One of the approaches used for improving the cost effectiveness of gas turbine power plants is Engine Health "Monitoring (EHM). The underlying principle in all such schemes is to compare the current set of engine health indicators with their corresponding known reference values to estimate deviations in engine performance. Deviations between the two sets are investigated by the scheme to locate the most probable source or sources of these observed changes. When the deviations exceed preestablished acceptable limits warning messages are sent out for the operator to take corrective action. These observed deviations in the engine health indicators, however, need not be only due to changes in engine performance but can also be due to instrumentation problems. Therefore for an engine health monitoring scheme to monitor the health of the engine and not of the instrumentation it is essential that instrumentation problems be seperated from engine troubles. A package has been developed which on the basis of thermodynamic gas path analysis validates the daily measurements for consistency. Based on this validated set of measurements the package also evaluates the current health indicators for the plant. To validate this package a hybrid computer model for a single spool gas turbine plant was assembled. This model had capabilities for severally or collectively varying the performance of the plant components to simulate the different engine health states. The data obtained from the model was used to supplement the data obtained from field tests.