Abstract: A system for lubricating aircraft mechanical members, comprising a main circuit and an emergency device; the main circuit comprising a main pump for sucking up lubricating oil from a main tank and connected by a delivery pipe to a number of oil supply nozzles; a number of oil recovery pumps; and a pipe for recirculating the oil to the main tank; and the emergency device comprising an auxiliary pump for sucking up oil from a storage tank series-connected to the delivery pipe; and a pair of monostable, hydraulically controlled valves respectively connecting the recovery pumps and auxiliary pump to the recirculating pipe and storage tank under normal operating conditions, and to the storage tank and an auxiliary delivery pipe to the nozzles in the event of a breakdown on the main circuit.