Abstract: A telescopic boom for a crane, access platform or the like comprises at least three telescopic boom sections the intermediate section being arranged to be extended by a hydraulic ram while the outer section being arranged to be extended by a pulley and chain arrangement. A telescoping boom safety system includes a wire rope and a pair of linked drag chains which extend from a first anchorage on the outer section around a guide to a second anchorage on the base section. Failure of the pulley and chain arrangement causes the safety system to prevent or contain relative movement of the outer and intermediate sections and thereby stop sudden and catastrophic retraction of the outer section.

Abstract: A multi-section telescopic jib or boom comprising a base section and three movable sections mounted to extend or retract relative to each other on operation of drive means within the sections, including a first ram connected between the base section and the innermost sections, a second ram connected between the innermost and central sections and a chain having ends connected between the innermost section or the first ram and engaging a chain wheel mounted on the central section or second ram, means being provided to releasably connect the chain to the outermost section to extend the boom.

Abstract: A multi-section telescopic jib or boom comprising a base section and three movable sections mounted to extend or retract relative to each other on operation of drive means within the sections, including a first ram connected between the base section and the innermost sections, a second ram connected between the innermost and central sections and a chain having .[.ends connected between the innermost section or the first ram.]. .Iadd.one end connected to the lowermost section or first ram and the other end connected to the innermost section .Iaddend.and engaging a chain wheel mounted on the central section or second ram, means being provided to releasably connect the chain to the outermost section to extend the boom.