Abstract: A system for testing the icing build-up of helicopter engines during flight, the system being self-contained on the helicopter and comprising: sources of air and water under pressure connected to a spray rig mounted externally of the aircraft and upstream from its engines air inlets to spray a mixture of air and water toward the engines air inlets. The spray rig has an adjustable outer housing being open at its front and rear for allowing and controlling ambient air flow therethrough and toward the engine air inlet and a plurality of spray nozzles mounted on a distribution tree positioned in the housing and connected to the sources of air and water.