Parker Aerospace’s Fluid Systems Division (FSD) has been 
a major supplier of aircraft fuel tank inerting systems and components since the 1960s. Fuel tank inerting systems create a non-combustible atmosphere in the air space or ullage gas present over the liquid fuel in an aircraft fuel tank. This non-combustible or inert atmosphere prevents a fire from occurring inside the fuel tank. The means by which that inert atmosphere is created has evolved considerably over the last 50 years and Parker has remained at the forefront of each technology advancement.
Nitrogen and Halon for military aircraft
Fuel tank inerting systems were initially developed to help protect military aircraft from hazards unique to combat and supersonic aircraft. Parker’s first aircraft fuel tank inerting system was a cryogenic liquid nitrogen (LN2) system used on the supersonic XB-70 aircraft. The LN2 system extracts liquid nitrogen from cryogenic-storage dewars installed onboard the aircraft, vaporizes the liquid into gaseous nitrogen and sends it to the fuel tanks to provide an inert blanket over the top of the fuel. Several research programs conducted by the Air Force and the Federal Aviation Administration (FAA) subsequent to the XB-70 also used Parker LN2 inerting equipment. In the early 1970s, LN2 technology produced by Parker Aerospace was put into regular service on all C-5 aircraft. This system remains in service today.
The evolution of fuel tank inerting systems away from the complexities of cryogenic LN2 systems to Halon-based systems followed in the late 1970s. Halon inerting systems discharge a fire-suppressing agent into the fuel tanks to create an inert atmosphere over the fuel. Parker proliferated Halon inerting equipment on programs such as the F-16 and F-117A. Like the LN2 systems that came before them, Halon inerting systems require a fixed amount of inertant to be loaded and stored on the aircraft before each flight. The capacity of these stored gas systems is limited to the amount of inertant that is carried onboard the aircraft.
Hollow-fiber membrane air separation module advancements
In the 1980s and 1990s, advances in hollow-fiber membrane air separation technology enabled nitrogen to be generated onboard an aircraft from atmospheric air. Air separation modules (ASMs) contain thousands of these hollow-fiber membranes and are the heart of the contemporary fuel tank inerting system. High-pressure air enters the ASM and is separated into nitrogen-enriched and oxygen-enriched air streams. The nitrogen-enriched air stream is directed to the fuel tank to provide a blanket of inert gas over the top of the liquid fuel in the tank.
The development of the ASM for aircraft use enabled a new class of inerting system that does not require inertant to be stored and carried onboard the aircraft. Inerting systems using Parker-supplied ASM technology were explored on several advanced aircraft programs and culminated in the widespread use of Parker ASMs on the F-22.
Fuel tank inerting comes to commercial aircraft
For many years, fuel tank inerting systems remained exclusively within the realm of military aircraft and were perceived to be unnecessary and impractical for use on commercial airliners. However, the loss of TWA 800 in 1996 forced a re-examination of the fuel tank safety paradigm for commercial transport aircraft. Between 1996 and 2001, an extraordinary body of work was performed by a consortium of industrial, academic and governmental researchers to determine viable means by which to improve fuel tank safety on commercial transport aircraft.
Parker led the way in demonstrating how hollow fiber membrane-based ASM technology developed for military aircraft applications could be implemented in a practical and viable way on commercial transport aircraft. Parker also worked closely with FAA and provided inerting equipment and expertise in support of a flight test program using the FAA’s 747SP. Technology advances demonstrated in this time frame ultimately paved the way for new rulemaking for fuel tank safety which was implemented by the FAA in 2008.
Modern aircraft inerting
Since 2008, inerting systems and equipment provided by Parker FSD have been installed on almost every large commercial airliner in domestic service today. In fact, Parker’s aircraft inerting systems and equipment are in operation on well over 10,000 aircraft worldwide. Parker FSD maintains its leadership position through a close working relationship with its sister division in the Parker Filtration Group, which manufactures the ASM used on many Parker inerting applications.
Parker continues to explore new ways of improving the performance as well as reducing the weight, cost and bleed air consumption of the existing ASM-based technology. At the same time, Parker is developing future inerting technologies that will be more ideally suited for helicopters, UAVs, and business jets.
This blog was contributed by Pat Fancher, engineering manager and Bryan Jensen, senior principal engineer, Parker Fluid Systems Division.
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