This document discusses a data-driven model for predicting remaining useful life (RUL) of jet engines using sensor data. It first defines the problem of predicting RUL based on measurements from engines. It then describes developing a health index (HI) from sensor data to characterize engine health over time. Finally, it explains a similarity-based approach to estimate RUL for a new engine by comparing its HI to models of HI developed from a training set of engine data. The accuracy of this approach is evaluated using different methods to determine the final RUL estimate.