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  • BSI Flex 1903 v2:2024-06 community preview

    This is an interactive version 2 of BSI Flex 1903. The aim of the standard is to create a lexicon of standard terms and acronyms used in this sector. Please note, content is still undergoing internal review and there may be minor changes at full publication.

    We welcome your engagement and comments on this version to help inform the development of the standard. We would also welcome general feedback including what terms could be considered for future versions and these can be made through our dedicated feedback page .

Terms and definitions

3.1 Terms and definitions
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A

  1. autonomous charging  

    ability of an aircraft to connect to a charging station, then initiate, monitor and complete the charging process without human intervention   NOTE 1  For an” eVTOL” (3.1.70) , this requires charging infrastructure which may be available, for example, at a “vertiport (VPT)” (3.1.143) NOTE 2 Human intervention remains possible during the charging process.
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  2. ampere-hour (AH)  

    unit for the quantity of electrical capacity obtained by integrating current in amperes over time in hours and used as a measure of battery capacity   [SOURCE: RTCA, RTCA DO-311A, Minimum operational performance standards for rechargeable lithium batteries and battery systems] [9]
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  3. assurance  

    planned and systematic actions necessary to provide adequate confidence a product, service or functional system conforms to and an organization complies with an applicable standard or acceptable means of compliance
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  4. automated  

    allocation of a task or operation, which might have previously been executed manually, to automation in whole or in part
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  5. autonomous  

    independently determined (system) operations, when there is no predefined rule(s) to achieve the goals/objectives set for that system
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  6. autonomous operation  

    operation during which an uncrewed aircraft operates without the remote pilot being able to intervene NOTE The terms “ autonomy” (3.1.24) and “autonomous operation” have different meanings. An autonomous operation defines a type of operation utilizing autonomy to the extent that the human is out of the loop [see human-out-of-the-loop (3.1.89). [SOURCE: UK Regulation (EU) 2019/947, modified “unmanned” replaced with “uncrewed”] [13]  
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  7. autonomy  

    characteristic of a system represented by a scale that describes the level of human oversight and control of the system   NOTE 1 Autonomy can be enabled by increasing the amount of automation of a task. This might involve AI-based development techniques. NOTE 2 The terms “autonomy” and “autonomous operation” (3.1.23) have different meanings. An autonomous operation defines a type of operation utilizing autonomy to the extent that the human is out of the loop [see human-out-of-the
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B

  1. battery cell  

    single electrochemical unit which exhibits a voltage across its two terminals and is used as the elementary unit of a battery module (3.1.30) or battery system (3.1.32)      [SOURCE: EASA, Third publication of means of compliance with the Special Condition VTOL] [14]
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  2. battery thermal management system (BTMS)  

    system designed to regulate and control the temperature of a battery, or for modularized batteries, the battery module, in order to optimize its performance, enhance safety and extend its lifespan   NOTE Components of a battery thermal management system include, but are not limited to, temperature sensing and monitoring, cooling and heating systems, thermal insulation and thermal control algorithms.
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  3. battery thermal runaway  

    thermal runaway of two cells that thermally affect at least one common adjacent third cell within the same battery or, for modularized batteries, within the same module; or thermal runaway of any three or more cells within the same battery or, for modularized batteries, within the same module   [SOURCE: EASA, Third publication of means of compliance with the Special Condition VTOL] [14]
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  4. battery system  

    assembly of electrically interconnected battery modules (modularized battery) or cells in series and/or parallel, plus any protective, monitoring, alerting circuitry or hardware inside or outside of the battery, its packaging, and the designed venting provisions   [SOURCE: EASA, Third publication of means of compliance with the Special Condition VTOL] [14]
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  5. battery power density  

    amount of power that a battery can deliver per unit of volume or mass, providing an indication of how quickly a battery can be charged or discharged   NOTE 1 Power density of a battery is typically measured in watts per unit volume or mass, e.g. watts per kilogram. NOTE 2 High power density in batteries is desirable for applications that require rapid charging and discharging. NOTE 3 Power density is distinct from energy density, which is more relevant for applications that p
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  6. battery module  

