US Patent 8074767 Aerial ladder system with powered rungs

An extensible, vehicle-mounted ladder with movable rungs is used to aid in raising and lowering in rescue operations. The ladder includes a rotatable base having storage space to hold extra rungs supporting the variable extended positions of the ladder. The ladder includes a plurality of ladder units or extensible booms. Each ladder unit includes four C-rails. A first ladder unit is attached to the rotatable base and the others extensible therefrom. The ladder includes rungs that slidably engage within two of the C-rails. A drive cable connects the rungs in a closed loop and is powered to enable rung rotation in a closed loop around the ladder units within the C-rails.