Complex sentence: Most company employees were placed on furlough and after an extensive rewrite of the company's operations manual the FAA granted an operating certificate for part 121 flight operations which was composed of jet service utilizing their BAC-111 aircraft.
Split into simpler sentences: Most company employees were placed on furlough and after an extensive rewrite of the company's operations manual the FAA granted an operating certificate for part 121 flight operations. Which was composed of jet service utilizing their BAC-111 aircraft.