INTRODUCTION AND PURPOSE OF DOCUMENT

This document contains guidance on the definition of lithium-ion cell failures, cell failure causes and materials level failure modes. It also informs on interdependencies between failure causes that may be considered when defining a verification and validation strategy for the cell, as defined in other cell related EUROCAE documents.

NOTE: Specific qualification testing is out of scope of this guidance.

How to use this document

The information provided in this document may be used by the applicant to support the different stages of a Safety Assessment, as per ED-79A/ARP4754A and ARP4761. Accordingly, a specific safety objective commensurate to the aircraft category must be met to ensure an acceptable level of safety for the Systems, Components and Equipment installed on the aircraft.

As such, each applicant must select and justify an allowable Qualitative Probability of failure for their installed equipment, i.e. the probability of more than one lithium-ion cell being unable to provide the required power/energy or entering thermal runaway within one flight as a result of the same failure mode. The system must be designed to meet the venting and failure containment requirements specific to the certification category.

This document contains considerations that may be made by the applicant when determining and evidencing a failure rate for the cell.

CHAPTER 2 describes failure causes by defining different types of limits for the cell that should be adhered to, to reduce the risk of initiating the associated failure modes. This Chapter also describes common interdependencies between different failure causes.

CHAPTER 3 describes cell failure modes, describes the effects that they have on the function of the cell and categorises each failure mode by failure condition, which is the worst-case failure type for the cell. This gives the applicant an indication of the level of risk that the failure mode poses to a cell upon exposure to a failure cause.

CHAPTER 4 describes how the failure effects described in CHAPTER 3 may progress. An example is given in Figure 1-3 alongside a general overview of the contents of the document.

The cell failure progression flow diagram in CHAPTER 4 also contains advisory information on the interdependencies between failure effects.