Development of a safety assessment methodology for the risk of collision of an Unmanned Aircraft System with the ground

aircraft, UAS performance characteristics are examined. This helps to clarify in which airspace classes the different available UAS may be able to fly. This concerns the broad range of size, various configurations and different performance characteristics. Next, causal models are developed for 15 accident scenario that may result in a collision with the ground. These causal models are represented as Event Sequence Diagrams (ESDs) and Fault Trees (FTs), and provide a logical structure showing how hazards and causal factors could combine to cause a collision with the ground. This approach utilizes the Causal model for Air Transport Safety (CATS) developed for the Dutch Ministry of Transport. Five specific UAS related ESDs are added to cover UAS specific hazards that do not exist in manned aircraft operation. Using the twenty ESDs, a UAS accident probability model for the risk of collision with the ground is developed.