## 2 Materials and Methods  
SORA is the methodology for the risk assessment to support an application for authorization to operate a UAS within a specific category. It was created and developed by JARUS (Joint Authorities for Rulemaking on Unmanned Systems). SORA aims to help the safe creation, evaluation, and conduction of UAS operations and to provide a sufficient level of confidence that a specific operation can be conducted safely [41, 42]. As noted by the authors of SORA, this method is not intended as a one-stop-shop for full integration of all type of drones in all classes of airspace. Like risk analysis methods, there are many different ways to reduce the risk. Their choice should depend on the type of UAV operation performed and its place. The methods of risk mitigation themselves can be classified differently. SORA, distinguishing operational safety objectives (OSO), groups them as follows:  
* Technical issue with the UAS (OSO # 1-OSO # 10);
* Deterioration of external systems supporting UAS operation (OSO # 11-OSO # 13);
* Human error (OSO # 14-OSO # 20);
* Adverse operating conditions (OSO # 21-OSO # 24). The list of OSOs is not exhaustive or comprehensive, so is, therefore, a solid starting point to determine further and next OSOs. Due to the time horizon of the introduction of the mitigations, SORA divides them into:* Tactical mitigations which aim to reduce the probability of mid-air collision, applicable during missions, allowing for reactions from a few seconds to several minutes (for instance: detect and avoid sensors, TCAS, ADS-B, FLARM, trackers, dynamic geofencing, active communication with ATC and other airspace users);
* Strategic mitigations which aim to reduce the probability violations of operational volume by other airspace users, applicable before missions, allowing for reactions from a few days to several weeks (for instance: operational time frame--day or night, flight in zones, atypical/segregated airspace, geocaching). Inspired by the troubleshooting and risk-management model 5M (Machine, Man, Mission, Management, Medium) used in aviation accident investigation, mitigation methods may be classified into one of the following groups [43; 44]:  
* Machine--type of vehicle, additional equipment, Ground Control Station, reliability, continuing airworthiness, technical documentation, and safety devices;
* Man--any person involved in an operation, training, competency, division of tasks, and assignment of responsibilities;
* Mission--the purpose of the flight, tasks, and difficulty level;
* Management--operational instructions, checklists, procedures, legal bases, activity supervision, and control;
* Medium--meteorological conditions, natural environment, topography, and time of day. Another model, which is used in aviation risk management and incident investigation, is the SHELL model [45]. It is focused on the relation between the human factor and other workplace components, which have an impact on it. The model consists of:  
* Software;
* Hardware;
* Environment;
* Liveware. As can be seen, these two different methods have lots of similarities, and differ in the level of generality of the classification of factors. One of the similarities between the two methods is their relationship with the UAV operator. It is a very key element of an unmanned aerial vehicle operation. The operator is responsible for the performance of activities such as:  
* Execution and use of a checklist;
* Use of observers with adequate communication;
* Operations performed by qualified operators with appropriate authorizations;
* Performing operations in specific weather conditions;
* Checking the manned air traffic;
* Checking the availability of airspace;
* Hardware knowledge. The neglect of the above activities can lead to accidents and unsafe situations involving unmanned aerial vehicles. One often overlooked operational element is the checklist--a list of elements that should be checked before commencing an air operation.