Abstract: A centrifugal compressor for a gas turbine turbo-shaft engine includes a stationary shroud cover over the inducer section of an impeller in the centrifugal compressor including a plurality of raised reinforcing bridges at the leading edge of the outer surface of the cover and having an annular control slot formed inboard of the bridges to communicate the inner surface of the shroud cover with surrounding gas and wherein the shroud surrounds an impeller which produces a variable cover static pressure at the point of the control slot so it serves combined functions of causing an inflow of gas from exteriorly of the cover into the impeller to add to the inlet flow to the impeller under high speed conditions of compressor operation and wherein the same slots serve to bleed gas flow from the impeller to a point exteriorly of the compressor at part speeds of rotation of the impeller thereby to flow stabilize the impeller at part speed phases of operation thereof.