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Received Jul 3, 2017; Revised Nov 7, 2017; Accepted Dec 10, 2017
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1. Introduction
Aircraft engines produce the power needed for aircraft. For this reason, aircraft engines are very important for flight safety [1]. Today’s complex and advanced technology systems require advanced and expensive maintenance strategies [2]. Maintenance services are costly for airline companies. For manufacturers, maintenance is a source of revenue. According to Dennis and Kambil, though after-sales service and parts sales constitute 25% of the manufacturer’s income, it makes up 40–50% of company profits [3].
Because of the high cost of maintenance, gas turbine engines must be operated within specified physical limits [4]. Today’s aircraft engines are made safer by increasing the number of control parameters and sensors [5]. The engines have a complex mechanical system. Because aircraft engines operate at high temperatures, high pressures, and high speeds, there are lots of possibilities of various faults in the aircrafts [6]. Gas turbine engines show the effects of wear and tear over time. A small fault during the flight does not prevent the engine from running, but if this fault is not detected, it could lead to a bigger fault. If these bigger faults cannot be prevented in the aircraft, it can lead to high maintenance costs and accidents. When aircrafts are taken for maintenance, the condition of the gas turbine engine is investigated by various tests and measurements [7]. Condition-based maintenance (CBM) is being performed to provide effective and efficient maintenance in today’s maintenance services. In the literature, there are major developments in the CBM method with studies on machine condition monitoring and fault diagnostics [8]. A typical CBM program consists of three steps [9]:
(i)
Data acquisition step
(ii)
Data processing step
(iii)
Maintenance decision-making step
In a CBM program, we can group two important parts as diagnostics and prognostics. With diagnostic monitoring, malfunctions or abnormal conditions are detected when a system or its subsystems are in operation [10]. With the prognostics approach, the current state of the motor and possible future failures can be predicted. The following diagnostic systems have been...