Abstract: A recirculating lubricating system includes a monitor filter unit (16) between a pump (13) and a main filter element (17). The monitor filter unit (16) includes diverting means (23, 31) to ensure that a proportion of the oil flowing between the pump and the main filter element is diverted through a removable monitor filter element (28).

Abstract: This invention concerns fibre reinforced plastics structures, and is particularly concerned with the attachment of such structures, for example, a helicopter rotor blade, to a supporting metal member by bolting through holes provided in the structure. Accordingly the invention teaches an arrangement in which the or each attachment hole is defined by at least two metal bushes secured in the structure with the outer ends of the outermost bushes flush with the surfaces of the structure and so that the bushes are spaced-apart axially within the structure.In a preferred embodiment, a resilient washer is located in the spacing between ends of adjacent bushes and in contact therewith.