This is the second of two papers on Quantitative Safety Assessment – vital to the successful introduction of future Air Traffic Management systems. The focus is en route European controlled commercial traffic, particularly the mid-air collision risk. Part 2 develops soundly based and practical methods for safety assessment. The objective is to determine the key questions and the best ways to answer them. Aspects covered include lessons from Hazard Analysis and Airproxes together with ‘realistic’ risk budgeting. Two abstract concepts are introduced: Position Integrity and Reasonable Intent (essentially the need to be on the ‘right’ flight path), and their implications for risk calculations are discussed.