The paper investigates transonic buffet for the XRF1 aircraft using Unsteady Reynolds Averaged Navier Stokes simulations at forced wing oscillations in the 4th bending mode at three amplitudes: \(A_{tip}=\{0.001, 0.01, 0.03 \} \cdot s\) , with the wing halfspan s. Flow conditions are based on experiments in the European Transonic Windtunnel, while wing eigenforms and -frequencies of the wind tunnel model are determined by a Ground Vibration Test. The mean surface pressure coefficient \(c_{p,mean}\) and the root mean square pressure \(c_{p,rms}\) indicate: The forced motion of the 4th wing bending mode leads to a harmonic shock oscillation over the whole wing. A power spectral density analysis shows a broadband answer of the fluid onto single frequency forcing. Dynamic mode decomposition of the forced motion finds a flow mode representing the second harmonic of the forcing frequency for all forcing amplitudes. For the third harmonic, mixing of a buffet mode with the fluid mode from the forced motion occurs.