Abstract: In low speed flutter tests, flutter models with small damping modes start continuous vibration usually at low speeds without obvious flutter divergence. Therefore, it's of some uncertainty on determing the critical flutter wind speeds by visual inspection or by “damping method (DM)” of modal parameter identification. Considering the similarity between the vibration phenomenon of a small damping modal flutter test and that of a fighter buffet test, a technique named “amplitude turning point method (ATPM)” similarly to that used in identifying buffet boundaries is proposed to determine the critical flutter wind speeds. The method is based on RMS of vibration amplitudes, the curves of normalized vibration RMS changing with wind speeds are drawn, and critical flutter wind speeds are determined according to the first turning points of curves. In a small damping modal flutter test, the method was applied in the test data processing of the engine hangers with variable parameters. Comparing the ATPM results with the DM results and the numerical results, the following conclusions are made: the results of three methods are in agreement, the ATPM results are more similar to the numerical results than the DM results, and the ATPM is concise and reliable, with good stability and applicability.