Analysis of a boeing 747 aircraft fuel tank vent system

This monograph presents an analysis of a 747 aircraft fuel vent system. The system is comprised of several fuel tanks feeding into a single vent tube. The analysis consisted of formulating equations that govern the venting and heating of the center tank. Flow losses along each section of the vent system were applied to correct the ideal flow from the center fuel tank. These equations were programmed for solution on a digital computer. Results were computed for a flight from Athens, Greece, to New York with a 5-hour delay on the ground before taking off again from New York. The heating caused by air conditioning and bleed air from the engines on the ground during the long delay caused vaporization of fuel and increased the density of the air-fuel vapor. The result was very sluggish venting and "choked" flow producing a significant overpressure, at 13,000 ft altitude, sufficient to fail some component of the center tank. This was a precursor event leading to serious consequences. The analysis supports a hypothesis of overpressure as the cause of the Trans World Airlines Flight 800 accident and shows that heating caused by air conditioning contributed to the sequence of events.