The satisfactory performance of an aircraft depends on the good performance of its engine installation and aerodynamic design. However, the information describing the performance characteristics of an engine installed on an aircraft is, in most cases, restricted to the manufacturer or technology developer country. Some indicators of the performance condition of helicopters and their installed engine are the power output and the fuel consumed by the engine. The general objective of this study is to estimate the in-flight-helicopter-engine installed performance. For this purpose, the H-225M (Airbus Helicopters) is used as the example helicopter. The specific objectives reached in this study are: (i) determine the influential parameters in the engine performance installed at final platform (helicopter); (ii) develop an experiment to collect performance data during the flight; (iii) analyze the results according to Analysis of Variance (ANOVA); (iv) obtain a mathematical model to estimate power and fuel consumption and verify the capability of the model prediction.