A comparative analysis has been performed on the Boeing 727-100 using three conceptual design codes. These programs were: The Aircraft Synthesis Program, ACSYNT, Advanced Aircraft Analysis, AAA, and RDS-Student. The objective of this study was to investigate differences in the conceptual design methodologies of these three programs.All three codes showed reasonable prediction of drag in the subsonic flow regime. However all three programs had difficulty predicting transonic drag rise characteristics. The principal cause was the inability to accurately predict the critical drag rise Mach number. Difficulties in estimating the shape of the drag rise curve, relative to the critical Mach number, also contributed to the errors in drag prediction. AAA and RDS-Student gave reasonable predictions of maximum lift coefficient. ACSYNT could not model the triple-slotted flap system on the 727-100.The three codes showed a consistent trend towards under-prediction of empty weight. The best empty weight predictions were seen in the propulsion group. The largest variations between predicted and actual weight were seen in the fixed equipment group. The wing structural weight prediction was also an area of concern.Performance analyses suffered from the accumulation of errors in the other analysis modules of all three codes. Prediction methods in the geometry, aerodynamics, propulsion, weights and high lift modules need to be calibrated to a reference configuration of similar characteristics before performance can be reliably predicted.