A Look At Boeing's Nitrogen Generation System

An effective solution to avoid a dangerous situation.

In aviation, a nitrogen-generation system (NGS) removes oxygen from the air into the center fuel tank. Boeing has these systems installed on its commercial aircraft. Here is a look at the overall process of the manufacturer's technology.

The system rose to the forefront of commercial operations following a series of accidents, including the tragedy of TWA flight 800. It has now been over 25 years since a TWA Boeing 747-100 exploded and crashed into the Atlantic Ocean soon after departing New York JFK. All 230 died on board the jumbo on July 17th, 1996.

The National Transportation Safety Board (NTSB) concluded that the probable cause of the accident was an explosion of the center wing fuel tank amid the ignition of the flammable fuel inside. The board added that fuel tank explosions could be avoided by “precluding all ignition sources and the design and certification of the Boeing 747” with heat sources below the center wing fuel tank.

Thus, the Federal Aviation Administration (FAA) didn’t look at lightweight inerting systems for commercial aircraft until after the crash. The incident had a wide impact on the industry. As such, the NTSB now issues safety recommendations that affect the way aircraft are designed.

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The Boeing 737 Technical Site explains that Boeing and its partners formed an NGS that reduces “the flammability exposure of the center wing tank" to a level similar to or lower than the main wing tanks. It is an onboard inert gas system that utilizes an air separation module to separate oxygen and nitrogen. Following separation, the nitrogen enriched air (NEA) makes its way to the center wing tank, while the oxygen enriched air (OEA) is vented out.

The NEA cuts down the oxygen content “to a level where the air volume (ullage) will not support combustion.” A figure of 12% is enough to avoid ignition, which can be met with one module on the 737 and up to six on the 747.

Jimmy Wu, president & CEO of Infinity Air and Allflight, shared the following about the system on LinkedIn:

“The current-day inerting system uses a hollow fiber membrane material that separates supplied air into nitrogen-enriched air. The inerting system runs continuously to reduce fuel vapor flammability whenever the aircraft's engines are running; and its goal is to reduce oxygen content within the fuel tank to 12%, lower than normal atmospheric oxygen content of 21%. This is accomplished by ventilating fuel vapor laden ullage gas out of the tank and into the atmosphere.”

Overall, the system involves an ozone converter, heat exchanger, and air separation module. However, the 787 Dreamliner's system is different. As a no-bleed aircraft, it has an electric-driven compressor to supply NGS. Still, the underlying functioning is similar.

In a nutshell, oxygen isn’t flammable. Instead, it is an accelerant. So, in a high-oxygen environment, there is a significant risk of fire. If enough oxygen is replaced with nitrogen, a potential fire will be avoided or put out.

What are your thoughts about the nitrogen-generation system (NGS) system on Boeing aircraft? What do you make of the technology involved? Let us know what you think in the comment section.

Sources: The Boeing 737 Technical Site; LinkedIn

Deputy Editor & Lead Journalist - Europe. Sumit comes to Simple Flying with more than eight years’ experience as a professional journalist. Having written for The Independent, Evening Standard, and others, his role here allows him to explore his enthusiasm for aviation and travel. Having built strong relationships with United Airlines, TAP Air Portugal, Icelandair, and more, Sumit excels in both aviation history and market analysis. Based in London, UK.