A method for estimating engine thrust values of an aircraft is disclosed, the method comprising calculating estimated thrust value of an engine based on an equation of longitudinal motion, aircraft data measured during flight and calibrated drag/lift models, and a method for determining the thrust of an aircraft engine, based on information available from tracking the aircraft air-speed, acceleration, and position, the method comprising calculating the thrust, using the following equation: Thrust=mg{dot over (H)}/V+m{dot over (V)}+Drag.