Control System Failure
Clearly, safe flight operations will require the control system to maintain adequate authority over the UAV at all times. Apart from failures due to hardware faults in the avionics, the most likely cause of control failure will be due to communications failures with the operators. Another common cause of accidents is running out of electrical power: if batteries are being used to support the avionics, particular care must be taken to ensure their condition before and during each flight, both in terms of their state of charge and also their overall health and ability to maintain charge. This will include making choices about capacity and battery chemistry to be used. We tend to avoid using LiPo-type batteries for control systems, preferring less power dense but more reliable types such as LiFe systems. At the initial design stage, the designer will wish to plan the desired degree of redundancy and resilience to control failures, so as to correctly budget for weight and cost impacts on the design.