UAV Crash Course

NASA released a report on UAV mishaps, Crash Course:
Lessons Learned from Accidents Involving Remotely Piloted and Autonomous Aircraft

The findings echo decades of flight operations experience: mishaps are usually the result of a "chain" of circumstances that individually would probably not cause a problem. Here's NASA's description of Crash Course:

This volume contains an investigation of remotely piloted research vehicle (RPRV) and unmanned aircraft system (UAS) mishaps and will examine their causes, consequences, resultant corrective actions, and lessons learned. Most undesired outcomes usually do not occur because of a single event, but rather from a series of events and actions involving equipment malfunctions and/or human factors. This book comprises a series of case studies focusing mostly on accidents and incidents involving experimental aircraft. The information provided should be of use to flight-test organizations, aircraft operators, educators, and students, among others. These lessons are not unique to the UAS environment and are also applicable to human aviation and space flight activities. Common elements include crew resource management, training, mission planning issues, management and programmatic pressures (e.g., schedule, budget, resources), cockpit/control station design, and other factors.