Low-speed rear-stage turbining occurs with excessive negative incidence leading to a pressure ratio less than one and the compressor stage absorbing power from the airflow. Two examples where crossing the surge line prevented accelerating to high speed occurred with the first designs of the Rolls-Royce Avon and the IAE V2500 and required major compressor redesigns. Rotating stall at low corrected speeds caused blade failures on early axial compressors.