  This paper addresses efficient feasibility evaluation of possible emergency
landing sites, online navigation, and path following for automatic landing
under engine-out failure subject to turbulent weather. The proposed Multi-level
Adaptive Safety Control framework enables unmanned aerial vehicles (UAVs) under
large uncertainties to perform safety maneuvers traditionally reserved for
human pilots with sufficient experience. In this framework, a simplified flight
model is first used for time-efficient feasibility evaluation of a set of
landing sites and trajectory generation. Then, an online path following
controller is employed to track the selected landing trajectory. We used a
high-fidelity simulation environment for a fixed-wing aircraft to test and
validate the proposed approach under various weather uncertainties. For the
case of emergency landing due to engine failure under severe weather
conditions, the simulation results show that the proposed automatic landing
framework is robust to uncertainties and adaptable at different landing stages
while being computationally inexpensive for planning and tracking tasks.
