Aircraft jet engine performance has a great impact on safety, operating costs and airline operator’s efficiency. In relation to this, it is necessary to continuously monitor engine performance parameters. Monitoring programs are developed by engine manufacturers and aviation authorities. Due to development of advanced technologies, it is now possible to predict failures and perform preventive activities. Certain engine parameters might be an early indication of a failure, and any deviation from standard values requires maintenance action to return it to the initial state. One of the most important engine parameters is an Exhaust Gas Temperature (EGT). The EGT is an indication of how efficient a jet engine is in terms of thrust production. Therefore, it is directly linked to fuel consumption. Engine performance degradation can lead to increased fuel consumption for the same amount of thrust compared to the engine without such degradation. This is directly connected to an increased EGT value that occurs after certain engine life cycles. The EGT can rise to its maximum value, beyond which there is a strong possibility of an engine damage. Engine maintenance has the function of restoring EGT to the initial value, at which the engine has optimal performance.