  In the last few years, Unmanned Aerial Vehicles (UAVs) are making a
revolution as an emerging technology with many different applications in the
military, civilian, and commercial fields. The advent of autonomous drones has
initiated serious challenges, including how to maintain their safe operation
during their missions. The safe operation of UAVs remains an open and sensitive
issue since any unexpected behavior of the drone or any hazard would lead to
potential risks that might be very severe. The motivation behind this work is
to propose a methodology for the safety assurance of drones over the Internet
{(Internet of drones (IoD))}. Two approaches will be used in performing the
safety analysis: (1) a qualitative safety analysis approach, and (2) a
quantitative safety analysis approach. The first approach uses the
international safety standards, namely ISO 12100 and ISO 13849 to assess the
safety of drone's missions by focusing on qualitative assessment techniques.
The methodology starts with hazard identification, risk assessment, risk
mitigation, and finally, draws the safety recommendations associated with a
drone delivery use case. The second approach presents a method for the
quantitative safety assessment using Bayesian Networks (BN) for probabilistic
modeling. BN utilizes the information provided by the first approach to model
the safety risks related to UAVs' flights. An illustrative UAV crash scenario
is presented as a case study, followed by scenario analysis, to demonstrate the
applicability of the proposed approach. These two analyses, qualitative and
quantitative, enable { all involved stakeholders} to detect, explore and
address the risks of UAV flights, which will help the industry to better manage
the safety concerns of UAVs.
