This paper describes the process used to analyse HF and safety issues in a new Air Traffic Management (ATM) procedure the Mediterranean Free Flight (MFF) Airborne Separation Assurance System (ASAS) applications. The paper describes: 1) the overall safety assessment process in MFF; 2) the human error analysis (HEA) method called TRACEr-lite; 3) the process of developing safety scenarios for simulations; and 4) the lessons learnt from the simulations using safety scenarios. By simulating hazardous events in ground-based simulations, it was possible to gain a greater understanding of the hazards in general, how hazards are detected and possible mitigation by discussing the issues with the air traffic controllers in debriefing sessions.