IntroductionThis paper presents a condition monitoring system with sensor optimization capabilities to prevent unscheduled delays in the aircraft industry. Unscheduled delays cost airlines a great deal of money but can be prevented by condition monitoring [11]. The aim was to develop a simple condition monitoring system that can be understood by humans and modified by experts to incorporate knowledge that is not in the learning data set, using decision trees as the main tool. Decision Gerdes M, GAlAr d, scholz d. decision trees and the effects of feature extraction parameters for robust sensor network design. eksploatacja i Niezawodnosc - Maintenance and reliability 2017; 19 (1): 31-42, http://dx.doi.org/10.17531/ein.2017.1.5. trees satisfy the requirements and provide a ranking of data sources for condition monitoring.The first section of the paper gives the motivation for developing a condition monitoring system with sensor optimization capabilities and explains the basic concepts of the proposed method. The second section explains the method in detail. Section three discusses the experiments validating it. The results of the validation experiments are given in section four. The paper concludes with a discussion of the results. New and better monitoring approaches are required for condition monitoring, because systems are becoming more complex and more difficult to monitor [32]. Condition monitoring requires reliable sensors. To obtain enough sensing data, special attention should be given to optimizing sensor allocation to ensure system diagnosability, lower sensing cost and reduce time to diagnosis [37]. Sensors can be used to determine the system health of control systems; a failed sensor can lead to a loss of process control [18]. The information about a system is incomplete, if a sensor fails. Complex systems are often monitored by multiple sensors. An advantage of a multi sensor system is that a single failed sensor shows its effects in multiple sensors [18].This means the system condition is defined by all information from the sensors. However, the system's health status becomes uncertain when a sensor fails or sends wrong data. This could trigger incorrect maintenance, including maintenance on a part with no failure, as well as long maintenance times to find the correct fault or not noticing the fault at all.The Safety Integrity Level (SIL) defines the probability that the system safety function for a Safety Instrumented System (SIS) can be executed. There are four SILs; level four is the level with the highest probability that an SIS can be performed. Sensor failure detection (sensor validation) is a critical part of the safety function of a system. When a failure is detected SIS is put into a safe state to avoid risk and damage to humans and machines [14,13].Redundancy is used to reduce the risk of model uncertainty [5]. One way to create sensor redundancy is hardware redundancy; another is analytical redundancy [5]. Analytical redundancy assumes multiple sensors deliver the same information, and,...