At the beginning of 21st century, we find ourselves exactly in a similar position that we were in the beginning of the Aero Engine age. With environment and current economy taking the front seat in civil applications, the objective is to propose novel and innovative concepts which make the process more effective and efficient which would help in saving time and money. This report proposes the use of an automatic control system to implement variable rating operation within the engine. Implementation of variable rating operation results in an increase engine life and decrease in NOx at a small expense of CO & UHC. This results in a decreased overall operating cost of the engines, especially the maintenance cost and the emission charges.The study is based on the engine performance taking payload, altitude and mission range into account. The parameters used are strongly related to a commercial flight. Implementation of Variable Rating Operation was done on different civil aero engine configurations i.e. High Bypass Turbofan, Open Rotor and the Gear Turbofan.