This paper describes an experimental study to compute the normal modes of vibrations of helicopters. The work presented herein details the normal modes characteristics between 5Hz and 50Hz of a developed helicopter. The Lynx helicopter airframe was used as the test aircraft. Each mode shape was recorded at 121 monitoring points on the airframe in the vertical, lateral and fore-and-aft directions. Complex response plots were obtained for each mode shape and the modal damping factors were estimated. The results of the experimental investigations were compared with a theoretical finite element modelling analysis. Good agreement between the finite element analysis and the experimental natural frequencies and mode shapes were obtained.