A complex integration of personnel, equipment and information is required to maintain aviation operations. From an aircraft's regularly scheduled service, to a pilot-identified defect noted in the aircraft's flight log, to an aircraft that has been damaged in flight, aircraft maintenance personnel are the professionals responsible for returning the aircraft back to flight status. Aircraft became increasingly sophisticated up to and beyond World War II. However, some of the greatest advances in engineering occurred with the advent of the jet aircraft. Aircraft maintenance—which was basically airframes and engines—was left primarily up to the owners of the aircraft. Competency-based education (CBE) for maintenance professionals "came from the pilot side and they are ahead of the maintenance side. CBE has gained popularity, based on the consideration that instruction and experience can be targeted toward the generic and type-specific competence of the individual, rather than focused on hours completed.