This study involves research and understanding of airfoil laminar boundary-layer transition based on three codes in written FORTRAN: panel code, boundary-layer code and stability code, namely HSPM, BLP2D and STP2D. All codes were connected to each other via inputs-outputs in the one code, called as PBS code. Firstly, the inviscid pressure distribution was obtained using Hess-Smith panel method. Secondly, differential boundary-layer equations were solved for obtained inviscid pressure distribution from panel code. Thirdly, stability calculation was performed using obtained boundary velocity profiles from boundary-layer code at each streamwise stations. Finally, the onset of transition location was predicted using en method based on linear small-disturbance theory. The PBS code was first validated on NACA 0012 and NACA 0015 airfoils making comparison with an experimental work in literature. After validation, three different thick airfoils designed for wind turbine applications were analyzed in terms of lift coefficient and transition location, namely NACA 64-618, DU91W250 and DU4050. The results were compared with XFoil’s viscous and inviscid solutions and experimental measurements based on infrared thermography. It was seen that amplified disturbance frequency magnitude, amplification starting point and choice of threshold value are key points to correctly predict transition point for en method. Additionally, it was found that followings: First, as airfoil thickness increases, the need of interactive boundary-layer method increases for accurate lift coefficient; however, transition point can be still correctly predicted using inviscid pressure distribution. Second, at high angle of attacks and high Reynolds numbers, laminar boundary-layer separation point can be directly taken as transition point instead of using the en method.