A system and method are provided for precisely adjusting individual aircraft airspeed system in order to provide more accurate cruise Indicated Airspeed (IAS). The system includes a flight data computer, an autopilot, and airspeed displays. The flight data computer includes a first component that records in-service data to determine actual fuel mileage for the aircraft for comparison to a production rating fuel mileage. The flight data computer also includes a user interface that allows a user to set a Mach trim value based on the comparison and a third component that adjusts indicated airspeed based on the determined Mach trim value. The autopilot and airspeed displays receive the adjusted indicated airspeed.