A method is provided for calculating an actual cost index (CI) for aircraft operations. A preliminary CI is generated for an aircraft based on in-flight data parameters. An actual CI is calculated by identifying unavoidable deviations from the flight plan and discounting the deviations from the preliminary CI. Also, an expected CI for the flight plan of the aircraft is generated based on the book performance data of the aircraft provided by the original equipment manufacturer (OEM). The actual CI is then compared with the expected CI with any differences between the two indices reported in a post flight compliance report.