    group of electrically interconnected cells in series and/or parallel arrangement contained in a single enclosure that ensures that no fluids, flames, gasses, smoke, or fragments enter other modules, and that no thermal runaway is propagated from one module to the others during normal operation or failure conditions   [SOURCE: EASA, Third publication of means of compliance with the Special Condition VTOL] [14]
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  7. battery management system (BMS)  

    electronic system designed to monitor, manage and control the individual battery cells within a battery system (3.1.32)   NOTE 1 BMS components include, but are not limited to, cell monitoring sensors, control algorithms, communication interfaces, safety features, and thermal management systems. NOTE 2 The BMS is a critical component of the energy storage system (ESS) (3.1.69). NOTE 3 While the BMS is focused on the management of individual cells within a battery system, the 
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  8. battery energy density  

    amount of energy that a battery can store per unit of volume or mass, providing an indication of the capacity of a battery to store electrical energy   NOTE 1 Energy density of a battery is typically measured in watt-hours per unit volume or mass, e.g. watt-hours per kilogram. NOTE 2 High energy density is desirable for applications that require a compact and lightweight energy storage solution with a large capacity. NOTE 3 Energy density is distinct from power density, which
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  9. battery energy  

    energy content expressed in watt-hours (Wh) and defined as the nominal battery voltage (V) times the capacity in ampere-hours (Ah) (3.1.14)   [SOURCE: RTCA, RTCA DO-311A, Minimum operational performance standards for rechargeable lithium batteries and battery systems [9]
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  10. battery  

    electrochemical energy storage system   [SOURCE: EASA, Third publication of means of compliance with the Special Condition VTOL] [14]
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C

  1. conventional take-off and landing (CTOL) capability aircraft  

    aircraft where either the safe lift-off and touchdown forward speed exceeds 45 knacross the ground, or the maximum forward speed for emergency touchdown exceeds 60 kn across the ground   NOTE 1 All VTOL-capable aircraft (3.1.143) are able to take-off and land vertically. Some also have the additional capability to take-off or land as conventional aeroplanes, accelerating and/or decelerating on a runway. NOTE 2 CTOL aircraft design conditions include additional, more stringent cons
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  2. continuing airworthiness  

    set of processes by which an aircraft, remote pilot station, engine, propeller or part conforms to the applicable airworthiness requirements and remains in a condition for safe operation throughout its operating life   NOTE 1 “Remote pilot station” is synonymous with the term “command unit”, which is more commonly used in the UK and EU. NOTE 2 In the context of airworthiness, “part” refers to any element of a product, as defined by that product’s type design, and “product” refers
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  3. certificate of airworthiness (CofA)  

    document issued by the aircraft’s state of registry when satisfied that an aircraft conforms to an approved design and is in a condition for safe operation   NOTE With regard to UAS (3.1.137) the complete system is required to conform to its type design and be in a condition for safe operation.
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  4. cell thermal runaway  

    rapid self-sustained heating of a battery cell (3.1.26) driven by exothermic chemical reactions of the materials within the cell   [SOURCE: EASA, Third publication of means of compliance with the Special Condition VTOL] [14]
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  5. C rate  

    measure used to express the rate at which a battery is charged or discharged in relation to its capacity   NOTE 1 For example, if a battery has a useful capacity of 10 ampere-hours (Ah), and its C rate is 1C, it can be charged or discharged at a rate of 10 amperes. If the C rate is 2C, it can be charged or discharged at a rate of 20 amperes and so on. NOTE 2 C rates are commonly used in the context of lithium-ion batteries and other rechargeable battery technologies. NOTE 3 C
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  6. cycle life  

    number of complete charge and discharge cycles that a rechargeable battery can undergo before its capacity significantly degrades    
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D

  1. depth of discharge (DOD)  

    percentage of a battery’s capacity that has been discharged relative to its maximum capacity NOTE DOD is typically expressed as a percentage value (0%–100%).  
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E

  1. energy storage device (ESD)  

    device that stores some form of energy that can be drawn upon at a later time to perform some useful operation   NOTE Energy storage devices include, but are not limited to, batteries, fuel cells and capacitors.   [SOURCE: ASTM, F2840-14: Standard practice for design and manufacture of electric propulsion units for light sport aircraft] [24]
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