Primary focus in aviation is on safety and reliability:

• Fail-operational instead of fail-safe.
• Widespread usage of redundancy and dissimilarity in system and component design.

Continued safe flight and landing (CSFL) at designated landing sites after any kind of failure has to be ensured. High priority on safe management of fire with high safety margins:

• Assumption of single-cell failure and demonstration of non-propagation under worst-case TR triggering condiftions
• Assumption of simultaneous multi-cell failure (20% of cells in a pack) and demonstration of safe management of resulting fire until landing.
• Demonstration of no fire after crash (drop from 15.2m – 62km/h impact on concrete surface).

Emphasis on battery weight instead of battery volume:

• Gravimetric energy density more important than volumetric.
• Higher importance of vehicle-level optimization instead of system-level optimization.

There are not yet fully finalized requirements for the certification of aviation propulsion batteries:

• SC-VTOL, the Special Condition under which eVTOLs can receive a Type Certificate by EASA, defines high-level objectives (the “What”, e.g. “no single failure catastrophic”, “safe management of fire”, “loss of life less than once every 1e9 flight hours”), but not what to do to achieve them or how they can be demonstrated to the authorities (the “How”, i.e. the Acceptable Means of Compliance (AMC)).
• Means of Compliance (MOC) are being currently developed and published by both regulators (EASA) and industry standardization bodies (EUROCAE, SAE) to answer this “How”.

Not everyone can develop and certify a battery system for use in aviation. Even if the final product passes all tests requested by the regulators for certification, it can not be used in a type certified aircraft unless:

• The technical experts of the certifying authority are supervising the development from the early stages of the project (Level of Involvement LOI).
• The certifying authority ensures that the company designing the system is following the required aviation development processes (Design Organization Approval DOA).
• The certifying authority ensures that the company manufacturing the system is following the required aviation manufacturing processes (Production Organization Approval POA).

These are two streams that run in parallel:

• Product development
• Certification

The company should hold a Design Organization Approval from the corresponding certification authority, ensuring that the required quality and development assurance processes are in place.

Product developement

• The product development process follows in general the V model as described in the standard ARP 4754A: Guidelines for Development of Civil Aircraft and Systems
• In order for the products to be able to be certified, their development has to follow certains standards:
• Hardware and software developemnt is done according to RTCA DO-178C: Software Considerations in Airborne Systems and Equipment Certification and RTCA DO-254: Design Assurance Guidance for Airborne Electronic Hardware
  
• Safety assessment is covered by ARP 4761: Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment
  
• Battery development and testing guidelines are defined in RTCA DO-311A: Minimum Operational Performance Standards for Rechargeable Lithium Batteries and Battery Systems, RTCA DO-160G: Environmental Conditions and Test Procedures for Airborne Equipment and various EUROCAE, SAE and ASTM standards currently under development
  
• Reviews like System Definition Review SDR, Preliminary Design Review PDR, Critical Design Review CDR, Test Readiness Review TRR and Flight Readiness Review FRR provide development gates.

Certification

• First, the certification basis has to be established, i.e. which high-level requirements the aircraft must fulfill, depending on it’s type. There is e.g. SC-VTOL for eVTOLs, CS-27/29 for helicopters or CS-23/25 for airplanes. SC-E19 for electric propulsion systems is also applicable in addition in the case of electric or hybrid aircraft. The applicant must find an agreement with the certification authorities about which of these requirements are applicable for their specific program.
• Based on this and the aircraft/systems design and specifications, the OEM creates Certification Plans (CP) for the aircraft and its systems, that describe how it will be shown that the systems fulfill each applicable certification requirement (Means of Compliance, i.e. which documents will be produced, which tests or analyses will be performed etc.), and what Level of Involvement the certification authorities will have in the compliance demonstration activities. The CP must be submitted and approved by the authorities.
• During the development of the components and systems, design descriptions, analysis documents, safety assessments, drawings, engineering tests etc. are created and properly documented. These are checked during the development review gates and partially submitted as compliance documents, as defined in the CP.
• When components or systems of the final design are ready, they are tested according to the CP. The certification authorities can witness any certification relevant test they wish and review any of the component’s development artifacts.
• After all test and development documentation, analysis reports etc. as defined in the CP have been collected, they are submitted to the authorities for approval and the Type Certificate is issued.

•  The Type Design Data that describes all aircrat components and their manufacturing and assembly processes are transferred to a Production Organization, which is a company allowed by the authorities to produce aircraft or aircraft components following the applicable quality management systems and ensuring that the aircraft or components produced during the lifetime of the program have the exact same properties as the aircraft or components that were tested during the certification process.