The purpose of this study and series of tests was: to determine the cause and provide preventive measures in aircraft to eliminate the hazard from fire in the air or in the event of a crash. Conclusions: 1. No fires were traced to ignition. 2. [With three exceptions], all fires which occurred resulted from gasoline entering hot exhaust manifolds and coming in contact with hot exhaust ports or valves. 3. Thoroughly ventilated and drained compartments are necessary in aircraft to prevent an accumulation of gasoline, oil, or vapor and possible ignition.