The First ATC Support Tools Implementation (FASTI) Programme aims to offer improvements in safety, capacity and efficiency by implementing new automated tools to support controllers in their tasks of conflict detection, planning, monitoring and coordination. EUROCONTROLs role is to coordinate, harmonise and expedite the uptake of the FASTI system. ANSPs, supported by industry, will be responsible for implementing operational systems. EUROCONTROL has developed a Preliminary Safety Case (PSC) comprising an argument and evidence that the concept and high level design of FASTI (so far as these have been proposed by EUROCONTROL) could be safely put into operation. Each ANSP will need to undertake more detailed definition and design, taking account of their specific operational context and needs, and them carry out implementation, transition and operation. In parallel with this, ANSPs will need to develop the PSC into a full Safety Case, demonstrating operational safety, and providing a basis for licensing and auditing by national safety regulators. This document contains guidance to assist ANSPs in adapting and extending the PSC to produce a full Safety Case for their own implementations of FASTI.