at least as long as the electric engine when using all
5.14.3 Testing would be a suitable means of compliance
possible engine electrical power sources.
with the “stress analysis” requirement, if it can be shown that
5.10.9.3 If any electrical power is supplied from the aircraft
all of the limiting conditions have been tested.
to the engine control system for powering on and operating the
5.15 Electric Engine Life Limited Parts and Critical Parts:
engine, the need for and the characteristics of this electrical
5.15.1 The manufacturer should determine whether the
power, including transient and steady state voltage limits, must
rotating/moving components, bearing, shafts, nonredundant
be identified and declared in the engine installation instruc-
mount components should be critical parts or life-limited parts,
tions.
as defined below:
5.10.10 Electric Engine Shut Down Means—Means must be
5.15.1.1 A “critical part” is a part whose primary failure
provided for shutting down the engine rapidly.
could cause a hazardous effect, but whose failure mechanisms
5.11 Instrument or Sensor Connection:
are limited to high cycle fatigue or overload such that the part
is not required to be removed by a certain number of flight
5.11.1 Provisions must be made for the installation of
cycles, engine operating hours, etc.
instrumentation or sensors necessary to ensure engine opera-
tion within all operating limitations. 5.15.1.2 A“life-limited part” is a critical part whose failure
mechanisms include low-cycle fatigue, creep, or other mecha-
5.11.2 The instrument or sensor connections must be de-
nisms such that the part must be removed after accumulating a
signed or labeled to ensure a correct connection.
certain number of flight cycles, operating hours, etc. to ensure
5.11.3 Any instrumentation on which the Safety Analysis
an acceptable level of safety. Electric engine life-limited parts
(see 5.19) depends must be specified and declared mandatory
may include, but are not limited to, rotating/moving
in the engine installation instructions and approval documen-
components, bearings, shafts, nonredundant mount
tation.
components, high-voltage electrical components or the entire
5.11.4 The sensors, together with their data transmission
engine.
hardware and signal conditioning, must be segregated electri-
5.15.2 Requirements for Critical Parts—The integrity of
cally and physically to the extent necessary, to ensure that the
each critical part identified by the safety analysis must be
probability of a fault propagating from instrumentation and
established by:
monitoring functions to control functions, or vice versa, is
5.15.2.1 A defined engineering process for ensuring the
consistent with the failure effect of the fault.
integrity of the critical part throughout its service life,
5.12 Vibration—The engine must be designed and con-
5.15.2.2 Adefined manufacturing process that identifies the
structed to function throughout its normal operating range of
requirements to consistently produce the critical part as re-
rotor speeds and engine output power without inducing exces-
quired by the engineering process, and
sive stress in any of the engine parts because of vibration and
5.15.2.3 A defined service management process that identi-
without imparting excessive vibration forces to the aircraft
fies the continued airworthiness requirements of the critical
structure. In addition to historical sources of vibration such as
part as required by the engineering process.
aerodynamic excitation, analysis of rotating component reso-
5.15.3 Requirements for Life-limited Parts—Operating limi-
nance induced by field-excitation, should also be assessed,
tations must be established by an approved procedure that
5.13 Electric Engine System and Component Tests: specifies the maximum allowable number of flight cycles for
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each life-limited part. The manufacturer will establish the The safety of these means shall be analyzed and demonstrated
integrity of each life-limited part by: nottointroduceadditionalhazardsincaseofmalfunctioningor
5.15.3.1 An engineering plan that contains the steps re- inadvertent operation.
quired to ensure each life-limited part is withdrawn from
5.18 Pressure Loads—All static parts subject to significant
service at an approved life before hazardous effects can occur.
gas or liquid pressure loads for a stabilized period of 1 min
These steps include validated analysis, test, or service experi-
shall not:
ence which ensures that the combination of loads, material
5.18.1 Exhibitpermanentdistortionbeyondserviceablelim-
properties, environmental influences and operating conditions,
its or exhibit leakage that could create a hazardous condition
including the effects of other parts influencing these
when subjected to the greater of the following pressures: (1)
parameters, are sufficiently well known and predictable so that
1.1 times the maximum working pressure; (2) 1.33 times the
the operating limitations can be established and maintained for
normal working pressure; or (3) 5 psi (35 kPa) above the
each life-limited part. Manufacturers must perform appropriate
normal working pressure.
damage tolerance assessments to address the potential for
5.18.2 Exhibit fracture or burst when subjected to the
failure from material, manufacturing, and service induced
greaterofthefollowingpressures: (1)1.15timesthemaximum
anomalies within the approved life of the part. Manufacturers
possible pressure; (2) 1.5 times the maximum working pres-
mustpublishalistoflife-limitedpartsandtheapprovedlifefor
sure; or (3) 5 psi (35 kPa) above the maximum possible
each part in the Airworthiness Limitations section of the
pressure.
Instructions for Continued Airworthiness.
5.18.3 Compliance with this subsection must take into
5.15.3.2 A manufacturing plan that identifies the specific
account: (1) The operating temperature of the part; (2) Any
manufacturing constraints necessary to consistently produce
other significant static loads in addition to pressure loads; (3)
each life-limited part with the attributes required by the
Minimumpropertiesrepresentativeofboththematerialandthe
engineering plan.
processes used in the construction of the part; and (4) Any
5.15.3.3 A service management plan that defines in-service
adverse geometry conditions allowed by the type design.
processesformaintenanceandthelimitationstorepairforeach
5.19 Safety Analysis:
life-limited part that will maintain attributes consistent with
5.19.1 The engine design must be analyzed, including the
those required by the engineering plan. These processes and
control system, to assess the likely consequences of all failures
limitations will become part of the Instructions for Continued
that can reasonably be expected to occur. This analysis will
Airworthiness.
include, if applicable:
5.15.3.4 Subsections 5.15.1 through 5.15.3 do not apply if
5.19.1.1 Aircraft-level devices and procedures assumed to
the manufacturer can show that a failed hub, rotor, or blade
be associated with a typical installation. All assumptions must
retention component will not create debris with sufficient
be stated in the analysis.
energy to penetrate the thruster or e-motor casing, and pro-
5.19.1.2 Secondary failures and latent failures that have
vided all contained failures are assigned a severity of major or
engine level consequences.
less. However, energy levels and trajectories of fragments
5.19.1.3 Multiple failures referred to in 5.19.4 of this
resulting from a failed hub, rotor, or blade retention component
section or that result in the hazardous electric engine effects
that lie outside the duct must be defined.
defined in 3.2.4.
5.16 Lubrication System—The lubrication system of the
5.19.2 Failures that could result in major electric engine
enginemustbedesignedandconstructedsothatitwillfunction
effects or hazardous elect
...