<p>Deterioration of composite helicopter main rotor blades caused by operational factors, aging, environmental impact requires continuous monitoring and evaluation of their condition. One promising method, available for application in field conditions and not requiring expensive equipment, is based on operational modal analysis provided by “passport” approach. The approach of modal passport allowing to diagnose condition of helicopter composite blades in the field without transporting them or entire helicopter to maintenance or repair shop was described. The set of techniques allows one to determine and evaluate the mechanical integrity of a composite blade by comparing its modal properties with the reference. The study results confirmed the possibility of using the modal passport methods for diagnostics of helicopter blades. The methodology, together with a compact set of equipment and tooling, allows one to carry out a field-testing of blades and obtain a conclusion on their state. Further research is planned to implement influence and localization functions of the modal passport in order to provide diagnostics of the blades in a given temperature range and to reveal hidden defects.</p>