GOBIGGS

[DVR15]

I am not from the aviation field, but am very interested in it. I recently heard about something called the Green OBIGGS (GOBIGGS, also known as the catalytic inerting system) and was wondering how it works. I am familiar with the common OBIGGS using ASM. I understand that GOBIGGS is a closed system that doesn't require the extraction of bleed air from the engines, but where does the air come from, then? As the fuel gradually decreases in flight, the amount of air in the ullage has to increase to maintain pressure, so where does does the air come from?

[Rigga]

I have heard of similar systems to that which you describe and I would guess that GOBIGGS means something like (Green) On Board Inert Gas Generating System. This implies the use of a molecular sieve used for filtering Nitrogen from normal (outside) air. A system like this was once proposed for use on a 747 but I believe it was rejected due to the size/weight of the system and its lack of capacity for filling those huge fuel tanks. The only pressure required is that to force our any flammable gasses and as Nitrogen can be cooled to be heavier that air that isn't really a difficult issue.
Other systems have been in use for many years now - but for sieving Oxygen from local air sources...OBOGS (On-Board Oxygen Generation Systems) - were/are fitted to Harriers and other military aircraft...but no civil aircraft as far as I know.

[WOTME?]

The two RAF BAe 146's that are painted grey have fuel tank inerting.

[Rigga]

The two RAF BAe 146's that are painted grey have fuel tank inerting.
I thought the Interting system on those was a gas bottle ready to flood tanks in a crash?