Spacecraft traversing the magnetotail plasma sheet frequently observe rapid large-amplitude variations of the magnetic field. These variations, interpreted as up-down oscillation of the current sheet, are known as current sheet flapping motion. The Cluster tetrahedron configuration allows determining the normal velocity of the flapping current sheet by multi-point timing analysis. Distributions of azimuthal and vertical components of the current sheet normals calculated by a timing analysis for 58 crossings in 2001 are presented in the figure for dawnside and duskside sectors separately. The results show a strong tendency for the normals to point outward, duskward on the evening side and toward dawn on the morning side of the plasma sheet, indicating waves propagating outward from the midnight sector. Hence, the source of rapid flapping waves is localized in the midnight sector of the magnetotail. A simple interpretation scheme summarizing the results is presented in the lower part of the figure.