Aircraft performance in crash Simulation (APICS) method has been developed for reconstructing aircraft flight profiles. Analysis is performed using nonlinear six degrees fo freedom equations of motion, PC-based, fixed stick simulation to establish the relative performance degradation resulting from several factors that are candidate causes or contributing factors to an accident. Nine scenarios are considered - heavy rain, wind shear, icing condition,engine failure, control system failure, center of gravity movement, take-off with flap retracted, early rotation during take-off and entering a spin. Results achieved are consistent to theoretical values. The method is also capable to verify the probable cause of an air crash. this capability is illustrated in confirming the L-10II crash in 1985 dn the B727 crash in 1988, both crashes occured at Dallas-Fort Worth International Airport.