The Pentagon has added $12 million to its 2014 spending plans to equip its Boeing 737-based C-40s with a fuel-tank inerting system, the same upgrade mandated for U.S. operators of Boeing commercial aircraft.

The 2013 spending plan anticipated spending about $1 million more than fiscal 2014-17 for various required modifications. In the fiscal 2014 request, the figure jumped $6.1 million for 2014 and another $6 million for the outyear estimates through fiscal 2017.

In procurement parlance, the project to retrofit a fuel tank inerting system (FTIS) on the C-40 fleet is a “new start,” something Pentagon planners have been avoiding as budget pressures have forced tough choices. The most recently procured C-40C had FTIS. The Air Force plans to modify 10 remaining C-40B/Cs, which are used for official transport.

An FAA rule, finalized in July 2008, set deadlines in 2014 and 2017 for commercial operators to complete the retrofits. The Air Force’s 2014 budget justification document says the service maintains FAA certification on its fleet and cites the same deadline for the inerting system that commercial carriers must meet: 50% completed by 2015 and the remainder by the end of 2017.

Last July, FAA proposed a $13.57 million civil fine against Boeing for missing the Dec. 27, 2010, deadline for submitting for FAA approval the service instructions for its FTIS.

Honeywell developed the system for Boeing, and theirs was the first system to be certified by the FAA. The “onboard inert gas generation system” (Obiggs) technology is based upon existing industrial gas-handling technologies that have been enhanced and tailored for aircraft applications, says Eric Blumer, Honeywell’s director for advanced technology. The resulting product is still relatively new, Blumer says, and Honeywell is still working to reduce weight and initial cost, and increase efficiency and operational life.

In general, Obiggs works by taking engine bleed air and pushing it through thread-like membranes that act like a molecular sieve. The oxygen leaks out and is dumped while the nitrogen continues through. Conditioning cooling occurs along the way, and the resulting nitrogen-rich air is delivered to the center tank to continuously fill the ullage space. The presence of the inert nitrogen and relative absence of oxygen (12% or less) reduces the likelihood of an explosion or fire. The systems also are generically known by the terms flammability reduction means or flammability reduction system.

Parker Aerospace supplied the inerting system for Airbus aircraft affected by the FAA rule, and a similar rule from the European Aviation Safety Agency.

[Editor’s Note: This story was amended to correctly identify Parker Aerospace as the supplier of fuel-tank inerting systems on Airbus aircraft.]