Optimization of Development Assurance Level Allocation

In the aeronautics domain, development errors may contribute to catastrophic failures and they shall be prevented by appropriate assurance activities. So the aeronautics standards propose Development Assurance Levels (DAL), which define the levels of development rigor applicable to functions, software or hardware items of an aircraft.The allocation of DALs to items follows rules. Basically, the DAL of each item shall be proportionate to the severity of the effects of the item development errors. Moreover, severe failures may results from a combination of independent development errors of several items. In such case, additional rules introduce the possibility to downgrade the DAL levels of the independent items. Thus, many DAL allocations are possible for a given system.Consequently, we have investigated means to assist the safety specialists when verifying or optimizing a DAL allocation. We propose a formalization of the DAL allocation as an optimization problem integrating user-defined constraints and cost criteria used to focus the exploration on most interesting allocations.Experimentation is conducted on large-scale aeronautics systems to highlight the scalability and benefits of our approach compared to the heuristic-based approach.

I. Introduction

In the aeronautics domain, systematic development errors may contribute to catastrophic events. To tackle this issue, the aeronautics standards ([1], [2]) propose to allocate a Development Assurance Level (DAL) indicating the level of rigor of the development of function, a software or hardware item of an aircraft. The DAL guides the assurance activities that should be applied at each stage of development to eliminate design errors that would have a safety effect on the aircraft.