This study presents a damage identification procedure for complex structures based on analysing changes in vibration data between healthy and damaged conditions. The procedure involves calculating and comparing the first six mode shapes of both the intact and damaged structures using finite element analysis. The case study of 5Mega Watt National Renewable Energy Laboratory offshore wind turbine blade has been used to demonstrate the application of the procedure. The main objective is to utilise this procedure to identify and evaluate the severity of damage in different scenarios. Additionally, the procedure can be applied at various stages to detect and identify early signs of damage, serving as an early warning system.