Suction embedded plate anchors, as used in practice, include a hinged keying flap aligned with the main anchor plate (fluke). The flap was designed to rotate away from the shank during keying of the anchor, to minimise loss of anchor embedment and the associated reduction in pull-out resistance. However, it has been observed experimentally that the flap is activated only once keying is nearly completed, and thus does not assist in reducing embedment loss. In this paper, the performance of the keying flap is investigated using a large deformation finite element approach based on frequent mesh regeneration. The moment acting at the flap hinges, determined from the soil pressures and shear forces on the keying flap, is quantified. The moment controlling the flap activation depends mainly on the net soil pressure on the front or back face of the flap, and this prevents activation of the flap while the anchor is rotating significantly. The flap is only activated once the anchor motion becomes dominated by forward translation, normal to the plate. Various factors affecting flap activation and embedment loss are explored, including flap height, eccentricity of the padeye, soil strength profile, initial anchor depth and load inclination. © 2012 Elsevier Ltd.