The problem of vibration-based technique application for the structural health monitoring (SHM) of small damage in the full-scale component of aircraft was investigated. The tail beam of helicopter Mi-8 used as an object for experimental study. This is typical Al alloy thin-walled structure and consists 17 ribs and 26 stringers. The ribs with the skin assembled by the rivet-joint and stringers with skin connected by combined point-welded and glue connection. The tail beam was placed on the test stand as a cantilever beam. The forced excitation was executed by the eccentric mass shaker (through the special imitator of the tail propeller beam) with controlled frequency of rotation. Experimentally defined first natural frequency of constrained tail beam was 3.9 Hz. Two rosettes of strain gauges were installed on the outer surface of a tail beam for static and dynamic measurement of strain in the root and middle of the beam. The damage was imitated using pseudo-defect technology. Maximum of the pseudo-defect size is not more than 50 mm. It is small in comparison of beam sizes but is close to the span of a stringer. Recording of dynamic response of the beam to harmonic excitation was done for intact and damaged structure of the beam. Excitation frequency was varied in range close to first natural frequency of a beam. The modal analysis of a cell of skin was obtained by computational simulation. The first natural frequency of this simulated small piece of a beam is close to 320 Hz. In general, the sensitivity of this elementary piece of a structure as a function of a damage sizes and location was investigated. Dynamic properties of some modes and they response to damage are sufficient for SHM. Results of test were analyzed by different method of feature extraction and compared with simulation. The conditions of reliable detection of structural damage by vibration-based method at low-frequency excitation are discussed.