  With the rising popularity of UAVs in the civilian world, we are currently
witnessing and paradim shift in terms of operational safety of flying vehicles.
Safe and ubiquitous human-system interaction shall remain the core requirement
but those prescribed in general aviation are not adapted for UAVs. Yet we
believe it is possible to leverage the specific aspects of unmanned aviation to
meet acceptable safety requirements. We start this paper with by discussing the
new operational context of civilian UAVs and investigate the meaning of safety
in light of this new context. Next, we explore the different approaches to
ensuring system safety from an avionics point of view. Subsets of operational
requirements such as geofencing or mechanical systems for termination or impact
limitation can easily be implemented. These are presented with the goal of
limiting the collateral damages of a system failure. We then present some
experimental results regarding two of the major problems with UAVs. With actual
impacts, we demonstrate how dangerous uncontrolled crashes can be. Furthermore,
with the large number of runaway drone experiences during civilian operations,
the risk is even higher as they can travel a long way before crashing. We
provide data on such a case where the software controller is working, keeping
the UAV in the air, but the operator is unable to actually control the system.
It should be terminated! Finally, after having analyzed the context and some
actual solutions, based on a minimal set of requirement and our own experience,
we are proposing a simple mechanical based safety system. It unequivocally
terminates the flight in the most efficient way by instantly removing parts of
the propellers leaving a minimal lifting surface. It takes advantage of what
controllability may remain but with a deterministic ending: a definite landing.
