I think there are lots of things that can fail in the hardware: electrical noise (standard stuff), radiation, metastability, etc. It's not just a bad speed signal... it's a valid speed signal but the software reading inconsistent states based on these errors, or having values change when they shouldn't, etc.
Drones are, in essence, flying autonomous vehicles. Pros and cons surrounding drones today might well foreshadow the debate over the development of self-driving cars. In the context of a strongly regulated aviation industry, "self-flying" drones pose a fresh challenge. How safe is it to fly drones in different environments? Should drones be required for visual line of sight – as are piloted airplanes? Join EE Times' Junko Yoshida as she moderates a panel of drone experts.