Preliminary Hazard Analysis
Preliminary hazard analysis (PHA) is performed to identify potential hazards that could cause an accident. Hazards are categorized according to their severity. A typical severity rating is shown below:
| Severity | Definition |
| Catastrophic | Results in multiple fatalities and/or loss of the system. The product becomes inoperative. |
| Hazardous | Reduces the capability of the system to deal with adverse operating conditions thereby causing serious or fatal injury to a small number of people. |
| Major | Reduces the capability of the system to cope with adverse operating conditions causing a significant reduction in safety margin,and physical distress or injuries to people. |
| Minor | Does not significantly reduce system safety, but may cause some physical discomfort to people. Minor environmental or property damage may occur. |
| No Effect | Has no effect on safety. |
The PHA should also consider the likelihood of occurrence, for example, marking hazards as probable, remote, extremely remote, or extremely improbable.
Examples of Dronology Hazards
The primary hazards associated with Dronology would be caused by midair collisions or by direct collisions with people and/or vehicles on the ground. For assigning likelihood of occurrence we consider the occurrence over hundreds of flights and not just a single flight.
| Hazard | Severity | Likelihood |
| UAS collides with a commercial airplane causing the plane to crash. | Catastrophic | Remote |
| UAS loses control and flies into moving traffic | Hazardous | Remote |
| UAS loses control and flies into a person (or people) on the ground | Major | Probable |
| Two or more UAS flying in a congested area collide – causing debris to fall to the ground | Major | Remote |
| UAS drops its payload | Major | Remote |
Learn how Hazards are used in the Failure Mode Effect Criticality Analysis here.