A flow around an NACA00 12 airfoil at special transonic flow conditions, characterised by damped oscillations of the main flow velocity, was investigated experimentally. On the basic of pressure measurements and flow visualisation, the time depending airfoil loading was reconstructed. Results, presented for a wide range of angle of attack ( a =Q-;-10°), show that during the excitation the normal aerodynamic force behaviour significantly differs from that of quasi- steady conditions. The pressure distributions on the airfoil surface depend on Mach number of the main flow as well on the phase of oscillation (deceleration or acceleration of the main flow velocity). The influence of the air humidity on the pressure distribution, normal aerodynamic force and centre of pressure is also considered.