An aircraft fuel tank flammability reduction method includes feeding pressurized air into an air separation module containing an oxygen separation membrane. The method includes contacting the separation membrane with the air feed, permeating oxygen from the air feed through the separation membrane, and producing nitrogen-enriched air from the air separation module as a result of removing oxygen from the air feed. The NEA from the air separation module is substantially cooled in a NEA flow heat exchanger and the substantially cooled, nitrogen-enriched air is fed into the fuel tank on board the aircraft. An aircraft fuel tank flammability reduction system includes a NEA flow heat exchanger configured to cool substantially the nitrogen-enriched air from the air separation module and a fuel tank on board the aircraft configured to receive the cooled nitrogen-enriched air.