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The Future Flight Standards Hub is designed to accelerate the development of Future Flight demonstrators and wider industry innovation based on emerging best practice, knowledge sharing, and standards support.

  • 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 .

energy storage system (ESS)



  • Definition

    onboard system whose main function is to provide an aircraft with accessible energy for safe flight and landing


    NOTE 1 ESS components include, but are not limited to, battery modules, the associated battery management system (BMS) (3.1.29), and all the associated wires, cabling and connections/terminals.

    NOTE 2 The ESS includes a means by which limits are placed on accessible energy, e.g. due to cell temperature or state of charge, it also provides predictions of battery states with regard to the planned flight profile.

    NOTE 3 State of function (SOF) (3.1.127) and state of health (SOH) (3.1.128) are key inputs to the ESS.


    [SOURCE: EUROCAE, ED-289, Guidance on determination of accessible energy in battery systems for eVTOL applications [25]

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