A method of obtaining extraction airflow from a compressor includes accelerating the extraction airflow to at least Mach 1 for obtaining choked airflow and decelerating the choked airflow to a speed less than Mach 1. An apparatus for carrying out the method includes a compressor casing having an extraction airflow port, first means for accelerating the extraction airflow channeled through the port to at least Mach 1 for obtaining choked airflow, and means for decelerating the choked airflow to a speed less than Mach 1. In an exemplary embodiment, a converging-diverging nozzle is provided for accelerating the extraction airflow to at least Mach 1 and then decelerating the choked airflow.