Complex sentence: A pilot was on board the Learjet, but it flew autonomously as a surrogate aircraft uploaded with the X- 47B's technology; such surrogates are often used as stand-ins for unmanned aircraft.
Split into simpler sentences: A pilot was on board the Learjet, but it flew autonomously as a surrogate aircraft uploaded with the X- 47B's technology. Surrogates are often used as stand-ins for unmanned aircraft.