The Central Institute of Aviation Motors (CIAM) has been engaged in the development of methods and technologies extending the range of stable operation for GTE axial compressors on the basis of systematic experimental and theoretical investigations of processes before and after flow disturbances for many years. The general sources of experimental data were stage models of various types. They are first supersonic stages with 0.3–0.45 hub ratio and subsonic stages with 0.75 hub ratio, as well as high-loaded stages with low aspect ratio. As a result of these investigations, a structural configuration of the casing treatment (CT) was designed to prevent local flow separation on flow passage surfaces of a compressor stage. The CT structure includes the following components: - Slotted spacer installed above the inlet rotor section; - Attached ring covering the slotted spacer. An approximate procedure for selecting the optimal CT geometric parameters and their interrelations was developed for CT designing. Using this procedure, special investigations were completed and detected the CT effects on operation of the axial compressor. These effects are: - Effect of air back and forward leakage through slots between the blade tips and the inlet rotor section; - Effect of stall deceleration in the stage flow passage; - Pulsation damping at the stage tip when flowing around the CT slotted spacer. Based on this methodology, CT prototypes were developed and tested in various single-stage and multi-stage compressors. As an example of CT advantages, we can show test results for a three-stage low-pressure compressor (LPC) designed by CIAM. The LPC in take-off conditions provides the following design parameters: - Pressure ratio: 3.4; - Corrected tip speed: 418 m/s; - Stall margin: 20% … 21% within 0.5–1.0 corrected RPM. According to experimental investigations, the use of CT results in a considerable increase in LPC stall margin without losses in other design parameters. Additionally, the results of 3D viscous flow calculation are shown for compressor performance analysis.