Flight data recorder data for a twinjet transport are employed to demonstrate the process of identifying how flight variables reduce the
lift-drag ratio of an aircraft in cruise. Since fuel economy of a jet transport is partially dependent on the lift-drag ratio, in addition to the engine health,the present concept provides a tool for aircraft performance engineers to monitor the cleanliness of aerodynamic components and reasonableness of operational conditions. Results for the twinjet transport are analyzed and interpreted in detail. Since the center of gravity location of an aircraft can also affect the fuel economy, the same data are also analyzed to illustrate the prediction of static margin. Center of gravity can be predicted if the aerodynamic center is known.