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As part of the continued emphasis on fuel tank safety, the Federal Aviation Administration (FAA) has developed a demonstration fuel tank inerting system and has tested it on a NASA-operated Boeing 747 aircraft. To support this, the FAA developed two models to predict both fuel tank oxygen concentration and flammability in an inerted ullage, based on previously developed models and calculations. Laboratory and aircraft test results indicated that the models duplicated measured data trends well and gave predicted peak values with a reasonable degree of accuracy. This allowed the FAA to develop a representative Boeing 747 aircraft flight cycle and give predictions of flammability exposure for the given ullage. The results indicated that the aircraft fuel tank would not be exposed to flammable conditions during the developed flight profile with the represented inerting system even though part of the tank ullage did achieve oxygen concentration levels of approximately 18%.