A plurality of skewed slots of a particular shape are provided within a compressor casing adjacent at least one stage of compressor blade tips, the slots having an axial length greater than that of the adjacent blade tips. The slots are provided such that upon occurrence of compressor surge or stall,...http://www.google.com/patents/US4086022?utm_source=gb-gplus-sharePatent US4086022 - Gas turbine engine with improved compressor casing for permitting higher air flow and pressure ratios before surge
