Abstract: An engagement structure adapted for securement to the end of an aircraft boarding bridge includes a bumper assembly formed of a first bumper and an auxiliary bumper. The auxiliary bumper is mechanically associated with a drive assembly adapted for displacing the auxiliary bumper relative to the first bumper to provide a dimensionally adjustable floor area of a boarding bridge proximate the interface of the bridge and an aircraft serviced by the bridge. The engagement structure may also include bifurcated arrangement wherein a sliding floor element is associated with a length adjustable bumper subassembly. The engagement structure provides a structure whereby the floor structure of the boarding bridge can be opened to provide a passageway for an opening or closing aircraft door.