An avionic system for producing the most economical engine thrust and airspeed settings in readily usable form during a jet aircraft flight is disclosed. The pilot inserts: the elevation of the destination airport; the zero fuel weight of the aircraft; the reserve fuel needed for the flight; the outside air temperature at the departure airport; and, a flight index number. The flight index number represents a chosen relationship between fuel costs and trip time-related costs. The system also receives data from various aircraft subsystems and sensors and uses the information it receives, and stored information, to produce signals representing the most economical engine thrust setting and airspeed for the phases of a flight. The thrust setting and airspeed signals drive bugs on thrust and airspeed indicators and/or used to control autothrottle/autopilot systems. The throttles and pitch attitude of the aircraft are controlled so that the indicator readings "track" the bug positions to cause the aircraft to follow the most economical flight path based on the chosen flight index number. Engine thrust limits are prevented from being exceeded by comparing calculated thrust values with stored engine thrust limit settings; and, using the maximum values to control the position of the thrust indicator bugs and the digital display. Still further, the system develops an aircraft idiosyncrasy factor (K) that is used to modify calculated thrust values in order to compensate for the drag and thrust peculiarities of the aircraft, zero fuel weight errors, etc.