This paper provides a review of different possible strategies to compute meaningful states of an unmanned aerial vehicle (UAV) in the presence of sensor faults. The paper reviews some strategies that enable to compute useful outputs and to reconstruct sensor data when some sensor(s) become(s) deficient. In addition to a classical sensor suite for UAVs (IMU, GPS, barometer and airspeed sensor), the paper introduces the benefits of using visual aids for sensor-fault tolerance. Finally, the paper provides the reader with an overview schematic - discussed throughout the paper- in order to summarize some possible sensor fault-tolerant systems in UAVs.