Gas turbines are known to contribute to economic gains. But then, they are also covertly responsible for environmental loads. In the conventional approach, manufacturer supplied tool is used for condition monitoring. Drawbacks of such a tool include (i) the tool being designed for limited number and known types of faults, (ii) a tool specifically designed for experienced users, (iii) a tool featured by separate modules for monitoring and reliability, and (iv) a tool designed focusing on a particular system only. Meanwhile, the purpose of diagnostics and reliability are to enhance preventive maintenance. Hence, we suggest that they should be integrated to benefit from synergized use of the two aspects. Based on this argument, the purpose of this paper is to explore on the methods that integrate performance diagnostics with reliability monitoring. As it turned out, there is no specific method that addresses all the issues in fault diagnostics system design. The thermo-economic approach proved to be powerful in estimating performance changes and energy loss due to the presence of malfunctions. Nevertheless, this method cannot be used to address problems encountered by sensors outside the thermodynamic zone (e.g. vibration signal, lubrication condition etc.). Regarding reliability, there seems to be a gap in (i) defining states of the system, and (ii) in integrating reliability with diagnostics. There is also no performance indicator to evaluate efficacy of a diagnostic system as it relates to environmental load and economic gains. The paper includes additional remarks potentially useful for further research.