The transformation from conventional hydro mechanical control system to modern digital control represents a revolutionary change with new capabilities, easy operation and lesser workload. Full Authority Digital Engine Control (FADEC) is a system consisting of digital computer known as Electronic Control Unit (ECU) with auxiliary components for controlling aircraft engine and propeller. It is produced for both piston engines and jet engines. The term Full Authority indicates that there is no manual override available, thus placing full authority over operating features to the computer. This technology with a characteristic feature of single lever control runs the engine in optimal condition with less consumption of fuel by controlling power and adjusting amount of fuel injection during the process of combustion. The basic objective is to give optimum efficiency for given flight condition. It manages starting phase and further engine operation from idle to full throttle. This paper deals with overall FADEC system and the application of FADEC in Lycoming Engine, MPM 20 Engine, Marine Gas Turbine. Also the System On Chip Technology (SOC) in FADEC which contributes to cost reduction and weight reduction of system. The functionality of this system relating with engine performance and parameters is being discussed.