A method and apparatus are disclosed for treating fuel to temporarily reduce its combustibility, and thereafter restore its combustibility. As used in an aircraft, the method comprises the following steps: (a) treating aircraft engine fuel to substantially reduce its combustibility in open air; (b) carrying the treated fuel in a fuel tank of an aircraft; (c) increasing the combustibility of a portion of the treated fuel, as needed by the aircraft engine; and (d) supplying the increased restored combustibility fuel to the aircraft engine. Using this method, the preponderance of the fuel on board the aircraft is maintained at low combustibility for safety.