A fuel tank inerting system for an aircraft comprises: an air separation module having an oxygen permeable membrane that separates process air into nitrogen-enriched air and oxygen-enriched air; an actuated valve upstream of the air separation module, wherein the actuated valve regulates the flow of process air to the air separation module; a compressor upstream of the actuated valve and the air separation module, the compressor configured to compress the process air; a variable vacuum source configured to increase a pressure differential across the oxygen permeable membrane; an oxygen sensor in a nitrogen-enriched air line downstream of the air separation module, the oxygen sensor configured to detect a concentration of oxygen in the nitrogen-enriched air; an at least one fuel tank, wherein the at least one fuel tank is downstream of the air separation module and the oxygen sensor and is fluidly connected to the air separation module via an inert gas outlet; a variable speed motor drive associated with the compressor; a controller for controlling the variable vacuum source and the variable speed motor drive, based on a concentration of oxygen in the nitrogen-enriched air detected by the oxygen sensor and data from the at least one fuel tank sufficient to adjust the oxygen concentration in the nitrogen-enriched air, to provide the pressure differential such that a desired purity of the nitrogen-enriched air for fuel tank inerting is produced, wherein the controller is configured to produce nitrogen-enriched air having an oxygen concentration of less than 12% for fuel tank inerting, a heat exchanger upstream of the air separation module, the heat exchanger configured to temperature control the process air; a filter upstream of the air separation module, the filter configured to filter the process air; and a pressure regulator downstream of the air separation module, the pressure regulator configured to regulate the pressure of the nitrogen-enriched air, wherein the controller is further configured to adjust the rate of flow of process air through the actuated valve based on the concentration of oxygen in the nitrogen-enriched air detected by the oxygen sensor and data from the at least one fuel tank. an air separation module having an oxygen permeable membrane that separates process air into nitrogen-enriched air and oxygen-enriched air; an actuated valve upstream of the air separation module, wherein the actuated valve regulates the flow of process air to the air separation module; a compressor upstream of the actuated valve and the air separation module, the compressor configured to compress the process air; a variable vacuum source configured to increase a pressure differential across the oxygen permeable membrane; an oxygen sensor in a nitrogen-enriched air line downstream of the air separation module, the oxygen sensor configured to detect a concentration of oxygen in the nitrogen-enriched air; an at least one fuel tank, wherein the at least one fuel tank is downstream of the air separation module and the oxygen sensor and is fluidly connected to the air separation module via an inert gas outlet; a variable speed motor drive associated with the compressor; a controller for controlling the variable vacuum source and the variable speed motor drive, based on a concentration of oxygen in the nitrogen-enriched air detected by the oxygen sensor and data from the at least one fuel tank sufficient to adjust the oxygen concentration in the nitrogen-enriched air, to provide the pressure differential such that a desired purity of the nitrogen-enriched air for fuel tank inerting is produced, wherein the controller is configured to produce nitrogen-enriched air having an oxygen concentration of less than 12% for fuel tank inerting, a heat exchanger upstream of the air separation module, the heat exchanger configured to temperature control the process air; a filter upstream of the air separation module, the filter configured to filter the process air; and a pressure regulator downstream of the air separation module, the pressure regulator configured to regulate the pressure of the nitrogen-enriched air, wherein the controller is further configured to adjust the rate of flow of process air through the actuated valve based on the concentration of oxygen in the nitrogen-enriched air detected by the oxygen sensor and data from the at least one fuel tank.