  Autonomous systems (AS) are systems that have the capability to take
decisions free from direct human control. AS are increasingly being considered
for adoption for applications where their behaviour may cause harm, such as
when used for autonomous driving, medical applications or in domestic
environments. For such applications, being able to ensure and demonstrate
(assure) the safety of the operation of the AS is crucial for their adoption.
This can be particularly challenging where AS operate in complex and changing
real-world environments. Establishing justified confidence in the safety of AS
requires the creation of a compelling safety case. This document introduces a
methodology for the Safety Assurance of Autonomous Systems in Complex
Environments (SACE). SACE comprises a set of safety case patterns and a process
for (1) systematically integrating safety assurance into the development of the
AS and (2) for generating the evidence base for explicitly justifying the
acceptable safety of the AS.
