Abstract: Object-Oriented Risk Assessment Methodology and Simulation Model (ORASM) combined the object-oriented analysis method with event tree analysis and discrete event simulation. By introduced the two response modes to event and probabilistic branch, the risk of the systems, in which events and their response are time dependent and are undetermined, can be assessed and simulated effectively by ORASM. It is applied to an aviation safety problem that considers mechanisms by which an aircraft might become involved in a runway incursion incident.